feat(model): LLM 多供应商适配（Adapter/OpenAI 非流式+SSE 流式/per-role 路由/主备降级/多模态检测/调用记录）

internal/runtime/model/adapter.go

@@ -0,0 +1,41 @@
+package model
+
+import (
+	"context"
+	"errors"
+)
+
+// Errors returned by the model package. Each is wrapped with %w on the way out
+// so callers can test for a category while keeping the underlying cause.
+var (
+	// ErrNoModel is returned when no model name can be resolved.
+	ErrNoModel = errors.New("model: no model configured")
+	// ErrNoSteps is returned when a fallback chain has no steps.
+	ErrNoSteps = errors.New("model: empty fallback chain")
+	// ErrUpstream is returned when the provider request fails (network, status,
+	// decode) or every fallback step fails.
+	ErrUpstream = errors.New("model: upstream request failed")
+	// ErrBadRequest is returned when the request cannot be encoded for the wire.
+	ErrBadRequest = errors.New("model: invalid request")
+	// ErrStream is returned when a stream ends before completion.
+	ErrStream = errors.New("model: stream closed before completion")
+)
+
+// Recorder receives a CallRecord after a successfully completed LLM call. It is
+// invoked by adapters so the runtime (M9 monitor/frontend) can collect usage
+// without coupling to a storage backend.
+type Recorder func(CallRecord)
+
+// Adapter abstracts a single LLM provider. Implementations are vendor-specific
+// but speak the normalized Request/Response vocabulary; a fallback Chain or a
+// Router can compose them without knowing which provider is behind each one.
+type Adapter interface {
+	// Name returns a stable identifier for the provider/adapter.
+	Name() string
+	// Chat performs a non-streaming completion and returns the full response.
+	Chat(ctx context.Context, req Request, opts Options) (Response, error)
+	// ChatStream streams token-level deltas via onChunk and returns the
+	// aggregated response (with usage when the provider reports it). onChunk may
+	// be nil to discard deltas while still aggregating.
+	ChatStream(ctx context.Context, req Request, onChunk func(delta string)) (Response, error)
+}