feat: foundations — canonical types, Parse grammar, env DSNs, health, chains

Phase 1 of the majordomo build:
- llm/ canonical contract (messages, parts, tools, capabilities, streaming,
  Model/Provider, error classification)
- health/ clock-injected tracker (threshold bench, exponential capped
  cooldown, reset-on-success)
- root Registry + Parse (verbatim model ids, inline recursive alias
  expansion with cycle detection, chain dedup), LLM_* env-DSN providers
  (go-llm parity: lazy fallback + eager LoadEnv), health-aware chain
  executor behind the Model interface
- provider/fake scriptable test provider; hermetic test suite incl. the
  trailing-thinking chain and foreman:// env loading
- ADRs 0001-0008, CLAUDE.md, README (honest matrix), CI workflow,
  docs/phase-1-design.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

llm/model.go

@@ -0,0 +1,58 @@
+package llm
+
+import "context"
+
+// Model is the canonical generation interface. A Model may be a single
+// provider-bound target or a failover chain — the two are interchangeable
+// and callers never branch on which they got.
+type Model interface {
+	// Generate performs one request/response round trip.
+	Generate(ctx context.Context, req Request, opts ...Option) (*Response, error)
+
+	// Stream performs one request with incremental delivery.
+	Stream(ctx context.Context, req Request, opts ...Option) (Stream, error)
+
+	// Capabilities reports what this model supports. For chains this is the
+	// head element's capabilities (the preferred target); per-attempt media
+	// normalization always uses the actual target's capabilities.
+	Capabilities() Capabilities
+}
+
+// ModelOption configures a Model at construction time (Provider.Model).
+type ModelOption func(*ModelConfig)
+
+// ModelConfig carries per-model construction settings shared by all
+// providers.
+type ModelConfig struct {
+	// Capabilities, when non-nil, overrides the provider's default
+	// capabilities for this model.
+	Capabilities *Capabilities
+}
+
+// ApplyModelOptions folds options into a config.
+func ApplyModelOptions(opts []ModelOption) ModelConfig {
+	var cfg ModelConfig
+	for _, opt := range opts {
+		opt(&cfg)
+	}
+	return cfg
+}
+
+// WithCapabilities overrides the provider's default capabilities for one
+// model (e.g. a vision-capable tag on an otherwise text-only provider).
+func WithCapabilities(caps Capabilities) ModelOption {
+	return func(cfg *ModelConfig) { cfg.Capabilities = &caps }
+}
+
+// Provider mints Models bound to one backend. Implementations translate the
+// canonical Request/Response to and from their wire format and enforce their
+// declared Capabilities.
+type Provider interface {
+	// Name is the registry identifier used in "provider/model" specs.
+	Name() string
+
+	// Model returns a Model bound to the given id. The id is whatever the
+	// backend accepts — majordomo passes it through verbatim and never
+	// validates it against a catalog.
+	Model(id string, opts ...ModelOption) (Model, error)
+}