feat(plh): flag plugin-agent frontmatter Claude Code ignores (v5.5.0 / E)

Plugin subagents silently ignore `hooks`/`mcpServers`/`permissionMode`
frontmatter — these are honored only for user/project agents in
.claude/agents/ (code.claude.com/docs sub-agents). Setting them in a
plugin agent is dead config; `permissionMode` is MEDIUM because it
implies a restriction Claude Code does not apply (false security).
hooks/mcpServers are LOW.

Additive to PLH's agent-frontmatter loop (no new scanner, count stays
13). One humanizer pattern covers the three field titles. Hermetic
temp-fixture test (positive + negative). Suite 954 -> 957, byte-stable.

Part of v5.5.0 "steering-model I". Foundation (active-config-reader
enumeration) deferred to v5.6 with B — A/E are additive and don't
consume it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8

tests/scanners/plugin-health-scanner.test.mjs

@@ -1,7 +1,9 @@
-import { describe, it } from 'node:test';
+import { describe, it, beforeEach, afterEach } from 'node:test';
 import assert from 'node:assert/strict';
 import { resolve, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
+import { mkdtemp, mkdir, writeFile, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
 import { resetCounter } from '../../scanners/lib/output.mjs';
 import { scan, discoverPlugins } from '../../scanners/plugin-health-scanner.mjs';
 
@@ -356,3 +358,68 @@ describe('finding format', () => {
     assert.ok(f.description);
   });
 });
+
+describe('PLH — plugin agent declares fields Claude Code ignores (E)', () => {
+  // Hermetic temp fixture: the path-guard blocks committing .claude-plugin/.
+  // Plugin subagents silently ignore hooks/mcpServers/permissionMode frontmatter
+  // (code.claude.com/docs sub-agents, V15) — dead config; permissionMode = false security.
+  let tmpRoot;
+  let result;
+
+  async function writePlugin(root, agentExtraFrontmatter) {
+    await mkdir(join(root, '.claude-plugin'), { recursive: true });
+    await mkdir(join(root, 'agents'), { recursive: true });
+    await writeFile(
+      join(root, '.claude-plugin', 'plugin.json'),
+      JSON.stringify({ name: 'demo', description: 'demo plugin for tests', version: '1.0.0' }, null, 2) + '\n',
+      'utf8',
+    );
+    await writeFile(
+      join(root, 'agents', 'doer.md'),
+      `---\nname: doer\ndescription: does things\n${agentExtraFrontmatter}---\n\n# Doer\n\nBody.\n`,
+      'utf8',
+    );
+  }
+
+  beforeEach(async () => {
+    resetCounter();
+    tmpRoot = await mkdtemp(join(tmpdir(), 'ca-plh-agentdead-'));
+    await writePlugin(tmpRoot, 'permissionMode: plan\nhooks: present\nmcpServers: present\n');
+    result = await scan(tmpRoot);
+  });
+
+  afterEach(async () => {
+    if (tmpRoot) await rm(tmpRoot, { recursive: true, force: true });
+  });
+
+  it('flags permissionMode as medium (false security)', () => {
+    const f = result.findings.find(x =>
+      x.scanner === 'PLH' && (x.evidence || '').startsWith('permissionMode:'));
+    assert.ok(f, `expected a permissionMode finding; got: ${result.findings.map(x => x.title).join(' | ')}`);
+    assert.equal(f.severity, 'medium');
+  });
+
+  it('flags hooks and mcpServers as low (dead config)', () => {
+    for (const key of ['hooks', 'mcpServers']) {
+      const f = result.findings.find(x =>
+        x.scanner === 'PLH' && (x.evidence || '').startsWith(`${key}:`));
+      assert.ok(f, `expected a ${key} finding`);
+      assert.equal(f.severity, 'low', `${key} should be low`);
+    }
+  });
+
+  it('does NOT flag a clean agent (name + description only)', async () => {
+    resetCounter();
+    const clean = await mkdtemp(join(tmpdir(), 'ca-plh-agentclean-'));
+    try {
+      await writePlugin(clean, '');
+      const r = await scan(clean);
+      const dead = r.findings.filter(x =>
+        x.scanner === 'PLH' && /which Claude Code ignores/.test(x.title || ''));
+      assert.equal(dead.length, 0,
+        `clean agent should have no ignored-field findings; got: ${dead.map(x => x.title).join(' | ')}`);
+    } finally {
+      await rm(clean, { recursive: true, force: true });
+    }
+  });
+});