Fix OpenCode adapter timeout and event handling

[gricha]

Summary

• Use async endpoint (prompt_async) instead of sync - prevents timeout on long-running operations
• Increase SSE timeout to 10 minutes for complex tool-use operations
• Filter SSE events by sessionID to prevent cross-session interference
• Remove duplicate error emission
• Verify session exists before using saved agentSessionId

Root Cause

The sync /session/:id/message endpoint blocks until the AI completes processing. Our curl had a 30-second timeout, so any operation taking longer would fail with "Connection failed". The async endpoint returns 204 immediately and we rely on SSE for the response.

Test plan

• Multi-message conversation test passes
• Long-running operation with tool calls completes without timeout
• Invalid session ID gracefully creates new session
• Manual testing in web/mobile UI

🤖 Generated with Claude Code

[sentry]

Bug: The new filtering logic discards SSE events if the optional sessionID field is missing, which could lead to timeouts or silently dropped messages.
_{Severity: CRITICAL}

🔍 Detailed Analysis

The filtering logic for session.idle and message.part.updated events assumes the sessionID field will always be present. However, the OpenCodeServerEvent interface defines sessionID as optional. If the OpenCode service sends a valid event for the current session but omits the sessionID, this code will incorrectly discard it. This can lead to two failure modes: a 10-minute stream timeout if a session.idle event is dropped, or silent loss of AI responses if a message.part.updated event is dropped.

💡 Suggested Fix

Modify the filtering logic to correctly handle events where sessionID is undefined. The logic should only filter out events that have a sessionID that does not match the current agentSessionId. Events without a sessionID should be processed, assuming they are relevant to the current session.

🤖 Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: src/session-manager/adapters/opencode.ts#L521-L524

Potential issue: The filtering logic for `session.idle` and `message.part.updated`
events assumes the `sessionID` field will always be present. However, the
`OpenCodeServerEvent` interface defines `sessionID` as optional. If the OpenCode service
sends a valid event for the current session but omits the `sessionID`, this code will
incorrectly discard it. This can lead to two failure modes: a 10-minute stream timeout
if a `session.idle` event is dropped, or silent loss of AI responses if a
`message.part.updated` event is dropped.

_{Did we get this right? 👍 / 👎 to inform future reviews.
Reference ID: 8438808}