fix(merge-dialog): resolve HEAD before caching diff base

getWorktreeStatus, getBranchLog, and getBranchCommits passed the literal
'HEAD' to detectDiffBase, which used it verbatim in the 30s cache key
and propagated it through refineDiffBaseWithCherryPick. When refine
returned `{sha:'HEAD', ref:'HEAD'}` for a fully patch-equivalent branch,
that value survived a new commit — callers ran `git log HEAD..HEAD` and
reported has_committed_changes=false even with real new work, while
ChangedFilesList (which calls pinHead first) showed the file correctly.

Resolve 'HEAD' to its SHA at the entry of detectDiffBase so the cache
key tracks HEAD movement and downstream values reference real commits.

Also clear MergeDialog's createResource data via mutate(undefined) on
open so unguarded reads of worktreeStatus()/mergeStatus() don't flash
the previous open's snapshot during the refetch window.

Author: johannesjo

electron/ipc/git.ts

@@ -446,7 +446,14 @@ async function detectDiffBase(
   baseBranch?: string,
 ): Promise<PickedMergeBase> {
   const branch = baseBranch ?? (await detectMainBranch(repoRoot));
-  const headRef = head ?? 'HEAD';
+  // Resolve the literal 'HEAD' to its commit SHA so the cache key tracks
+  // HEAD movement. Otherwise a cached `{sha:'HEAD', ref:'HEAD'}` (returned
+  // by refineDiffBaseWithCherryPick when the branch was fully patch-
+  // equivalent to base) survives a new commit on the branch — callers then
+  // run `git log HEAD..HEAD` against the literal and see no commits, even
+  // though HEAD just moved forward.
+  const requestedHead = head ?? 'HEAD';
+  const headRef = requestedHead === 'HEAD' ? await pinHead(repoRoot) : requestedHead;
   const key = `${cacheKey(repoRoot)}:${branch}:${headRef}`;
   const cached = diffBaseCache.get(key);
   if (cached) {

src/components/MergeDialog.tsx

@@ -28,22 +28,25 @@ export function MergeDialog(props: MergeDialogProps) {
 
   const resourceSource = () =>
     props.open ? { path: props.task.worktreePath, baseBranch: props.task.baseBranch } : null;
-  const [branchLog, { refetch: refetchBranchLog }] = createResource(resourceSource, (src) =>
-    invoke<string>(IPC.GetBranchLog, { worktreePath: src.path, baseBranch: src.baseBranch }),
-  );
-  const [worktreeStatus, { refetch: refetchWorktreeStatus }] = createResource(
+  const [branchLog, { refetch: refetchBranchLog, mutate: mutateBranchLog }] = createResource(
     resourceSource,
     (src) =>
+      invoke<string>(IPC.GetBranchLog, { worktreePath: src.path, baseBranch: src.baseBranch }),
+  );
+  const [worktreeStatus, { refetch: refetchWorktreeStatus, mutate: mutateWorktreeStatus }] =
+    createResource(resourceSource, (src) =>
       invoke<WorktreeStatus>(IPC.GetWorktreeStatus, {
         worktreePath: src.path,
         baseBranch: src.baseBranch,
       }),
-  );
-  const [mergeStatus, { refetch: refetchMergeStatus }] = createResource(resourceSource, (src) =>
-    invoke<MergeStatus>(IPC.CheckMergeStatus, {
-      worktreePath: src.path,
-      baseBranch: src.baseBranch,
-    }),
+    );
+  const [mergeStatus, { refetch: refetchMergeStatus, mutate: mutateMergeStatus }] = createResource(
+    resourceSource,
+    (src) =>
+      invoke<MergeStatus>(IPC.CheckMergeStatus, {
+        worktreePath: src.path,
+        baseBranch: src.baseBranch,
+      }),
   );
 
   const hasConflicts = () => (mergeStatus()?.conflicting_files.length ?? 0) > 0;
@@ -67,9 +70,15 @@ export function MergeDialog(props: MergeDialogProps) {
       setRebaseSuccess(false);
       setMerging(false);
       setRebasing(false);
-      // Force fresh data on every open — covers edge cases where
-      // createResource source tracking alone misses a refresh
-      // (e.g. external rebase by AI agent while dialog was closed).
+      // Drop the previous open's cached data so accessors return undefined
+      // during refetch — otherwise unguarded reads (uncommitted-changes
+      // warning, branch-mismatch banner) flash the stale snapshot until the
+      // new fetch resolves. Then trigger refetch as a safety net for cases
+      // where source tracking alone misses (e.g. external rebase by AI
+      // agent while dialog was closed).
+      mutateBranchLog(undefined);
+      mutateMergeStatus(undefined);
+      mutateWorktreeStatus(undefined);
       refetchBranchLog();
       refetchMergeStatus();
       refetchWorktreeStatus();