fix(acp): Fix memory leak in session event streams

[sauerdaniel]

Summary

Fix ACP session resource cleanup to prevent stale session state and leaked per-session resources.

Fixes #9154
Relates to #5363

Problem

ACP sessions were not fully cleaned up when sessions were deleted, leaving stale entries in session maps and per-session permission queues.

Solution

• Handle session-deleted events by explicitly closing the session
• Add closeSession(sessionId) in ACP agent to remove session state + permission queue entries
• Add agent dispose() cleanup path to clear remaining session state and abort global event stream
• Add delete()/clear() helpers to ACPSessionManager

Changes

• packages/opencode/src/acp/agent.ts
• packages/opencode/src/acp/session.ts

Testing

• TypeScript compilation passes (bun turbo typecheck)
• Unit tests pass

AI-Assisted

Yes

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[sauerdaniel]

Rebased onto latest dev and resolved merge conflicts.\n\nChanges adapted to the current architecture:\n- Added delete() and clear() methods to ACPSessionManager\n- Added dispose() method to Agent (aborts global event stream, clears sessions)\n- Added closeSession() method for per-session cleanup\n- Added handler for session.deleted event to auto-cleanup sessions\n- Removed per-session abortController from types (using global eventAbort pattern)\n\nAll typechecks pass. Ready for review.