docs: add implementation plan for Codex App compatibility (PRI-823)

8 tasks covering: environment detection in using-git-worktrees,
Step 1.5 + cleanup guard in finishing-a-development-branch,
Integration line updates, codex-tools.md docs, automated tests,
and final verification.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/superpowers/plans/2026-03-23-codex-app-compatibility.md

@@ -0,0 +1,564 @@
+# Codex App Compatibility Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Make `using-git-worktrees`, `finishing-a-development-branch`, and related skills work in the Codex App's sandboxed worktree environment without breaking existing behavior.
+
+**Architecture:** Read-only environment detection (`git-dir` vs `git-common-dir`) at the start of two skills. If already in a linked worktree, skip creation. If on detached HEAD, emit a handoff payload instead of the 4-option menu. Sandbox fallback catches permission errors during worktree creation.
+
+**Tech Stack:** Git, Markdown (skill files are instruction documents, not executable code)
+
+**Spec:** `docs/superpowers/specs/2026-03-23-codex-app-compatibility-design.md`
+
+---
+
+## File Structure
+
+| File | Responsibility | Action |
+|---|---|---|
+| `skills/using-git-worktrees/SKILL.md` | Worktree creation + isolation | Add Step 0 detection + sandbox fallback |
+| `skills/finishing-a-development-branch/SKILL.md` | Branch finishing workflow | Add Step 1.5 detection + cleanup guard |
+| `skills/subagent-driven-development/SKILL.md` | Plan execution with subagents | Update Integration description |
+| `skills/executing-plans/SKILL.md` | Plan execution inline | Update Integration description |
+| `skills/using-superpowers/references/codex-tools.md` | Codex platform reference | Add detection + finishing docs |
+
+---
+
+### Task 1: Add Step 0 to `using-git-worktrees`
+
+**Files:**
+- Modify: `skills/using-git-worktrees/SKILL.md:14-15` (insert after Overview, before Directory Selection Process)
+
+- [ ] **Step 1: Read the current skill file**
+
+Read `skills/using-git-worktrees/SKILL.md` in full. Identify the exact insertion point: after the "Announce at start" line (line 14) and before "## Directory Selection Process" (line 16).
+
+- [ ] **Step 2: Insert Step 0 section**
+
+Insert the following between the Overview section and "## Directory Selection Process":
+
+```markdown
+## Step 0: Check if Already in an Isolated Workspace
+
+Before creating a worktree, check if one already exists:
+
+```bash
+GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
+GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
+BRANCH=$(git branch --show-current)
+```
+
+**If `GIT_DIR` differs from `GIT_COMMON`:** You are already inside a linked worktree (created by the Codex App, Claude Code's Agent tool, a previous skill run, or the user). Do NOT create another worktree. Instead:
+
+1. Run project setup (auto-detect package manager as in "Run Project Setup" below)
+2. Verify clean baseline (run tests as in "Verify Clean Baseline" below)
+3. Report with branch state:
+   - On a branch: "Already in an isolated workspace at `<path>` on branch `<name>`. Tests passing. Ready to implement."
+   - Detached HEAD: "Already in an isolated workspace at `<path>` (detached HEAD, externally managed). Tests passing. Note: branch creation needed at finish time. Ready to implement."
+
+After reporting, STOP. Do not continue to Directory Selection or Creation Steps.
+
+**If `GIT_DIR` equals `GIT_COMMON`:** Proceed with the full worktree creation flow below.
+
+**Sandbox fallback:** If you proceed to Creation Steps but `git worktree add -b` fails with a permission error (e.g., "Operation not permitted"), treat this as a late-detected restricted environment. Fall back to the behavior above — run setup and baseline tests in the current directory, report accordingly, and STOP.
+```
+
+- [ ] **Step 3: Verify the insertion**
+
+Read the file again. Confirm:
+- Step 0 appears between Overview and Directory Selection Process
+- The rest of the file (Directory Selection, Safety Verification, Creation Steps, etc.) is unchanged
+- No duplicate sections or broken markdown
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add skills/using-git-worktrees/SKILL.md
+git commit -m "feat(using-git-worktrees): add Step 0 environment detection (PRI-823)
+
+Skip worktree creation when already in a linked worktree. Includes
+sandbox fallback for permission errors on git worktree add."
