fix(mount): fall back when GitHub tree cursor stalls

internal/mountsync/syncer.go

@@ -62,7 +62,7 @@ var sensitiveLogQueryValue = regexp.MustCompile(`(?i)([?&](?:token|access_token|
 // version instead of treating the failure as a fatal sync error.
 var ErrSchemaValidation = errors.New("schema validation failed")
 
-// ErrMalformedPagination is returned when an events feed reports a non-empty
+// ErrMalformedPagination is returned when a paginated feed reports a non-empty
 // cursor that does not advance pagination. The mount fails closed instead of
 // retrying the same page until its reconcile context expires.
 var ErrMalformedPagination = errors.New("malformed pagination")
@@ -335,8 +335,8 @@ func (e *HTTPError) Error() string {
 	return fmt.Sprintf("http %d: %s", e.StatusCode, e.Message)
 }
 
-// MalformedPaginationError reports a server response that cannot make an
-// events pagination walk advance. Cursor values are included so operators can
+// MalformedPaginationError reports a server response that cannot make a
+// pagination walk advance. Cursor values are included so operators can
 // identify the broken response and repair the server or upgrade the backend.
 type MalformedPaginationError struct {
 	Feed       string
@@ -6954,8 +6954,10 @@ type githubTreeFile struct {
 func (s *Syncer) githubWorkingTreeSnapshot(ctx context.Context, prog bootstrapProgress, strictComplete bool) (map[string]githubTreeFile, string, error) {
 	files := map[string]githubTreeFile{}
 	cursor := ""
+	seenCursors := make(map[string]struct{})
 	maxObservedRevision := ""
 	for {
+		pageStartCursor := cursor
 		page, err := s.client.ListTree(ctx, s.workspace, s.githubWorkingTree.ContentsRoot, 200, cursor)
 		if err != nil {
 			return nil, "", err
@@ -6994,10 +6996,27 @@ func (s *Syncer) githubWorkingTreeSnapshot(ctx context.Context, prog bootstrapPr
 				Mode:        entry.Mode,
 			}
 		}
-		if page.NextCursor == nil || strings.TrimSpace(*page.NextCursor) == "" {
+		nextCursor := ""
+		if page.NextCursor != nil {
+			nextCursor = strings.TrimSpace(*page.NextCursor)
+		}
+		if nextCursor == "" {
 			break
 		}
-		cursor = strings.TrimSpace(*page.NextCursor)
+		reason := "next cursor did not advance"
+		if nextCursor != pageStartCursor {
+			reason = "next cursor repeated a previous page"
+		}
+		if _, seen := seenCursors[nextCursor]; seen || nextCursor == pageStartCursor {
+			return nil, "", &MalformedPaginationError{
+				Feed:       "github working-tree",
+				Cursor:     pageStartCursor,
+				NextCursor: nextCursor,
+				Reason:     reason,
+			}
+		}
+		seenCursors[nextCursor] = struct{}{}
+		cursor = nextCursor
 	}
 	return files, maxObservedRevision, nil
 }

internal/mountsync/syncer_test.go

@@ -3023,6 +3023,103 @@ func TestGithubWorkingTreeSnapshotRejectsUnsupportedCompleteEntry(t *testing.T)
 	}
 }
 
