ci: copy ui-svelte/.npmrc before npm ci in fork-cuda build

npm ci ran without .npmrc (legacy-peer-deps=true), failing on the
tailwind/vite peer dependency conflict. Copy .npmrc with the manifest.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-cuda-image.yml

@@ -0,0 +1,76 @@
+name: Build CUDA image (fork)
+
+# Builds this fork's llama-swap (serial scheduler + embedded UI) from source and
+# layers it on a pinned llama.cpp CUDA server base, then pushes to the Gitea
+# container registry, e.g. gitea.stevedudenhoeffer.com/steve/llama-swap:v230-cuda-b9821
+#
+# Requires repo secrets: REGISTRY_USER, REGISTRY_PASSWORD (push to the registry).
+
+on:
+  workflow_dispatch:
+    inputs:
+      llama_swap_version:
+        description: "llama-swap version label (image tag prefix)"
+        required: false
+        default: "v230"
+      llamacpp_build:
+        description: "llama.cpp CUDA server build (base image tag suffix)"
+        required: false
+        default: "b9821"
+  # Building the build definition itself kicks off a fresh image.
+  push:
+    branches: [main]
+    paths:
+      - ".gitea/workflows/build-cuda-image.yml"
+      - "docker/fork-cuda.Containerfile"
+
+env:
+  REGISTRY: gitea.stevedudenhoeffer.com
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Compute image metadata
+        id: meta
+        run: |
+          LS_VER="${{ inputs.llama_swap_version || 'v230' }}"
+          LCPP="${{ inputs.llamacpp_build || 'b9821' }}"
+          {
+            echo "image=${REGISTRY}/${{ github.repository }}"
+            echo "tag=${LS_VER}-cuda-${LCPP}"
+            echo "base_tag=server-cuda-${LCPP}"
+            echo "ls_version=${LS_VER}"
+            echo "build_date=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+          } >> "$GITHUB_OUTPUT"
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ secrets.REGISTRY_USER }}
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: docker/fork-cuda.Containerfile
+          push: true
+          provenance: false
+          build-args: |
+            BASE_TAG=${{ steps.meta.outputs.base_tag }}
+            LS_VERSION=${{ steps.meta.outputs.ls_version }}
+            GIT_HASH=${{ github.sha }}
+            BUILD_DATE=${{ steps.meta.outputs.build_date }}
+          tags: ${{ steps.meta.outputs.image }}:${{ steps.meta.outputs.tag }}
+
+      - name: Summary
+        run: |
+          echo "Pushed ${{ steps.meta.outputs.image }}:${{ steps.meta.outputs.tag }}" >> "$GITHUB_STEP_SUMMARY"

AGENTS.md

@@ -5,16 +5,14 @@ llama-swap is a light weight, transparent proxy server that provides automatic m
 ## Tech stack
 
 - golang
-- typescript, vite and svelt5 for UI (located in ui/)
+- typescript, vite and svelte 5 for UI (located in ui-svelte/)
 
 ## Workflow Tasks
 
 - when summarizing changes only include details that require further action
-- just say "Done." when there is no further action
-- use the github CLI `gh` to create pull requests and work with github
 - Rules for creating pull requests:
-  - keep them short and focused on changes.
+  - keep them short and focused on changes
-  - never include a test plan
+  - skip the test plan
   - write the summary using the same style rules as commit message
 
 ## Testing
@@ -30,7 +28,7 @@ llama-swap is a light weight, transparent proxy server that provides automatic m
 ### Commit message example format:
 
 ```
-proxy: add new feature
+internal/server: add new feature
 
 Add new feature that implements functionality X and Y.
 

config-schema.json

@@ -601,10 +601,11 @@
                         "use": {
                             "type": "string",
                             "enum": [
+                                "serial",
                                 "fifo"
                             ],
-                            "default": "fifo",
+                            "default": "serial",
-                            "description": "Scheduler to use. Only 'fifo' is currently supported."
+                            "description": "Scheduler to use. 'serial' (default on this fork): strict one-model-at-a-time, requests run in exact arrival order, switching models evicts every other model first. 'fifo': throughput-oriented, batches same-model requests and allows parallel/co-resident models."
                         },
                         "settings": {
                             "type": "object",

config.example.yaml

@@ -556,11 +556,21 @@ routing:
           # expands to: [L]
           full: "L"
 
-  # scheduler: how queued requests are ordered.
+  # scheduler: how queued requests are ordered and run.
-  # The default and only valid scheduler is "fifo"
+  # - optional, default on this fork: "serial"
+  # - valid values:
+  #   - "serial": strict one-model-at-a-time. Requests run in exact arrival
+  #     order; only one request runs at a time; switching to a different model
+  #     evicts every other running model first so a single model occupies memory
+  #     at a time. This ignores group/matrix co-residency entirely. The "fifo"
+  #     settings below (priority) do not apply.
+  #   - "fifo": throughput-oriented. Same-model requests are batched to reduce
+  #     swaps and a model serves up to its concurrencyLimit in parallel; models
+  #     in non-exclusive groups can run concurrently. Requests may be reordered.
   scheduler:
-    use: fifo
+    use: serial
     settings:
+      # fifo settings only apply when use: fifo
       fifo:
         # priority: a dictionary of model ID -> priority
         # - optional, default: empty dictionary

docker/fork-cuda.Containerfile

@@ -0,0 +1,74 @@
+# Build a CUDA llama-swap image FROM THIS FORK's source (includes the serial
+# scheduler) and layer it on a pinned llama.cpp CUDA server base. Produces e.g.:
+#   gitea.stevedudenhoeffer.com/steve/llama-swap:v230-cuda-b9821
+#
+# BASE_TAG selects the llama.cpp CUDA runtime + llama-server build, e.g.
+# "server-cuda-b9821". The llama-swap binary (with the embedded Svelte UI) is
+# compiled from the repo at build time, so no GitHub release is required.
+#
+# Build context is the repo root:
+#   docker build -f docker/fork-cuda.Containerfile \
+#     --build-arg BASE_TAG=server-cuda-b9821 -t llama-swap:v230-cuda-b9821 .
+
+ARG BASE_IMAGE=ghcr.io/ggml-org/llama.cpp
+ARG BASE_TAG=server-cuda-b9821
+
+# ---- Stage 1: build the Svelte UI (embedded into the binary) ----
+FROM node:22-bookworm-slim AS ui
+WORKDIR /src/ui-svelte
+# Install deps first for layer caching. .npmrc carries legacy-peer-deps=true,
+# which the project relies on (tailwind/vite peer ranges), so copy it before
+# npm ci or the strict resolver fails with ERESOLVE.
+COPY ui-svelte/package.json ui-svelte/package-lock.json ui-svelte/.npmrc ./
+RUN npm ci
+COPY ui-svelte/ ./
+# `npm run build` is `vite build --emptyOutDir`; vite.config.ts writes to
+# ../internal/server/ui_dist, which //go:embed picks up in the next stage.
+RUN mkdir -p /src/internal/server && npm run build
+
+# ---- Stage 2: build the llama-swap binary with the embedded UI ----
+FROM golang:1.26-bookworm AS build
+WORKDIR /src
+# Cache modules independently of source churn.
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+# Overlay the freshly built UI so //go:embed ui_dist ships the real assets
+# instead of the committed placeholder.
+COPY --from=ui /src/internal/server/ui_dist/ ./internal/server/ui_dist/
+ARG LS_VERSION=v230
+ARG GIT_HASH=unknown
+ARG BUILD_DATE=unknown
+RUN CGO_ENABLED=0 GOOS=linux go build \
+    -ldflags="-X main.version=${LS_VERSION} -X main.commit=${GIT_HASH} -X main.date=${BUILD_DATE}" \
+    -o /out/llama-swap .
+
+# ---- Stage 3: runtime image on the pinned llama.cpp CUDA base ----
+FROM ${BASE_IMAGE}:${BASE_TAG}
+
+# Run as root by default to match the upstream `vNNN-cuda-bNNNN` (non-suffixed)
+# image that ragnaros pulls today: it needs root to reach the mounted docker
+# socket for container-backed models (sd-server). Override UID/GID at build time
+# for a non-root variant.
+ARG UID=0
+ARG GID=0
+ARG USER_HOME=/root
+ENV HOME=$USER_HOME
+
+RUN set -eux; \
+    if [ "$UID" -ne 0 ]; then \
+      if [ "$GID" -ne 0 ]; then groupadd --system --gid "$GID" app; fi; \
+      useradd --system --uid "$UID" --gid "$GID" --home "$USER_HOME" app; \
+    fi; \
+    mkdir --parents "$HOME" /app; \
+    chown --recursive "$UID:$GID" "$HOME" /app
+
+COPY --from=build --chown=$UID:$GID /out/llama-swap /app/llama-swap
+COPY --chown=$UID:$GID docker/config.example.yaml /app/config.yaml
+
+USER $UID:$GID
+WORKDIR /app
+ENV PATH="/app:${PATH}"
+
+HEALTHCHECK CMD curl -f http://localhost:8080/ || exit 1
+ENTRYPOINT [ "/app/llama-swap", "-config", "/app/config.yaml" ]

internal/config/commands.go

@@ -0,0 +1,57 @@
+package config
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+
+	"github.com/billziss-gh/golib/shlex"
+)
+
+func SanitizeCommand(cmdStr string) ([]string, error) {
+	var cleanedLines []string
+	for _, line := range strings.Split(cmdStr, "\n") {
+		trimmed := strings.TrimSpace(line)
+		// Skip comment lines
+		if strings.HasPrefix(trimmed, "#") {
+			continue
+		}
+		// Handle trailing backslashes by replacing with space
+		if strings.HasSuffix(trimmed, "\\") {
+			cleanedLines = append(cleanedLines, strings.TrimSuffix(trimmed, "\\")+" ")
+		} else {
+			cleanedLines = append(cleanedLines, line)
+		}
+	}
+
+	// put it back together
+	cmdStr = strings.Join(cleanedLines, "\n")
+
+	// Split the command into arguments
+	var args []string
+	if runtime.GOOS == "windows" {
+		args = shlex.Windows.Split(cmdStr)
+	} else {
+		args = shlex.Posix.Split(cmdStr)
+	}
+
+	// Ensure the command is not empty
+	if len(args) == 0 {
+		return nil, fmt.Errorf("empty command")
+	}
+
+	return args, nil
+}
+
+func StripComments(cmdStr string) string {
+	var cleanedLines []string
+	for _, line := range strings.Split(cmdStr, "\n") {
+		trimmed := strings.TrimSpace(line)
+		// Skip comment lines
+		if strings.HasPrefix(trimmed, "#") {
+			continue
+		}
+		cleanedLines = append(cleanedLines, line)
+	}
+	return strings.Join(cleanedLines, "\n")
+}

internal/config/config.go

@@ -2,16 +2,9 @@ package config
 
 import (
 	"fmt"
-	"io"
-	"net/url"
 	"os"
-	"regexp"
-	"runtime"
 	"sort"
-	"strings"
-	"time"
 
-	"github.com/billziss-gh/golib/shlex"
 	"gopkg.in/yaml.v3"
 )
 
@@ -85,12 +78,6 @@ type GroupConfig struct {
 	Members    []string `yaml:"members"`
 }
 
-var (
-	macroNameRegex    = regexp.MustCompile(`^[a-zA-Z0-9_-]+$`)
-	macroPatternRegex = regexp.MustCompile(`\$\{([a-zA-Z0-9_-]+)\}`)
-	envMacroRegex     = regexp.MustCompile(`\$\{env\.([a-zA-Z_][a-zA-Z0-9_]*)\}`)
-)
-
 // set default values for GroupConfig
 func (c *GroupConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	type rawGroupConfig GroupConfig
@@ -224,430 +211,6 @@ func LoadConfig(path string) (Config, error) {
 	return LoadConfigFromReader(file)
 }
 
-func LoadConfigFromReader(r io.Reader) (Config, error) {
-	data, err := io.ReadAll(r)
-	if err != nil {
-		return Config{}, err
-	}
-	yamlStr := string(data)
-
-	// Phase 1: Substitute all ${env.VAR} macros at string level
-	// This is safe because env values are simple strings without YAML formatting
-	yamlStr, err = substituteEnvMacros(yamlStr)
-	if err != nil {
-		return Config{}, err
-	}
-
-	// Unmarshal into full Config with defaults
-	config := Config{
-		HealthCheckTimeout: 120,
-		StartPort:          5800,
-		LogLevel:           "info",
-		LogTimeFormat:      "",
-		LogToStdout:        LogToStdoutProxy,
-		MetricsMaxInMemory: 1000,
-		CaptureBuffer:      5,
-		GlobalTTL:          0,
-	}
-	if err = yaml.Unmarshal([]byte(yamlStr), &config); err != nil {
-		return Config{}, err
-	}
-
-	if config.HealthCheckTimeout < 15 {
-		config.HealthCheckTimeout = 15
-	}
-
-	// Apply defaults for performance config when section is missing
-	if config.Performance.Every == 0 {
-		config.Performance.Every = 5 * time.Second
-	}
-	if err = config.Performance.Validate(); err != nil {
-		return Config{}, fmt.Errorf("performance: %w", err)
-	}
-
-	if config.StartPort < 1 {
-		return Config{}, fmt.Errorf("startPort must be greater than 1")
-	}
-
-	if config.GlobalTTL < 0 {
-		return Config{}, fmt.Errorf("globalTTL must be >= 0")
-	}
-
-	// Apply default for upstream.ignorePaths when not specified. The default
-	// matches common static-asset suffixes so they do not trigger a swap.
-	if len(config.Upstream.IgnorePaths) == 0 {
-		config.Upstream.IgnorePaths = DefaultUpstreamIgnorePaths()
-	}
-
-	switch config.LogToStdout {
-	case LogToStdoutProxy, LogToStdoutUpstream, LogToStdoutBoth, LogToStdoutNone:
-	default:
-		return Config{}, fmt.Errorf("logToStdout must be one of: proxy, upstream, both, none")
-	}
-
-	// Populate the aliases map
-	config.aliases = make(map[string]string)
-	for modelName, modelConfig := range config.Models {
-		for _, alias := range modelConfig.Aliases {
-			if _, found := config.aliases[alias]; found {
-				return Config{}, fmt.Errorf("duplicate alias %s found in model: %s", alias, modelName)
-			}
-			config.aliases[alias] = modelName
-		}
-	}
-
-	// Validate global macros
-	for _, macro := range config.Macros {
-		if err = validateMacro(macro.Name, macro.Value); err != nil {
-			return Config{}, err
-		}
-	}
-
-	// Get and sort all model IDs for consistent port assignment
-	modelIds := make([]string, 0, len(config.Models))
-	for modelId := range config.Models {
-		modelIds = append(modelIds, modelId)
-	}
-	sort.Strings(modelIds)
-
-	nextPort := config.StartPort
-	for _, modelId := range modelIds {
-		modelConfig := config.Models[modelId]
-		modelConfig.HealthCheckTimeout = config.HealthCheckTimeout
-
-		// Strip comments from command fields
-		modelConfig.Cmd = StripComments(modelConfig.Cmd)
-		modelConfig.CmdStop = StripComments(modelConfig.CmdStop)
-
-		// set model TTL to globalTTL it is the default value
-		if modelConfig.UnloadAfter == MODEL_CONFIG_DEFAULT_TTL {
-			modelConfig.UnloadAfter = config.GlobalTTL
-		}
-
-		if modelConfig.UnloadAfter < 0 {
-			return Config{}, fmt.Errorf("model %s: invalid TTL value %d", modelId, modelConfig.UnloadAfter)
-		}
-
-		// Validate model macros
-		for _, macro := range modelConfig.Macros {
-			if err = validateMacro(macro.Name, macro.Value); err != nil {
-				return Config{}, fmt.Errorf("model %s: %s", modelId, err.Error())
-			}
-		}
-
-		// Build merged macro list: MODEL_ID + global macros + model macros (model overrides global)
-		mergedMacros := make(MacroList, 0, len(config.Macros)+len(modelConfig.Macros)+1)
-		mergedMacros = append(mergedMacros, MacroEntry{Name: "MODEL_ID", Value: modelId})
-		mergedMacros = append(mergedMacros, config.Macros...)
