feat(#2088): migrate Codex onto the Embeddable Orchestration System (ADR-1239)

Drive Codex install/uninstall through the descriptor-driven Host-Integration
Interface (declarative embedding adapter → engine surface dispatch) and fold
every positive `runtime === 'codex'` / `isCodex` projection into descriptor-driven
`runtime.hostBehaviors`. Install/uninstall output stays byte-parity-gated
(tests/fixtures/golden-install-parity/codex.json); no other runtime changes.

Three Context7-verified upgrades, each with a test on the user-reachable surface:
- Skill root → canonical $HOME/.agents/skills via a skills-kind `home` override,
  with pre-move migration cleanup (stale ~/.codex/skills/gsd-* removed on install
  and uninstall; user content preserved). Fixes getGlobalSkillsBase, writeManifest,
  and the skill-manifest inventory to honor the override so --skills-root /
  sync-skills / the manifest report the real location.
- Six new hooks.json lifecycle events (PreToolUse, PermissionRequest, PreCompact,
  PostCompact, SubagentStop, UserPromptSubmit) shared by install + uninstall;
  extendedHookEvents reconciled [] -> the schema-valid wired subset.
- Explicit `[agents] max_depth = 1` in the managed config.toml block, pinning the
  negotiated dispatch.maxDepth:1 axis. validateCodexConfigSchema now permits a
  known-scalar-only bare `[agents]` AgentsToml table (still rejects [[agents]] and
  unknown-key break-forms, #2760); mergeCodexConfig preserves the user's own
  AgentsToml scalars (max_threads etc.) instead of dropping them.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/init.cts

@@ -37,7 +37,7 @@ import { formatGsdSlash, resolveRuntime } from './runtime-slash.cjs';
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- commands.cjs is an export= CommonJS module
 import commandsMod = require('./commands.cjs');
 import { validatePath, loadTrustedGlobalRoots } from './security.cjs';
-import { getGlobalSkillDir, getGlobalSkillDisplayPath, getGlobalSkillsBase } from './runtime-homes.cjs';
+import { getGlobalSkillDir, getGlobalSkillDisplayPath, getGlobalSkillsBase, getGlobalConfigDir } from './runtime-homes.cjs';
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- frontmatter.cjs is an export= CommonJS module
 import frontmatterMod = require('./frontmatter.cjs');
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- verification.cjs is an export= CommonJS module
@@ -2372,11 +2372,24 @@ function buildSkillManifest(cwd: string, skillsDir: string | null = null): Skill
           kind: 'skills',
         },
         {
-          root: '~/.codex/skills',
+          // ADR-1239 upgrade 3 (#2088): Codex's canonical skill root is
+          // $HOME/.agents/skills (per codex core-skills loader.rs), resolved via
+          // the skills-kind `home` override in getGlobalSkillsBase.
+          root: '~/.agents/skills',
           path: getGlobalSkillsBase('codex') as string,
           scope: 'global',
           kind: 'skills',
         },
+        {
+          // Codex's deprecated fallback skill root ($CODEX_HOME/skills). Kept as a
+          // discovery-only legacy root so pre-move installs remain inventoried;
+          // GSD no longer installs here (#2088).
+          root: '~/.codex/skills',
+          path: path.join(getGlobalConfigDir('codex'), 'skills'),
+          scope: 'global',
+          kind: 'skills',
+          deprecated: true,
+        },
         {
           root: '.claude/gsd-core/skills',
           path: path.join(os.homedir(), '.claude', 'gsd-core', 'skills'),