fix(agent): auto-deduplicate session titles on collision

[02356abc]

What does this PR do?

Fixes a bug where auto-generated session titles silently failed when the
LLM produced a title already in use by another session, leaving the new
session untitled.

Related Issue

No existing issue found. This is a standalone bug fix.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• `agent/title_generator.py`: In `auto_title_session`, catch the
  `ValueError` from `set_session_title` when the title collides, and
  fall back to `get_next_title_in_lineage()` which appends a `#N`
  suffix (e.g. "Hermes Agent Intro Support passing morph snapshot id #2").

Bug Report (Reproduction)

Observed behavior:

1. Start session A with "Who are you?" → auto-title: "Hermes Agent Intro"
2. Start session B with "Who are you?" → title generation succeeds but
   `set_session_title` raises `ValueError: Title already in use`
3. Session B remains untitled (title = null)

Root cause: `SessionDB` enforces a uniqueness constraint on session
titles (`idx_sessions_title_unique`). The auto-title generator did not
handle collisions, so repeated greetings or identical first exchanges
would silently leave sessions untitled.

Analysis: The codebase already has infrastructure for handling
duplicate titles:

• `resolve_session_by_title()` searches for "title #N" variants and
  returns the latest one
• `get_next_title_in_lineage()` computes the next available `#N` suffix

However, the auto-title path (`auto_title_session`) was not using this
infrastructure — it simply gave up when `set_session_title` failed.

Fix: When a collision is detected, automatically append a `#N`
suffix using the existing `get_next_title_in_lineage()` helper. This
aligns the auto-title behaviour with `resolve_session_by_title()` and
makes the title-unique constraint workable instead of silently broken.

How to Test

1. Start two sessions with the same first message (e.g. "Who are you?")
2. Both sessions should receive auto-generated titles
3. The second session's title should have a "Support passing morph snapshot id #2" suffix

Checklist

• pytest tests/agent/test_title_generator.py -v (20 passed)
• My commit messages follow Conventional Commits
• My PR contains only changes related to this fix

[teknium1]

Thanks for targeting a real current-main failure: auto_title_session() currently swallows the ValueError from set_session_title() at agent/title_generator.py:154-163, while SessionDB rejects duplicate titles at hermes_state.py:2717-2746.

Problems

• The added fallback is a one-shot read-then-write operation. get_next_title_in_lineage() reads variants at hermes_state.py:2865-2885, then set_session_title() performs a separate uniqueness-enforced write. Concurrent title workers can both choose the same #N; the losing retry remains untitled because the new nested handler only logs the second failure.
• The diff adds no regression test. Current tests cover only the ordinary success/callback path at tests/agent/test_title_generator.py:228-249. Related PR fix(title): use lineage fallback for generated titles #26471 also identified this duplicate and contains focused fallback tests.

Suggested changes

• Allocate/persist the numbered title atomically in SessionDB, or retry collisions safely until persistence succeeds.
• Add coverage for initial collision, fallback success and callback value, plus a competing fallback collision.

Automated hermes-sweeper review.

[teknium1]

Thanks for the contribution. Closing as a duplicate: #26471 by @JackALaing submitted the same lineage-fallback fix earlier the same day (May 15) with regression tests, and the version that ultimately landed (PR #66058, salvaging #50575) generalizes the retry into a shared helper with broader coverage. The collision → #N suffix behavior you targeted is now on main.