refactor(#1756): derive getDirName from a documented runtime.localConfigDir descriptor axis (#1757)

ADR-1239 Phase B (parent #1679). getDirName was a hand-maintained 15-branch
if-chain mapping each runtime to its local content-rewrite dot-dir. Relocate
those values into a documented runtime.localConfigDir descriptor field; derive
getDirName from registry.runtimes[id].runtime.localConfigDir (fallback .claude).

- 16 capability.json gain runtime.localConfigDir (byte-identical values)
- capability-validator.cjs requires it (non-empty dot-dir); registry regenerated
- docs/reference/capability-manifest.md documents the field + the three
  divergent values (copilot=.github, antigravity=.agents, kimi=.kimi-code)
- drift-guard test: golden value map + key-set equality both ways

Byte-identical install output for all 16 runtimes (golden-parity harness #1730).

Closes #1756

Co-authored-by: review-bot <review-bot@gsd>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests/capability-manifest-version.test.cjs

@@ -76,6 +76,7 @@ function runtimeCap(overrides) {
     engines: { gsd: '>=1.6.0' },
     runtime: {
       configHome: { kind: 'dot-home', name: '.demo', env: [] },
+      localConfigDir: '.demo',
       configFormat: 'settings-json',
       artifactLayout: { global: [], local: [] },
       commandStyle: 'slash-hyphen',

tests/capability-registry.test.cjs

@@ -1764,6 +1764,7 @@ describe('C3: role:runtime body validation', () => {
     tier: 'standard', requires: [],
     runtime: {
       configHome: { kind: 'dot-home', name: '.cursor', env: ['CURSOR_CONFIG_DIR'] },
+      localConfigDir: '.cursor',
       configFormat: 'settings-json',
       artifactLayout: { global: [], local: [] },
       commandStyle: 'slash-hyphen',
@@ -3217,6 +3218,7 @@ function makeRuntimeCap(overrides) {
     requires: [],
     runtime: {
       configHome: { kind: 'dot-home', name: '.test-rt', env: ['TEST_RT_DIR'] },
+      localConfigDir: '.test-rt',
       configFormat: 'settings-json',
       artifactLayout: { global: [], local: [] },
       commandStyle: 'slash-hyphen',
@@ -4292,6 +4294,7 @@ describe('ADR-857 phase 5f: cross-field consistency gate rejection tests (DEFECT
       requires: [],
       runtime: {
         configHome: { kind: 'dot-home', name: '.test-runtime', env: [] },
+        localConfigDir: '.test-runtime',
         configFormat: 'settings-json',
         artifactLayout: { global: [], local: [] },
         commandStyle: 'slash-hyphen',

