fix(engine): defend autostash drop against TOCTOU race

dropAutostashBySha resolved SHA→stash@{N} then ran git stash drop ${ref}
non-atomically. Any other process (interactive shell, parallel merger,
fix-agent) pushing a stash between resolve and drop shifted the index, so
we silently dropped the wrong entry while leaving ours behind. The task
log then claimed "Restored pre-merge autostash X cleanly" even though the
stash was still in the list — observed on FN-3558 (e81e922) and others.

Verify the ref still resolves to our SHA via git rev-parse before dropping;
on mismatch, re-resolve and retry up to 5x. Return success/failure so the
caller can record honest status to the task feed instead of unconditionally
logging "cleanly".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/README.md

@@ -62,6 +62,7 @@ For a full walkthrough (installation, onboarding, first task, and daily workflow
 |---|---|
 | [Plugin Management](./plugin-management.md) | End-user guide for discovering, installing, enabling, configuring, updating, uninstalling, and troubleshooting Fusion plugins |
 | [Plugin Authoring](./PLUGIN_AUTHORING.md) | Developer guide for building Fusion plugins (manifest, SDK hooks, routes, UI/runtime contributions) |
+| [Even Realities Glasses Plugin](../plugins/fusion-plugin-even-realities-glasses/README.md) | Task-focused Even Realities glasses bridge with quick capture, polling notifications, and agent actions |
 | [Memory Plugin Contract](./memory-plugin-contract.md) | Pluggable memory backend architecture, interface contract, and migration strategy |
 
 ### Audit Reports