This preserves per-message failure isolation when an Intercom bulk
message chunk cannot be committed. Query timeouts are retried once after
the failed transaction rolls back, while other database failures move
directly to an entry-by-entry fallback.
The fallback reacquires the import lock and refreshes each entry before
writing, so a competing worker cannot create duplicate messages. Each
individual write uses a savepoint, and search indexing happens only
after the import lock transaction commits.
This is Phase 2, Task 6 of CW-7615 and is stacked on #15111. The review
delta is one commit across the importer and its focused spec.
## Closes
-
[CW-7615](https://linear.app/chatwoot/issue/CW-7615/optimize-intercom-import-reliability-and-bulk-message-ingestion)
## How to test
1. Run an Intercom import where a bulk mapping write times out once and
confirm the chunk succeeds on retry.
2. Force a persistent timeout or database write failure and confirm
valid messages are imported through the fallback.
3. Force one fallback record to fail and confirm only that message is
recorded as an import error.
4. Simulate another worker repairing a message before fallback and
confirm no duplicate is created.