+```
+
+---
+
+### Task 2: Update `using-git-worktrees` Integration section
+
+**Files:**
+- Modify: `skills/using-git-worktrees/SKILL.md:211-215` (Integration > Called by)
+
+- [ ] **Step 1: Update the three "Called by" entries**
+
+Change lines 212-214 from:
+
+```markdown
+- **brainstorming** (Phase 4) - REQUIRED when design is approved and implementation follows
+- **subagent-driven-development** - REQUIRED before executing any tasks
+- **executing-plans** - REQUIRED before executing any tasks
+```
+
+To:
+
+```markdown
+- **brainstorming** - REQUIRED: Ensures isolated workspace (creates one or verifies existing)
+- **subagent-driven-development** - REQUIRED: Ensures isolated workspace (creates one or verifies existing)
+- **executing-plans** - REQUIRED: Ensures isolated workspace (creates one or verifies existing)
+```
+
+- [ ] **Step 2: Verify the Integration section**
+
+Read the Integration section. Confirm all three entries are updated, "Pairs with" is unchanged.
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add skills/using-git-worktrees/SKILL.md
+git commit -m "docs(using-git-worktrees): update Integration descriptions (PRI-823)
+
+Clarify that skill ensures a workspace exists, not that it always creates one."
+```
+
+---
+
+### Task 3: Add Step 1.5 to `finishing-a-development-branch`
+
+**Files:**
+- Modify: `skills/finishing-a-development-branch/SKILL.md:38` (insert after Step 1, before Step 2)
+
+- [ ] **Step 1: Read the current skill file**
+
+Read `skills/finishing-a-development-branch/SKILL.md` in full. Identify the insertion point: after "**If tests pass:** Continue to Step 2." (line 38) and before "### Step 2: Determine Base Branch" (line 40).
+
+- [ ] **Step 2: Insert Step 1.5 section**
+
+Insert the following between Step 1 and Step 2:
+
+```markdown
+### Step 1.5: Detect Environment
+
+```bash
+GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
+GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
+BRANCH=$(git branch --show-current)
+```
+
+**Path A — `GIT_DIR` differs from `GIT_COMMON` AND `BRANCH` is empty (externally managed worktree, detached HEAD):**
+
+First, ensure all work is staged and committed (`git add` + `git commit`).
+
+Then present this to the user (do NOT present the 4-option menu):
+
+```
+Implementation complete. All tests passing.
+Current HEAD: <full-commit-sha>
+
+This workspace is externally managed (detached HEAD).
+I cannot create branches, push, or open PRs from here.
+
+⚠ These commits are on a detached HEAD. If you do not create a branch,
+they may be lost when this workspace is cleaned up.
+
+If your host application provides these controls:
+- "Create branch" — to name a branch, then commit/push/PR
+- "Hand off to local" — to move changes to your local checkout
+
+Suggested branch name: <ticket-id/short-description>
+Suggested commit message: <summary-of-work>
+```
+
+Branch name: use ticket ID if available (e.g., `pri-823/codex-compat`), otherwise slugify the first 5 words of the plan title, otherwise omit. Avoid sensitive content in branch names.
+
+Skip to Step 5 (cleanup is a no-op — see guard below).
+
+**Path B — `GIT_DIR` differs from `GIT_COMMON` AND `BRANCH` exists (externally managed worktree, named branch):**
+
+Proceed to Step 2 and present the 4-option menu as normal.
+
+**Path C — `GIT_DIR` equals `GIT_COMMON` (normal environment):**
+
+Proceed to Step 2 and present the 4-option menu as normal.
+```
+
+- [ ] **Step 3: Verify the insertion**
+
+Read the file again. Confirm:
+- Step 1.5 appears between Step 1 and Step 2
+- Steps 2-5 are unchanged
+- Path A handoff includes commit SHA and data loss warning
+- Paths B and C proceed to Step 2 normally
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add skills/finishing-a-development-branch/SKILL.md
+git commit -m "feat(finishing-a-development-branch): add Step 1.5 environment detection (PRI-823)
+
+Detect externally managed worktrees with detached HEAD and emit handoff
+payload instead of 4-option menu. Includes commit SHA and data loss warning."