-
-		// Add model macros (override globals with same name)
-		for _, entry := range modelConfig.Macros {
-			found := false
-			for i, existing := range mergedMacros {
-				if existing.Name == entry.Name {
-					mergedMacros[i] = entry
-					found = true
-					break
-				}
-			}
-			if !found {
-				mergedMacros = append(mergedMacros, entry)
-			}
-		}
-
-		// Substitute remaining macros in model fields (LIFO order)
-		for i := len(mergedMacros) - 1; i >= 0; i-- {
-			entry := mergedMacros[i]
-			macroSlug := fmt.Sprintf("${%s}", entry.Name)
-			macroStr := fmt.Sprintf("%v", entry.Value)
-
-			modelConfig.Cmd = strings.ReplaceAll(modelConfig.Cmd, macroSlug, macroStr)
-			modelConfig.CmdStop = strings.ReplaceAll(modelConfig.CmdStop, macroSlug, macroStr)
-			modelConfig.Proxy = strings.ReplaceAll(modelConfig.Proxy, macroSlug, macroStr)
-			modelConfig.CheckEndpoint = strings.ReplaceAll(modelConfig.CheckEndpoint, macroSlug, macroStr)
-			modelConfig.Filters.StripParams = strings.ReplaceAll(modelConfig.Filters.StripParams, macroSlug, macroStr)
-			modelConfig.Name = strings.ReplaceAll(modelConfig.Name, macroSlug, macroStr)
-			modelConfig.Description = strings.ReplaceAll(modelConfig.Description, macroSlug, macroStr)
-
-			// Substitute macros in SetParamsByID keys and values
-			if len(modelConfig.Filters.SetParamsByID) > 0 {
-				newSetParamsByID := make(map[string]map[string]any, len(modelConfig.Filters.SetParamsByID))
-				for key, paramMap := range modelConfig.Filters.SetParamsByID {
-					newKey := strings.ReplaceAll(key, macroSlug, macroStr)
-					newValAny, err := substituteMacroInValue(any(paramMap), entry.Name, entry.Value)
-					if err != nil {
-						return Config{}, fmt.Errorf("model %s filters.setParamsByID: %s", modelId, err.Error())
-					}
-					newParamMap, ok := newValAny.(map[string]any)
-					if !ok {
-						return Config{}, fmt.Errorf("model %s filters.setParamsByID: unexpected type after macro substitution", modelId)
-					}
-					newSetParamsByID[newKey] = newParamMap
-				}
-				modelConfig.Filters.SetParamsByID = newSetParamsByID
-			}
-
-			// Substitute in metadata (type-preserving)
-			if len(modelConfig.Metadata) > 0 {
-				result, err := substituteMacroInValue(modelConfig.Metadata, entry.Name, entry.Value)
-				if err != nil {
-					return Config{}, fmt.Errorf("model %s metadata: %s", modelId, err.Error())
-				}
-				modelConfig.Metadata = result.(map[string]any)
-			}
-		}
-
-		// Handle PORT macro - only allocate if cmd uses it
-		cmdHasPort := strings.Contains(modelConfig.Cmd, "${PORT}")
-		proxyHasPort := strings.Contains(modelConfig.Proxy, "${PORT}")
-		if cmdHasPort || proxyHasPort {
-			if !cmdHasPort && proxyHasPort {
-				return Config{}, fmt.Errorf("model %s: proxy uses ${PORT} but cmd does not - ${PORT} is only available when used in cmd", modelId)
-			}
-
-			macroSlug := "${PORT}"
-			macroStr := fmt.Sprintf("%v", nextPort)
-
-			modelConfig.Cmd = strings.ReplaceAll(modelConfig.Cmd, macroSlug, macroStr)
-			modelConfig.CmdStop = strings.ReplaceAll(modelConfig.CmdStop, macroSlug, macroStr)
-			modelConfig.Proxy = strings.ReplaceAll(modelConfig.Proxy, macroSlug, macroStr)
-			modelConfig.Name = strings.ReplaceAll(modelConfig.Name, macroSlug, macroStr)
-			modelConfig.Description = strings.ReplaceAll(modelConfig.Description, macroSlug, macroStr)
-
-			if len(modelConfig.Metadata) > 0 {
-				result, err := substituteMacroInValue(modelConfig.Metadata, "PORT", nextPort)
-				if err != nil {
-					return Config{}, fmt.Errorf("model %s metadata: %s", modelId, err.Error())
-				}
-				modelConfig.Metadata = result.(map[string]any)
-			}
-
-			nextPort++
-		}
-
-		// Validate no unknown macros remain
-		fieldMap := map[string]string{
-			"cmd":                 modelConfig.Cmd,
-			"cmdStop":             modelConfig.CmdStop,
-			"proxy":               modelConfig.Proxy,
-			"checkEndpoint":       modelConfig.CheckEndpoint,
-			"filters.stripParams": modelConfig.Filters.StripParams,
-			"name":                modelConfig.Name,
-			"description":         modelConfig.Description,
-		}
-
-		for fieldName, fieldValue := range fieldMap {
-			matches := macroPatternRegex.FindAllStringSubmatch(fieldValue, -1)
-			for _, match := range matches {
-				macroName := match[1]
-				if macroName == "PID" && fieldName == "cmdStop" {
-					continue // replaced at runtime
-				}
-				if macroName == "PORT" || macroName == "MODEL_ID" {
-					return Config{}, fmt.Errorf("macro '${%s}' should have been substituted in %s.%s", macroName, modelId, fieldName)
-				}
-				return Config{}, fmt.Errorf("unknown macro '${%s}' found in %s.%s", macroName, modelId, fieldName)
-			}
-		}
-
-		if len(modelConfig.Metadata) > 0 {
-			if err := validateNestedForUnknownMacros(modelConfig.Metadata, fmt.Sprintf("model %s metadata", modelId)); err != nil {
-				return Config{}, err
-			}
-		}
-
-		if err = modelConfig.Capabilities.Validate(); err != nil {
-			return Config{}, fmt.Errorf("model %s: %w", modelId, err)
-		}
-
-		// Validate SetParamsByID keys and values
-		for key, paramMap := range modelConfig.Filters.SetParamsByID {
-			if matches := macroPatternRegex.FindAllStringSubmatch(key, -1); len(matches) > 0 {
-				return Config{}, fmt.Errorf("unknown macro '${%s}' found in model %s filters.setParamsByID key", matches[0][1], modelId)
-			}
-			if err := validateNestedForUnknownMacros(any(paramMap), fmt.Sprintf("model %s filters.setParamsByID[%s]", modelId, key)); err != nil {
-				return Config{}, err
-			}
-		}
-
-		// Auto-register setParamsByID keys as aliases (skip the model's own ID)
-		for key := range modelConfig.Filters.SetParamsByID {
-			if key == modelId {
-				continue
-			}
-			if _, exists := config.Models[key]; exists {
-				return Config{}, fmt.Errorf("model %s filters.setParamsByID: key '%s' conflicts with an existing model ID", modelId, key)
-			}
-			if existingModel, exists := config.aliases[key]; exists {
-				if existingModel != modelId {
-					return Config{}, fmt.Errorf("duplicate alias '%s' in model %s filters.setParamsByID, already used by model %s", key, modelId, existingModel)
-				}
-				continue // already registered as explicit alias for this model
-			}
-			config.aliases[key] = modelId
-			modelConfig.Aliases = append(modelConfig.Aliases, key)
-		}
-
-		if _, err := url.Parse(modelConfig.Proxy); err != nil {
-			return Config{}, fmt.Errorf("model %s: invalid proxy URL: %w", modelId, err)
-		}
-
-		if modelConfig.SendLoadingState == nil {
-			v := config.SendLoadingState
-			modelConfig.SendLoadingState = &v
-		}
-
-		config.Models[modelId] = modelConfig
-	}
-
-	// Normalize routing config. The legacy top-level `matrix`/`groups` keys and
-	// the new `routing.router` block are mutually exclusive: a config may use
-	// either style, never both.
-	hasTopLevel := config.Matrix != nil || len(config.Groups) > 0
-	rtr := config.Routing.Router
-	hasRouting := rtr.Use != "" || rtr.Settings.Matrix != nil || len(rtr.Settings.Groups) > 0
-
-	if hasTopLevel && hasRouting {
-		return Config{}, fmt.Errorf("config uses both the legacy top-level 'matrix'/'groups' keys and the new 'routing.router' block; please migrate the top-level keys into 'routing.router' and remove them")
-	}
-
-	if !hasTopLevel {
-		// Both groups and matrix may be defined under routing.router.settings;
-		// routing.router.use selects which one is active, so there is no conflict.
-		rs := config.Routing.Router.Settings
-		switch config.Routing.Router.Use {
-		case "matrix":
-			if rs.Matrix == nil {
-				return Config{}, fmt.Errorf("routing.router.use is 'matrix' but routing.router.settings.matrix is not set")
-			}
-			config.Matrix = rs.Matrix
-		case "group", "":
-			config.Groups = rs.Groups
-		default:
-			return Config{}, fmt.Errorf("routing.router.use: unknown router %q (valid: group, matrix)", config.Routing.Router.Use)
-		}
-	}
-
-	// groups XOR matrix
-	if config.Matrix != nil && len(config.Groups) > 0 {
-		return Config{}, fmt.Errorf("config cannot use both 'groups' and 'matrix'")
-	}
-
-	if config.Matrix != nil {
-		expandedSets, err := ValidateMatrix(*config.Matrix, config.Models)
-		if err != nil {
-			return Config{}, fmt.Errorf("matrix: %w", err)
-		}
-		config.Matrix.ExpandedSets = expandedSets
-	} else {
-		config = AddDefaultGroupToConfig(config)
-
-		// Validate group members
-		memberUsage := make(map[string]string)
-		for groupID, groupConfig := range config.Groups {
-			prevSet := make(map[string]bool)
-			for _, member := range groupConfig.Members {
-				if _, found := prevSet[member]; found {
-					return Config{}, fmt.Errorf("duplicate model member %s found in group: %s", member, groupID)
-				}
-				prevSet[member] = true
-
-				if existingGroup, exists := memberUsage[member]; exists {
-					return Config{}, fmt.Errorf("model member %s is used in multiple groups: %s and %s", member, existingGroup, groupID)
-				}
-				memberUsage[member] = groupID
-			}
-		}
-	}
-
-	// Build the canonical Config.Routing from the effective result. Both legacy
-	// and new-style configs converge here. The Matrix pointer is shared so
-	// ExpandedSets stays in one place.
-	if config.Matrix != nil {
-		config.Routing.Router.Use = "matrix"
-	} else {
-		config.Routing.Router.Use = "group"
-	}
-	config.Routing.Router.Settings.Matrix = config.Matrix
-	config.Routing.Router.Settings.Groups = config.Groups
-
-	if config.Routing.Scheduler.Use == "" {
-		config.Routing.Scheduler.Use = "fifo"
-	}
-	if config.Routing.Scheduler.Use != "fifo" {
-		return Config{}, fmt.Errorf("routing.scheduler.use: unknown scheduler %q (valid: fifo)", config.Routing.Scheduler.Use)
-	}
-	for modelID := range config.Routing.Scheduler.Settings.Fifo.Priority {
-		if _, found := config.RealModelName(modelID); !found {
-			return Config{}, fmt.Errorf("routing.scheduler.settings.fifo.priority references unknown model %q", modelID)
-		}
-	}
-
-	// Clean up hooks preload
-	if len(config.Hooks.OnStartup.Preload) > 0 {
-		var toPreload []string
-		for _, modelID := range config.Hooks.OnStartup.Preload {
-			modelID = strings.TrimSpace(modelID)
-			if modelID == "" {
-				continue
-			}
-			if real, found := config.RealModelName(modelID); found {
-				toPreload = append(toPreload, real)
-			}
-		}
-		config.Hooks.OnStartup.Preload = toPreload
-	}
-
-	// Validate API keys (env macros already substituted at string level)
-	for i, apikey := range config.RequiredAPIKeys {
-		if apikey == "" {
-			return Config{}, fmt.Errorf("empty api key found in apiKeys")
-		}
-		if strings.Contains(apikey, " ") {
-			return Config{}, fmt.Errorf("api key cannot contain spaces: `%s`", apikey)
-		}
-		config.RequiredAPIKeys[i] = apikey
-	}
-
-	// Process peers with global macro substitution
-	for peerName, peerConfig := range config.Peers {
-		// Substitute global macros (LIFO order)
-		for i := len(config.Macros) - 1; i >= 0; i-- {
-			entry := config.Macros[i]
-			macroSlug := fmt.Sprintf("${%s}", entry.Name)
-			macroStr := fmt.Sprintf("%v", entry.Value)
-
-			peerConfig.ApiKey = strings.ReplaceAll(peerConfig.ApiKey, macroSlug, macroStr)
-			peerConfig.Filters.StripParams = strings.ReplaceAll(peerConfig.Filters.StripParams, macroSlug, macroStr)
-
-			// Substitute in setParams (type-preserving)
-			if len(peerConfig.Filters.SetParams) > 0 {
-				result, err := substituteMacroInValue(peerConfig.Filters.SetParams, entry.Name, entry.Value)
-				if err != nil {
-					return Config{}, fmt.Errorf("peers.%s.filters.setParams: %w", peerName, err)
-				}
-				peerConfig.Filters.SetParams = result.(map[string]any)
-			}
-		}
-
-		// Validate no unknown macros remain
-		if matches := macroPatternRegex.FindAllStringSubmatch(peerConfig.ApiKey, -1); len(matches) > 0 {
-			return Config{}, fmt.Errorf("peers.%s.apiKey: unknown macro '${%s}'", peerName, matches[0][1])
-		}
-		if matches := macroPatternRegex.FindAllStringSubmatch(peerConfig.Filters.StripParams, -1); len(matches) > 0 {
-			return Config{}, fmt.Errorf("peers.%s.filters.stripParams: unknown macro '${%s}'", peerName, matches[0][1])
-		}
-		if len(peerConfig.Filters.SetParams) > 0 {
-			if err := validateNestedForUnknownMacros(peerConfig.Filters.SetParams, fmt.Sprintf("peers.%s.filters.setParams", peerName)); err != nil {
-				return Config{}, err
-			}
-		}
-		config.Peers[peerName] = peerConfig
-	}
-
-	return config, nil
-}
-
 // rewrites the yaml to include a default group with any orphaned models
 func AddDefaultGroupToConfig(config Config) Config {
 
@@ -692,233 +255,3 @@ func AddDefaultGroupToConfig(config Config) Config {
 
 	return config
 }
-
-func SanitizeCommand(cmdStr string) ([]string, error) {
-	var cleanedLines []string
-	for _, line := range strings.Split(cmdStr, "\n") {
-		trimmed := strings.TrimSpace(line)
-		// Skip comment lines
-		if strings.HasPrefix(trimmed, "#") {
-			continue
-		}
-		// Handle trailing backslashes by replacing with space
-		if strings.HasSuffix(trimmed, "\\") {
-			cleanedLines = append(cleanedLines, strings.TrimSuffix(trimmed, "\\")+" ")
-		} else {
-			cleanedLines = append(cleanedLines, line)
-		}
-	}
-
-	// put it back together
-	cmdStr = strings.Join(cleanedLines, "\n")
-
-	// Split the command into arguments
-	var args []string
-	if runtime.GOOS == "windows" {
-		args = shlex.Windows.Split(cmdStr)
-	} else {
-		args = shlex.Posix.Split(cmdStr)
-	}
-
-	// Ensure the command is not empty
-	if len(args) == 0 {
-		return nil, fmt.Errorf("empty command")
-	}
-
-	return args, nil
-}
-
-func StripComments(cmdStr string) string {
-	var cleanedLines []string
-	for _, line := range strings.Split(cmdStr, "\n") {
-		trimmed := strings.TrimSpace(line)
-		// Skip comment lines
-		if strings.HasPrefix(trimmed, "#") {
-			continue
-		}
-		cleanedLines = append(cleanedLines, line)
-	}
-	return strings.Join(cleanedLines, "\n")
-}
-
-// validateMacro validates macro name and value constraints
-func validateMacro(name string, value any) error {
-	if len(name) >= 64 {
-		return fmt.Errorf("macro name '%s' exceeds maximum length of 63 characters", name)
-	}
-	if !macroNameRegex.MatchString(name) {
-		return fmt.Errorf("macro name '%s' contains invalid characters, must match pattern ^[a-zA-Z0-9_-]+$", name)
-	}
-
-	// Validate that value is a scalar type
-	switch v := value.(type) {
-	case string:
-		// Check for self-reference
-		macroSlug := fmt.Sprintf("${%s}", name)
-		if strings.Contains(v, macroSlug) {
-			return fmt.Errorf("macro '%s' contains self-reference", name)
-		}
-	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, bool:
-		// These types are allowed
-	default:
-		return fmt.Errorf("macro '%s' has invalid type %T, must be a scalar type (string, int, float, or bool)", name, value)
-	}
-
-	switch name {
-	case "PORT", "MODEL_ID":
-		return fmt.Errorf("macro name '%s' is reserved", name)
-	}
-
-	return nil
-}
-
-// validateNestedForUnknownMacros recursively checks for any remaining macro references in nested structures
-func validateNestedForUnknownMacros(value any, context string) error {
-	switch v := value.(type) {
-	case string:
-		matches := macroPatternRegex.FindAllStringSubmatch(v, -1)
-		for _, match := range matches {
-			macroName := match[1]
-			return fmt.Errorf("%s: unknown macro '${%s}'", context, macroName)
-		}
-		// Check for unsubstituted env macros
-		envMatches := envMacroRegex.FindAllStringSubmatch(v, -1)
-		for _, match := range envMatches {
-			varName := match[1]
-			return fmt.Errorf("%s: environment variable '%s' not set", context, varName)
-		}
-		return nil
-
-	case map[string]any:
-		for _, val := range v {
-			if err := validateNestedForUnknownMacros(val, context); err != nil {
-				return err
-			}
-		}
-		return nil
-
-	case []any:
-		for _, val := range v {
-			if err := validateNestedForUnknownMacros(val, context); err != nil {
-				return err
-			}
-		}
-		return nil
-
-	default:
-		// Scalar types don't contain macros
-		return nil
-	}
-}
-
-// substituteMacroInValue recursively substitutes a single macro in a value structure
-// This is called once per macro, allowing LIFO substitution order
-func substituteMacroInValue(value any, macroName string, macroValue any) (any, error) {
-	macroSlug := fmt.Sprintf("${%s}", macroName)
-	macroStr := fmt.Sprintf("%v", macroValue)
-
-	switch v := value.(type) {
-	case string:
-		// Check if this is a direct macro substitution
-		if v == macroSlug {
-			return macroValue, nil
-		}
-		// Handle string interpolation
-		if strings.Contains(v, macroSlug) {
-			return strings.ReplaceAll(v, macroSlug, macroStr), nil
-		}
-		return v, nil
-
-	case map[string]any:
-		// Recursively process map values
-		newMap := make(map[string]any)
-		for key, val := range v {
-			newVal, err := substituteMacroInValue(val, macroName, macroValue)
-			if err != nil {
-				return nil, err
-			}
-			newMap[key] = newVal
-		}
-		return newMap, nil
-
-	case []any:
-		// Recursively process slice elements
-		newSlice := make([]any, len(v))
-		for i, val := range v {
-			newVal, err := substituteMacroInValue(val, macroName, macroValue)
-			if err != nil {
-				return nil, err
-			}
-			newSlice[i] = newVal
-		}
-		return newSlice, nil
-
-	default:
-		// Return scalar types as-is
-		return value, nil
-	}
-}
-
-// substituteEnvMacros replaces ${env.VAR_NAME} with environment variable values.
