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
+}

internal/adapters/seriatim/fake_test.go

@@ -51,3 +51,51 @@ func TestFakeRunnerError(t *testing.T) {
 		t.Fatal("expected error, got nil")
 	}
 }
+
+func TestFakeRunnerTrimCapturesRequestAndReturnsPath(t *testing.T) {
+	fake := &FakeRunner{}
+	dir := t.TempDir()
+	req := TrimRequest{
+		GeneratedConfigPath: filepath.Join(dir, "config", "seriatim.trim.yml"),
+		InputTranscriptPath: filepath.Join(dir, "transcripts", "processed.json"),
+		OutputTrimmedPath:   filepath.Join(dir, "transcripts", "trimmed.json"),
+		KeepSelector:        "1-10",
+		StdoutLogPath:       filepath.Join(dir, "logs", "seriatim.trim.stdout.log"),
+		StderrLogPath:       filepath.Join(dir, "logs", "seriatim.trim.stderr.log"),
+	}
+
+	res, err := fake.Trim(context.Background(), req)
+	if err != nil {
+		t.Fatalf("Trim() error = %v", err)
+	}
+	if len(fake.TrimRequests) != 1 || fake.TrimRequests[0].GeneratedConfigPath == "" {
+		t.Fatalf("trim requests = %#v, want captured request", fake.TrimRequests)
+	}
+	if res.OutputTrimmedPath != req.OutputTrimmedPath {
+		t.Fatalf("trimmed path = %q, want %q", res.OutputTrimmedPath, req.OutputTrimmedPath)
+	}
+	if res.KeepSelector != req.KeepSelector {
+		t.Fatalf("keep selector = %q, want %q", res.KeepSelector, req.KeepSelector)
+	}
+
+	cfgData, err := os.ReadFile(req.GeneratedConfigPath)
+	if err != nil {
+		t.Fatalf("read generated config: %v", err)
+	}
+	if !strings.Contains(string(cfgData), "command: trim") {
+		t.Fatalf("generated config = %q, want trim command marker", string(cfgData))
+	}
+	for _, logPath := range []string{req.StdoutLogPath, req.StderrLogPath} {
+		if _, err := os.Stat(logPath); err != nil {
+			t.Fatalf("expected log file %q to exist: %v", logPath, err)
+		}
+	}
+}
+
+func TestFakeRunnerTrimError(t *testing.T) {
+	fake := &FakeRunner{TrimErr: errors.New("boom")}
+	_, err := fake.Trim(context.Background(), TrimRequest{})
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+}

internal/adapters/seriatim/runner.go

@@ -1,4 +1,4 @@
-// Package seriatim declares the adapter contract for transcript merge execution.
+// Package seriatim declares the adapter contract for transcript merge/trim execution.
 package seriatim
 
 import (
@@ -8,9 +8,10 @@ import (
 
 // TODO: implement a real Seriatim subprocess adapter.
 
-// Runner is the adapter boundary for seriatim merge invocations.
+// Runner is the adapter boundary for seriatim merge/trim invocations.
 type Runner interface {
 	Run(ctx context.Context, req MergeRequest) (MergeResult, error)
+	Trim(ctx context.Context, req TrimRequest) (TrimResult, error)
 }
 
 // MergeRequest describes a seriatim merge invocation.
@@ -38,3 +39,28 @@ type MergeResult struct {
 	OutputSchema         string
 	Metadata             map[string]any
 }
+
+// TrimRequest describes a seriatim trim invocation.
+type TrimRequest struct {
+	Binary              string
+	InputTranscriptPath string
+	OutputTrimmedPath   string
+	KeepSelector        string
+	StdoutLogPath       string
+	StderrLogPath       string
+	GeneratedConfigPath string
+	Timeout             time.Duration
+}
+
+// TrimResult describes a trim output.
+type TrimResult struct {
+	OutputTrimmedPath   string
+	StdoutLogPath       string
+	StderrLogPath       string
+	GeneratedConfigPath string
+	ExitCode            int
+	Duration            time.Duration
+	InvokedBinary       string
+	KeepSelector        string
+	Metadata            map[string]any
+}

internal/adapters/seriatim/subprocess.go

@@ -111,11 +111,11 @@ func (r *SubprocessRunner) Run(ctx context.Context, req MergeRequest) (MergeResu
 		return MergeResult{}, fmt.Errorf("seriatim report is enabled but report path is missing")
 	}
 
