fix(#1515): make Codex installs resolve their own runtime and fail closed on worktrees (#1519)

* fix(#1515): make Codex installs resolve their own runtime and fail closed on worktrees

A Codex install with a runtime-neutral .planning/config.json resolved
RUNTIME=claude and enabled git worktree isolation, which Codex's
spawn_agent cannot honor. Two root causes:

1. Workflows read `config-get runtime` / `config-get workflow.use_worktrees`
   without `--raw`, so config-get's JSON-quoted output ("codex") was captured
   verbatim into the bash var and broke every `[ "$RUNTIME" = ... ]` check —
   the Codex fail-closed guard was dead even when runtime:codex was explicit,
   and Claude's own worktree degrade-check was dead too. Add `--raw` to those
   reads across execute-phase, autonomous, manager, diagnose-issues, quick.

2. The conversion engine emitted `--default claude` for every runtime. Stamp
   the codex-emitted workflows to `--default codex` (runtime) and
   `--default false` (use_worktrees) in _applyRuntimeRewrites case 'codex', so
   a neutral config on a Codex install resolves runtime=codex / worktrees off.

Also extend the Codex fail-closed worktree guard to quick.md and
diagnose-issues.md (they spawned isolation="worktree" with no runtime guard).

Regression test asserts source<->engine parity across all five workflows
(DEFECT.GENERATIVE-FIX) plus fast-check property coverage of the stamping.

Closes #1515

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013vX5eUtWa2wsZEyeMf5i3r

* chore(#1515): backfill changeset PR number (#1519)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013vX5eUtWa2wsZEyeMf5i3r

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/CONFIGURATION.md

@@ -248,7 +248,7 @@ All workflow toggles follow the **absent = enabled** pattern. If a key is missin
 | `workflow.max_discuss_passes` | number | `3` | Maximum number of question rounds in discuss-phase before the workflow stops asking. Useful in headless/auto mode to prevent infinite discussion loops. |
 | `workflow.skip_discuss` | boolean | `false` | When `true`, `/gsd-autonomous` bypasses the discuss-phase entirely, writing minimal CONTEXT.md from the ROADMAP phase goal. Useful for projects where developer preferences are fully captured in PROJECT.md/REQUIREMENTS.md. Added in v1.28 |
 | `workflow.text_mode` | boolean | `false` | Replaces AskUserQuestion TUI menus with plain-text numbered lists. Required for Claude Code remote sessions (`/rc` mode) where TUI menus don't render. Can also be set per-session with `--text` flag on discuss-phase. Added in v1.28 |
-| `workflow.use_worktrees` | boolean | `true` | When `false`, disables git worktree isolation for parallel execution. Users who prefer sequential execution or whose environment does not support worktrees can disable this. Added in v1.31. **Branch-divergence note:** when your branch has diverged from `origin/HEAD`, GSD auto-degrades to sequential and prints a warning. See [`worktree.baseRef`](#worktree-settings) to restore parallel execution on a diverged branch. |
+| `workflow.use_worktrees` | boolean | `true` | When `false`, disables git worktree isolation for parallel execution. Users who prefer sequential execution or whose environment does not support worktrees can disable this. Added in v1.31. **Branch-divergence note:** when your branch has diverged from `origin/HEAD`, GSD auto-degrades to sequential and prints a warning. See [`worktree.baseRef`](#worktree-settings) to restore parallel execution on a diverged branch. **Codex note:** Codex maps subagents to `spawn_agent` and cannot honor Claude Code's `isolation="worktree"`, so a Codex-installed workflow resolves its runtime as `codex` and defaults this key to `false` even when `.planning/config.json` is runtime-neutral; forcing `use_worktrees: true` on a Codex install fails closed before any executor dispatch (#1515). |
 | `workflow.worktree_skip_hooks` | boolean | `false` | When `true`, executor agents in worktree mode pass `--no-verify` (skipping pre-commit hooks) and post-wave hook validation runs against the merged result instead. Opt-in escape hatch for projects whose hooks cannot run in agent worktrees. Default `false` runs hooks on every commit (#2924). |
 | `workflow.code_review` | boolean | `true` | Enable `/gsd-code-review` and `/gsd-code-review --fix` commands. When `false`, the commands exit with a configuration gate message. Added in v1.34 |
 | `workflow.code_review_depth` | string | `standard` | Default review depth for `/gsd-code-review`: `quick` (pattern-matching only), `standard` (per-file analysis), or `deep` (cross-file with import graphs). Can be overridden per-run with `--depth=`. Added in v1.34 |