fix(web): keep the branch toolbar in sync with the real checkout

apps/web/src/components/BranchToolbar.logic.test.ts

@@ -82,6 +82,29 @@ describe("resolveBranchToolbarValue", () => {
       }),
     ).toBe("main");
   });
+
+  it("falls back to the thread branch while local status is still loading", () => {
+    expect(
+      resolveBranchToolbarValue({
+        envMode: "local",
+        activeWorktreePath: null,
+        activeThreadBranch: "feature/base",
+        currentGitBranch: null,
+      }),
+    ).toBe("feature/base");
+  });
+
+  it("does not cling to a deleted thread branch when the checkout is detached", () => {
+    expect(
+      resolveBranchToolbarValue({
+        envMode: "local",
+        activeWorktreePath: null,
+        activeThreadBranch: "throwaway/repro-error",
+        currentGitBranch: null,
+        isDetachedCheckout: true,
+      }),
+    ).toBeNull();
+  });
 });
 
 describe("resolveEnvironmentOptionLabel", () => {

apps/web/src/components/BranchToolbar.logic.ts

@@ -89,11 +89,22 @@ export function resolveBranchToolbarValue(input: {
   activeWorktreePath: string | null;
   activeThreadBranch: string | null;
   currentGitBranch: string | null;
+  /**
+   * True when git authoritatively reports the checkout is on no branch
+   * (detached HEAD) — e.g. the thread's branch was deleted out from under us.
+   * In that case the local-mode trigger must reflect reality instead of
+   * clinging to the now-dangling thread branch.
+   */
+  isDetachedCheckout?: boolean;
 }): string | null {
-  const { envMode, activeWorktreePath, activeThreadBranch, currentGitBranch } = input;
+  const { envMode, activeWorktreePath, activeThreadBranch, currentGitBranch, isDetachedCheckout } =
+    input;
   if (envMode === "worktree" && !activeWorktreePath) {
     return activeThreadBranch ?? currentGitBranch;
   }
+  if (isDetachedCheckout) {
+    return currentGitBranch;
+  }
   return currentGitBranch ?? activeThreadBranch;
 }
 

apps/web/src/components/BranchToolbarBranchSelector.tsx

@@ -15,7 +15,7 @@ import {
 
 import { useComposerDraftStore, type DraftId } from "../composerDraftStore";
 import { readEnvironmentApi } from "../environmentApi";
-import { useVcsStatus } from "../lib/vcsStatusState";
+import { refreshVcsStatus, useVcsStatus } from "../lib/vcsStatusState";
 import { useVcsRefs, vcsRefManager } from "../lib/vcsRefState";
 import { newCommandId } from "../lib/utils";
 import { cn } from "../lib/utils";
@@ -220,6 +220,11 @@ export function BranchToolbarBranchSelector({
   const isInitialBranchesLoadPending = branchRefState.isPending && branchRefState.data === null;
   const currentGitBranch =
     branchStatusQuery.data?.refName ?? refs.find((refName) => refName.current)?.name ?? null;
+  // Git reports an in-repo checkout with no branch (detached HEAD) — e.g. the
+  // thread's branch was deleted externally. Only trust this once status data has
+  // loaded, so we don't flash "Select ref" while the initial status is pending.
+  const isDetachedCheckout =
+    branchStatusQuery.data?.isRepo === true && (branchStatusQuery.data?.refName ?? null) === null;
   const sourceControlPresentation = useMemo(
     () => getSourceControlPresentation(branchStatusQuery.data?.sourceControlProvider),
     [branchStatusQuery.data?.sourceControlProvider],
@@ -230,6 +235,7 @@ export function BranchToolbarBranchSelector({
     activeWorktreePath,
     activeThreadBranch,
     currentGitBranch,
+    isDetachedCheckout,
   });
   const branchNames = useMemo(() => refs.map((refName) => refName.name), [refs]);
   const branchByName = useMemo(
@@ -300,6 +306,7 @@ export function BranchToolbarBranchSelector({
       await vcsRefManager
         .load(branchRefTarget, undefined, { limit: 100, preserveLoadedRefs: true })
         .catch(() => undefined);
+      void refreshVcsStatus({ environmentId, cwd: branchCwd });
     });
   };
 
@@ -414,11 +421,15 @@ export function BranchToolbarBranchSelector({
         setBranchQuery("");
         return;
       }
+      // Reload refs AND status together: opening the picker is the moment to
+      // reconcile with reality, including branch changes made outside the app
+      // (the status stream has no .git watcher, so it won't push those on its own).
       void vcsRefManager
         .load(branchRefTarget, undefined, { limit: 100, preserveLoadedRefs: true })
         .catch(() => undefined);
+      void refreshVcsStatus({ environmentId, cwd: branchCwd });
     },
-    [branchRefTarget],
+    [branchCwd, branchRefTarget, environmentId],
   );
 
   const branchListScrollElementRef = useRef<HTMLDivElement | null>(null);