-	args := r.buildArgs(req)
+	args := r.buildMergeArgs(req)
 	env := r.buildEnvOverrides()
 
 	if req.GeneratedConfigPath != "" {
-		if err := r.writeInvocationConfig(req, args); err != nil {
+		if err := r.writeMergeInvocationConfig(req, args); err != nil {
 			return MergeResult{}, fmt.Errorf("write seriatim invocation config %q: %w", req.GeneratedConfigPath, err)
 		}
 	}
@@ -188,7 +188,90 @@ func (r *SubprocessRunner) Run(ctx context.Context, req MergeRequest) (MergeResu
 	}, nil
 }
 
-func (r *SubprocessRunner) buildArgs(req MergeRequest) []string {
+// Trim executes Seriatim trim with deterministic flags and validates output artifacts.
+func (r *SubprocessRunner) Trim(ctx context.Context, req TrimRequest) (TrimResult, error) {
+	if r == nil {
+		return TrimResult{}, fmt.Errorf("seriatim subprocess runner is nil")
+	}
+	if strings.TrimSpace(req.InputTranscriptPath) == "" {
+		return TrimResult{}, fmt.Errorf("seriatim trim input path is required")
+	}
+	if strings.TrimSpace(req.OutputTrimmedPath) == "" {
+		return TrimResult{}, fmt.Errorf("seriatim trim output path is required")
+	}
+	if strings.TrimSpace(req.KeepSelector) == "" {
+		return TrimResult{}, fmt.Errorf("seriatim trim keep selector is required")
+	}
+
+	binary := r.binary
+	if strings.TrimSpace(req.Binary) != "" {
+		binary = strings.TrimSpace(req.Binary)
+	}
+
+	timeout := r.timeout
+	if req.Timeout < 0 {
+		return TrimResult{}, fmt.Errorf("seriatim trim timeout must be >= 0")
+	}
+	if req.Timeout > 0 {
+		timeout = req.Timeout
+	}
+
+	args := buildTrimArgs(req)
+	if req.GeneratedConfigPath != "" {
+		if err := writeTrimInvocationConfig(req, args, binary, timeout); err != nil {
+			return TrimResult{}, fmt.Errorf("write seriatim trim invocation config %q: %w", req.GeneratedConfigPath, err)
+		}
+	}
+
+	runRes, err := subprocess.Run(ctx, subprocess.RunRequest{
+		Executable:    binary,
+		Args:          args,
+		Timeout:       timeout,
+		StdoutLogPath: req.StdoutLogPath,
+		StderrLogPath: req.StderrLogPath,
+	})
+	if err != nil {
+		return TrimResult{
+			OutputTrimmedPath:   req.OutputTrimmedPath,
+			StdoutLogPath:       req.StdoutLogPath,
+			StderrLogPath:       req.StderrLogPath,
+			GeneratedConfigPath: req.GeneratedConfigPath,
+			ExitCode:            runRes.ExitCode,
+			Duration:            runRes.Duration,
+			InvokedBinary:       binary,
+			KeepSelector:        req.KeepSelector,
+		}, fmt.Errorf("run seriatim trim (binary=%q): %w", binary, err)
+	}
+
+	if err := validateJSONFileWithSegments(req.OutputTrimmedPath); err != nil {
+		return TrimResult{
+			OutputTrimmedPath:   req.OutputTrimmedPath,
+			StdoutLogPath:       req.StdoutLogPath,
+			StderrLogPath:       req.StderrLogPath,
+			GeneratedConfigPath: req.GeneratedConfigPath,
+			ExitCode:            runRes.ExitCode,
+			Duration:            runRes.Duration,
+			InvokedBinary:       binary,
+			KeepSelector:        req.KeepSelector,
+		}, fmt.Errorf("validate seriatim trimmed output %q: %w", req.OutputTrimmedPath, err)
+	}
+
+	return TrimResult{
+		OutputTrimmedPath:   req.OutputTrimmedPath,
+		StdoutLogPath:       req.StdoutLogPath,
+		StderrLogPath:       req.StderrLogPath,
+		GeneratedConfigPath: req.GeneratedConfigPath,
+		ExitCode:            runRes.ExitCode,
+		Duration:            runRes.Duration,
+		InvokedBinary:       binary,
+		KeepSelector:        req.KeepSelector,
+		Metadata: map[string]any{
+			"adapter": "seriatim_subprocess",
+		},
+	}, nil
+}
+
+func (r *SubprocessRunner) buildMergeArgs(req MergeRequest) []string {
 	args := []string{"merge"}
 
 	for _, path := range req.InputTranscriptPaths {
@@ -234,10 +317,11 @@ func (r *SubprocessRunner) buildEnvOverrides() map[string]string {
 	return out
 }
 
