---
name: investigate
preamble-tier: 2
version: 1.0.0
description: |
  Systematic debugging with root cause investigation. Four phases: investigate,
  analyze, hypothesize, implement. Iron Law: no fixes without root cause.
  Use when asked to "debug this", "fix this bug", "why is this broken",
  "investigate this error", or "root cause analysis".
  Proactively suggest when the user reports errors, unexpected behavior, or
  is troubleshooting why something stopped working.
allowed-tools:
  - Bash
  - Read
  - Write
  - Edit
  - Grep
  - Glob
  - AskUserQuestion
  - WebSearch
hooks:
  PreToolUse:
    - matcher: "Edit"
      hooks:
        - type: command
          command: "bash ${CLAUDE_SKILL_DIR}/../freeze/bin/check-freeze.sh"
          statusMessage: "Checking debug scope boundary..."
    - matcher: "Write"
      hooks:
        - type: command
          command: "bash ${CLAUDE_SKILL_DIR}/../freeze/bin/check-freeze.sh"
          statusMessage: "Checking debug scope boundary..."
---
<!-- AUTO-GENERATED from SKILL.md.tmpl — do not edit directly -->
<!-- Regenerate: bun run gen:skill-docs -->

## Preamble (run first)

```bash
_UPD=$(~/.claude/skills/gstack/bin/gstack-update-check 2>/dev/null || .claude/skills/gstack/bin/gstack-update-check 2>/dev/null || true)
[ -n "$_UPD" ] && echo "$_UPD" || true
mkdir -p ~/.gstack/sessions
touch ~/.gstack/sessions/"$PPID"
_SESSIONS=$(find ~/.gstack/sessions -mmin -120 -type f 2>/dev/null | wc -l | tr -d ' ')
find ~/.gstack/sessions -mmin +120 -type f -delete 2>/dev/null || true
_CONTRIB=$(~/.claude/skills/gstack/bin/gstack-config get gstack_contributor 2>/dev/null || true)
_PROACTIVE=$(~/.claude/skills/gstack/bin/gstack-config get proactive 2>/dev/null || echo "true")
_PROACTIVE_PROMPTED=$([ -f ~/.gstack/.proactive-prompted ] && echo "yes" || echo "no")
_BRANCH=$(git branch --show-current 2>/dev/null || echo "unknown")
echo "BRANCH: $_BRANCH"
echo "PROACTIVE: $_PROACTIVE"
echo "PROACTIVE_PROMPTED: $_PROACTIVE_PROMPTED"
source <(~/.claude/skills/gstack/bin/gstack-repo-mode 2>/dev/null) || true
REPO_MODE=${REPO_MODE:-unknown}
echo "REPO_MODE: $REPO_MODE"
_LAKE_SEEN=$([ -f ~/.gstack/.completeness-intro-seen ] && echo "yes" || echo "no")
echo "LAKE_INTRO: $_LAKE_SEEN"
_TEL=$(~/.claude/skills/gstack/bin/gstack-config get telemetry 2>/dev/null || true)
_TEL_PROMPTED=$([ -f ~/.gstack/.telemetry-prompted ] && echo "yes" || echo "no")
_TEL_START=$(date +%s)
_SESSION_ID="$$-$(date +%s)"
echo "TELEMETRY: ${_TEL:-off}"
echo "TEL_PROMPTED: $_TEL_PROMPTED"
mkdir -p ~/.gstack/analytics
echo '{"skill":"investigate","ts":"'$(date -u +%Y-%m-%dT%H:%M:%SZ)'","repo":"'$(basename "$(git rev-parse --show-toplevel 2>/dev/null)" 2>/dev/null || echo "unknown")'"}'  >> ~/.gstack/analytics/skill-usage.jsonl 2>/dev/null || true
# zsh-compatible: use find instead of glob to avoid NOMATCH error
for _PF in $(find ~/.gstack/analytics -maxdepth 1 -name '.pending-*' 2>/dev/null); do [ -f "$_PF" ] && ~/.claude/skills/gstack/bin/gstack-telemetry-log --event-type skill_run --skill _pending_finalize --outcome unknown --session-id "$_SESSION_ID" 2>/dev/null || true; break; done
```

If `PROACTIVE` is `"false"`, do not proactively suggest gstack skills AND do not
auto-invoke skills based on conversation context. Only run skills the user explicitly
types (e.g., /qa, /ship). If you would have auto-invoked a skill, instead briefly say:
"I think /skillname might help here — want me to run it?" and wait for confirmation.
The user opted out of proactive behavior.

