fix(title): handle duplicate auto-generated session titles gracefully

[alloevil]

Summary

• When set_session_title() raises ValueError due to a title collision, use get_next_title_in_lineage() to generate a unique variant (e.g. "Debugging Import Errors Support passing morph snapshot id #2") instead of silently dropping the title
• The title_callback is now called with the final title (whether original or deduplicated)
• Fixes fix(title): duplicate auto-generated session titles cause unhandled ValueError #50537

Changes

In agent/title_generator.py → auto_title_session():

Before: All exceptions from set_session_title() were caught and silently logged as debug, leaving the session with no title.

After: ValueError (title collision) is caught specifically. When it occurs, get_next_title_in_lineage() generates a unique " #N" suffix and retries. Other exceptions are still logged and silently skipped.

Tests

• Verified that get_next_title_in_lineage() is already tested in the existing test suite
• The fix is minimal and follows the exact approach suggested in the issue

[alt-glitch]

Duplicate of #26389 — both fix #50537 with the identical mechanism: catch the ValueError title collision in auto_title_session() and retry via get_next_title_in_lineage(). #26389 (open) is the earliest version of this fix.

Related: #26471 (same-mechanism sibling, adds a test), #50538 (broader cron-title reliability PR that also closes #50537).