+```
+
+---
+
+### Task 4: Add Step 5 cleanup guard to `finishing-a-development-branch`
+
+**Files:**
+- Modify: `skills/finishing-a-development-branch/SKILL.md` (Step 5: Cleanup Worktree — find by section heading, line numbers will have shifted after Task 3)
+
+- [ ] **Step 1: Read the current Step 5 section**
+
+Find the "### Step 5: Cleanup Worktree" section in `skills/finishing-a-development-branch/SKILL.md` (line numbers will have shifted after Task 3's insertion). The current Step 5 is:
+
+```markdown
+### Step 5: Cleanup Worktree
+
+**For Options 1, 2, 4:**
+
+Check if in worktree:
+```bash
+git worktree list | grep $(git branch --show-current)
+```
+
+If yes:
+```bash
+git worktree remove <worktree-path>
+```
+
+**For Option 3:** Keep worktree.
+```
+
+- [ ] **Step 2: Add the cleanup guard before existing logic**
+
+Replace the Step 5 section with:
+
+```markdown
+### Step 5: Cleanup Worktree
+
+**First, check if worktree is externally managed:**
+
+```bash
+GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
+GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
+```
+
+If `GIT_DIR` differs from `GIT_COMMON`: skip worktree removal — the host environment owns this workspace.
+
+**Otherwise, for Options 1 and 4:**
+
+Check if in worktree:
+```bash
+git worktree list | grep $(git branch --show-current)
+```
+
+If yes:
+```bash
+git worktree remove <worktree-path>
+```
+
+**For Option 3:** Keep worktree.
+```
+
+Note: the original text said "For Options 1, 2, 4" but the Quick Reference table and Common Mistakes section say "Options 1 & 4 only." This edit aligns Step 5 with those sections.
+
+- [ ] **Step 3: Verify the replacement**
+
+Read Step 5. Confirm:
+- Cleanup guard (re-detection) appears first
+- Existing removal logic preserved for non-externally-managed worktrees
+- "Options 1 and 4" (not "1, 2, 4") matches Quick Reference and Common Mistakes
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add skills/finishing-a-development-branch/SKILL.md
+git commit -m "feat(finishing-a-development-branch): add Step 5 cleanup guard (PRI-823)
+
+Re-detect externally managed worktree at cleanup time and skip removal.
+Also fixes pre-existing inconsistency: cleanup now correctly says
+Options 1 and 4 only, matching Quick Reference and Common Mistakes."
+```
+
+---
+
+### Task 5: Update Integration lines in `subagent-driven-development` and `executing-plans`
+
+**Files:**
+- Modify: `skills/subagent-driven-development/SKILL.md:268`
+- Modify: `skills/executing-plans/SKILL.md:68`
+
+- [ ] **Step 1: Update `subagent-driven-development`**
+
+Change line 268 from:
+```
+- **superpowers:using-git-worktrees** - REQUIRED: Set up isolated workspace before starting
+```
+To:
+```
+- **superpowers:using-git-worktrees** - REQUIRED: Ensures isolated workspace (creates one or verifies existing)
+```
+
+- [ ] **Step 2: Update `executing-plans`**
+
+Change line 68 from:
+```
+- **superpowers:using-git-worktrees** - REQUIRED: Set up isolated workspace before starting
+```
+To:
+```
+- **superpowers:using-git-worktrees** - REQUIRED: Ensures isolated workspace (creates one or verifies existing)
+```
+
+- [ ] **Step 3: Verify both files**
+
+Read line 268 of `skills/subagent-driven-development/SKILL.md` and line 68 of `skills/executing-plans/SKILL.md`. Confirm both say "Ensures isolated workspace (creates one or verifies existing)".
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add skills/subagent-driven-development/SKILL.md skills/executing-plans/SKILL.md
+git commit -m "docs(sdd, executing-plans): update worktree Integration descriptions (PRI-823)
+
+Clarify that using-git-worktrees ensures a workspace exists rather than
+always creating one."