+type repeatedGithubTreeCursorClient struct {
+	*fakeClient
+	requestedCursors []string
+}
+
+func (c *repeatedGithubTreeCursorClient) ListTree(_ context.Context, _, _ string, _ int, cursor string) (TreeResponse, error) {
+	c.requestedCursors = append(c.requestedCursors, cursor)
+	next := "page-2"
+	return TreeResponse{NextCursor: &next}, nil
+}
+
+func TestGithubWorkingTreeSnapshotRejectsRepeatedCursor(t *testing.T) {
+	localDir := t.TempDir()
+	client := &repeatedGithubTreeCursorClient{fakeClient: &fakeClient{}}
+	syncer, err := NewSyncer(client, SyncerOptions{
+		WorkspaceID: "ws_repeated_github_cursor", RemoteRoot: "/github/repos/o/r/contents",
+		LocalRoot: localDir, StateFile: filepath.Join(localDir, ".state.json"), WebSocket: boolPtr(false),
+	})
+	if err != nil {
+		t.Fatalf("NewSyncer failed: %v", err)
+	}
+
+	_, _, err = syncer.githubWorkingTreeSnapshot(context.Background(), bootstrapProgress{}, true)
+	var paginationErr *MalformedPaginationError
+	if !errors.As(err, &paginationErr) {
+		t.Fatalf("error = %v, want MalformedPaginationError", err)
+	}
+	if !errors.Is(err, ErrMalformedPagination) {
+		t.Fatalf("error = %v, want ErrMalformedPagination", err)
+	}
+	if paginationErr.Feed != "github working-tree" || paginationErr.Cursor != "page-2" || paginationErr.NextCursor != "page-2" {
+		t.Fatalf("unexpected pagination error: %#v", paginationErr)
+	}
+	if got, want := client.requestedCursors, []string{"", "page-2"}; !slices.Equal(got, want) {
+		t.Fatalf("ListTree cursors = %#v, want %#v", got, want)
+	}
+}
+
+type repeatedGithubSnapshotCursorClient struct {
+	*fakeExportClient
+	snapshotCursors []string
+}
+
+func (c *repeatedGithubSnapshotCursorClient) ListTree(ctx context.Context, workspaceID, path string, depth int, cursor string) (TreeResponse, error) {
+	if depth == 200 {
+		c.snapshotCursors = append(c.snapshotCursors, cursor)
+		next := "page-2"
+		return TreeResponse{Path: path, NextCursor: &next}, nil
+	}
+	return c.fakeClient.ListTree(ctx, workspaceID, path, depth, cursor)
+}
+
+func TestReconcileFallsBackToBoundedTreeWhenGithubSnapshotCursorRepeats(t *testing.T) {
+	localDir := t.TempDir()
+	contentsRoot := "/github/repos/AgentWorkforce/cloud/contents"
+	headSHA := "head123"
+	readme := []byte("# Cloud\n")
+	readmeRemote := contentsRoot + "/README.md@" + headSHA + ".json"
+	sentinelPath := "/github/repos/AgentWorkforce/cloud/.relayfile/clone.json"
+	base := &fakeExportClient{fakeClient: &fakeClient{files: map[string]RemoteFile{
+		sentinelPath: {
+			Path: sentinelPath, Revision: "rev_1", ContentType: "application/json",
+			Content: `{"headSha":"` + headSHA + `","defaultBranch":"main","sourceProfile":"complete-v1","filesExpected":1,"eventsCursor":"evt_1"}`,
+		},
+		readmeRemote: {
+			Path: readmeRemote, Revision: "rev_2", ContentType: "application/json",
+			Content: string(readme), ContentHash: hashBytes(readme),
+		},
+	}}}
+	client := &repeatedGithubSnapshotCursorClient{fakeExportClient: base}
+	syncer, err := NewSyncer(client, SyncerOptions{
+		WorkspaceID: "ws_repeated_github_cursor_fallback", RemoteRoot: contentsRoot,
+		LocalRoot: localDir, StateFile: filepath.Join(localDir, ".state.json"),
+		WebSocket: boolPtr(false), FullPullEvery: -1,
+	})
+	if err != nil {
+		t.Fatalf("NewSyncer failed: %v", err)
+	}
+
+	if err := syncer.Reconcile(context.Background()); err != nil {
+		t.Fatalf("Reconcile should fall back to bounded tree traversal: %v", err)
+	}
+	if got, want := client.snapshotCursors, []string{"", "page-2"}; !slices.Equal(got, want) {
+		t.Fatalf("snapshot ListTree cursors = %#v, want %#v", got, want)
+	}
+	if client.tarCalls != 0 {
+		t.Fatalf("tar export must not run after its verification snapshot fails, got %d calls", client.tarCalls)
+	}
+	if base.listTreeCalls == 0 {
+		t.Fatal("bounded tree fallback did not run")
+	}
+	if !syncer.state.BootstrapComplete {
+		t.Fatal("bounded tree fallback did not complete bootstrap")
+	}
+	assertLocalFileContent(t, filepath.Join(localDir, "README.md"), string(readme))
+}
+
 func TestValidateSymlinkTargetAcceptsInRootSymlinkChain(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("symlink creation requires developer mode or elevated privileges on Windows")