tests/getdirname-registry-derivation.test.cjs

@@ -0,0 +1,93 @@
+'use strict';
+/**
+ * Drift-guard: getDirName must be derived from the capability registry.
+ * Verifies:
+ *   1. For every known runtime id, getDirName(id) equals the hardcoded golden
+ *      expected map — a pinned oracle that catches BOTH formula bugs AND
+ *      unintended registry drift (adding/removing a runtime or changing its
+ *      localConfigDir forces a deliberate golden-map update here).
+ *   2. getDirName('unknown') and getDirName('') fall back to '.claude'.
+ *   3. Every registry runtime entry has a non-empty dot-dir localConfigDir string —
+ *      cross-check from a different angle than the production derivation formula.
+ *
+ * ADR-1239 Phase B (#1679).
+ * Behavioral tests only: assert on returned values, no source-grep.
+ */
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const runtimeNamePolicy = require('../gsd-core/bin/lib/runtime-name-policy.cjs');
+const registry = require('../gsd-core/bin/lib/capability-registry.cjs');
+
+const { getDirName } = runtimeNamePolicy;
+
+// Golden oracle: hardcoded expected map of all 16 runtime ids to their local config dir.
+// A pinned expected value in a TEST is correct — the test IS the oracle (non-circular).
+// Only PRODUCTION code should derive dynamically from the registry.
+// If this map diverges from getDirName output, either the formula is wrong
+// OR the registry changed — both require a deliberate golden-map update here.
+const GOLDEN_DIR_MAP = {
+  claude:      '.claude',
+  copilot:     '.github',
+  opencode:    '.opencode',
+  gemini:      '.gemini',
+  kilo:        '.kilo',
+  codex:       '.codex',
+  antigravity: '.agents',
+  cursor:      '.cursor',
+  windsurf:    '.windsurf',
+  augment:     '.augment',
+  trae:        '.trae',
+  qwen:        '.qwen',
+  hermes:      '.hermes',
+  kimi:        '.kimi-code',
+  codebuddy:   '.codebuddy',
+  cline:       '.cline',
+};
+
+test('getDirName: golden map matches for all 16 known runtime ids', () => {
+  for (const [id, expected] of Object.entries(GOLDEN_DIR_MAP)) {
+    const actual = getDirName(id);
+    assert.strictEqual(
+      actual,
+      expected,
+      `getDirName('${id}') diverged from golden.\n` +
+      `  actual:   ${JSON.stringify(actual)}\n` +
+      `  expected: ${JSON.stringify(expected)}`,
+    );
+  }
+});
+
+test('drift guard: registry runtime id set EXACTLY equals the golden map (adding/removing a runtime forces a golden update)', () => {
+  // Without this, a newly-added runtime would pass (its value never checked) and
+  // removing `claude` could pass via the .claude fallback. Pin the set both ways.
+  const registryIds = Object.keys(registry.runtimes).sort();
+  const goldenIds = Object.keys(GOLDEN_DIR_MAP).sort();
+  assert.deepEqual(registryIds, goldenIds,
+    'registry.runtimes id set must exactly match GOLDEN_DIR_MAP — update the golden map when adding/removing a runtime');
+});
+
+test('getDirName fallback: unknown runtime returns ".claude"', () => {
+  assert.strictEqual(getDirName('unknown'), '.claude',
+    'getDirName("unknown") must return ".claude" (default fallback)');
+});
+
+test('getDirName fallback: empty string returns ".claude"', () => {
+  assert.strictEqual(getDirName(''), '.claude',
+    'getDirName("") must return ".claude" (empty-input fallback)');
+});
+
+test('registry cross-check: every runtimes[id].runtime.localConfigDir is a non-empty dot-dir string', () => {
+  for (const [id, entry] of Object.entries(registry.runtimes)) {
+    if (!entry || typeof entry !== 'object') continue;
+    const runtimeBlock = entry.runtime;
+    if (!runtimeBlock || typeof runtimeBlock !== 'object') continue;
+    const dir = runtimeBlock.localConfigDir;
+    assert.strictEqual(typeof dir, 'string',
+      `registry.runtimes['${id}'].runtime.localConfigDir must be a string (got: ${typeof dir})`);
+    assert.ok(dir.length > 0,
+      `registry.runtimes['${id}'].runtime.localConfigDir must be non-empty`);
+    assert.ok(dir.startsWith('.'),
+      `registry.runtimes['${id}'].runtime.localConfigDir must start with '.' (got: ${JSON.stringify(dir)})`);
+  }
+});

tests/host-integration-validator-parity.test.cjs

@@ -51,6 +51,7 @@ function makeMinimalRuntimeCap(overrides = {}) {
       sandboxTier: 'none',
       supportTier: 1,
       installSurface: 'profile-marker-only',
+      localConfigDir: '.test-runtime',
       writesSharedSettings: false,
       permissionWriter: null,
       extendedHookEvents: [],
@@ -331,6 +332,7 @@ describe('Fix 3: reserved-key guard on hostIntegration and hostIntegration.dispa
       sandboxTier: 'none',
       supportTier: 1,
       installSurface: 'settings-json',
+      localConfigDir: '.test-runtime',
       writesSharedSettings: true,
       permissionWriter: null,
       extendedHookEvents: ['SubagentStop', 'Stop', 'PreCompact', 'FileChanged'],