-func (r *SubprocessRunner) writeInvocationConfig(req MergeRequest, args []string) error {
+func (r *SubprocessRunner) writeMergeInvocationConfig(req MergeRequest, args []string) error {
 	payload := map[string]any{
 		"schema":                 "seriatim.generated.v1",
 		"binary":                 r.binary,
+		"command":                "merge",
 		"args":                   args,
 		"timeout":                r.timeout.String(),
 		"output_schema":          r.outputSchema,
@@ -261,6 +345,29 @@ func (r *SubprocessRunner) writeInvocationConfig(req MergeRequest, args []string
 	return subprocess.WriteYAMLAtomic(req.GeneratedConfigPath, payload, 0o644)
 }
 
+func buildTrimArgs(req TrimRequest) []string {
+	return []string{
+		"trim",
+		"--input-file", req.InputTranscriptPath,
+		"--output-file", req.OutputTrimmedPath,
+		"--keep", req.KeepSelector,
+	}
+}
+
+func writeTrimInvocationConfig(req TrimRequest, args []string, binary string, timeout time.Duration) error {
+	payload := map[string]any{
+		"schema":        "seriatim.generated.v1",
+		"command":       "trim",
+		"binary":        binary,
+		"args":          args,
+		"timeout":       timeout.String(),
+		"input_path":    req.InputTranscriptPath,
+		"output_path":   req.OutputTrimmedPath,
+		"keep_selector": req.KeepSelector,
+	}
+	return subprocess.WriteYAMLAtomic(req.GeneratedConfigPath, payload, 0o644)
+}
+
 func validateJSONFile(path string) error {
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -272,3 +379,24 @@ func validateJSONFile(path string) error {
 	}
 	return nil
 }
+
+func validateJSONFileWithSegments(path string) error {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return fmt.Errorf("read file: %w", err)
+	}
+
+	var payload map[string]any
+	if err := json.Unmarshal(data, &payload); err != nil {
+		return fmt.Errorf("parse json: %w", err)
+	}
+
+	segments, ok := payload["segments"]
+	if !ok {
+		return fmt.Errorf("top-level segments is required")
+	}
+	if _, ok := segments.([]any); !ok {
+		return fmt.Errorf("top-level segments must be an array")
+	}
+	return nil
+}

internal/adapters/seriatim/subprocess_test.go

@@ -209,6 +209,172 @@ func TestSubprocessRunnerInvalidReportJSONFails(t *testing.T) {
 	}
 }
 
