feat(web): regenerate thread titles from sidebar

[t3dotgg]

Thread titles can stop reflecting the conversation as work evolves, while Sidebar v2 only supports replacing them manually.

This adds a Regenerate title action that sends recent thread context and the previous title through the configured text-generation model. The server keeps the work off the provider command queue, preserves manual renames made while generation is running, and capability-gates the action for version-skewed environments.

Testing

• 96 focused contract, prompt, environment, and reactor tests
• Typechecked contracts, client-runtime, server, and web
• Targeted lint and formatting checks

Generated by gpt-5.6-sol with the Codex harness in T3 Code.

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Note

Medium Risk
Touches orchestration commands/events, projection persistence, and async reactor behavior with race handling; changes are well-tested but span server and web with a new migration.

Overview
Adds Regenerate title for threads whose titles no longer match the conversation, exposed from Sidebar v2 (single and bulk selection) and gated by a new threadTitleRegeneration server capability.

Clients send thread.meta.update with regenerateTitle: true. The decider records pending titleRegeneration state and emits completion via thread.title.regeneration.complete. ProviderCommandReactor handles regeneration on a dedicated async worker (not the provider turn queue): it builds bounded thread context (8k chars, up to four attachments), calls text generation with previousTitle, skips fallback/unchanged titles, and avoids overwriting manual renames made while a run is in flight or queued.

SQLite migration 035 adds projection columns; snapshots and the client reducer surface titleRegeneration so rows can dim, set aria-busy, and time out after 30s if the server never clears pending state.

^{Reviewed by Cursor Bugbot for commit 88b3bd1. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add thread title regeneration from the sidebar context menu

• Adds 'Regenerate title' to per-thread and multi-select context menus in SidebarV2.tsx, calling updateThreadMetadata with regenerateTitle: true and showing a disabled 'Regenerating…' label while pending.
• Introduces server-side title regeneration in ProviderCommandReactor.ts: a thread.meta-updated event with regenerateTitle=true triggers async LLM title generation, then emits a thread.title.regeneration.complete command to update the thread.
• Adds previousTitle support to buildThreadTitlePrompt across all text generation providers so regeneration prompts reflect prior title context and use tail-preserving truncation on long thread histories.
• Persists in-flight regeneration state (titleRegenerationRequestId, titleRegenerationStartedAt) via a new DB migration (035_ProjectionThreadTitleRegeneration.ts) and propagates it through the read model to the client.
• Exposes a threadTitleRegeneration capability flag in the server environment descriptor so clients can gate the UI feature on server support.

^{Macroscope summarized 88b3bd1.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new user-facing feature (thread title regeneration) with database schema changes, new orchestration logic, and UI components. New features introducing new workflows warrant human review regardless of implementation quality.

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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