Add Seriatim trim adapter support

internal/adapters/seriatim/fake.go

@@ -29,11 +29,33 @@ func (n *NoopRunner) Run(ctx context.Context, req MergeRequest) (MergeResult, er
 	}, nil
 }
 
+// Trim returns the requested output path with placeholder metadata.
+func (n *NoopRunner) Trim(ctx context.Context, req TrimRequest) (TrimResult, error) {
+	if err := ctx.Err(); err != nil {
+		return TrimResult{}, err
+	}
+	if err := materializeTrimPlaceholders(req); err != nil {
+		return TrimResult{}, err
+	}
+	return TrimResult{
+		OutputTrimmedPath:   req.OutputTrimmedPath,
+		StdoutLogPath:       req.StdoutLogPath,
+		StderrLogPath:       req.StderrLogPath,
+		GeneratedConfigPath: req.GeneratedConfigPath,
+		InvokedBinary:       "noop",
+		KeepSelector:        req.KeepSelector,
+		Metadata:            map[string]any{"placeholder": true},
+	}, nil
+}
+
 // FakeRunner captures merge requests and returns deterministic responses.
 type FakeRunner struct {
-	Requests []MergeRequest
-	Err      error
-	Result   MergeResult
+	Requests     []MergeRequest
+	Err          error
+	Result       MergeResult
+	TrimRequests []TrimRequest
+	TrimErr      error
+	TrimResult   TrimResult
 }
 
 // Run records request and returns configured response.
@@ -73,6 +95,43 @@ func (f *FakeRunner) Run(ctx context.Context, req MergeRequest) (MergeResult, er
 	return res, nil
 }
 
+// Trim records request and returns configured response.
+func (f *FakeRunner) Trim(ctx context.Context, req TrimRequest) (TrimResult, error) {
+	if err := ctx.Err(); err != nil {
+		return TrimResult{}, err
+	}
+	f.TrimRequests = append(f.TrimRequests, req)
+	if f.TrimErr != nil {
+		return TrimResult{}, f.TrimErr
+	}
+	if err := materializeTrimPlaceholders(req); err != nil {
+		return TrimResult{}, err
+	}
+	res := f.TrimResult
+	if res.OutputTrimmedPath == "" {
+		res.OutputTrimmedPath = req.OutputTrimmedPath
+	}
+	if res.StdoutLogPath == "" {
+		res.StdoutLogPath = req.StdoutLogPath
+	}
+	if res.StderrLogPath == "" {
+		res.StderrLogPath = req.StderrLogPath
+	}
+	if res.GeneratedConfigPath == "" {
+		res.GeneratedConfigPath = req.GeneratedConfigPath
+	}
+	if res.InvokedBinary == "" {
+		res.InvokedBinary = "fake"
+	}
+	if res.KeepSelector == "" {
+		res.KeepSelector = req.KeepSelector
+	}
+	if res.Metadata == nil {
+		res.Metadata = map[string]any{"fake": true}
+	}
+	return res, nil
+}
+
 func materializePlaceholders(req MergeRequest) error {
 	if req.OutputMergedTranscriptPath != "" {
 		if err := subprocess.WriteFileAtomic(req.OutputMergedTranscriptPath, []byte(`{"schema":"seriatim.intermediate.v1","segments":[]}`), 0o644); err != nil {
@@ -107,3 +166,35 @@ func materializePlaceholders(req MergeRequest) error {
 	}
 	return nil
 }
+
+func materializeTrimPlaceholders(req TrimRequest) error {
+	if req.OutputTrimmedPath != "" {
+		if err := subprocess.WriteFileAtomic(req.OutputTrimmedPath, []byte(`{"schema":"seriatim.intermediate.v1","segments":[]}`), 0o644); err != nil {
+			return fmt.Errorf("write trimmed transcript %q: %w", req.OutputTrimmedPath, err)
+		}
+	}
+	if req.GeneratedConfigPath != "" {
+		payload := map[string]any{
+			"schema":        "seriatim.generated.v1",
+			"placeholder":   true,
+			"command":       "trim",
+			"input_path":    req.InputTranscriptPath,
+			"output_path":   req.OutputTrimmedPath,
+			"keep_selector": req.KeepSelector,
+		}
+		if err := subprocess.WriteYAMLAtomic(req.GeneratedConfigPath, payload, 0o644); err != nil {
+			return fmt.Errorf("write generated config %q: %w", req.GeneratedConfigPath, err)
+		}
+	}
+	if req.StdoutLogPath != "" {
+		if err := subprocess.WriteFileAtomic(req.StdoutLogPath, []byte("seriatim noop/fake trim stdout placeholder\n"), 0o644); err != nil {
+			return fmt.Errorf("write stdout log %q: %w", req.StdoutLogPath, err)
+		}
+	}
+	if req.StderrLogPath != "" {
+		if err := subprocess.WriteFileAtomic(req.StderrLogPath, []byte("seriatim noop/fake trim stderr placeholder\n"), 0o644); err != nil {
+			return fmt.Errorf("write stderr log %q: %w", req.StderrLogPath, err)
+		}
+	}
+	return nil
+}