Fork tasks from snapshots; snapshot only when text follows tool calls

internal/claude/session.go

@@ -33,6 +33,7 @@ type Options struct {
 	Model       string
 	SessionID   string
 	Resume      string
+	ResumeAt    string
 	ForkSession bool
 	GitName     string
 	GitEmail    string
@@ -154,6 +155,14 @@ func (e Event) ParentToolUseID() (string, error) {
 	return msg.ParentToolUseID, err
 }
 
+func (e Event) UUID() (string, error) {
+	msg := struct {
+		UUID string `json:"uuid"`
+	}{}
+	err := json.Unmarshal(e.Raw, &msg)
+	return msg.UUID, err
+}
+
 func (e Event) TextDelta() (string, error) {
 	msg := struct {
 		ParentToolUseID *string `json:"parent_tool_use_id"`
@@ -326,6 +335,10 @@ func (s *Session) buildArgs(opts Options) ([]string, error) {
 		args = append(args, "--resume="+opts.Resume)
 	}
 
+	if opts.ResumeAt != "" {
+		args = append(args, "--resume-session-at="+opts.ResumeAt)
+	}
+
 	if opts.ForkSession {
 		args = append(args, "--fork-session")
 	}

internal/claude/session_test.go

@@ -262,6 +262,67 @@ func TestResume(t *testing.T) {
 	}
 }
 
+func TestForkAt(t *testing.T) {
+	t.Parallel()
+	ctx := testContext(t)
+
+	first, err := claude.Start(ctx, options(t, "first", claude.Options{Cwd: scratchRepo(t)}))
+	if err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	send(t, first, "Run the bash command `echo APPLE-1`. After it finishes, run the bash command `echo BANANA-2`. Then reply with the single word ok.")
+	cut := ""
+	waitResult(t, ctx, first, func(ev claude.Event) {
+		if cut != "" || ev.Type != "user" {
+			return
+		}
+		blocks, err := ev.Blocks()
+		if err != nil {
+			t.Fatalf("parse user: %v", err)
+		}
+		for _, b := range blocks {
+			if b.Type == "tool_result" && strings.Contains(string(b.Content), "APPLE-1") {
+				cut, err = ev.UUID()
+				if err != nil {
+					t.Fatalf("parse uuid: %v", err)
+				}
+			}
+		}
+	})
+	id := first.ID()
+	closeSession(t, first)
+
+	if cut == "" {
+		t.Fatalf("never saw the APPLE-1 tool result")
+	}
+
+	forkID := "8a1b2c3d-0000-4000-8000-" + strings.ReplaceAll(time.Now().Format("150405.000000"), ".", "")
+	fork, err := claude.Start(ctx, options(t, "fork", claude.Options{
+		Cwd:         scratchRepo(t),
+		SessionID:   forkID,
+		Resume:      id,
+		ResumeAt:    cut,
+		ForkSession: true,
+	}))
+	if err != nil {
+		t.Fatalf("fork: %v", err)
+	}
+	t.Cleanup(func() { closeSession(t, fork) })
+
+	send(t, fork, "Without running anything, list the exact output of every bash command you have run in this conversation, one per line, and nothing else.")
+	text := waitResult(t, ctx, fork, nil)
+
+	if !strings.Contains(text, "APPLE-1") {
+		t.Fatalf("fork lost the conversation before the cut; assistant said %q", text)
+	}
+	if strings.Contains(text, "BANANA-2") {
+		t.Fatalf("fork kept the conversation after the cut; assistant said %q", text)
+	}
+	if fork.ID() != forkID {
+		t.Fatalf("fork has session id %s, want %s", fork.ID(), forkID)
+	}
+}
+
 func testContext(t *testing.T) context.Context {
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Minute)
 	t.Cleanup(cancel)