Summary

Subagent completion announcements are silently dropped when the parent session has an active but non-consuming embedded Pi run (between turns, idle). The user only sees the result after sending another message that re-triggers the session.

This is a reopen of #75663. The original fix attempt (#75669) was closed because upstream has restructured the subagent completion delivery infrastructure — the agent-mediated completion path was removed and replaced with a sendMessage-based fallback system.

Root Cause (Current Upstream)

In sendSubagentAnnounceDirectly (src/agents/subagent-announce-delivery.ts), when requesterActivity.isActive is true but the embedded Pi run is not consuming messages:

1. queueEmbeddedPiMessage returns false (run not streaming)
2. The code enters the if (requesterActivity.isActive) block
3. The function returns { delivered: false } as a dead-end — preventing fallthrough to the callGateway("agent", { expectFinal: true }) path that would start a new run and deliver the message

Proposed Fix

Replace the early-return dead-end with a sendMessage-based fallback attempt, then fall through to the gateway call if the fallback fails. This requires:

1. Adding sendMessage to imports from subagent-announce-delivery.runtime.js
2. Adding sendMessage to SubagentAnnounceDeliveryDeps type and defaults
3. Adding extractThreadCompletionFallbackText, sendCompletionFallback, resolveCompletionFallbackPath helper functions
4. Replacing the early return at if (requesterActivity.isActive) with fallback-then-fallthrough logic
5. Updating tests to mock sendMessage via deps

Environment

• Channel: Telegram (push-based, most affected)
• Less affected: WebChat (polling picks up queued messages)
• Upstream version: v2026.5.7-beta.1

Related

• Supersedes Bug: Subagent completion announcements silently drop on Telegram when parent session is idle between turns #75663 (closed), fix(subagents): fall through to gateway call when steer+fallback fail #75669 (closed PR)
• Authored by: yozakura-ava