-// Returns error if any referenced env var is not set or contains invalid characters.
-// Env macros inside YAML comments are ignored by unmarshalling the YAML first
-// (which strips comments) and only checking the comment-free version for macros.
-func substituteEnvMacros(s string) (string, error) {
-	// Unmarshal and remarshal to strip YAML comments
-	var raw any
-	if err := yaml.Unmarshal([]byte(s), &raw); err != nil {
-		// If YAML is invalid, fall back to scanning the original string
-		// so the user gets the env var error rather than a confusing YAML parse error
-		return substituteEnvMacrosInString(s, s)
-	}
-	clean, err := yaml.Marshal(raw)
-	if err != nil {
-		return substituteEnvMacrosInString(s, s)
-	}
-
-	return substituteEnvMacrosInString(s, string(clean))
-}
-
-// substituteEnvMacrosInString finds ${env.VAR} macros in scanStr and substitutes
-// them in target. This separation allows scanning comment-free YAML while
-// substituting in the original string.
-func substituteEnvMacrosInString(target, scanStr string) (string, error) {
-	result := target
-	matches := envMacroRegex.FindAllStringSubmatch(scanStr, -1)
-	for _, match := range matches {
-		fullMatch := match[0] // ${env.VAR_NAME}
-		varName := match[1]   // VAR_NAME
-
-		value, exists := os.LookupEnv(varName)
-		if !exists {
-			return "", fmt.Errorf("environment variable '%s' is not set", varName)
-		}
-
-		// Sanitize the value for safe YAML substitution
-		value, err := sanitizeEnvValueForYAML(value, varName)
-		if err != nil {
-			return "", err
-		}
-
-		result = strings.ReplaceAll(result, fullMatch, value)
-	}
-	return result, nil
-}
-
-// sanitizeEnvValueForYAML ensures an environment variable value is safe for YAML substitution.
-// It rejects values with characters that break YAML structure and escapes quotes/backslashes
-// for compatibility with double-quoted YAML strings.
-func sanitizeEnvValueForYAML(value, varName string) (string, error) {
-	// Reject values that would break YAML structure regardless of quoting context
-	if strings.ContainsAny(value, "\n\r\x00") {
-		return "", fmt.Errorf("environment variable '%s' contains newlines or null bytes which are not allowed in YAML substitution", varName)
-	}
-
-	// Escape backslashes and double quotes for safe use in double-quoted YAML strings.
-	// In unquoted contexts, these escapes appear literally (harmless for most use cases).
-	// In double-quoted contexts, they are interpreted correctly.
-	value = strings.ReplaceAll(value, `\`, `\\`)
-	value = strings.ReplaceAll(value, `"`, `\"`)
-
-	return value, nil
-}

internal/config/config_posix_test.go

@@ -277,7 +277,7 @@ groups:
 				},
 			},
 			Scheduler: SchedulerConfig{
-				Use: "fifo",
+				Use: "serial",
 			},
 		},
 	}

internal/config/config_test.go

@@ -777,22 +777,27 @@ func TestConfig_APIKeys_Invalid(t *testing.T) {
 		{
 			name:        "blank spaces only",
 			content:     `apiKeys: ["   "]`,
-			expectedErr: "api key cannot contain spaces: `   `",
+			expectedErr: "apiKeys[0]: api key cannot contain spaces",
 		},
 		{
 			name:        "contains leading space",
 			content:     `apiKeys: [" key123"]`,
-			expectedErr: "api key cannot contain spaces: ` key123`",
+			expectedErr: "apiKeys[0]: api key cannot contain spaces",
 		},
 		{
 			name:        "contains trailing space",
 			content:     `apiKeys: ["key123 "]`,
-			expectedErr: "api key cannot contain spaces: `key123 `",
+			expectedErr: "apiKeys[0]: api key cannot contain spaces",
 		},
 		{
 			name:        "contains middle space",
 			content:     `apiKeys: ["key 123"]`,
-			expectedErr: "api key cannot contain spaces: `key 123`",
+			expectedErr: "apiKeys[0]: api key cannot contain spaces",
+		},
+		{
+			name:        "space in second key reports correct index",
+			content:     `apiKeys: ["valid-key", "bad key"]`,
+			expectedErr: "apiKeys[1]: api key cannot contain spaces",
 		},
 		{
 			name:        "empty in list with valid keys",
@@ -1567,7 +1572,7 @@ groups:
 	assert.Equal(t, "group", cfg.Routing.Router.Use)
 	// default group injected for orphaned models (none here) still leaves g1
 	assert.Contains(t, cfg.Routing.Router.Settings.Groups, "g1")
-	assert.Equal(t, "fifo", cfg.Routing.Scheduler.Use)
+	assert.Equal(t, "serial", cfg.Routing.Scheduler.Use)
 }
 
 func TestConfig_Routing_LegacyTopLevelMatrix(t *testing.T) {
@@ -1626,7 +1631,7 @@ func TestConfig_Routing_DefaultsToGroup(t *testing.T) {
 	cfg, err := LoadConfigFromReader(strings.NewReader(twoModels))
 	require.NoError(t, err)
 	assert.Equal(t, "group", cfg.Routing.Router.Use)
-	assert.Equal(t, "fifo", cfg.Routing.Scheduler.Use)
+	assert.Equal(t, "serial", cfg.Routing.Scheduler.Use)
 }
 
 func TestConfig_Routing_LegacyAndRoutingConflict(t *testing.T) {

internal/config/config_windows_test.go

@@ -266,7 +266,7 @@ groups:
 				},
 			},
 			Scheduler: SchedulerConfig{
-				Use: "fifo",
+				Use: "serial",
 			},
 		},
 	}

internal/config/load.go

@@ -0,0 +1,441 @@
+package config
+
+import (
+	"fmt"
+	"io"
+	"net/url"
+	"sort"
+	"strings"
+	"time"
+
+	"gopkg.in/yaml.v3"
+)
+
+func LoadConfigFromReader(r io.Reader) (Config, error) {
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return Config{}, err
+	}
+	yamlStr := string(data)
+
+	// Phase 1: Substitute all ${env.VAR} macros at string level
+	// This is safe because env values are simple strings without YAML formatting
+	yamlStr, err = substituteEnvMacros(yamlStr)
+	if err != nil {
+		return Config{}, err
+	}
+
+	// Unmarshal into full Config with defaults
+	config := Config{
+		HealthCheckTimeout: 120,
+		StartPort:          5800,
+		LogLevel:           "info",
+		LogTimeFormat:      "",
+		LogToStdout:        LogToStdoutProxy,
+		MetricsMaxInMemory: 1000,
+		CaptureBuffer:      5,
+		GlobalTTL:          0,
+	}
+	if err = yaml.Unmarshal([]byte(yamlStr), &config); err != nil {
+		return Config{}, err
+	}
+
+	if config.HealthCheckTimeout < 15 {
+		config.HealthCheckTimeout = 15
+	}
+
+	// Apply defaults for performance config when section is missing
+	if config.Performance.Every == 0 {
+		config.Performance.Every = 5 * time.Second
+	}
+	if err = config.Performance.Validate(); err != nil {
+		return Config{}, fmt.Errorf("performance: %w", err)
+	}
+
+	if config.StartPort < 1 {
+		return Config{}, fmt.Errorf("startPort must be greater than 1")
+	}
+
+	if config.GlobalTTL < 0 {
+		return Config{}, fmt.Errorf("globalTTL must be >= 0")
+	}
+
+	// Apply default for upstream.ignorePaths when not specified. The default
+	// matches common static-asset suffixes so they do not trigger a swap.
+	if len(config.Upstream.IgnorePaths) == 0 {
+		config.Upstream.IgnorePaths = DefaultUpstreamIgnorePaths()
+	}
+
+	switch config.LogToStdout {
+	case LogToStdoutProxy, LogToStdoutUpstream, LogToStdoutBoth, LogToStdoutNone:
+	default:
+		return Config{}, fmt.Errorf("logToStdout must be one of: proxy, upstream, both, none")
+	}
+
+	// Populate the aliases map
+	config.aliases = make(map[string]string)
+	for modelName, modelConfig := range config.Models {
+		for _, alias := range modelConfig.Aliases {
+			if _, found := config.aliases[alias]; found {
+				return Config{}, fmt.Errorf("duplicate alias %s found in model: %s", alias, modelName)
+			}
+			config.aliases[alias] = modelName
+		}
+	}
+
+	// Validate global macros
+	for _, macro := range config.Macros {
+		if err = validateMacro(macro.Name, macro.Value); err != nil {
+			return Config{}, err
+		}
+	}
+
+	// Get and sort all model IDs for consistent port assignment
+	modelIds := make([]string, 0, len(config.Models))
+	for modelId := range config.Models {
+		modelIds = append(modelIds, modelId)
+	}
+	sort.Strings(modelIds)
+
+	nextPort := config.StartPort
+	for _, modelId := range modelIds {
+		modelConfig := config.Models[modelId]
+		modelConfig.HealthCheckTimeout = config.HealthCheckTimeout
+
+		// Strip comments from command fields
+		modelConfig.Cmd = StripComments(modelConfig.Cmd)
+		modelConfig.CmdStop = StripComments(modelConfig.CmdStop)
+
+		// set model TTL to globalTTL it is the default value
+		if modelConfig.UnloadAfter == MODEL_CONFIG_DEFAULT_TTL {
+			modelConfig.UnloadAfter = config.GlobalTTL
+		}
+
+		if modelConfig.UnloadAfter < 0 {
+			return Config{}, fmt.Errorf("model %s: invalid TTL value %d", modelId, modelConfig.UnloadAfter)
+		}
+
+		// Validate model macros
+		for _, macro := range modelConfig.Macros {
+			if err = validateMacro(macro.Name, macro.Value); err != nil {
+				return Config{}, fmt.Errorf("model %s: %s", modelId, err.Error())
+			}
+		}
+
+		// Build merged macro list: MODEL_ID + global macros + model macros (model overrides global)
+		mergedMacros := make(MacroList, 0, len(config.Macros)+len(modelConfig.Macros)+1)
+		mergedMacros = append(mergedMacros, MacroEntry{Name: "MODEL_ID", Value: modelId})
+		mergedMacros = append(mergedMacros, config.Macros...)
