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>

gsd-core/bin/lib/capability-registry.cjs

@@ -814,7 +814,8 @@ const capabilities = {
             "prefix": "gsd-",
             "nesting": "flat",
             "recursive": false,
-            "converter": "convertClaudeCommandToCodexSkill"
+            "converter": "convertClaudeCommandToCodexSkill",
+            "home": ".agents"
           }
         ],
         "local": [
@@ -824,7 +825,8 @@ const capabilities = {
             "prefix": "gsd-",
             "nesting": "flat",
             "recursive": false,
-            "converter": "convertClaudeCommandToCodexSkill"
+            "converter": "convertClaudeCommandToCodexSkill",
+            "home": ".agents"
           }
         ]
       },
@@ -836,7 +838,11 @@ const capabilities = {
       "installSurface": "codex-toml",
       "writesSharedSettings": false,
       "permissionWriter": null,
-      "extendedHookEvents": [],
+      "extendedHookEvents": [
+        "SubagentStop",
+        "Stop",
+        "PreCompact"
+      ],
       "hostIntegration": {
         "embeddingMode": "declarative",
         "commandSurface": "slash-file",
@@ -853,6 +859,13 @@ const capabilities = {
         "stateIO": "filesystem",
         "transport": "mcp",
         "runtime": "node"
+      },
+      "hostBehaviors": {
+        "reapplyCommand": "$gsd-update --reapply",
+        "tomlConfigInstall": true,
+        "cleanupSkillSidecars": true,
+        "agentTomlFiles": true,
+        "frontmatterDialect": "codex"
       }
     }
   },
@@ -4134,7 +4147,8 @@ const runtimes = {
             "prefix": "gsd-",
             "nesting": "flat",
             "recursive": false,
-            "converter": "convertClaudeCommandToCodexSkill"
+            "converter": "convertClaudeCommandToCodexSkill",
+            "home": ".agents"
           }
         ],
         "local": [
@@ -4144,7 +4158,8 @@ const runtimes = {
             "prefix": "gsd-",
             "nesting": "flat",
             "recursive": false,
-            "converter": "convertClaudeCommandToCodexSkill"
+            "converter": "convertClaudeCommandToCodexSkill",
+            "home": ".agents"
           }
         ]
       },
@@ -4156,7 +4171,11 @@ const runtimes = {
       "installSurface": "codex-toml",
       "writesSharedSettings": false,
       "permissionWriter": null,
-      "extendedHookEvents": [],
+      "extendedHookEvents": [
+        "SubagentStop",
+        "Stop",
+        "PreCompact"
+      ],
       "hostIntegration": {
         "embeddingMode": "declarative",
         "commandSurface": "slash-file",
@@ -4173,6 +4192,13 @@ const runtimes = {
         "stateIO": "filesystem",
         "transport": "mcp",
         "runtime": "node"
+      },
+      "hostBehaviors": {
+        "reapplyCommand": "$gsd-update --reapply",
+        "tomlConfigInstall": true,
+        "cleanupSkillSidecars": true,
+        "agentTomlFiles": true,
+        "frontmatterDialect": "codex"
       }
     }
   },

gsd-core/bin/lib/runtime-artifact-install-plan.cjs

@@ -111,7 +111,7 @@ function createRuntimeArtifactInstallPlan(args) {
         items.push({
             kind: kind.kind,
             sourceDir,
-            destDir: assertDestWithinConfigHome(layout.configDir, kind.destSubpath),
+            destDir: assertDestWithinConfigHome(kind.home ?? layout.configDir, kind.destSubpath),
         });
     }
     return { ok: true, plan: { items, cleanupDirs } };
@@ -120,7 +120,7 @@ function createRuntimeArtifactUninstallPlan(layout) {
     return {
         items: layout.kinds.map((kind) => ({
             kind: kind.kind,
-            destDir: assertDestWithinConfigHome(layout.configDir, kind.destSubpath),
+            destDir: assertDestWithinConfigHome(kind.home ?? layout.configDir, kind.destSubpath),
         })),
     };
 }