Sub-agent session causes gateway blocking: before_prompt_build hooks need subagent skip logic

[jlin53882]

Problem

When a sub-agent (e.g. via /new command or delegate) runs, its before_prompt_build hooks execute synchronously inside the same Node.js process as the gateway, blocking the event loop. User sessions waiting on the gateway's IPC response are starved.

This manifests as:

• 30-50% of /new sessions fail to produce a response (Issue memoryReflection hook in before_prompt_build starves user session (beta.10) #492)
• Sessions marked done in sessions.json but no JSONL file written
• User sees no reply on Telegram/Discord

The root cause is that memory-lancedb-pro registers multiple before_prompt_build hooks (priority 12 and 15) that call await loadAgentReflectionSlices() which does store.list() -- a blocking DB operation during prompt build. The agent:bootstrap hook has subagent skip logic but before_prompt_build hooks do not.

Proposed Solution

A per-agent exclusion mechanism via the existing autoRecallExcludeAgents config field, extended to also protect the memoryReflection hooks.

Changes

1. New helper function isAgentOrSessionExcluded

Supports three pattern types:

• Exact match: memory-distiller
• Wildcard prefix: pi- (matches pi-agent, pi-coder)
• Special temp:* for internal reflection sessions

2. Fixed auto-recall before_prompt_build exclusion check

Removed the ineffective agentId !== undefined check (always true due to || "main" fallback).

3. Added exclusion checks to both reflection before_prompt_build hooks (priority 12 & 15)

Both hooks now have isInternalReflectionSessionKey guard first, followed by isAgentOrSessionExcluded check.

4. Three-layer guard on runMemoryReflection command hook

• Internal session guard
• Re-entrant guard (global lock via Symbol.for + globalThis)
• Serial cooldown guard (120s)

5. Added internal session guard to appendSelfImprovementNote

Consistent with agent:bootstrap hook behavior.

6. Enhanced early-return logging

All early returns now include sessionKey/sessionId for observability.

Protection Matrix

Hook	Protection
before_prompt_build (auto-recall)	exclusion check
before_prompt_build (priority 12)	isInternal guard + exclusion
before_prompt_build (priority 15)	isInternal guard + exclusion
command:new/reset -> runMemoryRefl.	three-layer guard
appendSelfImprovementNote	internal session guard

Usage

{
  "memory-lancedb-pro": {
    "autoRecallExcludeAgents": ["memory-distiller", "pi-", "temp:*"]
  }
}

Questions for Maintainers

1. Is this approach acceptable? autoRecallExcludeAgents now serves both auto-recall and reflection exclusion purposes.
2. Should we split into reflectionExcludeAgents for clarity?
3. Is the 120s cooldown (SERIAL_GUARD_COOLDOWN_MS) reasonable, or should it be configurable?
4. Any concerns about using globalThis with Symbol.for for the lock maps?

---

Related: #492

[jlin53882]

Related to PR #516

This issue is a duplicate of #492 and is addressed by PR #516 (fix: complete Issue #492 protection -- per-agent exclusion + internal session guards).

PR #516 implements a comprehensive fix covering:

• Per-agent exclusion via autoRecallExcludeAgents (dual-purpose: auto-recall + reflection)
• Three-layer guard on runMemoryReflection (internal session key + re-entrant lock + 120s cooldown)
• Internal session guards on both before_prompt_build hooks

This issue can be closed once PR #516 is merged. See also: #514 (proposal), #492 (original bug report), #600 (duplicate).

[jlin53882]

Duplicate of #492, addressed by PR #516

[jlin53882]

Merged into #601

This issue is merged into the canonical issue #601 for tracking. The root cause, analysis, and fix are identical — please follow #601 for updates.

PR #516 will address this once its blockers are resolved.