feat(llm): client interface and fake test double

internal/llm/fake.go

@@ -0,0 +1,39 @@
+package llm
+
+import "context"
+
+// Fake is a deterministic Client for tests.
+type Fake struct {
+	VisionResp      string
+	TranscribeResp  string
+	VisionErr       error
+	TranscribeErr   error
+	VisionCalls     []VisionCall
+	TranscribeCalls []TranscribeCall
+}
+
+// VisionCall records a Vision invocation.
+type VisionCall struct {
+	Prompt string
+	Opts   Options
+	Images []Image
+}
+
+// TranscribeCall records a Transcribe invocation.
+type TranscribeCall struct {
+	Filename string
+	Opts     Options
+	Audio    []byte
+}
+
+// Vision implements Client.
+func (f *Fake) Vision(_ context.Context, prompt string, images []Image, opts Options) (string, error) {
+	f.VisionCalls = append(f.VisionCalls, VisionCall{Prompt: prompt, Images: images, Opts: opts})
+	return f.VisionResp, f.VisionErr
+}
+
+// Transcribe implements Client.
+func (f *Fake) Transcribe(_ context.Context, audio []byte, filename string, opts Options) (string, error) {
+	f.TranscribeCalls = append(f.TranscribeCalls, TranscribeCall{Audio: audio, Filename: filename, Opts: opts})
+	return f.TranscribeResp, f.TranscribeErr
+}