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/runtime-homes.cts

@@ -118,6 +118,9 @@ type ConfigHomeDescriptor =
 interface RuntimeArtifactKindDescriptor {
   kind: string;
   destSubpath: string;
+  // ADR-1239 upgrade 3 (#2088): optional split-home override (relative to
+  // os.homedir()), e.g. Codex skills → ".agents". Absent for most runtimes.
+  home?: string;
 }
 
 interface RuntimeDescriptor {
@@ -416,6 +419,14 @@ export function getGlobalSkillsBase(runtime: string): string | null {
   const runtimeEntry = getRegistry().runtimes[runtime];
   const descriptor = runtimeEntry?.runtime;
   const globalSkillsKind = descriptor?.artifactLayout?.global?.find((entry) => entry.kind === 'skills');
+  // ADR-1239 upgrade 3 (#2088): honor a skills-kind `home` override (e.g. Codex
+  // → $HOME/.agents/skills, independent of $CODEX_HOME) so the reported skills
+  // root matches where the installer actually writes (the artifact layout /
+  // _resolveSkillsRootDir). Without this, `--skills-root` and the sync-skills
+  // workflow would look under configHome/skills while skills live under ~/.agents.
+  if (globalSkillsKind?.home && globalSkillsKind?.destSubpath) {
+    return path.join(os.homedir(), globalSkillsKind.home, globalSkillsKind.destSubpath);
+  }
   if (descriptor?.configHome && globalSkillsKind?.destSubpath) {
     return resolveSkillsBaseFromDescriptor(
       descriptor.configHome,