+
+		// Add model macros (override globals with same name)
+		for _, entry := range modelConfig.Macros {
+			found := false
+			for i, existing := range mergedMacros {
+				if existing.Name == entry.Name {
+					mergedMacros[i] = entry
+					found = true
+					break
+				}
+			}
+			if !found {
+				mergedMacros = append(mergedMacros, entry)
+			}
+		}
+
+		// Substitute remaining macros in model fields (LIFO order)
+		for i := len(mergedMacros) - 1; i >= 0; i-- {
+			entry := mergedMacros[i]
+			macroSlug := fmt.Sprintf("${%s}", entry.Name)
+			macroStr := fmt.Sprintf("%v", entry.Value)
+
+			modelConfig.Cmd = strings.ReplaceAll(modelConfig.Cmd, macroSlug, macroStr)
+			modelConfig.CmdStop = strings.ReplaceAll(modelConfig.CmdStop, macroSlug, macroStr)
+			modelConfig.Proxy = strings.ReplaceAll(modelConfig.Proxy, macroSlug, macroStr)
+			modelConfig.CheckEndpoint = strings.ReplaceAll(modelConfig.CheckEndpoint, macroSlug, macroStr)
+			modelConfig.Filters.StripParams = strings.ReplaceAll(modelConfig.Filters.StripParams, macroSlug, macroStr)
+			modelConfig.Name = strings.ReplaceAll(modelConfig.Name, macroSlug, macroStr)
+			modelConfig.Description = strings.ReplaceAll(modelConfig.Description, macroSlug, macroStr)
+
+			// Substitute macros in SetParamsByID keys and values
+			if len(modelConfig.Filters.SetParamsByID) > 0 {
+				newSetParamsByID := make(map[string]map[string]any, len(modelConfig.Filters.SetParamsByID))
+				for key, paramMap := range modelConfig.Filters.SetParamsByID {
+					newKey := strings.ReplaceAll(key, macroSlug, macroStr)
+					newValAny, err := substituteMacroInValue(any(paramMap), entry.Name, entry.Value)
+					if err != nil {
+						return Config{}, fmt.Errorf("model %s filters.setParamsByID: %s", modelId, err.Error())
+					}
+					newParamMap, ok := newValAny.(map[string]any)
+					if !ok {
+						return Config{}, fmt.Errorf("model %s filters.setParamsByID: unexpected type after macro substitution", modelId)
+					}
+					newSetParamsByID[newKey] = newParamMap
+				}
+				modelConfig.Filters.SetParamsByID = newSetParamsByID
+			}
+
+			// Substitute in metadata (type-preserving)
+			if len(modelConfig.Metadata) > 0 {
+				result, err := substituteMacroInValue(modelConfig.Metadata, entry.Name, entry.Value)
+				if err != nil {
+					return Config{}, fmt.Errorf("model %s metadata: %s", modelId, err.Error())
+				}
+				modelConfig.Metadata = result.(map[string]any)
+			}
+		}
+
+		// Handle PORT macro - only allocate if cmd uses it
+		cmdHasPort := strings.Contains(modelConfig.Cmd, "${PORT}")
+		proxyHasPort := strings.Contains(modelConfig.Proxy, "${PORT}")
+		if cmdHasPort || proxyHasPort {
+			if !cmdHasPort && proxyHasPort {
+				return Config{}, fmt.Errorf("model %s: proxy uses ${PORT} but cmd does not - ${PORT} is only available when used in cmd", modelId)
+			}
+
+			macroSlug := "${PORT}"
+			macroStr := fmt.Sprintf("%v", nextPort)
+
+			modelConfig.Cmd = strings.ReplaceAll(modelConfig.Cmd, macroSlug, macroStr)
+			modelConfig.CmdStop = strings.ReplaceAll(modelConfig.CmdStop, macroSlug, macroStr)
+			modelConfig.Proxy = strings.ReplaceAll(modelConfig.Proxy, macroSlug, macroStr)
+			modelConfig.Name = strings.ReplaceAll(modelConfig.Name, macroSlug, macroStr)
+			modelConfig.Description = strings.ReplaceAll(modelConfig.Description, macroSlug, macroStr)
+
+			if len(modelConfig.Metadata) > 0 {
+				result, err := substituteMacroInValue(modelConfig.Metadata, "PORT", nextPort)
+				if err != nil {
+					return Config{}, fmt.Errorf("model %s metadata: %s", modelId, err.Error())
+				}
+				modelConfig.Metadata = result.(map[string]any)
+			}
+
+			nextPort++
+		}
+
+		// Validate no unknown macros remain
+		fieldMap := map[string]string{
+			"cmd":                 modelConfig.Cmd,
+			"cmdStop":             modelConfig.CmdStop,
+			"proxy":               modelConfig.Proxy,
+			"checkEndpoint":       modelConfig.CheckEndpoint,
+			"filters.stripParams": modelConfig.Filters.StripParams,
+			"name":                modelConfig.Name,
+			"description":         modelConfig.Description,
+		}
+
+		for fieldName, fieldValue := range fieldMap {
+			matches := macroPatternRegex.FindAllStringSubmatch(fieldValue, -1)
+			for _, match := range matches {
+				macroName := match[1]
+				if macroName == "PID" && fieldName == "cmdStop" {
+					continue // replaced at runtime
+				}
+				if macroName == "PORT" || macroName == "MODEL_ID" {
+					return Config{}, fmt.Errorf("macro '${%s}' should have been substituted in %s.%s", macroName, modelId, fieldName)
+				}
+				return Config{}, fmt.Errorf("unknown macro '${%s}' found in %s.%s", macroName, modelId, fieldName)
+			}
+		}
+
+		if len(modelConfig.Metadata) > 0 {
+			if err := validateNestedForUnknownMacros(modelConfig.Metadata, fmt.Sprintf("model %s metadata", modelId)); err != nil {
+				return Config{}, err
+			}
+		}
+
+		if err = modelConfig.Capabilities.Validate(); err != nil {
+			return Config{}, fmt.Errorf("model %s: %w", modelId, err)
+		}
+
+		// Validate SetParamsByID keys and values
+		for key, paramMap := range modelConfig.Filters.SetParamsByID {
+			if matches := macroPatternRegex.FindAllStringSubmatch(key, -1); len(matches) > 0 {
+				return Config{}, fmt.Errorf("unknown macro '${%s}' found in model %s filters.setParamsByID key", matches[0][1], modelId)
+			}
+			if err := validateNestedForUnknownMacros(any(paramMap), fmt.Sprintf("model %s filters.setParamsByID[%s]", modelId, key)); err != nil {
+				return Config{}, err
+			}
+		}
+
+		// Auto-register setParamsByID keys as aliases (skip the model's own ID)
+		for key := range modelConfig.Filters.SetParamsByID {
+			if key == modelId {
+				continue
+			}
+			if _, exists := config.Models[key]; exists {
+				return Config{}, fmt.Errorf("model %s filters.setParamsByID: key '%s' conflicts with an existing model ID", modelId, key)
+			}
+			if existingModel, exists := config.aliases[key]; exists {
+				if existingModel != modelId {
+					return Config{}, fmt.Errorf("duplicate alias '%s' in model %s filters.setParamsByID, already used by model %s", key, modelId, existingModel)
+				}
+				continue // already registered as explicit alias for this model
+			}
+			config.aliases[key] = modelId
+			modelConfig.Aliases = append(modelConfig.Aliases, key)
+		}
+
+		if _, err := url.Parse(modelConfig.Proxy); err != nil {
+			return Config{}, fmt.Errorf("model %s: invalid proxy URL: %w", modelId, err)
+		}
+
+		if modelConfig.SendLoadingState == nil {
+			v := config.SendLoadingState
+			modelConfig.SendLoadingState = &v
+		}
+
+		config.Models[modelId] = modelConfig
+	}
+
+	// Normalize routing config. The legacy top-level `matrix`/`groups` keys and
+	// the new `routing.router` block are mutually exclusive: a config may use
+	// either style, never both.
+	hasTopLevel := config.Matrix != nil || len(config.Groups) > 0
+	rtr := config.Routing.Router
+	hasRouting := rtr.Use != "" || rtr.Settings.Matrix != nil || len(rtr.Settings.Groups) > 0
+
+	if hasTopLevel && hasRouting {
+		return Config{}, fmt.Errorf("config uses both the legacy top-level 'matrix'/'groups' keys and the new 'routing.router' block; please migrate the top-level keys into 'routing.router' and remove them")
+	}
+
+	if !hasTopLevel {
+		// Both groups and matrix may be defined under routing.router.settings;
+		// routing.router.use selects which one is active, so there is no conflict.
+		rs := config.Routing.Router.Settings
+		switch config.Routing.Router.Use {
+		case "matrix":
+			if rs.Matrix == nil {
+				return Config{}, fmt.Errorf("routing.router.use is 'matrix' but routing.router.settings.matrix is not set")
+			}
+			config.Matrix = rs.Matrix
+		case "group", "":
+			config.Groups = rs.Groups
+		default:
+			return Config{}, fmt.Errorf("routing.router.use: unknown router %q (valid: group, matrix)", config.Routing.Router.Use)
+		}
+	}
+
+	// groups XOR matrix
+	if config.Matrix != nil && len(config.Groups) > 0 {
+		return Config{}, fmt.Errorf("config cannot use both 'groups' and 'matrix'")
+	}
+
+	if config.Matrix != nil {
+		expandedSets, err := ValidateMatrix(*config.Matrix, config.Models)
+		if err != nil {
+			return Config{}, fmt.Errorf("matrix: %w", err)
+		}
+		config.Matrix.ExpandedSets = expandedSets
+	} else {
+		config = AddDefaultGroupToConfig(config)
+
+		// Validate group members
+		memberUsage := make(map[string]string)
+		for groupID, groupConfig := range config.Groups {
+			prevSet := make(map[string]bool)
+			for _, member := range groupConfig.Members {
+				if _, found := prevSet[member]; found {
+					return Config{}, fmt.Errorf("duplicate model member %s found in group: %s", member, groupID)
+				}
+				prevSet[member] = true
+
+				if existingGroup, exists := memberUsage[member]; exists {
+					return Config{}, fmt.Errorf("model member %s is used in multiple groups: %s and %s", member, existingGroup, groupID)
+				}
+				memberUsage[member] = groupID
+			}
+		}
+	}
+
+	// Build the canonical Config.Routing from the effective result. Both legacy
+	// and new-style configs converge here. The Matrix pointer is shared so
+	// ExpandedSets stays in one place.
+	if config.Matrix != nil {
+		config.Routing.Router.Use = "matrix"
+	} else {
+		config.Routing.Router.Use = "group"
+	}
+	config.Routing.Router.Settings.Matrix = config.Matrix
+	config.Routing.Router.Settings.Groups = config.Groups
+
+	// This fork defaults to the "serial" scheduler: one model loaded at a time,
+	// requests served in strict arrival order. Set use: fifo for the upstream
+	// throughput-oriented behavior that batches same-model requests.
+	if config.Routing.Scheduler.Use == "" {
+		config.Routing.Scheduler.Use = "serial"
+	}
+	switch config.Routing.Scheduler.Use {
+	case "fifo", "serial":
+	default:
+		return Config{}, fmt.Errorf("routing.scheduler.use: unknown scheduler %q (valid: fifo, serial)", config.Routing.Scheduler.Use)
+	}
+	for modelID := range config.Routing.Scheduler.Settings.Fifo.Priority {
+		if _, found := config.RealModelName(modelID); !found {
+			return Config{}, fmt.Errorf("routing.scheduler.settings.fifo.priority references unknown model %q", modelID)
+		}
+	}
+
+	// Clean up hooks preload
+	if len(config.Hooks.OnStartup.Preload) > 0 {
+		var toPreload []string
+		for _, modelID := range config.Hooks.OnStartup.Preload {
+			modelID = strings.TrimSpace(modelID)
+			if modelID == "" {
+				continue
+			}
+			if real, found := config.RealModelName(modelID); found {
+				toPreload = append(toPreload, real)
+			}
+		}
+		config.Hooks.OnStartup.Preload = toPreload
+	}
+
+	// Validate API keys (env macros already substituted at string level)
+	for i, apikey := range config.RequiredAPIKeys {
+		if apikey == "" {
+			return Config{}, fmt.Errorf("empty api key found in apiKeys")
+		}
+		if strings.Contains(apikey, " ") {
+			return Config{}, fmt.Errorf("apiKeys[%d]: api key cannot contain spaces", i)
+		}
+		config.RequiredAPIKeys[i] = apikey
+	}
+
+	// Process peers with global macro substitution
+	for peerName, peerConfig := range config.Peers {
+		// Substitute global macros (LIFO order)
+		for i := len(config.Macros) - 1; i >= 0; i-- {
+			entry := config.Macros[i]
+			macroSlug := fmt.Sprintf("${%s}", entry.Name)
+			macroStr := fmt.Sprintf("%v", entry.Value)
+
+			peerConfig.ApiKey = strings.ReplaceAll(peerConfig.ApiKey, macroSlug, macroStr)
+			peerConfig.Filters.StripParams = strings.ReplaceAll(peerConfig.Filters.StripParams, macroSlug, macroStr)
+
+			// Substitute in setParams (type-preserving)
+			if len(peerConfig.Filters.SetParams) > 0 {
+				result, err := substituteMacroInValue(peerConfig.Filters.SetParams, entry.Name, entry.Value)
+				if err != nil {
+					return Config{}, fmt.Errorf("peers.%s.filters.setParams: %w", peerName, err)
+				}
+				peerConfig.Filters.SetParams = result.(map[string]any)
+			}
+		}
+
+		// Validate no unknown macros remain
+		if matches := macroPatternRegex.FindAllStringSubmatch(peerConfig.ApiKey, -1); len(matches) > 0 {
+			return Config{}, fmt.Errorf("peers.%s.apiKey: unknown macro '${%s}'", peerName, matches[0][1])
+		}
+		if matches := macroPatternRegex.FindAllStringSubmatch(peerConfig.Filters.StripParams, -1); len(matches) > 0 {
+			return Config{}, fmt.Errorf("peers.%s.filters.stripParams: unknown macro '${%s}'", peerName, matches[0][1])
+		}
+		if len(peerConfig.Filters.SetParams) > 0 {
+			if err := validateNestedForUnknownMacros(peerConfig.Filters.SetParams, fmt.Sprintf("peers.%s.filters.setParams", peerName)); err != nil {
+				return Config{}, err
+			}
+		}
+		config.Peers[peerName] = peerConfig
+	}
+
+	return config, nil
+}

internal/config/macros.go

@@ -0,0 +1,198 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+var (
+	macroNameRegex    = regexp.MustCompile(`^[a-zA-Z0-9_-]+$`)
+	macroPatternRegex = regexp.MustCompile(`\$\{([a-zA-Z0-9_-]+)\}`)
+	envMacroRegex     = regexp.MustCompile(`\$\{env\.([a-zA-Z_][a-zA-Z0-9_]*)\}`)
+)
+
+// validateMacro validates macro name and value constraints
+func validateMacro(name string, value any) error {
+	if len(name) >= 64 {
+		return fmt.Errorf("macro name '%s' exceeds maximum length of 63 characters", name)
+	}
+	if !macroNameRegex.MatchString(name) {
+		return fmt.Errorf("macro name '%s' contains invalid characters, must match pattern ^[a-zA-Z0-9_-]+$", name)
+	}
+
+	// Validate that value is a scalar type
+	switch v := value.(type) {
+	case string:
+		// Check for self-reference
+		macroSlug := fmt.Sprintf("${%s}", name)
+		if strings.Contains(v, macroSlug) {
+			return fmt.Errorf("macro '%s' contains self-reference", name)
+		}
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, bool:
+		// These types are allowed
+	default:
+		return fmt.Errorf("macro '%s' has invalid type %T, must be a scalar type (string, int, float, or bool)", name, value)
+	}
+
+	switch name {
+	case "PORT", "MODEL_ID":
+		return fmt.Errorf("macro name '%s' is reserved", name)
+	}
+
+	return nil
+}
+
+// validateNestedForUnknownMacros recursively checks for any remaining macro references in nested structures
+func validateNestedForUnknownMacros(value any, context string) error {
+	switch v := value.(type) {
+	case string:
+		matches := macroPatternRegex.FindAllStringSubmatch(v, -1)
+		for _, match := range matches {
+			macroName := match[1]
+			return fmt.Errorf("%s: unknown macro '${%s}'", context, macroName)
+		}
+		// Check for unsubstituted env macros
+		envMatches := envMacroRegex.FindAllStringSubmatch(v, -1)
+		for _, match := range envMatches {
+			varName := match[1]
+			return fmt.Errorf("%s: environment variable '%s' not set", context, varName)
+		}
+		return nil
+
+	case map[string]any:
+		for _, val := range v {
+			if err := validateNestedForUnknownMacros(val, context); err != nil {
+				return err
+			}
+		}
+		return nil
+
+	case []any:
+		for _, val := range v {
+			if err := validateNestedForUnknownMacros(val, context); err != nil {
+				return err
+			}
+		}
+		return nil
+
+	default:
+		// Scalar types don't contain macros
+		return nil
+	}
+}
+
+// substituteMacroInValue recursively substitutes a single macro in a value structure
+// This is called once per macro, allowing LIFO substitution order
+func substituteMacroInValue(value any, macroName string, macroValue any) (any, error) {
+	macroSlug := fmt.Sprintf("${%s}", macroName)
+	macroStr := fmt.Sprintf("%v", macroValue)
+
+	switch v := value.(type) {
+	case string:
+		// Check if this is a direct macro substitution
+		if v == macroSlug {
+			return macroValue, nil
+		}
+		// Handle string interpolation
+		if strings.Contains(v, macroSlug) {
+			return strings.ReplaceAll(v, macroSlug, macroStr), nil
+		}
+		return v, nil
+
+	case map[string]any:
+		// Recursively process map values
+		newMap := make(map[string]any)
+		for key, val := range v {
+			newVal, err := substituteMacroInValue(val, macroName, macroValue)
+			if err != nil {
+				return nil, err
+			}
+			newMap[key] = newVal
+		}
+		return newMap, nil
+
+	case []any:
+		// Recursively process slice elements
+		newSlice := make([]any, len(v))
+		for i, val := range v {
+			newVal, err := substituteMacroInValue(val, macroName, macroValue)
+			if err != nil {
+				return nil, err
+			}
+			newSlice[i] = newVal
+		}
+		return newSlice, nil
+
+	default:
+		// Return scalar types as-is
+		return value, nil
+	}
+}
+
+// substituteEnvMacros replaces ${env.VAR_NAME} with environment variable values.
