Per AGENTS.md rule 8, this commit lands the failing regression test
ahead of the fix so the red → green pair is visible in git log.
Cursor Bugbot flagged the deadlock at HIGH severity on commit b09a097:
`Omnigraph::refresh()` holds `coordinator.write().await` from
omnigraph.rs:468 through function exit, including across the call to
`reload_schema_if_source_changed()` at line 484. That helper, when the
on-disk schema source differs from the in-memory cache, attempts
`self.coordinator.read().await` at line 496. Tokio's RwLock isn't
reentrant — the read blocks waiting for the write to release, the
write isn't released until refresh() returns. Hard hang.
Reachable from `branch_delete` (omnigraph.rs:910 calls `self.refresh()`)
and `branch_merge_as` (post-merge refresh at merge.rs:1100).
Cross-handle setup is the realistic trigger: handle A applies a
schema, advancing _schema.pg on disk and updating A's ArcSwap cache
in-line; handle B has stale in-memory schema_source. B's next
refresh() (here via branch_delete) hits the read-after-write reload
path because B's cache no longer matches disk. Single-handle is
unreachable since apply_schema updates the local cache atomically.
Test currently fails on b09a097 with the timeout firing at 15s,
proving branch_delete hung. The next commit scopes the write guard
to the recovery section so reload_schema_if_source_changed runs
without the write held — uncontested read acquisition, no deadlock.
The test extends `composite_flow.rs` with a broader sequence
(apply_schema → branch_create → branch_delete → branch_merge → mutate
with new column → reopen) so the post-fix path's correctness is
pinned alongside the deadlock pin per the user's request.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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