Detect external changes with deep context (#1888)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Adds commit-aware deep context by computing hasExternalChanges (via
latest assistant commit vs current repo + dirty check) and propagating
commitHash through messages/provider options.
> 
> - **Deep Smart Context**:
> - Add `hasExternalChanges` to `VersionedFiles`; compute by comparing
latest assistant `commitHash` with `getCurrentCommitHash` and checking
`isGitStatusClean`.
> - Make `sourceCommitHash` nullable; add `commitHash` in
`DyadEngineProviderOptions` and use it when scanning history.
> - **Chat Handling**:
> - Include `commitHash` in `messageHistory` and pass through
`providerOptions['dyad-engine']`.
> - **Git Utilities**:
> - New `isGitStatusClean(path)` supporting native git and
isomorphic-git.
> - **Tests/Snapshots**:
> - Mock `getCurrentCommitHash` and `isGitStatusClean`; update snapshot
to include `hasExternalChanges`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
ad92d9dd5ead941de822e8da59c8819e4db8b775. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->







<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Detects external code changes in deep context by comparing the latest
assistant commit with the current repo state. Exposes a
hasExternalChanges flag so the engine can adapt responses when the
workspace diverges.

- **New Features**
  - Added hasExternalChanges to VersionedFiles.
- Computes by comparing the latest assistant commitHash with
getCurrentCommitHash and checking isGitStatusClean.
- Passes commitHash through chat messages and dyad-engine
providerOptions; sourceCommitHash is now nullable.
  - Defaults to true if detection fails (with a warning).

<sup>Written for commit 6ebb0b125c9a3421b4e5673870b204c9cb279265.
Summary will update automatically on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

src/ipc/utils/git_utils.ts

@@ -39,6 +39,23 @@ export async function getCurrentCommitHash({
   });
 }
 
+export async function isGitStatusClean({
+  path,
+}: {
+  path: string;
+}): Promise<boolean> {
+  const settings = readSettings();
+  if (settings.enableNativeGit) {
+    const { stdout } = await execAsync(`git -C "${path}" status --porcelain`);
+    return stdout.trim() === "";
+  } else {
+    const statusMatrix = await git.statusMatrix({ fs, dir: path });
+    return statusMatrix.every(
+      (row) => row[1] === 1 && row[2] === 1 && row[3] === 1,
+    );
+  }
+}
+
 export async function gitCommit({
   path,
   message,