+// Returns error if any referenced env var is not set or contains invalid characters.
+// Env macros inside YAML comments are ignored by unmarshalling the YAML first
+// (which strips comments) and only checking the comment-free version for macros.
+func substituteEnvMacros(s string) (string, error) {
+	// Unmarshal and remarshal to strip YAML comments
+	var raw any
+	if err := yaml.Unmarshal([]byte(s), &raw); err != nil {
+		// If YAML is invalid, fall back to scanning the original string
+		// so the user gets the env var error rather than a confusing YAML parse error
+		return substituteEnvMacrosInString(s, s)
+	}
+	clean, err := yaml.Marshal(raw)
+	if err != nil {
+		return substituteEnvMacrosInString(s, s)
+	}
+
+	return substituteEnvMacrosInString(s, string(clean))
+}
+
+// substituteEnvMacrosInString finds ${env.VAR} macros in scanStr and substitutes
+// them in target. This separation allows scanning comment-free YAML while
+// substituting in the original string.
+func substituteEnvMacrosInString(target, scanStr string) (string, error) {
+	result := target
+	matches := envMacroRegex.FindAllStringSubmatch(scanStr, -1)
+	for _, match := range matches {
+		fullMatch := match[0] // ${env.VAR_NAME}
+		varName := match[1]   // VAR_NAME
+
+		value, exists := os.LookupEnv(varName)
+		if !exists {
+			return "", fmt.Errorf("environment variable '%s' is not set", varName)
+		}
+
+		// Sanitize the value for safe YAML substitution
+		value, err := sanitizeEnvValueForYAML(value, varName)
+		if err != nil {
+			return "", err
+		}
+
+		result = strings.ReplaceAll(result, fullMatch, value)
+	}
+	return result, nil
+}
+
+// sanitizeEnvValueForYAML ensures an environment variable value is safe for YAML substitution.
+// It rejects values with characters that break YAML structure and escapes quotes/backslashes
+// for compatibility with double-quoted YAML strings.
+func sanitizeEnvValueForYAML(value, varName string) (string, error) {
+	// Reject values that would break YAML structure regardless of quoting context
+	if strings.ContainsAny(value, "\n\r\x00") {
+		return "", fmt.Errorf("environment variable '%s' contains newlines or null bytes which are not allowed in YAML substitution", varName)
+	}
+
+	// Escape backslashes and double quotes for safe use in double-quoted YAML strings.
+	// In unquoted contexts, these escapes appear literally (harmless for most use cases).
+	// In double-quoted contexts, they are interpreted correctly.
+	value = strings.ReplaceAll(value, `\`, `\\`)
+	value = strings.ReplaceAll(value, `"`, `\"`)
+
+	return value, nil
+}

internal/config/merge.go

@@ -0,0 +1,300 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+// identityMapPaths is the set of dotted paths whose direct children are
+// identity-keyed maps. A child key present in two sources is a hard error;
+// such keys name discrete entities (a model, a group, a peer, etc.) and a
+// duplicate means the user has split one entity across files by mistake.
+var identityMapPaths = map[string]bool{
+	"models":                         true,
+	"groups":                         true,
+	"profiles":                       true,
+	"peers":                          true,
+	"matrix":                         true,
+	"routing.router.settings.groups": true,
+	"routing.router.settings.matrix": true,
+}
+
+// LoadConfigSources loads and merges configuration from -config (optional)
+// and -config-dir (optional). At least one must be provided. The -config file
+// is loaded first; *.yml/*.yaml files directly under -config-dir are then
+// merged in sorted filename order. The merged document is passed through the
+// existing LoadConfigFromReader pipeline unchanged.
+func LoadConfigSources(configPath, configDir string) (Config, error) {
+	if configPath == "" && configDir == "" {
+		return Config{}, fmt.Errorf("at least one of -config or -config-dir must be provided")
+	}
+
+	var sourcePaths []string
+
+	if configPath != "" {
+		sourcePaths = append(sourcePaths, configPath)
+	}
+
+	if configDir != "" {
+		dirFiles, err := listYAMLFiles(configDir)
+		if err != nil {
+			return Config{}, fmt.Errorf("-config-dir %s: %w", configDir, err)
+		}
+
+		if configPath != "" {
+			absConfig, err := filepath.Abs(configPath)
+			if err != nil {
+				return Config{}, fmt.Errorf("failed to resolve -config path: %w", err)
+			}
+			for _, f := range dirFiles {
+				absF, err := filepath.Abs(f)
+				if err != nil {
+					return Config{}, fmt.Errorf("failed to resolve config dir file %s: %w", f, err)
+				}
+				if absConfig == absF {
+					return Config{}, fmt.Errorf("-config path %s is also present in -config-dir %s; remove it from one", configPath, configDir)
+				}
+			}
+		}
+
+		sourcePaths = append(sourcePaths, dirFiles...)
+	}
+
+	if len(sourcePaths) == 0 {
+		return Config{}, fmt.Errorf("no configuration sources found")
+	}
+
+	var merged *yaml.Node
+	for _, p := range sourcePaths {
+		node, err := parseSource(p)
+		if err != nil {
+			return Config{}, err
+		}
+		if node == nil {
+			continue // empty file
+		}
+		if merged == nil {
+			merged = node
+			continue
+		}
+		if err := mergeNodes(merged, node, "", p); err != nil {
+			return Config{}, err
+		}
+	}
+
+	if merged == nil {
+		// All sources were empty; run the pipeline on empty input so defaults
+		// and validation still apply (e.g. startPort, performance defaults).
+		return LoadConfigFromReader(strings.NewReader(""))
+	}
+
+	out, err := yaml.Marshal(merged)
+	if err != nil {
+		return Config{}, fmt.Errorf("failed to marshal merged config: %w", err)
+	}
+	return LoadConfigFromReader(strings.NewReader(string(out)))
+}
+
+// listYAMLFiles returns the top-level *.yml and *.yaml files in dir, sorted by
+// filename for deterministic merge order. Subdirectories are not traversed.
+func listYAMLFiles(dir string) ([]string, error) {
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, err
+	}
+	var files []string
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		name := e.Name()
+		if !strings.HasSuffix(name, ".yml") && !strings.HasSuffix(name, ".yaml") {
+			continue
+		}
+		files = append(files, filepath.Join(dir, name))
+	}
+	sort.Strings(files)
+	return files, nil
+}
+
+// parseSource reads and parses one YAML config file into a root mapping node.
+// Returns a nil node (no error) when the file is empty or contains only
+// comments.
+//
+// Env macros (${env.VAR}) are substituted at the string level before YAML
+// parsing so that flow-style constructs like [${env.API_KEY}] parse
+// correctly — the brace would otherwise be interpreted as a flow mapping.
+func parseSource(path string) (*yaml.Node, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read config %s: %w", path, err)
+	}
+	yamlStr, err := substituteEnvMacros(string(data))
+	if err != nil {
+		return nil, fmt.Errorf("config %s: %w", path, err)
+	}
+	var doc yaml.Node
+	if err := yaml.Unmarshal([]byte(yamlStr), &doc); err != nil {
+		return nil, fmt.Errorf("failed to parse config %s: %w", path, err)
+	}
+	// yaml.Unmarshal into a yaml.Node yields a DocumentNode whose Content[0]
+	// is the actual root. Unwrap it so callers see the real top-level node.
+	root := &doc
+	if root.Kind == yaml.DocumentNode && len(root.Content) > 0 {
+		root = root.Content[0]
+	}
+	if root.Kind == 0 || root.Content == nil {
+		return nil, nil
+	}
+	if root.Kind != yaml.MappingNode {
+		return nil, fmt.Errorf("config %s: top-level YAML must be a mapping", path)
+	}
+	return root, nil
+}
+
+// mergeNodes merges src into dst (both MappingNodes) in place. Keys present in
+// only one side are kept; shared keys are merged recursively under the rules
+// in mergeValue. srcPath is included in error messages to identify the file
+// that introduced the conflict.
+func mergeNodes(dst, src *yaml.Node, path, srcPath string) error {
+	srcIdx := indexMapping(src)
+
+	// First pass: merge shared keys in place.
+	for i := 0; i+1 < len(dst.Content); i += 2 {
+		keyNode := dst.Content[i]
+		dstVal := dst.Content[i+1]
+		key := keyNode.Value
+
+		srcVal, ok := srcIdx[key]
+		if !ok {
+			continue // dst-only key, keep as-is
+		}
+
+		childPath := joinPath(path, key)
+
+		if identityMapPaths[childPath] {
+			// Identity-keyed map: each child key names a discrete entity
+			// (a model, group, peer, ...). A shared child key is a hard
+			// error; src-only children are appended in the second pass.
+			if err := mergeIdentityMap(dstVal, srcVal, childPath, key, srcPath); err != nil {
+				return err
+			}
+			continue
+		}
+
+		if err := mergeValue(dstVal, srcVal, childPath, srcPath); err != nil {
+			return err
+		}
+	}
+
+	// Second pass: append src-only keys.
+	dstIdx := indexMapping(dst)
+	for i := 0; i+1 < len(src.Content); i += 2 {
+		keyNode := src.Content[i]
+		srcVal := src.Content[i+1]
+		key := keyNode.Value
+
+		if _, ok := dstIdx[key]; ok {
+			continue // already merged above
+		}
+		keyCopy := *keyNode
+		valCopy := *srcVal
+		dst.Content = append(dst.Content, &keyCopy, &valCopy)
+	}
+
+	return nil
+}
+
+// mergeIdentityMap merges two identity-keyed mapping nodes (e.g. `models`,
+// `groups`, `peers`). Any child key present in both sides is a duplicate
+// entity and produces an error naming the conflicting key and source file.
+// src-only keys are appended to dst.
+func mergeIdentityMap(dst, src *yaml.Node, path, mapName, srcPath string) error {
+	if dst.Kind != yaml.MappingNode || src.Kind != yaml.MappingNode {
+		return fmt.Errorf("conflict at %q: expected a mapping, introduced by %s", path, srcPath)
+	}
+	dstIdx := indexMapping(dst)
+	for i := 0; i+1 < len(src.Content); i += 2 {
+		keyNode := src.Content[i]
+		srcVal := src.Content[i+1]
+		key := keyNode.Value
+		if _, dup := dstIdx[key]; dup {
+			return fmt.Errorf("duplicate %s %q found in %s (already defined in another config source)", mapName, key, srcPath)
+		}
+		keyCopy := *keyNode
+		valCopy := *srcVal
+		dst.Content = append(dst.Content, &keyCopy, &valCopy)
+	}
+	return nil
+}
+
+// mergeValue merges srcVal into dstVal (both pointing into the parent's
+// Content slice). Mapping+Mapping recurses; Sequence+Sequence concatenates;
+// Scalar+Scalar errors on value mismatch; null on either side yields to the
+// non-null side.
+func mergeValue(dstVal, srcVal *yaml.Node, path, srcPath string) error {
+	switch {
+	case dstVal.Kind == yaml.MappingNode && srcVal.Kind == yaml.MappingNode:
+		return mergeNodes(dstVal, srcVal, path, srcPath)
+
+	case dstVal.Kind == yaml.SequenceNode && srcVal.Kind == yaml.SequenceNode:
+		dstVal.Content = append(dstVal.Content, srcVal.Content...)
+		return nil
+
+	case dstVal.Kind == yaml.ScalarNode && srcVal.Kind == yaml.ScalarNode:
+		if isNullScalar(dstVal) {
+			*dstVal = *srcVal
+			return nil
+		}
+		if isNullScalar(srcVal) {
+			return nil
+		}
+		if dstVal.Value == srcVal.Value && dstVal.Tag == srcVal.Tag {
+			return nil
+		}
+		return fmt.Errorf("conflict at %q: %s sets a different value than a previous source", path, srcPath)
+
+	case isNull(dstVal):
+		*dstVal = *srcVal
+		return nil
+
+	case isNull(srcVal):
+		return nil
+
+	default:
+		return fmt.Errorf("conflict at %q: incompatible YAML node kinds (kind %d vs %d) introduced by %s", path, dstVal.Kind, srcVal.Kind, srcPath)
+	}
+}
+
+// isNull reports whether n represents a YAML null (empty or !!null).
+func isNull(n *yaml.Node) bool {
+	if n == nil || n.Kind == 0 {
+		return true
+	}
+	return isNullScalar(n)
+}
+
+func isNullScalar(n *yaml.Node) bool {
+	return n.Kind == yaml.ScalarNode && (n.Tag == "!!null" || n.Tag == "") && n.Value == ""
+}
+
+// indexMapping builds a key -> value-node index for a mapping node.
+func indexMapping(n *yaml.Node) map[string]*yaml.Node {
+	idx := make(map[string]*yaml.Node, len(n.Content)/2)
+	for i := 0; i+1 < len(n.Content); i += 2 {
+		idx[n.Content[i].Value] = n.Content[i+1]
+	}
+	return idx
+}
+
+func joinPath(parent, key string) string {
+	if parent == "" {
+		return key
+	}
+	return parent + "." + key
+}

internal/config/merge_test.go

@@ -0,0 +1,304 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// writeYAML writes content to a file named name inside dir. Returns the full
+// path of the written file.
+func writeYAML(t *testing.T, dir, name, content string) string {
+	t.Helper()
+	p := filepath.Join(dir, name)
+	require.NoError(t, os.MkdirAll(filepath.Dir(p), 0o755))
+	require.NoError(t, os.WriteFile(p, []byte(content), 0o644))
+	return p
+}
+
+// modelCfg builds a single-model YAML snippet indented for nesting under a
+// `models:` key. The proxy uses a fixed port so tests don't depend on
+// ${PORT} allocation.
