feat(prime): project child progress notes (#2282) and evaluation of rlm.collect for Agents view

[rynfar]

Background & Upstream Changes

Upstream Prime Agent introduced:

1. Child progress notes (#2282):
   • Added schema 28 capability / payload fields for in-flight sub-agent reporting:
     • progressNote: optional string emitted by children via rlm.progress.note (throttled).
     • lastActivityAt: monotonic timestamp of the last tracked child activity.
     • activityStaleMs: duration since last activity, held unset while a child is executing so long tool invocations do not falsely flag as stale.
   • These surface in the child session snapshot and roster (rlm.list_subagents()).
2. rlm.collect (#2282 / release 0.9.5):
   • A typed, non-steering fan-in mechanism for subagents that awaits direct children with a bounded timeout and returns per-child result envelopes (status, settled, answer preview, error, duration, tool_count) without inflating the parent's conversational message queue.

Analysis for Pylon

1. Projecting Child Progress Notes into Pylon Agents Surface

• Pylon Invariants:
  • Pylon's PrimeAgentDaemonSessionRuntime tracks child rosters via authoritative roster snapshots and live event sequences (authoritative_child_roster capability).
  • Pylon represents agents in its Agents UI with status, activity, and subagent tree views.
• Proposed Projection:
  • In PrimeAgentDaemonEvents.ts and PrimeAgentDaemonSessionRuntime.ts, extend the child roster event types and session snapshot decoders to include optional progressNote, lastActivityAt, and activityStaleMs.
  • In Pylon's UI / web state, surface the child's latest progressNote directly on the child's row in the agent hierarchy (similar to how tool execution status or compact summaries are displayed).
  • Gate decoding on schema capability or optional field presence rather than raw schema revision numbers to prevent schema version conflict with fork revisions 28–33.

2. rlm.collect Integration

• Internal vs Exposed Action:
  • rlm.collect is designed as a kernel-level aggregation primitive for multi-agent workflows running in the Python REPL harness.
  • Exposing rlm.collect directly as a user-facing action in Pylon is unnecessary and could collide with Pylon's turn settlement and occurrence model.
  • Recommendation: Keep rlm.collect purely internal to the agent kernel / subagent runtime. However, Pylon should ensure that when an agent calls rlm.collect, Pylon's turn-settlement and prompt lifecycle fencing recognize that the parent turn is awaiting subagents and does not prematurely settle or time out.

Action Items

• Extend Pylon child roster schema decoder to parse progressNote and activityStaleMs when present.
• Update Agents view subagent rows to render active progress notes.
• Verify that rlm.collect execution inside the agent kernel respects Pylon's turn quiescence and timeout policies.