fix(coding-agent): footer git branch not updating after external branch switches

Git uses atomic writes (temp file + rename) which changes the inode.
fs.watch on a file stops working after the inode changes.
Now watches the directory containing HEAD and filters for HEAD changes.

packages/coding-agent/CHANGELOG.md

@@ -23,6 +23,7 @@
 
 - Session picker respects custom keybindings when using `--resume` ([#633](https://github.com/badlogic/pi-mono/pull/633) by [@aos](https://github.com/aos))
 - Custom footer extensions now see model changes: `ctx.model` is now a getter that returns the current model instead of a snapshot from when the context was created ([#634](https://github.com/badlogic/pi-mono/pull/634) by [@ogulcancelik](https://github.com/ogulcancelik))
+- Footer git branch not updating after external branch switches. Git uses atomic writes (temp file + rename), which changes the inode and breaks `fs.watch` on the file. Now watches the directory instead.
 - Extension loading errors are now displayed to the user instead of being silently ignored ([#639](https://github.com/badlogic/pi-mono/pull/639) by [@aliou](https://github.com/aliou))
 
 ## [0.42.5] - 2026-01-11

packages/coding-agent/src/core/footer-data-provider.ts

@@ -103,10 +103,17 @@ export class FooterDataProvider {
 		const gitHeadPath = findGitHeadPath();
 		if (!gitHeadPath) return;
 
+		// Watch the directory containing HEAD, not HEAD itself.
+		// Git uses atomic writes (write temp, rename over HEAD), which changes the inode.
+		// fs.watch on a file stops working after the inode changes.
+		const gitDir = dirname(gitHeadPath);
+
 		try {
-			this.gitWatcher = watch(gitHeadPath, () => {
-				this.cachedBranch = undefined;
-				for (const cb of this.branchChangeCallbacks) cb();
+			this.gitWatcher = watch(gitDir, (_eventType, filename) => {
+				if (filename === "HEAD") {
+					this.cachedBranch = undefined;
+					for (const cb of this.branchChangeCallbacks) cb();
+				}
 			});
 		} catch {
 			// Silently fail if we can't watch