+func TestSubprocessRunnerTrimSuccessInvocationAndProvenance(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("helper wrapper script uses /bin/sh")
+	}
+
+	t.Setenv("GO_WANT_SERIATIM_HELPER", "1")
+	t.Setenv("SERIATIM_HELPER_MODE", "trim_success")
+	recordPath := filepath.Join(t.TempDir(), "record.json")
+	t.Setenv("SERIATIM_HELPER_RECORD_PATH", recordPath)
+
+	wrapper := writeHelperWrapper(t)
+	runner := mustRunner(t, wrapper, false)
+	req := trimReqForTest(t)
+
+	res, err := runner.Trim(context.Background(), req)
+	if err != nil {
+		t.Fatalf("Trim() error = %v", err)
+	}
+	if res.OutputTrimmedPath != req.OutputTrimmedPath {
+		t.Fatalf("OutputTrimmedPath = %q, want %q", res.OutputTrimmedPath, req.OutputTrimmedPath)
+	}
+	if res.KeepSelector != req.KeepSelector {
+		t.Fatalf("KeepSelector = %q, want %q", res.KeepSelector, req.KeepSelector)
+	}
+	if res.InvokedBinary != wrapper {
+		t.Fatalf("InvokedBinary = %q, want %q", res.InvokedBinary, wrapper)
+	}
+	if res.ExitCode != 0 {
+		t.Fatalf("ExitCode = %d, want 0", res.ExitCode)
+	}
+	if res.Duration <= 0 {
+		t.Fatalf("Duration = %s, want >0", res.Duration)
+	}
+	if res.Metadata == nil || res.Metadata["adapter"] != "seriatim_subprocess" {
+		t.Fatalf("Metadata = %#v, want adapter marker", res.Metadata)
+	}
+
+	assertJSONFile(t, req.OutputTrimmedPath)
+	if _, err := os.Stat(req.StdoutLogPath); err != nil {
+		t.Fatalf("stdout log missing: %v", err)
+	}
+	if _, err := os.Stat(req.StderrLogPath); err != nil {
+		t.Fatalf("stderr log missing: %v", err)
+	}
+	if _, err := os.Stat(req.GeneratedConfigPath); err != nil {
+		t.Fatalf("generated config missing: %v", err)
+	}
+
+	stdoutData, err := os.ReadFile(req.StdoutLogPath)
+	if err != nil {
+		t.Fatalf("read stdout log: %v", err)
+	}
+	if !strings.Contains(string(stdoutData), "seriatim helper trim stdout") {
+		t.Fatalf("stdout log = %q, want trim helper stdout marker", string(stdoutData))
+	}
+	stderrData, err := os.ReadFile(req.StderrLogPath)
+	if err != nil {
+		t.Fatalf("read stderr log: %v", err)
+	}
+	if !strings.Contains(string(stderrData), "seriatim helper trim stderr") {
+		t.Fatalf("stderr log = %q, want trim helper stderr marker", string(stderrData))
+	}
+
+	cfgData, err := os.ReadFile(req.GeneratedConfigPath)
+	if err != nil {
+		t.Fatalf("read generated config: %v", err)
+	}
+	cfgText := string(cfgData)
+	if !strings.Contains(cfgText, "command: trim") {
+		t.Fatalf("generated config = %q, want command: trim", cfgText)
+	}
+	if !strings.Contains(cfgText, "keep_selector: 5-12") {
+		t.Fatalf("generated config = %q, want keep selector", cfgText)
+	}
+
+	rec := readHelperRecord(t, recordPath)
+	wantArgs := []string{
+		"trim",
+		"--input-file", req.InputTranscriptPath,
+		"--output-file", req.OutputTrimmedPath,
+		"--keep", req.KeepSelector,
+	}
+	if strings.Join(rec.Args, "\n") != strings.Join(wantArgs, "\n") {
+		t.Fatalf("args = %#v, want %#v", rec.Args, wantArgs)
+	}
+}
+
+func TestSubprocessRunnerTrimSubprocessFailure(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("helper wrapper script uses /bin/sh")
+	}
+	t.Setenv("GO_WANT_SERIATIM_HELPER", "1")
+	t.Setenv("SERIATIM_HELPER_MODE", "fail")
+	t.Setenv("SERIATIM_HELPER_RECORD_PATH", filepath.Join(t.TempDir(), "record.json"))
+
+	runner := mustRunner(t, writeHelperWrapper(t), false)
+	req := trimReqForTest(t)
+	_, err := runner.Trim(context.Background(), req)
+	if err == nil {
+		t.Fatal("Trim() error = nil, want non-nil")
+	}
+	if !strings.Contains(err.Error(), "run seriatim trim") {
+		t.Fatalf("error = %q, want subprocess context", err.Error())
+	}
+	if !strings.Contains(err.Error(), "exit code") {
+		t.Fatalf("error = %q, want exit code context", err.Error())
+	}
+}
+
+func TestSubprocessRunnerTrimMissingOutputFails(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("helper wrapper script uses /bin/sh")
+	}
+	t.Setenv("GO_WANT_SERIATIM_HELPER", "1")
+	t.Setenv("SERIATIM_HELPER_MODE", "missing_output")
+	t.Setenv("SERIATIM_HELPER_RECORD_PATH", filepath.Join(t.TempDir(), "record.json"))
+
+	runner := mustRunner(t, writeHelperWrapper(t), false)
+	req := trimReqForTest(t)
+	_, err := runner.Trim(context.Background(), req)
+	if err == nil {
+		t.Fatal("Trim() error = nil, want non-nil")
+	}
+	if !strings.Contains(err.Error(), "validate seriatim trimmed output") {
+		t.Fatalf("error = %q, want output validation context", err.Error())
+	}
+}
+
+func TestSubprocessRunnerTrimInvalidOutputJSONFails(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("helper wrapper script uses /bin/sh")
+	}
+	t.Setenv("GO_WANT_SERIATIM_HELPER", "1")
+	t.Setenv("SERIATIM_HELPER_MODE", "invalid_output")
+	t.Setenv("SERIATIM_HELPER_RECORD_PATH", filepath.Join(t.TempDir(), "record.json"))
+
+	runner := mustRunner(t, writeHelperWrapper(t), false)
+	req := trimReqForTest(t)
+	_, err := runner.Trim(context.Background(), req)
+	if err == nil {
+		t.Fatal("Trim() error = nil, want non-nil")
+	}
+	if !strings.Contains(err.Error(), "parse json") {
+		t.Fatalf("error = %q, want parse json context", err.Error())
+	}
+}
+
+func TestSubprocessRunnerTrimOutputMissingSegmentsFails(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("helper wrapper script uses /bin/sh")
+	}
+	t.Setenv("GO_WANT_SERIATIM_HELPER", "1")
+	t.Setenv("SERIATIM_HELPER_MODE", "trim_missing_segments")
+	t.Setenv("SERIATIM_HELPER_RECORD_PATH", filepath.Join(t.TempDir(), "record.json"))
+
+	runner := mustRunner(t, writeHelperWrapper(t), false)
+	req := trimReqForTest(t)
+	_, err := runner.Trim(context.Background(), req)
+	if err == nil {
+		t.Fatal("Trim() error = nil, want non-nil")
+	}
+	if !strings.Contains(err.Error(), "top-level segments is required") {
+		t.Fatalf("error = %q, want missing segments context", err.Error())
+	}
+}
+
 func TestSubprocessRunnerConstructorValidation(t *testing.T) {
 	_, err := NewSubprocessRunnerFromConfigValues("", "10m", "seriatim-intermediate", nil, true, EnvConfig{})
 	if err == nil {
@@ -250,14 +416,14 @@ func TestSeriatimSubprocessHelper(t *testing.T) {
 		_, _ = os.Stderr.WriteString("missing -- args separator\n")
 		os.Exit(2)
 	}
-	mergeArgs := args[start:]
+	cmdArgs := args[start:]
 
