[Fix] Slack Fast sessions remain titled Thread

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Replaced the per-turn title-response gate from [Improve] Show Fast activity in Slack agent sessions #1881 with a shared Slack title synchronizer that renames after initial generation even when agents.sessions.setStatus omits its current title.
• Added Redis locking, a durable latest-title handoff, and hashed title deduplication so unchanged titles do not rename, contended updates are drained by the current holder, and stale callers revalidate the latest canonical title before writing Slack.
• Wired titles generated after turn settlement back into Slack, and made later manual Fast Session renames update both canonical title records before using the same best-effort sync path.
• Blank or unavailable titles remain omitted; no fallback title is introduced.

Why this change was made

Manual testing of #1881 showed ordinary Fast conversations remained named Thread. Slack did not provide a usable current title in the status response, so the ephemeral turn adapter skipped rename and had no durable retry after the generated title was persisted.

Impact

New Slack Fast sessions acquire their generated Roomote title after generation, including sub-300ms turns and generation that finishes after settlement. Subsequent generated and manual title changes stay synchronized without redundant renames; active/processing status calls carry lifecycle only, and concurrent older updates cannot overwrite a newer canonical title. Slack, Redis, installation, and credential failures remain best-effort and never fail the Fast turn or title edit.

[roomote-community]

No new code issues found. See task

• packages/slack/src/agent-session-title-sync.ts:50 A newer title update can time out behind a slow stale rename and leave Slack permanently on the stale title.

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