If output shows `UPGRADE_AVAILABLE <old> <new>`: read `~/.claude/skills/gstack/gstack-upgrade/SKILL.md` and follow the "Inline upgrade flow" (auto-upgrade if configured, otherwise AskUserQuestion with 4 options, write snooze state if declined). If `JUST_UPGRADED <from> <to>`: tell user "Running gstack v{to} (just updated!)" and continue.

If `LAKE_INTRO` is `no`: Before continuing, introduce the Completeness Principle.
Tell the user: "gstack follows the **Boil the Lake** principle — always do the complete
thing when AI makes the marginal cost near-zero. Read more: https://garryslist.org/posts/boil-the-ocean"
Then offer to open the essay in their default browser:

```bash
open https://garryslist.org/posts/boil-the-ocean
touch ~/.gstack/.completeness-intro-seen
```

Only run `open` if the user says yes. Always run `touch` to mark as seen. This only happens once.

If `TEL_PROMPTED` is `no` AND `LAKE_INTRO` is `yes`: After the lake intro is handled,
ask the user about telemetry. Use AskUserQuestion:

> Help gstack get better! Community mode shares usage data (which skills you use, how long
> they take, crash info) with a stable device ID so we can track trends and fix bugs faster.
> No code, file paths, or repo names are ever sent.
> Change anytime with `gstack-config set telemetry off`.

Options:
- A) Help gstack get better! (recommended)
- B) No thanks

If A: run `~/.claude/skills/gstack/bin/gstack-config set telemetry community`

If B: ask a follow-up AskUserQuestion:

> How about anonymous mode? We just learn that *someone* used gstack — no unique ID,
> no way to connect sessions. Just a counter that helps us know if anyone's out there.

Options:
- A) Sure, anonymous is fine
- B) No thanks, fully off

If B→A: run `~/.claude/skills/gstack/bin/gstack-config set telemetry anonymous`
If B→B: run `~/.claude/skills/gstack/bin/gstack-config set telemetry off`

Always run:
```bash
touch ~/.gstack/.telemetry-prompted
```

This only happens once. If `TEL_PROMPTED` is `yes`, skip this entirely.

If `PROACTIVE_PROMPTED` is `no` AND `TEL_PROMPTED` is `yes`: After telemetry is handled,
ask the user about proactive behavior. Use AskUserQuestion:

> gstack can proactively figure out when you might need a skill while you work —
> like suggesting /qa when you say "does this work?" or /investigate when you hit
> a bug. We recommend keeping this on — it speeds up every part of your workflow.

Options:
- A) Keep it on (recommended)
- B) Turn it off — I'll type /commands myself

If A: run `~/.claude/skills/gstack/bin/gstack-config set proactive true`
If B: run `~/.claude/skills/gstack/bin/gstack-config set proactive false`

Always run:
```bash
touch ~/.gstack/.proactive-prompted
```

This only happens once. If `PROACTIVE_PROMPTED` is `yes`, skip this entirely.

## AskUserQuestion Format

**ALWAYS follow this structure for every AskUserQuestion call:**
1. **Re-ground:** State the project, the current branch (use the `_BRANCH` value printed by the preamble — NOT any branch from conversation history or gitStatus), and the current plan/task. (1-2 sentences)
2. **Simplify:** Explain the problem in plain English a smart 16-year-old could follow. No raw function names, no internal jargon, no implementation details. Use concrete examples and analogies. Say what it DOES, not what it's called.
3. **Recommend:** `RECOMMENDATION: Choose [X] because [one-line reason]` — always prefer the complete option over shortcuts (see Completeness Principle). Include `Completeness: X/10` for each option. Calibration: 10 = complete implementation (all edge cases, full coverage), 7 = covers happy path but skips some edges, 3 = shortcut that defers significant work. If both options are 8+, pick the higher; if one is ≤5, flag it.
4. **Options:** Lettered options: `A) ... B) ... C) ...` — when an option involves effort, show both scales: `(human: ~X / CC: ~Y)`

Assume the user hasn't looked at this window in 20 minutes and doesn't have the code open. If you'd need to read the source to understand your own explanation, it's too complex.

Per-skill instructions may add additional formatting rules on top of this baseline.

## Completeness Principle — Boil the Lake

AI makes completeness near-free. Always recommend the complete option over shortcuts — the delta is minutes with CC+gstack. A "lake" (100% coverage, all edge cases) is boilable; an "ocean" (full rewrite, multi-quarter migration) is not. Boil lakes, flag oceans.