+func modelCfg(id, cmd string) string {
+	return "  " + id + ":\n    cmd: " + cmd + "\n    proxy: \"http://localhost:9999\"\n"
+}
+
+func TestLoadConfigSources_NeitherProvided(t *testing.T) {
+	_, err := LoadConfigSources("", "")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "at least one of -config or -config-dir")
+}
+
+func TestLoadConfigSources_ConfigOnly(t *testing.T) {
+	dir := t.TempDir()
+	cfgPath := writeYAML(t, dir, "config.yaml", `
+models:
+`+modelCfg("model1", "echo hi")+`
+groups:
+  group1:
+    members: ["model1"]
+`)
+	cfg, err := LoadConfigSources(cfgPath, "")
+	require.NoError(t, err)
+	_, id, ok := cfg.FindConfig("model1")
+	require.True(t, ok)
+	assert.Equal(t, "model1", id)
+}
+
+func TestLoadConfigSources_DirOnly(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("alpha", "echo a"))
+	writeYAML(t, dir, "b.yaml", "models:\n"+modelCfg("beta", "echo b"))
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	for _, want := range []string{"alpha", "beta"} {
+		_, _, ok := cfg.FindConfig(want)
+		assert.True(t, ok, "model %s should be present", want)
+	}
+}
+
+func TestLoadConfigSources_ConfigPlusDirAdditive(t *testing.T) {
+	// -config lives outside -config-dir; both contribute models additively.
+	dir := t.TempDir()
+	cfgPath := writeYAML(t, dir, "config.yaml", "models:\n"+modelCfg("base", "echo base"))
+	cfgDir := t.TempDir()
+	writeYAML(t, cfgDir, "extra.yaml", "models:\n"+modelCfg("ext", "echo ext"))
+
+	cfg, err := LoadConfigSources(cfgPath, cfgDir)
+	require.NoError(t, err)
+	for _, want := range []string{"base", "ext"} {
+		_, _, ok := cfg.FindConfig(want)
+		assert.True(t, ok, "model %s should be present after merge", want)
+	}
+}
+
+// TestLoadConfigSources_ConfigInDirOverlap verifies that a -config file that
+// is also a member of -config-dir is rejected.
+func TestLoadConfigSources_ConfigInDirOverlap(t *testing.T) {
+	dir := t.TempDir()
+	cfgPath := writeYAML(t, dir, "main.yaml", "models:\n"+modelCfg("base", "echo base"))
+
+	_, err := LoadConfigSources(cfgPath, dir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "is also present in -config-dir")
+}
+
+func TestLoadConfigSources_DuplicateModelID(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("dup", "echo a"))
+	writeYAML(t, dir, "b.yaml", "models:\n"+modelCfg("dup", "echo b"))
+
+	_, err := LoadConfigSources("", dir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `duplicate models "dup"`)
+}
+
+func TestLoadConfigSources_DuplicateGroupID(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", `
+models:
+`+modelCfg("m1", "echo m1")+"groups:\n  g1:\n    members: [m1]\n")
+	writeYAML(t, dir, "b.yaml", `
+models:
+`+modelCfg("m2", "echo m2")+"groups:\n  g1:\n    members: [m2]\n")
+
+	_, err := LoadConfigSources("", dir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `duplicate groups "g1"`)
+}
+
+func TestLoadConfigSources_DuplicatePeer(t *testing.T) {
+	dir := t.TempDir()
+	peerA := "peers:\n  remote:\n    proxy: http://x:1\n    models: [m1]\n"
+	peerB := "peers:\n  remote:\n    proxy: http://x:2\n    models: [m2]\n"
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("m1", "echo m1")+"\n"+peerA)
+	writeYAML(t, dir, "b.yaml", "models:\n"+modelCfg("m2", "echo m2")+"\n"+peerB)
+
+	_, err := LoadConfigSources("", dir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `duplicate peers "remote"`)
+}
+
+func TestLoadConfigSources_ScalarConflict(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("m1", "echo m1")+"\nglobalTTL: 100\n")
+	writeYAML(t, dir, "b.yaml", "models:\n"+modelCfg("m2", "echo m2")+"\nglobalTTL: 200\n")
+
+	_, err := LoadConfigSources("", dir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `conflict at "globalTTL"`)
+}
+
+func TestLoadConfigSources_ScalarSameValueNoConflict(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("m1", "echo m1")+"\nglobalTTL: 100\n")
+	writeYAML(t, dir, "b.yaml", "models:\n"+modelCfg("m2", "echo m2")+"\nglobalTTL: 100\n")
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	assert.Equal(t, 100, cfg.GlobalTTL)
+}
+
+func TestLoadConfigSources_MacrosConcatenate(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "macros:\n  LOW: 1\nmodels:\n"+modelCfg("m1", "echo ${LOW}"))
+	writeYAML(t, dir, "b.yaml", "macros:\n  HIGH: 2\nmodels:\n"+modelCfg("m2", "echo ${HIGH}"))
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	// Both macros are available globally after merge.
+	low, ok := cfg.Macros.Get("LOW")
+	require.True(t, ok)
+	assert.Equal(t, 1, low)
+	high, ok := cfg.Macros.Get("HIGH")
+	require.True(t, ok)
+	assert.Equal(t, 2, high)
+}
+
+func TestLoadConfigSources_APIKeysConcatenate(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("m1", "echo m1")+"\napiKeys: [key-a]\n")
+	writeYAML(t, dir, "b.yaml", "models:\n"+modelCfg("m2", "echo m2")+"\napiKeys: [key-b]\n")
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []string{"key-a", "key-b"}, cfg.RequiredAPIKeys)
+}
+
+func TestLoadConfigSources_RoutingGroupsMerge(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", `
+models:
+`+modelCfg("m1", "echo m1")+`
+routing:
+  router:
+    settings:
+      groups:
+        groupA:
+          members: [m1]
+`)
+	writeYAML(t, dir, "b.yaml", `
+models:
+`+modelCfg("m2", "echo m2")+`
+routing:
+  router:
+    settings:
+      groups:
+        groupB:
+          members: [m2]
+`)
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	groups := cfg.Routing.Router.Settings.Groups
+	assert.Contains(t, groups, "groupA")
+	assert.Contains(t, groups, "groupB")
+	// default group added by pipeline for orphaned/leftover routing groups...
+	// here both groups reference distinct models
+}
+
+func TestLoadConfigSources_EnvMacrosSubstituted(t *testing.T) {
+	dir := t.TempDir()
+	// Use ${PORT} in cmd so the pipeline allocates a port and substitutes it;
+	// verifies env/macro substitution runs on the merged document.
+	writeYAML(t, dir, "a.yaml", "models:\n  m1:\n    cmd: serve --port ${PORT}\n    proxy: \"http://localhost:${PORT}\"\n")
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	m := cfg.Models["m1"]
+	assert.NotContains(t, m.Cmd, "${PORT}", "PORT macro should have been substituted")
+	assert.NotContains(t, m.Proxy, "${PORT}", "PORT macro should have been substituted in proxy")
+}
+
+func TestLoadConfigSources_EnvMacroInFlowStyleList(t *testing.T) {
+	// Regression: flow-style lists with ${env.*} must parse. Previously
+	// parseSource unmarshalled before env substitution, so the brace in
+	// [${env.API_KEY}] was misread as a flow mapping and parsing failed.
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n  m1:\n    cmd: echo hi\n    proxy: \"http://localhost:9999\"\n")
+	writeYAML(t, dir, "keys.yaml", "apiKeys: [${env.TEST_API_KEY}]\nmodels:\n  m2:\n    cmd: echo hi\n    proxy: \"http://localhost:9998\"\n")
+
+	t.Setenv("TEST_API_KEY", "secret123")
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	assert.Contains(t, cfg.RequiredAPIKeys, "secret123")
+}
+
+func TestLoadConfigSources_SortedOrderDeterministic(t *testing.T) {
+	// Two files defining distinct models, scanned in z..a order by filename.
+	// Determine merged result is the same regardless of how the FS returns them.
+	dir := t.TempDir()
+	writeYAML(t, dir, "z.yaml", "models:\n"+modelCfg("zmodel", "echo z"))
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("amodel", "echo a"))
+
+	const runs = 3
+	for i := 0; i < runs; i++ {
+		cfg, err := LoadConfigSources("", dir)
+		require.NoError(t, err)
+		// startPort-based allocation: first allocated model gets 5800.
+		// Sorted order means amodel gets 5800, zmodel gets 5801.
+		_, _, ok := cfg.FindConfig("amodel")
+		assert.True(t, ok)
+		_, _, ok = cfg.FindConfig("zmodel")
+		assert.True(t, ok)
+	}
+}
+
+func TestLoadConfigSources_EmptyDirWithConfig(t *testing.T) {
+	dir := t.TempDir()
+	cfgDir := t.TempDir()
+	cfgPath := writeYAML(t, dir, "main.yaml", "models:\n"+modelCfg("m1", "echo m1"))
+
+	cfg, err := LoadConfigSources(cfgPath, cfgDir)
+	require.NoError(t, err)
+	assert.Contains(t, cfg.Models, "m1")
+}
+
+func TestLoadConfigSources_EmptyDirOnly(t *testing.T) {
+	// An empty -config-dir with no -config is an error: there is nothing to
+	// load and silently producing an empty config would mask the misconfig.
+	cfgDir := t.TempDir()
+	_, err := LoadConfigSources("", cfgDir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "no configuration sources found")
+}
+
+func TestLoadConfigSources_AssertNoUnknownMacrosAfterMerge(t *testing.T) {
+	// Macros defined in one file should not satisfy unknown-macro validation in
+	// another — they do, because merge concats global macros before validation
+	// runs. This test documents that a macro from file A is usable in file B.
+	dir := t.TempDir()
+	writeYAML(t, dir, "macros.yaml", "macros:\n  SHARED: hello\nmodels:\n"+modelCfg("dummy", "echo dummy"))
+	writeYAML(t, dir, "use.yaml", "models:\n"+modelCfg("user", "echo ${SHARED}"))
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	m := cfg.Models["user"]
+	assert.Contains(t, m.Cmd, "hello")
+	assert.NotContains(t, m.Cmd, "${SHARED}")
+}
+
+func TestLoadConfigSources_KindMismatchErrors(t *testing.T) {
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "startPort: 5800\nmodels:\n"+modelCfg("m1", "echo m1"))
+	writeYAML(t, dir, "b.yaml", "startPort: [5800, 5801]\nmodels:\n"+modelCfg("m2", "echo m2"))
+
+	_, err := LoadConfigSources("", dir)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "incompatible YAML node kinds")
+}
+
+func TestLoadConfigSources_NullYieldsToValue(t *testing.T) {
+	// File A: routing.router block absent (null on root for routing);
+	// file B: defines routing.router.settings.groups. Merge should keep B's.
+	dir := t.TempDir()
+	writeYAML(t, dir, "a.yaml", "models:\n"+modelCfg("m1", "echo m1"))
+	writeYAML(t, dir, "b.yaml", "routing:\n  router:\n    settings:\n      groups:\n        g1:\n          members: [m1]\nmodels:\n"+modelCfg("m2", "echo m2"))
+
+	cfg, err := LoadConfigSources("", dir)
+	require.NoError(t, err)
+	assert.Contains(t, cfg.Routing.Router.Settings.Groups, "g1")
+}

internal/router/scheduler/scheduler.go

@@ -92,9 +92,14 @@ type Effects interface {
 	StopProcesses(timeout time.Duration, ids []string)
 }
 
-// New returns a Scheduler selected by conf.Routing.Scheduler.Use, configured
+// New returns a Scheduler selected by conf.Routing.Scheduler.Use, configured from
-// from conf and bound to the given planner and effects. Currently only "fifo"
+// conf and bound to the given planner and effects. Supported values are "fifo"
-// (the default) is supported.
+// (throughput-oriented, batches same-model requests) and "serial" (strict
+// one-model-at-a-time, exact arrival order).
+//
+// The deployment default is applied by config loading (LoadConfig sets Use to
+// "serial" when unset). The "" fallback here is the library default and remains
+// "fifo" so callers that build a Config directly keep the original behavior.
 func New(conf config.Config, name string, logger *logmon.Monitor, planner Swapper, eff Effects) (Scheduler, error) {
 	use := conf.Routing.Scheduler.Use
 	if use == "" {
@@ -103,6 +108,9 @@ func New(conf config.Config, name string, logger *logmon.Monitor, planner Swappe
 	switch use {
 	case "fifo":
 		return NewFIFO(name, logger, planner, conf.Routing.Scheduler.Settings.Fifo, conf.Models, eff), nil
+	case "serial":
+		// Serial ignores the group planner: it always evicts every other model.
+		return NewSerial(name, logger, eff), nil
 	default:
 		return nil, fmt.Errorf("unsupported scheduler type: %q", use)
 	}

internal/router/scheduler/serial.go

@@ -0,0 +1,253 @@
+package scheduler
+
+import (
+	"fmt"
+	"sort"
+	"time"
+
+	"github.com/mostlygeek/llama-swap/internal/logmon"
+	"github.com/mostlygeek/llama-swap/internal/process"
+)
+
+// Serial is a strict one-model-at-a-time scheduler. Unlike FIFO it never reorders
+// or batches: requests run in exact arrival order and at most one request runs at
+// any instant. When the next request targets a model other than the one loaded,
+// every other running model is evicted and the target is loaded before it runs,
+// so a single model occupies memory at a time — at the cost of throughput.
+//
+// Example: A B C A is served as A B C A. The final A reloads its model even
+// though it ran first, because B and C displaced it in between. (FIFO, by
+// contrast, would batch the two A requests: A A B C.)
+//
+// Serial ignores group/eviction policy entirely: it always evicts every other
+// running model, regardless of how groups are configured. That is what makes the
+// single-model guarantee a property of the scheduler rather than of the config.
+//
+// Like FIFO, every method runs on the router's single run-loop goroutine, so no
+// internal locking is needed.
+type Serial struct {
+	name    string
+	logger  *logmon.Monitor
+	effects Effects
+
+	// queued holds requests in strict arrival order. It is never reordered.
+	queued []HandlerReq
+
+	// active is the one request currently being processed (loading or serving),
+	// or nil when idle. phase is meaningful only while active != nil.
+	active *HandlerReq
+	phase  serialPhase
+}
+
+// serialPhase is the lifecycle stage of the active request.
+type serialPhase int
+
+const (
+	phaseIdle     serialPhase = iota
+	phaseSwapping             // waiting for OnSwapDone for active.Model
+	phaseServing              // waiting for OnServeDone for active.Model
+)
+
+// NewSerial builds a Serial scheduler. It takes no Swapper: eviction is always
+// "stop every other running model", so the group planner is not consulted.
+func NewSerial(name string, logger *logmon.Monitor, eff Effects) *Serial {
+	return &Serial{
+		name:    name,
+		logger:  logger,
+		effects: eff,
+	}
+}
+
+// OnRequest validates the model and appends the request to the tail of the queue,
+// then tries to start the next job. Unknown models fail immediately.
+func (s *Serial) OnRequest(req HandlerReq) {
+	if _, ok := s.effects.ModelState(req.Model); !ok {
+		s.logger.Debugf("%s: model %s not handled by this router", s.name, req.Model)
+		s.effects.GrantError(req, ErrModelNotFound)
+		return
+	}
+	s.queued = append(s.queued, req)
+	broadcastQueuePositions(s.queued)
+	s.startNext()
+}
+
+// startNext begins processing the head of the queue when nothing is active. It
+// fast-paths a request whose model is already the sole loaded-and-ready process;
+// otherwise it launches a swap that evicts every other running model first. The
+// loop skips over requests for models that vanished (e.g. a config reload) and
+// requests whose caller disconnected before they could be served.
