Agent frontmatter hooks silently fail for team-spawned subagents (session ID mismatch)

Description

Hooks defined in .claude/agents/*.md YAML frontmatter never fire for agents spawned via the team/agent system (TeamCreate + Task with subagent_type). The hooks are registered but never matched at dispatch time due to a session ID mismatch.

Reproduction

1. Create .claude/agents/worker.md:

---
name: worker
description: Test agent
hooks:
  PreToolUse:
    - matcher: "Read"
      hooks:
        - type: command
          command: "touch /tmp/hook-fired.txt"
---
Worker agent instructions here.

1. Create a team and spawn the agent:

TeamCreate → Task with subagent_type: "worker"

1. The agent uses Read (and other tools) — but /tmp/hook-fired.txt is never created.

1. Meanwhile, hooks in .claude/settings.json with the same matchers DO fire for all agents.

Root cause (from source analysis)

Binary analyzed: Claude Code 2.1.50 (ELF/Bun SEA)

Registration (when agent spawns):

// In agent spawn code:
if (H.hooks) UaD(A.setAppState, C, H.hooks, `agent '${H.agentType}'`, true);

Hooks are stored in appState.sessionHooks[C] where C is the session ID at spawn time.

Dispatch (when agent calls a tool):

// In VR (hook dispatch):
let U = D?.agentId ?? v$();
let J = hmA(G, U, E, H);

Lookup:

// In pS$ (session hook resolver):
function pS$(appState, sessionId) {
  let sessionData = appState.sessionHooks[sessionId];
  if (!sessionData) return new Map;  // ← returns empty, hooks not found
  ...
}

The registration session ID (C) and the dispatch session ID (D?.agentId ?? v$()) don't match for team-spawned agents. The hooks are stored under one key but looked up under another, so pS$ returns an empty Map and hooks silently never fire.

Settings.json hooks are unaffected because they're resolved via a different path (TwH()) that doesn't use session IDs.

Environment

• Claude Code: 2.1.50
• Platform: Linux (Fedora 43, x86_64)
• Agent spawn method: TeamCreate + Task with custom subagent_type

Impact

Agent-scoped hooks are completely non-functional for team workflows. This affects:

• Rule injection / compliance enforcement
• Agent-specific logging
• Any hook-based agent customization

The documentation states frontmatter hooks should work for project agents (and the registration code runs — Registered N frontmatter hook(s) is logged), but they are silently dropped at dispatch time.