MUL-2794 fix(agent): stop Cursor sessions on terminal result (#3165)

Treats Cursor's stream-json terminal `result` event as the protocol completion boundary so a lingering Cursor worker process can no longer hold the daemon task open after the agent has produced its final result.

- Tighten `cmd.WaitDelay` to 500ms (set before `Start()`)
- Set `resultSeen` and `cancel()` on terminal `result`
- Preserve completed/failed status across the cancellation via two `!resultSeen` guards in the post-loop status decision
- Add unix fake-CLI coverage for success and `is_error` terminal results

server/pkg/agent/cursor.go

@@ -39,7 +39,7 @@ func (b *cursorBackend) Execute(ctx context.Context, prompt string, opts ExecOpt
 	cmd := exec.CommandContext(runCtx, argv0, cmdArgs...)
 	hideAgentWindow(cmd)
 	b.cfg.Logger.Info("agent command", "exec", argv0, "args", cmdArgs)
-	cmd.WaitDelay = 20 * time.Second
+	cmd.WaitDelay = 500 * time.Millisecond
 	if opts.Cwd != "" {
 		cmd.Dir = opts.Cwd
 	}
@@ -78,6 +78,7 @@ func (b *cursorBackend) Execute(ctx context.Context, prompt string, opts ExecOpt
 		var sessionID string
 		finalStatus := "completed"
 		var finalError string
+		resultSeen := false
 		// stepUsage accumulates per-step token counts from "step_finish" events.
 		// resultUsage holds authoritative session totals from "result" events.
 		// If the result event includes usage, we use resultUsage exclusively;
@@ -140,6 +141,7 @@ func (b *cursorBackend) Execute(ctx context.Context, prompt string, opts ExecOpt
 				})
 
 			case "result":
+				resultSeen = true
 				if evt.IsError || evt.Subtype == "error" {
 					finalStatus = "failed"
 					finalError = cursorErrorText(&evt)
@@ -151,6 +153,10 @@ func (b *cursorBackend) Execute(ctx context.Context, prompt string, opts ExecOpt
 				if evt.Usage != nil {
 					hasResultUsage = true
 				}
+				// Current Cursor Agent versions can emit the terminal result
+				// event but keep a worker process alive. Treat result as the
+				// protocol boundary so the daemon can report completion.
+				cancel()
 
 			case "error":
 				errMsg := cursorErrorText(&evt)
@@ -198,10 +204,10 @@ func (b *cursorBackend) Execute(ctx context.Context, prompt string, opts ExecOpt
 		if runCtx.Err() == context.DeadlineExceeded {
 			finalStatus = "timeout"
 			finalError = fmt.Sprintf("cursor-agent timed out after %s", timeout)
-		} else if runCtx.Err() == context.Canceled {
+		} else if runCtx.Err() == context.Canceled && !resultSeen {
 			finalStatus = "aborted"
 			finalError = "execution cancelled"
-		} else if exitErr != nil && finalStatus == "completed" {
+		} else if exitErr != nil && finalStatus == "completed" && !resultSeen {
 			finalStatus = "failed"
 			finalError = fmt.Sprintf("cursor-agent exited with error: %v", exitErr)
 		}

server/pkg/agent/cursor_execute_unix_test.go

@@ -0,0 +1,77 @@
+//go:build unix
+
+package agent
+
+import (
+	"log/slog"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestCursorExecuteStopsAfterTerminalResult(t *testing.T) {
+	t.Parallel()
+
+	script := `#!/bin/sh
+printf '%s\n' '{"type":"system","subtype":"init","session_id":"sess-terminal"}'
+printf '%s\n' '{"type":"result","subtype":"success","is_error":false,"result":"done","session_id":"sess-terminal"}'
+sleep 10
+`
+	result := executeFakeCursor(t, script)
+
+	if result.Status != "completed" {
+		t.Fatalf("status = %q, want completed; error=%q", result.Status, result.Error)
+	}
+	if result.Output != "done" {
+		t.Fatalf("output = %q, want done", result.Output)
+	}
+	if result.SessionID != "sess-terminal" {
+		t.Fatalf("session id = %q, want sess-terminal", result.SessionID)
+	}
+}
+
+func TestCursorExecuteStopsAfterTerminalErrorResult(t *testing.T) {
+	t.Parallel()
+
+	script := `#!/bin/sh
+printf '%s\n' '{"type":"system","subtype":"init","session_id":"sess-terminal-error"}'
+printf '%s\n' '{"type":"result","subtype":"error","is_error":true,"result":"failed hard","session_id":"sess-terminal-error"}'
+sleep 10
+`
+	result := executeFakeCursor(t, script)
+
+	if result.Status != "failed" {
+		t.Fatalf("status = %q, want failed; error=%q", result.Status, result.Error)
+	}
+	if result.Error != "failed hard" {
+		t.Fatalf("error = %q, want failed hard", result.Error)
+	}
+	if result.Output != "failed hard" {
+		t.Fatalf("output = %q, want failed hard", result.Output)
+	}
+	if result.SessionID != "sess-terminal-error" {
+		t.Fatalf("session id = %q, want sess-terminal-error", result.SessionID)
+	}
+}
+
+func executeFakeCursor(t *testing.T, script string) Result {
+	t.Helper()
+
+	fakePath := filepath.Join(t.TempDir(), "cursor-agent")
+	writeTestExecutable(t, fakePath, []byte(script))
+
+	backend, err := New("cursor", Config{ExecutablePath: fakePath, Logger: slog.Default()})
+	if err != nil {
+		t.Fatalf("New(cursor): %v", err)
+	}
+	session, err := backend.Execute(t.Context(), "hello", ExecOptions{Timeout: 5 * time.Second})
+	if err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+
+	result := <-session.Result
+	if result.Status == "timeout" {
+		t.Fatalf("cursor backend timed out instead of stopping after terminal result; error=%q", result.Error)
+	}
+	return result
+}