fix(daemon/execenv): refuse to write .gc_meta.json when issue_id is empty (#2077)

A non-trivial fraction of completed task workdirs (~28% in field reports)
end up with .gc_meta.json files containing issue_id: "". Empty issue_id
defeats the daemon's own GC loop (gc.go:139 calls
GetIssueGCCheck(meta.IssueID)) and external retention scripts that
cross-reference issue status before deleting orphaned workdirs.

Refuse to write the file when issueID is empty, logging a Warn so
operators have a starting point for debugging the upstream race
condition. Skip is preferred over a sentinel-marker file: it keeps the
data invariant clean (a .gc_meta.json file always carries a valid
issue_id) and matches the repo CLAUDE.md preference for not preserving
dual-state behavior.

WriteGCMeta now takes a *slog.Logger so it can emit the warning. The
package already uses log/slog (Prepare/reuseEnv), and daemon.go:884 has
taskLog in scope at the only call site.

Closes #1913

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

server/internal/daemon/daemon.go

@@ -1461,7 +1461,7 @@ func (d *Daemon) handleTask(ctx context.Context, task Task, slot int) {
 	// can look up the issue later. Written last so that a mid-task crash
 	// leaves the directory as an orphan (cleaned up by GCOrphanTTL).
 	if result.EnvRoot != "" {
-		if err := execenv.WriteGCMeta(result.EnvRoot, task.IssueID, task.WorkspaceID); err != nil {
+		if err := execenv.WriteGCMeta(result.EnvRoot, task.IssueID, task.WorkspaceID, taskLog); err != nil {
 			taskLog.Warn("write gc meta failed (non-fatal)", "error", err)
 		}
 	}

server/internal/daemon/execenv/execenv.go

@@ -53,7 +53,7 @@ type TaskContextForEnv struct {
 	ProjectTitle            string                  // human-readable project title
 	ProjectResources        []ProjectResourceForEnv // resources attached to the project
 	ChatSessionID           string                  // non-empty for chat tasks
-	AutopilotRunID          string              // non-empty for autopilot run_only tasks
+	AutopilotRunID          string                  // non-empty for autopilot run_only tasks
 	AutopilotID             string
 	AutopilotTitle          string
 	AutopilotDescription    string
@@ -214,7 +214,11 @@ type GCMeta struct {
 const gcMetaFile = ".gc_meta.json"
 
 // WriteGCMeta writes GC metadata into the given directory.
-func WriteGCMeta(envRoot, issueID, workspaceID string) error {
+func WriteGCMeta(envRoot, issueID, workspaceID string, logger *slog.Logger) error {
+	if issueID == "" {
+		logger.Warn("execenv: skipping .gc_meta.json write: issue_id is empty", "envRoot", envRoot, "workspaceID", workspaceID)
+		return nil
+	}
 	if envRoot == "" {
 		return nil
 	}

server/internal/daemon/execenv/execenv_test.go

@@ -2,6 +2,7 @@ package execenv
 
 import (
 	"encoding/json"
+	"io"
 	"log/slog"
 	"os"
 	"path/filepath"
@@ -14,6 +15,10 @@ func testLogger() *slog.Logger {
 	return slog.Default()
 }
 
+func discardLogger() *slog.Logger {
+	return slog.New(slog.NewTextHandler(io.Discard, nil))
+}
+
 func TestShortID(t *testing.T) {
 	t.Parallel()
 	tests := []struct {
@@ -1916,7 +1921,7 @@ func TestWriteReadGCMeta(t *testing.T) {
 	issueID := "a1b2c3d4-e5f6-7890-abcd-ef1234567890"
 	wsID := "ws-test-001"
 
-	if err := WriteGCMeta(dir, issueID, wsID); err != nil {
+	if err := WriteGCMeta(dir, issueID, wsID, discardLogger()); err != nil {
 		t.Fatalf("WriteGCMeta: %v", err)
 	}
 
@@ -1938,11 +1943,23 @@ func TestWriteReadGCMeta(t *testing.T) {
 
 func TestWriteGCMeta_EmptyRoot(t *testing.T) {
 	t.Parallel()
-	if err := WriteGCMeta("", "issue", "ws"); err != nil {
+	if err := WriteGCMeta("", "issue", "ws", discardLogger()); err != nil {
 		t.Fatalf("expected nil for empty root, got %v", err)
 	}
 }
 
+func TestWriteGCMeta_EmptyIssueID(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+
+	if err := WriteGCMeta(dir, "", "ws", discardLogger()); err != nil {
+		t.Fatalf("expected nil for empty issue ID, got %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(dir, gcMetaFile)); !os.IsNotExist(err) {
+		t.Fatalf("expected gc meta file to be absent, got err=%v", err)
+	}
+}
+
 func TestReadGCMeta_NoFile(t *testing.T) {
 	t.Parallel()
 	dir := t.TempDir()