acp: generated session titles are never pushed to clients (no session_info_update with title) #56894

Summary

When running opencode acp, auto-generated session titles never reach the ACP client. Core OpenCode generates a title after the first user message and internally publishes the rename (bus event SessionEvent.Renamed), but the ACP adapter never forwards it: no session/update notification with sessionUpdate: "session_info_update" and a title field is ever sent. The generated title is only discoverable via session/list.

ACP clients that display dynamic session names from session_info_update (as documented in the ACP core schema — SessionInfoUpdate: "This allows clients to display dynamic session names") therefore keep a static fallback label forever. Example consumer: the ACP Pro VS Code extension, which updates tab titles exclusively from session_info_update — with OpenCode its tabs never rename after the first prompt, while agents that do push titles (e.g. Claude Code's ACP adapter) rename correctly.

Environment

• opencode version: 2.0.32 (also verified in v1.19.3 sources — same gap)
• OS: Windows_NT 10.0.22621.6060 (win32 x64)
• Terminal: Unavailable — ACP runs over stdio (opencode acp) from an IDE client; no terminal involved
• Shell: C:\Windows\system32\cmd.exe (ComSpec)
• Install/channel: latest (npm global @opencode/cli, channel=latest from CLI logs)
• Active plugins: none configured (cli.json / opencode.jsonc contain no plugins entries)

Reproduction

With a minimal scripted ACP client against opencode acp (v2.0.32):

1. initialize → session/new (cwd = project directory, no mcpServers) → wait for the response.
2. session/prompt with a short message → wait for stopReason: "end_turn" (the turn completes normally, usage_update and message chunks are received as expected).
3. Record every session/update notification for the entire session lifetime → zero session_info_update messages are received.
4. ~9 seconds after the turn, call session/list: the new session is listed with the LLM-generated title (e.g. "Тест: ответ одним словом" for the prompt "Ответь ровно одним словом: ок") — the title has been generated server-side, but was never pushed to the client.

Reproducible consistently (3 independent runs, v2.0.32). Also reproducible from a GUI client: ACP Pro 0.3.9 + OpenCode, first prompt → tab label never renames.

Expected Behavior

Per the ACP schema, an agent should notify the client when session metadata changes:

{
  "sessionUpdate": "session_info_update",
  "title": "<generated title>",
  "updatedAt": "<iso ts>"
}

OpenCode already has the exact hook for this: packages/core/src/session/title.ts publishes SessionEvent.Renamed to the bus when a title is generated or regenerated. Forwarding that event through the ACP adapter as a session_info_update would make dynamic session names work for all ACP clients.

Additionally, session/load replay (packages/cli/src/acp/replay.ts) never tells the client the loaded session's current title either — pushing one session_info_update at the start of the replay would let clients label restored sessions correctly.

Actual Behavior

No session_info_update with a title is ever sent. In the current source (HEAD 501b15af26915ba52682e20e220e7e137e89e92f):

• packages/cli/src/acp/translate.ts — session_info_update is used only for the retry marker _meta["opencode/retry"]; nothing maps SessionEvent.Renamed / title changes.
• packages/cli/src/acp/service.ts — listSessions maps session.title into the session/list response (with a "New session - <timestamp>" fallback), so titles surface only when the client re-lists sessions on its own.
• packages/cli/src/acp/replay.ts — contains no title forwarding.

Same for tag v1.19.3 (packages/opencode/src/acp/*): session/list returns title, nothing pushes renames. So no OpenCode release has ever implemented this part of the protocol; clients never received a push.

Additional Context

• Title generation itself works in ACP mode: session/list returned generated titles seconds after a completed turn in every test run, so the fix is purely the push (plus a one-time title announcement on session/load).
• Title generation can fail (e.g. AI_APICallError: Insufficient account funds seen in logs for the title agent's small model); in that case session/list keeps the timestamped fallback. Even when generation succeeds, though, nothing is pushed — the client can't tell the difference without polling session/list.
• Current client-side workaround: re-open the session (the client picks the title up from session/list), or poll session/list after each turn end.
• Frequency: always; user-visible impact: ACP client tab/session labels never auto-rename with OpenCode.

References

• ACP agent never sends session_info_update session updates #21013 — the same report from 2026-04: "ACP agent never sends session_info_update session updates". It was auto-closed by the stale bot on 2026-07-03 with the note "If the issue is still relevant please open a new one" — this is that new issue, still reproducible on 2.0.32.
• PR fix(acp): forward session title updates to ACP clients via session_info_update #21111 — a ready fix for this exact gap ("fix(acp): forward session title updates to ACP clients via session_info_update"), closed unmerged by the automated PR cleanup bot on 2026-05-15 (age/reactions criteria, not a substantive decline). It targets the pre-V2 layout (packages/opencode/src/acp/agent.ts), but the approach ports directly to the current packages/cli/src/acp/ adapter.
• [FEATURE]: ACP sessions should get auto-generated titles instead of "ACP Session <UUID>" #13139 (completed, 2026-04-13) — "ACP sessions should get auto-generated titles instead of 'ACP Session '": title generation for ACP sessions did land; only the client notification is missing.