-	outputPath := flagValue(mergeArgs, "--output-file")
-	reportPath := flagValue(mergeArgs, "--report-file")
+	outputPath := flagValue(cmdArgs, "--output-file")
+	reportPath := flagValue(cmdArgs, "--report-file")
 	recordPath := os.Getenv("SERIATIM_HELPER_RECORD_PATH")
 	if strings.TrimSpace(recordPath) != "" {
 		rec := helperRecord{
-			Args: mergeArgs,
+			Args: cmdArgs,
 			Env: map[string]string{
 				"SERIATIM_OVERLAP_WORD_RUN_GAP":            os.Getenv("SERIATIM_OVERLAP_WORD_RUN_GAP"),
 				"SERIATIM_OVERLAP_WORD_RUN_REORDER_WINDOW": os.Getenv("SERIATIM_OVERLAP_WORD_RUN_REORDER_WINDOW"),
@@ -280,6 +446,11 @@ func TestSeriatimSubprocessHelper(t *testing.T) {
 		_, _ = os.Stdout.WriteString("seriatim helper success stdout\n")
 		_, _ = os.Stderr.WriteString("seriatim helper success stderr\n")
 		os.Exit(0)
+	case "trim_success":
+		writeSeriatimHelperFile(outputPath, `{"schema":"seriatim.intermediate.v1","segments":[]}`)
+		_, _ = os.Stdout.WriteString("seriatim helper trim stdout\n")
+		_, _ = os.Stderr.WriteString("seriatim helper trim stderr\n")
+		os.Exit(0)
 	case "fail":
 		_, _ = os.Stderr.WriteString("seriatim helper failure\n")
 		os.Exit(9)
@@ -300,6 +471,9 @@ func TestSeriatimSubprocessHelper(t *testing.T) {
 			writeSeriatimHelperFile(reportPath, `not-json`)
 		}
 		os.Exit(0)
+	case "trim_missing_segments":
+		writeSeriatimHelperFile(outputPath, `{"schema":"seriatim.intermediate.v1"}`)
+		os.Exit(0)
 	default:
 		_, _ = os.Stderr.WriteString(fmt.Sprintf("unknown helper mode %q\n", mode))
 		os.Exit(2)
@@ -340,6 +514,21 @@ func mergeReqForTest(t *testing.T, withReport bool) MergeRequest {
 	return req
 }
 
+func trimReqForTest(t *testing.T) TrimRequest {
+	t.Helper()
+	dir := t.TempDir()
+	input := filepath.Join(dir, "processed.json")
+	writeSeriatimFile(t, input, `{"schema":"seriatim.intermediate.v1","segments":[]}`)
+	return TrimRequest{
+		InputTranscriptPath: input,
+		OutputTrimmedPath:   filepath.Join(dir, "trimmed.json"),
+		KeepSelector:        "5-12",
+		GeneratedConfigPath: filepath.Join(dir, "seriatim.trim.generated.yml"),
+		StdoutLogPath:       filepath.Join(dir, "seriatim.trim.stdout.log"),
+		StderrLogPath:       filepath.Join(dir, "seriatim.trim.stderr.log"),
+	}
+}
+
 func mustRunner(t *testing.T, binary string, report bool) *SubprocessRunner {
 	t.Helper()
 	coalesce := 3.0