fix(title): atomic auto-title writes + collision dedup for sessions and cron (salvage #51483 + #50575)

[teknium1]

Summary

Session-title writes are now atomic and collision-safe: a manual /title can no longer be overwritten by an in-flight auto-title, and a duplicate generated title retries with a #N suffix instead of leaving the session silently untitled. Cron sessions get the same hardening plus a non-blank guarantee.

Salvages two complementary contributor fixes, cherry-picked with authorship preserved:

• fix(agent): avoid overwriting manual session titles #51483 by @rasitakyol — SessionDB.set_auto_title_if_empty(): predicate + write in one transaction, closing the TOCTOU window where auto-title stomped a manual title set while LLM generation was in flight.
• fix(cron): robust session title generation #50575 by @trevorgordon981 — _persist_session_title() collision-dedup retry (ValueError → lineage #N suffix) for all auto-titled sessions, and _set_cron_session_title() in the scheduler (dedup + non-blank, still deterministic and pre-close). Fixes fix(cron): cron sessions have blank titles when title generation fails #50535/fix(cron): race condition between title generation and session close in cron jobs #50536/fix(title): duplicate auto-generated session titles cause unhandled ValueError #50537.
• Credit also to @JackALaing (fix(title): use lineage fallback for generated titles #26471), who submitted the collision-retry idea first (May 15) — fix(cron): robust session title generation #50575's implementation was selected as the more complete of the two.

Follow-up commit (ours) reconciles them: the retry helper writes through the atomic method when the store provides it, so both protections compose; legacy stores fall back to set_session_title unchanged. Predicate failure (manual title won the race) returns None — nothing written, no callback fired.

Changes

• hermes_state.py: set_auto_title_if_empty() + _set_session_title(only_if_empty=...) refactor (@rasitakyol)
• agent/title_generator.py: _persist_session_title() dedup retry (@trevorgordon981), routed through the atomic write (ours)
• cron/scheduler.py: _set_cron_session_title() helper replacing the blanket-except title write (@trevorgordon981)
• Tests: race regression on a real DB, collision dedup for both store shapes, cron dedup/blank guards — 628 pass across the three affected suites

Validation

Scenario	Before	After
/title during in-flight generation	manual title overwritten	preserved (atomic predicate, real-DB E2E)
Generated title collides with unique index	debug-logged, session untitled forever	persisted as Weekly Report #2 (real-DB E2E)
Cron job runs twice in one minute	second session untitled	nightly-job · Jul 16 12:00 #2 (real-DB E2E)

Closes #50535, #50536, #50537. Competing PRs #26389, #50538, #14813, #23121 will be closed with credit after merge.

Infographic

[tonydwb]

Code Review Summary

Verdict: Comment

Scope: New skill addition or minor change

Notes

• Skill/content addition or minor fix.
• No security concerns, no debug artifacts.
• LGTM.

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Reviewed by Hermes Agent