+```
+
+---
+
+### Task 6: Add environment detection docs to `codex-tools.md`
+
+**Files:**
+- Modify: `skills/using-superpowers/references/codex-tools.md:25` (append at end)
+
+- [ ] **Step 1: Read the current file**
+
+Read `skills/using-superpowers/references/codex-tools.md` in full. Confirm it ends at line 25-26 after the multi_agent section.
+
+- [ ] **Step 2: Append two new sections**
+
+Add at the end of the file:
+
+```markdown
+
+## Environment Detection
+
+Skills that create worktrees or finish branches should detect their
+environment with read-only git commands before proceeding:
+
+```bash
+GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
+GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
+BRANCH=$(git branch --show-current)
+```
+
+- `GIT_DIR != GIT_COMMON` → already in a linked worktree (skip creation)
+- `BRANCH` empty → detached HEAD (cannot branch/push/PR from sandbox)
+
+See `using-git-worktrees` Step 0 and `finishing-a-development-branch`
+Step 1.5 for how each skill uses these signals.
+
+## Codex App Finishing
+
+When the sandbox blocks branch/push operations (detached HEAD in an
+externally managed worktree), the agent commits all work and informs
+the user to use the App's native controls:
+
+- **"Create branch"** — names the branch, then commit/push/PR via App UI
+- **"Hand off to local"** — transfers work to the user's local checkout
+
+The agent can still run tests, stage files, and output suggested branch
+names, commit messages, and PR descriptions for the user to copy.
+```
+
+- [ ] **Step 3: Verify the additions**
+
+Read the full file. Confirm:
+- Two new sections appear after the existing content
+- Bash code block renders correctly (not escaped)
+- Cross-references to Step 0 and Step 1.5 are present
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add skills/using-superpowers/references/codex-tools.md
+git commit -m "docs(codex-tools): add environment detection and App finishing docs (PRI-823)
+
+Document the git-dir vs git-common-dir detection pattern and the Codex
+App's native finishing flow for skills that need to adapt."
+```
+
+---
+
+### Task 7: Automated test — environment detection
+
+**Files:**
+- Create: `tests/codex-app-compat/test-environment-detection.sh`
+
+- [ ] **Step 1: Create test directory**
+
+```bash
+mkdir -p tests/codex-app-compat
+```
+
+- [ ] **Step 2: Write the detection test script**
+
+Create `tests/codex-app-compat/test-environment-detection.sh`:
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Test environment detection logic from PRI-823
+# Tests the git-dir vs git-common-dir comparison used by
+# using-git-worktrees Step 0 and finishing-a-development-branch Step 1.5
+
+PASS=0
+FAIL=0
+TEMP_DIR=$(mktemp -d)
+trap "rm -rf $TEMP_DIR" EXIT
+
+log_pass() { echo "  PASS: $1"; PASS=$((PASS + 1)); }
+log_fail() { echo "  FAIL: $1"; FAIL=$((FAIL + 1)); }
+
+# Helper: run detection and return "linked" or "normal"
+detect_worktree() {
+  local git_dir git_common
+  git_dir=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
+  git_common=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
+  if [ "$git_dir" != "$git_common" ]; then
+    echo "linked"
+  else
+    echo "normal"
+  fi
+}
+
+echo "=== Test 1: Normal repo detection ==="
+cd "$TEMP_DIR"
+git init test-repo > /dev/null 2>&1
+cd test-repo
+git commit --allow-empty -m "init" > /dev/null 2>&1
+result=$(detect_worktree)
+if [ "$result" = "normal" ]; then
+  log_pass "Normal repo detected as normal"
+else
+  log_fail "Normal repo detected as '$result' (expected 'normal')"
+fi
+
+echo "=== Test 2: Linked worktree detection ==="
+git worktree add "$TEMP_DIR/test-wt" -b test-branch > /dev/null 2>&1
+cd "$TEMP_DIR/test-wt"
