Why

The 2026-06-10 in-app update on this fork failed at the rebuild stage with "Update didn't finish". Root cause: the fork upstream sync in _sync_with_upstream_if_needed merged upstream/main into local main, hit conflicts (fork is 57 ahead / 85 behind), printed "Skipping upstream sync" — and returned without aborting the merge. The tree was left mid-merge with conflict markers in 25 files, including hermes_cli/main.py (SyntaxError at line 471 on <<<<<<< HEAD, making hermes itself unbootable) and apps/desktop/package.json (npm EJSONPARSE), so npm install, the web UI build, and the desktop rebuild all failed.

The existing post-pull syntax guard only protects the git pull step; the upstream-sync merge runs after it, unguarded.

What changed

• hermes_cli/main.py: on merge failure, verify a merge actually started (git rev-parse -q --verify MERGE_HEAD) and run git merge --abort to restore a clean tree before skipping the sync. The message now reports whether the tree was restored, or warns with a git status hint if the abort itself failed.
• tests/hermes_cli/test_update_fork_sync_conflict_abort.py (new): scripted-git tests covering conflicted-merge-aborts-and-restores, failed-abort-warns, and merge-error-without-MERGE_HEAD-skips-abort.

Evidence

• PYTHONPATH=$PWD venv/python -m pytest tests/hermes_cli/test_update_fork_sync_conflict_abort.py tests/hermes_cli/test_update_post_pull_syntax_guard.py tests/hermes_cli/test_cmd_update.py -q → 36 passed (3 new + 33 existing).
• Incident log (~/.hermes/logs/bootstrap-installer.log): ✗ Merge failed (conflict). Skipping upstream sync. followed by SyntaxError: invalid syntax at main.py:471 <<<<<<< HEAD and npm error code EJSONPARSE in apps/desktop/package.json.
• Live recovery on the affected install was the same operation this patch automates: git merge --abort returned the tree to fork main and py_compile + JSON.parse both pass again.

Risks

• Scope is the conflict branch only; successful merges and the push path are untouched.
• git merge --abort is skipped when no MERGE_HEAD exists (e.g. merge refused before starting), so the warning can't fire spuriously.
• Upstream does not carry this code path (it skips sync entirely on divergence, fork commit 6d74667 added the merge), so no upstream mirror PR applies.