ACP agent never sends session_info_update session updates #21013

Description

Problem
The ACP protocol defines session_info_update as a valid SessionUpdate type (with title and updatedAt fields), but the OpenCode ACP agent implementation never emits it.

In packages/opencode/src/acp/agent.ts), the handleEvent method only handles three event types:

1.permission.asked
2.message.part.updated
3.message.part.delta

There is no handler for session metadata changes (e.g. when a session title is auto-generated after the first prompt turn).

Expected behavior
When the session title is generated or updated, the ACP agent should send a session_info_update to connected clients:

await connection.sessionUpdate({
sessionId,
update: {
sessionUpdate: "session_info_update",
title: newTitle,
},
})

Context
The SessionInfoUpdate type is already defined in the ACP SDK (@agentclientprotocol/[email protected]) with title?: string | null and updatedAt?: string | null fields.
Session titles are generated asynchronously in packages/opencode/src/session/prompt.ts after the assistant responds.
ACP clients (e.g. editors) have no way to learn that a session title has changed, since the update is never forwarded.

Impact
ACP clients cannot display up-to-date session titles. The title shown at session creation time remains stale forever.

Plugins

No response

OpenCode version

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Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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