+result=$(detect_worktree)
+if [ "$result" = "linked" ]; then
+  log_pass "Linked worktree detected as linked"
+else
+  log_fail "Linked worktree detected as '$result' (expected 'linked')"
+fi
+
+echo "=== Test 3: Detached HEAD detection ==="
+git checkout --detach HEAD > /dev/null 2>&1
+branch=$(git branch --show-current)
+if [ -z "$branch" ]; then
+  log_pass "Detached HEAD: branch is empty"
+else
+  log_fail "Detached HEAD: branch is '$branch' (expected empty)"
+fi
+
+echo "=== Test 4: Linked worktree + detached HEAD (Codex App simulation) ==="
+result=$(detect_worktree)
+branch=$(git branch --show-current)
+if [ "$result" = "linked" ] && [ -z "$branch" ]; then
+  log_pass "Codex App simulation: linked + detached HEAD"
+else
+  log_fail "Codex App simulation: result='$result', branch='$branch'"
+fi
+
+echo "=== Test 5: Cleanup guard — linked worktree should NOT remove ==="
+cd "$TEMP_DIR/test-wt"
+result=$(detect_worktree)
+if [ "$result" = "linked" ]; then
+  log_pass "Cleanup guard: linked worktree correctly detected (would skip removal)"
+else
+  log_fail "Cleanup guard: expected 'linked', got '$result'"
+fi
+
+echo "=== Test 6: Cleanup guard — main repo SHOULD remove ==="
+cd "$TEMP_DIR/test-repo"
+result=$(detect_worktree)
+if [ "$result" = "normal" ]; then
+  log_pass "Cleanup guard: main repo correctly detected (would proceed with removal)"
+else
+  log_fail "Cleanup guard: expected 'normal', got '$result'"
+fi
+
+# Cleanup worktree before temp dir removal
+cd "$TEMP_DIR/test-repo"
+git worktree remove "$TEMP_DIR/test-wt" > /dev/null 2>&1 || true
+
+echo ""
+echo "=== Results: $PASS passed, $FAIL failed ==="
+if [ "$FAIL" -gt 0 ]; then
+  exit 1
+fi
+```
+
+- [ ] **Step 3: Make it executable and run it**
+
+```bash
+chmod +x tests/codex-app-compat/test-environment-detection.sh
+./tests/codex-app-compat/test-environment-detection.sh
+```
+
+Expected output: 6 passed, 0 failed.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add tests/codex-app-compat/test-environment-detection.sh
+git commit -m "test: add environment detection tests for Codex App compat (PRI-823)
+
+Tests git-dir vs git-common-dir comparison in normal repo, linked
+worktree, detached HEAD, and cleanup guard scenarios."
+```
+
+---
+
+### Task 8: Final verification
+
+**Files:**
+- Read: all 5 modified skill files
+
+- [ ] **Step 1: Run the automated detection tests**
+
+```bash
+./tests/codex-app-compat/test-environment-detection.sh
+```
+
+Expected: 6 passed, 0 failed.
+
+- [ ] **Step 2: Read each modified file and verify changes**
+
+Read each file end-to-end:
+- `skills/using-git-worktrees/SKILL.md` — Step 0 present, rest unchanged
+- `skills/finishing-a-development-branch/SKILL.md` — Step 1.5 present, cleanup guard present, rest unchanged
+- `skills/subagent-driven-development/SKILL.md` — line 268 updated
+- `skills/executing-plans/SKILL.md` — line 68 updated
+- `skills/using-superpowers/references/codex-tools.md` — two new sections at end
+
+- [ ] **Step 3: Verify no unintended changes**
+
+```bash
+git diff --stat HEAD~7
+```
+
+Should show exactly 6 files changed (5 skill files + 1 test file). No other files modified.
+
+- [ ] **Step 4: Run existing test suite**
+
+If test runner exists:
+```bash
+# Run skill-triggering tests
+./tests/skill-triggering/run-all.sh 2>/dev/null || echo "Skill triggering tests not available in this environment"
+
+# Run SDD integration test
+./tests/claude-code/test-subagent-driven-development-integration.sh 2>/dev/null || echo "SDD integration test not available in this environment"
+```
+
+Note: these tests require Claude Code with `--dangerously-skip-permissions`. If not available, document that regression tests should be run manually.