+func (s *Serial) startNext() {
+	if s.active != nil {
+		return // a job is already loading or serving
+	}
+	for len(s.queued) > 0 {
+		req := s.queued[0]
+		s.queued = s.queued[1:]
+		broadcastQueuePositions(s.queued)
+
+		state, ok := s.effects.ModelState(req.Model)
+		if !ok {
+			s.effects.GrantError(req, ErrModelNotFound)
+			continue
+		}
+
+		r := req
+		s.active = &r
+
+		evict := s.otherRunning(req.Model)
+		if state == process.StateReady && len(evict) == 0 {
+			// Already loaded and the only model running — serve immediately.
+			s.logger.Debugf("%s: serving model %s (already loaded)", s.name, req.Model)
+			if s.serve() {
+				return
+			}
+			continue // caller gone; pick the next request
+		}
+
+		s.logger.Debugf("%s: swapping to model %s, evicting %v", s.name, req.Model, evict)
+		s.phase = phaseSwapping
+		s.effects.StartSwap(req.Model, evict)
+		return
+	}
+}
+
+// serve hands the active request its tracked handler. It returns true when the
+// request is now serving (await OnServeDone); false when the caller had already
+// disconnected, in which case active is cleared so the next job can start.
+func (s *Serial) serve() bool {
+	if s.effects.GrantServe(*s.active, s.active.Model) {
+		s.phase = phaseServing
+		return true
+	}
+	s.logger.Debugf("%s: caller for model %s gone before serve", s.name, s.active.Model)
+	s.active = nil
+	s.phase = phaseIdle
+	return false
+}
+
+// OnSwapDone fires when the load for the active request completes. On success the
+// request is served; on failure its caller receives the error and the queue
+// advances. A SwapDone that does not match the active load (e.g. its request was
+// unloaded or cancelled mid-load) is ignored.
+func (s *Serial) OnSwapDone(ev SwapDone) {
+	if s.active == nil || s.phase != phaseSwapping || s.active.Model != ev.ModelID {
+		return
+	}
+	if ev.Err != nil {
+		s.logger.Debugf("%s: swap for model %s failed: %v", s.name, ev.ModelID, ev.Err)
+		s.effects.GrantError(*s.active, ev.Err)
+		s.active = nil
+		s.phase = phaseIdle
+		s.startNext()
+		return
+	}
+	if !s.serve() {
+		s.startNext() // caller vanished while the model loaded; move on
+	}
+}
+
+// OnServeDone fires when the active request's handler returns. The slot is freed
+// and the next queued request begins.
+func (s *Serial) OnServeDone(ev ServeDoneEvent) {
+	if s.active == nil || s.phase != phaseServing {
+		return
+	}
+	s.active = nil
+	s.phase = phaseIdle
+	s.startNext()
+}
+
+// OnCancel removes a disconnected client's request from the queue. A request that
+// is already active is left to finish: if it was loading, OnSwapDone's serve()
+// will find the caller gone (GrantServe false) and advance; if it was serving,
+// its handler returns normally and reaches OnServeDone.
+func (s *Serial) OnCancel(req HandlerReq) {
+	if len(s.queued) == 0 {
+		return
+	}
+	kept := s.queued[:0]
+	removed := false
+	for _, q := range s.queued {
+		if q.Respond == req.Respond {
+			removed = true
+			continue
+		}
+		kept = append(kept, q)
+	}
+	s.queued = kept
+	if removed {
+		s.logger.Debugf("%s: cancelled request for model %s pruned from queue", s.name, req.Model)
+		broadcastQueuePositions(s.queued)
+	}
+}
+
+// OnUnload reconciles state for an unload, stops the targeted processes, and
+// advances the queue. It mirrors the FIFO contract: queued requests for unloaded
+// models are failed; an active *loading* request for an unloaded model is failed
+// (its swap goroutine is left to finish and its SwapDone is then ignored); an
+// active *serving* request is left for its handler to end when StopProcesses
+// kills the upstream. The Stop is synchronous so callers of Unload can rely on
+// the processes being stopped on return.
+func (s *Serial) OnUnload(targets []string, timeout time.Duration) {
+	unloadErr := fmt.Errorf("%s: model unloaded", s.name)
+
+	targetSet := make(map[string]bool, len(targets))
+	for _, id := range targets {
+		targetSet[id] = true
+	}
+
+	if s.active != nil && s.phase == phaseSwapping && targetSet[s.active.Model] {
+		s.effects.GrantError(*s.active, unloadErr)
+		s.active = nil
+		s.phase = phaseIdle
+	}
+
+	if len(s.queued) > 0 {
+		kept := s.queued[:0]
+		for _, q := range s.queued {
+			if targetSet[q.Model] {
+				s.effects.GrantError(q, unloadErr)
+				continue
+			}
+			kept = append(kept, q)
+		}
+		s.queued = kept
+		broadcastQueuePositions(s.queued)
+	}
+
+	s.effects.StopProcesses(timeout, targets)
+
+	// A still-serving active request advances via OnServeDone when its killed
+	// handler returns; only start the next job when nothing is active now.
+	if s.active == nil {
+		s.startNext()
+	}
+}
+
+// OnShutdown grants err to every request the scheduler still holds: an active
+// loading request and all queued requests. A serving request is torn down with
+// its process by the baseRouter.
+func (s *Serial) OnShutdown(err error) {
+	if s.active != nil && s.phase == phaseSwapping {
+		s.effects.GrantError(*s.active, err)
+		s.active = nil
+		s.phase = phaseIdle
+	}
+	for _, q := range s.queued {
+		s.effects.GrantError(q, err)
+	}
+	s.queued = nil
+}
+
+// otherRunning returns every running model except target, sorted for
+// deterministic eviction.
+func (s *Serial) otherRunning(target string) []string {
+	var out []string
+	for id := range s.effects.RunningModels() {
+		if id != target {
+			out = append(out, id)
+		}
+	}
+	sort.Strings(out)
+	return out
+}

internal/router/scheduler/serial_test.go

@@ -0,0 +1,391 @@
+package scheduler
+
+import (
+	"errors"
+	"io"
+	"testing"
+	"time"
+
+	"github.com/mostlygeek/llama-swap/internal/logmon"
+	"github.com/mostlygeek/llama-swap/internal/process"
+)
+
+// Serial methods all run on the router's single run-loop goroutine, so these
+// tests drive them directly and synchronously, reusing fakeEffects and the
+// req/reqCh helpers from fifo_test.go. A load completes via OnSwapDone and a
+// served request finishes via OnServeDone — the events the run loop delivers.
+
+func newSerial(eff Effects) *Serial {
+	return NewSerial("test", logmon.NewWriter(io.Discard), eff)
+}
+
+// lastStart returns the most recent StartSwap record.
+func lastStart(t *testing.T, eff *fakeEffects) startRec {
+	t.Helper()
+	if len(eff.starts) == 0 {
+		t.Fatal("no StartSwap recorded")
+	}
+	return eff.starts[len(eff.starts)-1]
+}
+
+func sameSet(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	m := map[string]int{}
+	for _, x := range a {
+		m[x]++
+	}
+	for _, x := range b {
+		m[x]--
+	}
+	for _, v := range m {
+		if v != 0 {
+			return false
+		}
+	}
+	return true
+}
+
+// servedOrder returns the model IDs of every successful serve grant in order.
+func servedOrder(eff *fakeEffects) []string {
+	var out []string
+	for _, g := range eff.grants {
+		if g.err == nil && g.serve {
+			out = append(out, g.model)
+		}
+	}
+	return out
+}
+
+func TestSerial_FastPath_AlreadyLoaded(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateReady
+	s := newSerial(eff)
+
+	s.OnRequest(req("a"))
+
+	if got := len(eff.starts); got != 0 {
+		t.Errorf("StartSwap calls=%d want 0 (already loaded, no swap)", got)
+	}
+	if got := eff.served("a"); got != 1 {
+		t.Errorf("served(a)=%d want 1", got)
+	}
+}
+
+func TestSerial_ColdStart_LoadsThenServes(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a"))
+	if got := eff.startsFor("a"); got != 1 {
+		t.Fatalf("StartSwap(a)=%d want 1", got)
+	}
+	if got := eff.served("a"); got != 0 {
+		t.Errorf("served(a)=%d want 0 before load completes", got)
+	}
+
+	eff.states["a"] = process.StateReady
+	s.OnSwapDone(SwapDone{ModelID: "a"})
+	if got := eff.served("a"); got != 1 {
+		t.Errorf("served(a)=%d want 1 after load", got)
+	}
+}
+
+func TestSerial_UnknownModel(t *testing.T) {
+	eff := newFakeEffects() // no states => unknown
+	s := newSerial(eff)
+
+	s.OnRequest(req("ghost"))
+
+	if len(eff.starts) != 0 {
+		t.Errorf("StartSwap calls=%d want 0", len(eff.starts))
+	}
+	if eff.errored("ghost") != 1 {
+		t.Fatalf("errored(ghost)=%d want 1", eff.errored("ghost"))
+	}
+	if !errors.Is(eff.grants[0].err, ErrModelNotFound) {
+		t.Errorf("err=%v want ErrModelNotFound", eff.grants[0].err)
+	}
+}
+
+func TestSerial_EvictsEveryOtherModel(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["x"] = process.StateReady // already running
+	eff.states["y"] = process.StateReady // also running (e.g. left over)
+	eff.states["a"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a"))
+
+	st := lastStart(t, eff)
+	if st.model != "a" {
+		t.Fatalf("loading %s want a", st.model)
+	}
+	if !sameSet(st.evict, []string{"x", "y"}) {
+		t.Errorf("evict=%v want [x y] (serial evicts ALL other models)", st.evict)
+	}
+}
+
+// TestSerial_OneJobAtATime verifies a second request waits while the first is
+// serving, and only starts after the first finishes.
+func TestSerial_OneJobAtATime(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateReady
+	eff.states["b"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a")) // served immediately
+	s.OnRequest(req("b")) // must wait — a is serving
+
+	if got := eff.startsFor("b"); got != 0 {
+		t.Fatalf("StartSwap(b)=%d want 0 while a is serving", got)
+	}
+	if got := eff.served("a"); got != 1 {
+		t.Fatalf("served(a)=%d want 1", got)
+	}
+
+	// a finishes -> b may now load (evicting a).
+	s.OnServeDone(ServeDoneEvent{ModelID: "a"})
+	if got := eff.startsFor("b"); got != 1 {
+		t.Fatalf("StartSwap(b)=%d want 1 after a finished", got)
+	}
+	if st := lastStart(t, eff); !sameSet(st.evict, []string{"a"}) {
+		t.Errorf("b evict=%v want [a]", st.evict)
+	}
+}
+
+// TestSerial_SameModelConsecutive_NoReload verifies back-to-back requests for the
+// already-loaded model run without a reload, one after another.
+func TestSerial_SameModelConsecutive_NoReload(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a")) // cold load
+	s.OnRequest(req("a")) // queued behind the first
+
+	eff.states["a"] = process.StateReady
+	s.OnSwapDone(SwapDone{ModelID: "a"}) // first serves
+	if got := eff.served("a"); got != 1 {
+		t.Fatalf("served(a)=%d want 1 (one at a time)", got)
+	}
+
+	s.OnServeDone(ServeDoneEvent{ModelID: "a"}) // first done -> second serves
+	if got := eff.served("a"); got != 2 {
+		t.Fatalf("served(a)=%d want 2", got)
+	}
+	if got := eff.startsFor("a"); got != 1 {
+		t.Errorf("StartSwap(a)=%d want 1 (second request must not reload)", got)
+	}
+}
+
+// TestSerial_StrictArrivalOrder is the core guarantee: qwen36, qwen35, sdxl,
+// qwen36 execute in EXACTLY that order with evictions between each model switch,
+// including reloading qwen36 at the end even though it ran first.
+func TestSerial_StrictArrivalOrder(t *testing.T) {
+	eff := newFakeEffects()
+	for _, m := range []string{"qwen36", "qwen35", "sdxl"} {
+		eff.states[m] = process.StateStopped
+	}
+	s := newSerial(eff)
+
+	for _, m := range []string{"qwen36", "qwen35", "sdxl", "qwen36"} {
+		s.OnRequest(req(m))
+	}
+
+	// Only the first job starts loading; the rest wait their turn.
+	if len(eff.starts) != 1 || eff.starts[0].model != "qwen36" {
+		t.Fatalf("starts=%+v want only [qwen36] loading first", eff.starts)
+	}
+
+	// step completes the current model's load+serve and returns control to the
+	// scheduler, which must start the next queued model.
+	step := func(model string, wantEvict []string) {
+		t.Helper()
+		st := lastStart(t, eff)
+		if st.model != model {
+			t.Fatalf("loading %q want %q", st.model, model)
+		}
+		if !sameSet(st.evict, wantEvict) {
+			t.Fatalf("loading %q evict=%v want %v", model, st.evict, wantEvict)
+		}
+		// Simulate the eviction + load actually happening.
+		for _, e := range st.evict {
+			eff.states[e] = process.StateStopped
+		}
+		eff.states[model] = process.StateReady
+		s.OnSwapDone(SwapDone{ModelID: model})
+		s.OnServeDone(ServeDoneEvent{ModelID: model})
+	}
+
+	step("qwen36", nil)                // cold load, nothing else running
+	step("qwen35", []string{"qwen36"}) // evict qwen36
+	step("sdxl", []string{"qwen35"})   // evict qwen35
+	step("qwen36", []string{"sdxl"})   // RELOAD qwen36, evict sdxl
+
+	want := []string{"qwen36", "qwen35", "sdxl", "qwen36"}
+	if got := servedOrder(eff); !sameOrder(got, want) {
+		t.Fatalf("serve order=%v want %v", got, want)
+	}
+}
+
+func sameOrder(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+func TestSerial_SwapError_FailsCallerAndAdvances(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	eff.states["b"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a"))
+	s.OnRequest(req("b")) // queued behind a
+
+	// a's load fails: its caller is errored and b proceeds.
+	s.OnSwapDone(SwapDone{ModelID: "a", Err: errors.New("boom")})
+	if eff.errored("a") != 1 {
+		t.Fatalf("errored(a)=%d want 1", eff.errored("a"))
+	}
+	if got := eff.startsFor("b"); got != 1 {
+		t.Fatalf("StartSwap(b)=%d want 1 after a's load failed", got)
+	}
+}
+
+// TestSerial_GrantServeFalse_Advances verifies that when the active request's
+// caller has disconnected by serve time, the queue advances to the next request.
+func TestSerial_GrantServeFalse_Advances(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	eff.states["b"] = process.StateStopped
+	eff.serveResult["a"] = false // a's caller is gone by grant time
+	s := newSerial(eff)
+
+	s.OnRequest(req("a"))
+	s.OnRequest(req("b")) // queued
+
+	eff.states["a"] = process.StateReady
+	s.OnSwapDone(SwapDone{ModelID: "a"}) // grant fails -> advance to b
+
+	if got := eff.served("a"); got != 0 {
+		t.Errorf("served(a)=%d want 0 (caller gone)", got)
+	}
+	if got := eff.startsFor("b"); got != 1 {
+		t.Fatalf("StartSwap(b)=%d want 1 (advanced after gone caller)", got)
+	}
+}
+
+func TestSerial_OnCancel_QueuedRequest(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	eff.states["b"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(reqCh("a")) // starts loading a
+	cancelled := reqCh("b")
+	s.OnRequest(cancelled) // queued behind a
+	if len(s.queued) != 1 {
+		t.Fatalf("queued=%d want 1", len(s.queued))
+	}
+
+	s.OnCancel(cancelled)
+	if len(s.queued) != 0 {
+		t.Fatalf("queued=%d want 0 after cancel", len(s.queued))
+	}
+
+	// a completes; b is gone, so nothing starts for it.
