Session source in lifecycle hooks

Context

Daemon session creation already forwards optional sourceType and sourceId values to ACP in _meta['qwen.session.source']. The ACP runtime currently uses the source type to disable native cron for channel sessions, but lifecycle hook payloads cannot observe either value. Receivers therefore cannot attribute a new session when SessionStart fires before the bridge persists its source.

Design

Parse the existing source metadata once at the ACP session boundary. Store the two optional strings on the session's Config, alongside the session id and other session-scoped state, and expose read-only getters.

The hook event handler adds present source values to its common input:

• sourceType becomes source_type.
• sourceId becomes source_id.

Conditional object spreads omit absent values instead of serializing empty or undefined fields. Because every lifecycle event uses the common input builder, SessionStart, UserPromptSubmit, Stop, and SessionEnd receive the same attribution without event-specific wiring.

Boundaries

This is a read-through of existing creation metadata. It does not change the REST create request, ACP bridge metadata key, capability negotiation, session persistence, or resume behavior. A session created without source metadata keeps the previous hook payload shape.

Verification

• Hook handler tests cover present and absent source fields on SessionStart payloads.
• ACP session tests cover propagation of channel source metadata into the session Config.
• Existing channel worker tests continue to cover creation metadata, including the channel instance name as sourceId.