Core dispatch drops /compact reply — replies=0 on all channels

After /compact is dispatched, the core pipeline completes with replies=0. The compaction itself runs fine, but the reply ("Compacted X tokens") is silently discarded. This affects all channels (confirmed on Feishu DM and WebChat).

PR #87171 (commit fb6f2c61) attempted to fix this in #87107 but did not fully resolve it.

Evidence from gateway logs (2026-06-04)

Normal user message (works correctly):

15:04:44 | dispatching to agent (session=agent:main:feishu:direct:ou_...)
15:04:46 | dispatch complete (queuedFinal=true, replies=1)  ← ✅ reply delivered

/compact command (reply silently lost):

15:03:51 | received message: /compact
15:03:51 | dispatching to agent (session=agent:main:feishu:direct:ou_...)
15:03:52 | dispatch complete (queuedFinal=false, replies=0)  ← ❌ reply lost
15:03:54 | compaction-safeguard: compaction runs...            ← compaction itself works

Key observations:

1. The command IS received and dispatched to the agent
2. The compaction DOES execute (safeguard log proves it)
3. But the reply is never produced (replies=0)
4. No fallback message is sent
5. Reproducible on all channels

Environment

Related issues

• /compact command reply silently dropped after upgrade to 2026.5.22 (delivered=true but no actual delivery) #87107 — Original report (closed, fix incomplete)
• Bug: Feishu channel does not handle text slash commands (/compact, /new, /stop) #79409, [Bug]: Discord native /compact slash command produces no visible reply despite successful compaction #89950 — Same symptom on other channels
• Bug: compaction.notifyUser notices gated behind onBlockReply — async compactions silently notify nothing #88933 — notifyUser notification silently skipped (separate bug)
• [feishu] Streaming card sends incremental diff instead of full text to CardKit API #88335, [Bug]: Feishu streaming card: only the last character displayed after streaming completes #88867, [Bug] Feishu streaming card: abnormal typewriter effect and final content truncated to last character #88929 — CardKit streaming rendering corruption (separate bug)