+	eff.states["a"] = process.StateReady
+	s.OnSwapDone(SwapDone{ModelID: "a"})
+	s.OnServeDone(ServeDoneEvent{ModelID: "a"})
+	if got := eff.startsFor("b"); got != 0 {
+		t.Errorf("StartSwap(b)=%d want 0 (cancelled before its turn)", got)
+	}
+}
+
+func TestSerial_OnShutdown_FailsQueuedAndActiveLoad(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	eff.states["b"] = process.StateStopped
+	eff.states["c"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a")) // active (loading)
+	s.OnRequest(req("b")) // queued
+	s.OnRequest(req("c")) // queued
+
+	s.OnShutdown(errors.New("shutting down"))
+
+	if got := eff.errored(""); got != 3 {
+		t.Errorf("error grants=%d want 3 (active load + 2 queued)", got)
+	}
+	if len(s.queued) != 0 {
+		t.Errorf("queued=%d want 0 after shutdown", len(s.queued))
+	}
+}
+
+// TestSerial_OnUnload_WhileServing verifies that unloading the model that is
+// actively serving does not strand the queue: OnUnload stops the process but
+// leaves the active request to end via OnServeDone, which then advances.
+func TestSerial_OnUnload_WhileServing(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateReady
+	eff.states["b"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a")) // served immediately (a ready)
+	s.OnRequest(req("b")) // queued behind a
+	if got := eff.served("a"); got != 1 {
+		t.Fatalf("served(a)=%d want 1", got)
+	}
+
+	// Unload a while it is serving: the process is stopped, but the queue must
+	// not advance yet — the active serve is still outstanding.
+	s.OnUnload([]string{"a"}, time.Second)
+	if len(eff.stops) != 1 || !sameSet(eff.stops[0].ids, []string{"a"}) {
+		t.Errorf("StopProcesses=%+v want one call stopping [a]", eff.stops)
+	}
+	if got := eff.startsFor("b"); got != 0 {
+		t.Fatalf("StartSwap(b)=%d want 0 before the serving request ends", got)
+	}
+
+	// The killed handler returns -> OnServeDone advances to b.
+	eff.states["a"] = process.StateStopped
+	s.OnServeDone(ServeDoneEvent{ModelID: "a"})
+	if got := eff.startsFor("b"); got != 1 {
+		t.Fatalf("StartSwap(b)=%d want 1 after the serving request ended", got)
+	}
+}
+
+func TestSerial_OnUnload_DropsQueuedAndStops(t *testing.T) {
+	eff := newFakeEffects()
+	eff.states["a"] = process.StateStopped
+	eff.states["b"] = process.StateStopped
+	s := newSerial(eff)
+
+	s.OnRequest(req("a")) // active (loading a)
+	s.OnRequest(req("b")) // queued
+
+	// Unload a: its active load is failed and a is stopped.
+	s.OnUnload([]string{"a"}, time.Second)
+
+	if eff.errored("a") != 1 {
+		t.Errorf("errored(a)=%d want 1 (active load failed)", eff.errored("a"))
+	}
+	if len(eff.stops) != 1 || !sameSet(eff.stops[0].ids, []string{"a"}) {
+		t.Errorf("StopProcesses=%+v want one call stopping [a]", eff.stops)
+	}
+	// b was queued and not unloaded; with a's load cancelled it now starts.
+	if got := eff.startsFor("b"); got != 1 {
+		t.Errorf("StartSwap(b)=%d want 1 after unload advanced the queue", got)
+	}
+}

internal/watcher/dirwatcher.go

@@ -0,0 +1,137 @@
+package configwatcher
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+)
+
+// DirWatcher polls a directory for changes to its set of *.yml / *.yaml files.
+// It fires OnChange when a file is added, removed, or has its mod time/size
+// change. Like Watcher it is poll-based so it works in Docker bind-mounts and
+// k8s ConfigMap projections where inotify is unreliable.
+//
+// The baseline poll establishes initial state and does not fire OnChange.
+type DirWatcher struct {
+	Path     string
+	Interval time.Duration
+	OnChange func()
+}
+
+// dirSnapshot is an ordered map of file name -> file state. The ordering is
+// derived from sorted filenames so two snapshots compare deterministically
+// regardless of readdir order. exists reflects whether the directory was
+// readable at scan time; a missing directory yields exists=false.
+type dirSnapshot struct {
+	exists bool
+	names  []string
+	states map[string]snapshot
+}
+
+func newDirSnapshot() dirSnapshot {
+	return dirSnapshot{states: make(map[string]snapshot)}
+}
+
+// equal reports whether two snapshots describe the same file set and per-file
+// state. A missing directory (exists=false) is treated as equal to any other
+// missing directory regardless of cached names.
+func (s dirSnapshot) equal(other dirSnapshot) bool {
+	if !s.exists && !other.exists {
+		return true
+	}
+	if s.exists != other.exists {
+		return false
+	}
+	if len(s.names) != len(other.names) {
+		return false
+	}
+	for i, n := range s.names {
+		if other.names[i] != n {
+			return false
+		}
+	}
+	for _, n := range s.names {
+		a, b := s.states[n], other.states[n]
+		if a.exists != b.exists || a.size != b.size || !a.modTime.Equal(b.modTime) {
+			return false
+		}
+	}
+	return true
+}
+
+// Run blocks until ctx is canceled. It polls Path on Interval and invokes
+// OnChange whenever the directory's YAML file set changes.
+//
+// Policy mirrors the single-file Watcher: disappearance (directory missing or
+// empty) is treated as a transient rename-style write and stays quiet; the
+// transition back to present-with-content fires OnChange.
+func (w *DirWatcher) Run(ctx context.Context) {
+	interval := w.Interval
+	if interval <= 0 {
+		interval = DefaultInterval
+	}
+
+	prev := scanDir(w.Path)
+
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			cur := scanDir(w.Path)
+			// Suppress transitions involving an empty or missing directory —
+			// these are treated as transient rename-style writes, mirroring
+			// the single-file Watcher. Only present-with-content →
+			// present-with-content (changed) or no-content →
+			// present-with-content fires OnChange.
+			prevHasContent := prev.exists && len(prev.names) > 0
+			curHasContent := cur.exists && len(cur.names) > 0
+			if curHasContent && (!prevHasContent || !prev.equal(cur)) && w.OnChange != nil {
+				w.OnChange()
+			}
+			prev = cur
+		}
+	}
+}
+
+// scanDir returns a snapshot of the *.yml/*.yaml files in dir. If the
+// directory cannot be read (missing, permission denied) the snapshot reports
+// exists=false; the next successful scan will detect the recovery and fire
+// OnChange.
+func scanDir(dir string) dirSnapshot {
+	snap := newDirSnapshot()
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return snap // exists=false
+	}
+	snap.exists = true
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		name := e.Name()
+		if !strings.HasSuffix(name, ".yml") && !strings.HasSuffix(name, ".yaml") {
+			continue
+		}
+		fi, err := os.Stat(filepath.Join(dir, name))
+		if err != nil {
+			// File disappeared between ReadDir and Stat; skip it — the
+			// next poll will observe the removal cleanly.
+			continue
+		}
+		snap.names = append(snap.names, name)
+		snap.states[name] = snapshot{
+			exists:  true,
+			modTime: fi.ModTime(),
+			size:    fi.Size(),
+		}
+	}
+	sort.Strings(snap.names)
+	return snap
+}

internal/watcher/dirwatcher_test.go

@@ -0,0 +1,199 @@
+package configwatcher
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// startDirWatcher launches w.Run in a goroutine and returns a function that
+// cancels the context and waits for Run to return.
+func startDirWatcher(t *testing.T, w *DirWatcher) func() {
+	t.Helper()
+	ctx, cancel := context.WithCancel(context.Background())
+	done := make(chan struct{})
+	go func() {
+		w.Run(ctx)
+		close(done)
+	}()
+	return func() {
+		cancel()
+		select {
+		case <-done:
+		case <-time.After(2 * time.Second):
+			t.Fatal("DirWatcher did not stop within 2s of cancel")
+		}
+	}
+}
+
+func writeYAMLInDir(t *testing.T, dir, name, content string) {
+	t.Helper()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, name), []byte(content), 0o644))
+}
+
+func TestDirWatcher_NoFireOnBaseline(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+
+	time.Sleep(testInterval * 5)
+	require.Equal(t, int64(0), atomic.LoadInt64(&n), "baseline poll must not fire")
+}
+
+func TestDirWatcher_DetectsFileAdd(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+	time.Sleep(testInterval * 2)
+
+	writeYAMLInDir(t, dir, "b.yaml", "b")
+	require.True(t, waitForCount(t, &n, 1, time.Second), "callback should fire when a file is added")
+}
+
+func TestDirWatcher_DetectsFileRemoval(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+	writeYAMLInDir(t, dir, "b.yaml", "b")
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+	time.Sleep(testInterval * 2)
+
+	require.NoError(t, os.Remove(filepath.Join(dir, "b.yaml")))
+	require.True(t, waitForCount(t, &n, 1, time.Second), "callback should fire when a file is removed")
+}
+
+func TestDirWatcher_DetectsModTimeChange(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	base := time.Now().Add(-1 * time.Hour).Truncate(time.Second)
+	require.NoError(t, os.Chtimes(filepath.Join(dir, "a.yaml"), base, base))
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+	time.Sleep(testInterval * 2)
+
+	require.NoError(t, os.Chtimes(filepath.Join(dir, "a.yaml"), base.Add(10*time.Second), base.Add(10*time.Second)))
+	require.True(t, waitForCount(t, &n, 1, time.Second), "callback should fire after mtime change")
+}
+
+func TestDirWatcher_IgnoresNonYAMLFiles(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+	time.Sleep(testInterval * 2)
+
+	// Adding a .txt file must not fire.
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "notes.txt"), []byte("hi"), 0o644))
+	time.Sleep(testInterval * 4)
+	require.Equal(t, int64(0), atomic.LoadInt64(&n), "non-YAML files must be ignored")
+
+	// Adding a .yml file must fire.
+	writeYAMLInDir(t, dir, "b.yml", "b")
+	require.True(t, waitForCount(t, &n, 1, time.Second), "callback should fire for *.yml files")
+}
+
+func TestDirWatcher_MissingDirRecovers(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+	time.Sleep(testInterval * 2)
+
+	// Remove the directory. No fire expected on disappearance alone.
+	require.NoError(t, os.RemoveAll(dir))
+	time.Sleep(testInterval * 3)
+	require.Equal(t, int64(0), atomic.LoadInt64(&n), "directory removal alone must not fire")
+
+	// Recreate the directory and a YAML file; the recovery should fire.
+	require.NoError(t, os.MkdirAll(dir, 0o755))
+	writeYAMLInDir(t, dir, "recovered.yaml", "r")
+	require.True(t, waitForCount(t, &n, 1, time.Second), "callback should fire when dir returns with content")
+}
+
+func TestDirWatcher_EmptyDirSuppressedThenRecovers(t *testing.T) {
+	// Present-with-content → empty (all YAML removed, dir still exists)
+	// must stay quiet — treated as transient per the documented policy.
+	// The transition back to content fires.
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	var n int64
+	stop := startDirWatcher(t, &DirWatcher{
+		Path:     dir,
+		Interval: testInterval,
+		OnChange: func() { atomic.AddInt64(&n, 1) },
+	})
+	defer stop()
+	time.Sleep(testInterval * 2)
+
+	// Remove the only YAML file. Dir still exists but is empty of YAML.
+	require.NoError(t, os.Remove(filepath.Join(dir, "a.yaml")))
+	time.Sleep(testInterval * 4)
+	require.Equal(t, int64(0), atomic.LoadInt64(&n), "emptying the directory must not fire")
+
+	// Add a YAML file back; transition to present-with-content fires.
+	writeYAMLInDir(t, dir, "c.yaml", "c")
+	require.True(t, waitForCount(t, &n, 1, time.Second), "callback should fire when content returns")
+}
+
+func TestDirWatcher_ContextCancelStopsRun(t *testing.T) {
+	dir := t.TempDir()
+	writeYAMLInDir(t, dir, "a.yaml", "a")
+
+	w := &DirWatcher{Path: dir, Interval: testInterval}
+	ctx, cancel := context.WithCancel(context.Background())
+	done := make(chan struct{})
+	go func() { w.Run(ctx); close(done) }()
+
+	time.Sleep(testInterval * 2)
+	cancel()
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("Run did not return within 2s of cancel")
+	}
+}

llama-swap.go

@@ -55,7 +55,8 @@ var logTimeFormats = map[string]string{
 }
 
 func main() {
-	flagConfig := flag.String("config", "", "path to config file (required)")
+	flagConfig := flag.String("config", "", "path to config file")
+	flagConfigDir := flag.String("config-dir", "", "directory of *.yml/*.yaml config files (additive to -config)")
 	flagListen := flag.String("listen", "", "listen address (default :8080 or :8443 for TLS)")
 	flagCertFile := flag.String("tls-cert-file", "", "TLS certificate file")
 	flagKeyFile := flag.String("tls-key-file", "", "TLS key file")
@@ -68,8 +69,8 @@ func main() {
 		os.Exit(0)
 	}
 
-	if *flagConfig == "" {
+	if *flagConfig == "" && *flagConfigDir == "" {
-		slog.Error("-config is required")
+		slog.Error("at least one of -config or -config-dir must be provided")
 		os.Exit(1)
 	}
 
@@ -88,10 +89,9 @@ func main() {
 		}
 	}
 
-	configPath := *flagConfig
+	cfg, err := config.LoadConfigSources(*flagConfig, *flagConfigDir)
-	cfg, err := config.LoadConfig(configPath)
 	if err != nil {
-		slog.Error("failed to load config", "path", configPath, "error", err)
+		slog.Error("failed to load config", "config", *flagConfig, "config-dir", *flagConfigDir, "error", err)
 		os.Exit(1)
 	}
 
@@ -187,7 +187,7 @@ func main() {
 
 		proxyLog.Info("reloading configuration")
 
-		newCfg, err := config.LoadConfig(configPath)
+		newCfg, err := config.LoadConfigSources(*flagConfig, *flagConfigDir)
 		if err != nil {
 			proxyLog.Warnf("failed to reload config: %v", err)
 			return
@@ -230,19 +230,37 @@ func main() {
 	defer watcherCancel()
 
 	if *flagWatchConfig {
-		absConfigPath, err := filepath.Abs(configPath)
-		if err != nil {
-			slog.Error("watch-config: failed to resolve config path", "error", err)
-			os.Exit(1)
-		}
 		proxyLog.Info("watching configuration for changes (poll-based, 2s interval)")
-		go func() {
+
-			(&configwatcher.Watcher{
+		if *flagConfig != "" {
-				Path:     absConfigPath,
+			absConfigPath, err := filepath.Abs(*flagConfig)
-				Interval: configwatcher.DefaultInterval,
+			if err != nil {
-				OnChange: reload,
+				slog.Error("watch-config: failed to resolve config path", "error", err)
-			}).Run(watcherCtx)
+				os.Exit(1)
-		}()
+			}
+			go func() {
+				(&configwatcher.Watcher{
+					Path:     absConfigPath,
+					Interval: configwatcher.DefaultInterval,
+					OnChange: reload,
+				}).Run(watcherCtx)
+			}()
+		}
+
+		if *flagConfigDir != "" {
+			absConfigDir, err := filepath.Abs(*flagConfigDir)
+			if err != nil {
+				slog.Error("watch-config: failed to resolve config-dir path", "error", err)
+				os.Exit(1)
+			}
+			go func() {
+				(&configwatcher.DirWatcher{
+					Path:     absConfigDir,
+					Interval: configwatcher.DefaultInterval,
+					OnChange: reload,
+				}).Run(watcherCtx)
+			}()
+		}
 	}
 
 	sigChan := make(chan os.Signal, 1)