Admin-gated Settings: runtime model selection, enforce is_admin (#79)

Moves the agent model out of env-only config into an admin-editable Settings
section, and enforces is_admin for the first time — it has been in the schema
since migration 0001, plumbed to the client, and checked nowhere.

Backend:
- Migration 0010: instance_settings, a single-row (CHECK id=1) table — pansy's
  first instance-level state. Holds agent_model ('' = inherit env) and
  agent_enabled (NULL = inherit env), version-guarded like every mutable row.
  SECRETS STAY IN ENV: OLLAMA_CLOUD_API_KEY is never stored here.
- requireAdmin at the service seam (authoritative) plus a cheap middleware
  early-403. Non-admin gets 403, not 404 — settings existence isn't masked.
- EffectiveAgent resolves DB-over-env (model, enabled); key always from env.
- The live Runner is hot-swapped, not built once. agentHolder holds it behind
  an atomic.Pointer; the chat routes are now registered UNCONDITIONALLY and
  nil-check agent.get(), so a settings change turns the assistant on/off/onto a
  new model with no restart and no race against in-flight readers. /capabilities
  reads the pointer, so it reports what's live, not what booted.
- internal/agentmodel is a new leaf package holding the one place that knows how
  to turn a spec into a model. Both agent (to run) and service (to validate a
  spec before storing it) import it; it can't live in agent, which imports
  service. Settings PATCH validates the spec via Parse, so a typo is a 400 now
  rather than a broken assistant on the next turn.

Frontend:
- /settings route (admin guard), a Settings page (model field, tri-state
  enabled, live status), nav link shown only to admins.
- useCapabilities drops staleTime:Infinity — the assistant can now change under
  a running page — and the settings save invalidates it.

Contract change: chat routes always exist, so "assistant off" is a runtime 503
+ capabilities:false, not a missing route. Updated the test that asserted the
old shape.

Verified live against the built binary: disable flips capabilities to false and
logs it; re-enable with a new model swaps it back; a bad spec is rejected 400;
the setting persists across a restart. Swap is race-clean under `go test -race`.

Docs: README (precedence + key-stays-in-env), DESIGN (decision + routes),
CLAUDE (don't re-add conditional route registration; key never in the DB).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

internal/agentmodel/agentmodel.go

@@ -0,0 +1,57 @@
+// Package agentmodel holds the ONE place that knows how pansy turns a model spec
+// into a majordomo model: which provider to register and under which token.
+//
+// It exists as a leaf so both internal/agent (which builds the run loop) and
+// internal/service (which validates a spec before storing it as a setting) can
+// share that knowledge without an import cycle — agent imports service, so the
+// shared bit can live in neither of them.
+package agentmodel
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"gitea.stevedudenhoeffer.com/steve/majordomo"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/provider/ollama"
+)
+
+// registry builds the private majordomo registry pansy uses.
+//
+// Private, not the package-level default: pansy passes the key it was configured
+// with rather than depending on ambient environment, and majordomo's own
+// ollama-cloud preset reads OLLAMA_API_KEY while pansy (like gadfly) is
+// configured with OLLAMA_CLOUD_API_KEY. Registering the provider explicitly
+// makes that bridge visible instead of a mysterious empty token.
+func registry(apiKey string) *majordomo.Registry {
+	reg := majordomo.New()
+	reg.RegisterProvider(ollama.Cloud(ollama.WithToken(apiKey)))
+	return reg
+}
+
+// Resolve parses a model spec against pansy's registry into a live model. The
+// spec goes to Parse VERBATIM — the grammar, including comma-separated failover
+// chains, is majordomo's, and re-implementing any of it here would only mean two
+// places to update when it grows.
+func Resolve(apiKey, spec string) (llm.Model, error) {
+	if strings.TrimSpace(spec) == "" {
+		return nil, errors.New("agentmodel: empty model spec")
+	}
+	m, err := registry(apiKey).Parse(spec)
+	if err != nil {
+		return nil, fmt.Errorf("agentmodel: resolve %q: %w", spec, err)
+	}
+	return m, nil
+}
+
+// Validate reports whether a spec resolves, without building anything the caller
+// keeps — the cheap, deterministic check a settings save runs to reject a typo.
+//
+// It does NOT make a live call, so it needs no working key and won't catch a
+// model that is merely absent upstream; that surfaces on first use. Parse
+// resolving (known provider, well-formed spec) is the half worth doing eagerly.
+func Validate(apiKey, spec string) error {
+	_, err := Resolve(apiKey, spec)
+	return err
+}

internal/agentmodel/agentmodel_test.go

@@ -0,0 +1,35 @@
+package agentmodel
+
+import "testing"
+
+// TestValidate is what the settings PATCH relies on to reject a typo at save
+// time rather than on the next chat turn.
+func TestValidate(t *testing.T) {
+	if err := Validate("k", "ollama-cloud/glm-5.2:cloud"); err != nil {
+		t.Errorf("valid spec rejected: %v", err)
+	}
+	// No key needed to validate — Parse resolves the provider, it doesn't call it.
+	if err := Validate("", "ollama-cloud/glm-5.2:cloud"); err != nil {
+		t.Errorf("valid spec rejected without a key: %v", err)
+	}
+	// A comma-separated failover chain is majordomo grammar and must resolve.
+	if err := Validate("k", "ollama-cloud/glm-5.2:cloud,ollama-cloud/kimi-k2.6:cloud"); err != nil {
+		t.Errorf("failover chain rejected: %v", err)
+	}
+	for _, bad := range []string{"", "   ", "nonesuch/model"} {
+		if err := Validate("k", bad); err == nil {
+			t.Errorf("Validate accepted %q", bad)
+		}
+	}
+}
+
+// TestResolveReturnsAModel confirms a good spec yields a usable model handle.
+func TestResolveReturnsAModel(t *testing.T) {
+	m, err := Resolve("k", "ollama-cloud/glm-5.2:cloud")
+	if err != nil {
+		t.Fatalf("resolve: %v", err)
+	}
+	if m == nil {
+		t.Fatal("resolve returned a nil model with no error")
+	}
+}