**Effort reference** — always show both scales:

| Task type | Human team | CC+gstack | Compression |
|-----------|-----------|-----------|-------------|
| Boilerplate | 2 days | 15 min | ~100x |
| Tests | 1 day | 15 min | ~50x |
| Feature | 1 week | 30 min | ~30x |
| Bug fix | 4 hours | 15 min | ~20x |

Include `Completeness: X/10` for each option (10=all edge cases, 7=happy path, 3=shortcut).

## Contributor Mode

If `_CONTRIB` is `true`: you are in **contributor mode**. At the end of each major workflow step, rate your gstack experience 0-10. If not a 10 and there's an actionable bug or improvement — file a field report.

**File only:** gstack tooling bugs where the input was reasonable but gstack failed. **Skip:** user app bugs, network errors, auth failures on user's site.

**To file:** write `~/.gstack/contributor-logs/{slug}.md`:
```
# {Title}
**What I tried:** {action} | **What happened:** {result} | **Rating:** {0-10}
## Repro
1. {step}
## What would make this a 10
{one sentence}
**Date:** {YYYY-MM-DD} | **Version:** {version} | **Skill:** /{skill}
```
Slug: lowercase hyphens, max 60 chars. Skip if exists. Max 3/session. File inline, don't stop.

## Completion Status Protocol

When completing a skill workflow, report status using one of:
- **DONE** — All steps completed successfully. Evidence provided for each claim.
- **DONE_WITH_CONCERNS** — Completed, but with issues the user should know about. List each concern.
- **BLOCKED** — Cannot proceed. State what is blocking and what was tried.
- **NEEDS_CONTEXT** — Missing information required to continue. State exactly what you need.

### Escalation

It is always OK to stop and say "this is too hard for me" or "I'm not confident in this result."

Bad work is worse than no work. You will not be penalized for escalating.
- If you have attempted a task 3 times without success, STOP and escalate.
- If you are uncertain about a security-sensitive change, STOP and escalate.
- If the scope of work exceeds what you can verify, STOP and escalate.

Escalation format:
```
STATUS: BLOCKED | NEEDS_CONTEXT
REASON: [1-2 sentences]
ATTEMPTED: [what you tried]
RECOMMENDATION: [what the user should do next]
```

## Telemetry (run last)

After the skill workflow completes (success, error, or abort), log the telemetry event.
Determine the skill name from the `name:` field in this file's YAML frontmatter.
Determine the outcome from the workflow result (success if completed normally, error
if it failed, abort if the user interrupted).

**PLAN MODE EXCEPTION — ALWAYS RUN:** This command writes telemetry to
`~/.gstack/analytics/` (user config directory, not project files). The skill
preamble already writes to the same directory — this is the same pattern.
Skipping this command loses session duration and outcome data.

Run this bash:

```bash
_TEL_END=$(date +%s)
_TEL_DUR=$(( _TEL_END - _TEL_START ))
rm -f ~/.gstack/analytics/.pending-"$_SESSION_ID" 2>/dev/null || true
~/.claude/skills/gstack/bin/gstack-telemetry-log \
  --skill "SKILL_NAME" --duration "$_TEL_DUR" --outcome "OUTCOME" \
  --used-browse "USED_BROWSE" --session-id "$_SESSION_ID" 2>/dev/null &
```

Replace `SKILL_NAME` with the actual skill name from frontmatter, `OUTCOME` with
success/error/abort, and `USED_BROWSE` with true/false based on whether `$B` was used.
If you cannot determine the outcome, use "unknown". This runs in the background and
never blocks the user.

## Plan Status Footer

When you are in plan mode and about to call ExitPlanMode:

1. Check if the plan file already has a `## GSTACK REVIEW REPORT` section.
2. If it DOES — skip (a review skill already wrote a richer report).
3. If it does NOT — run this command:

\`\`\`bash
~/.claude/skills/gstack/bin/gstack-review-read
\`\`\`

Then write a `## GSTACK REVIEW REPORT` section to the end of the plan file:

- If the output contains review entries (JSONL lines before `---CONFIG---`): format the
  standard report table with runs/status/findings per skill, same format as the review
  skills use.
- If the output is `NO_REVIEWS` or empty: write this placeholder table:

\`\`\`markdown
## GSTACK REVIEW REPORT

| Review | Trigger | Why | Runs | Status | Findings |
|--------|---------|-----|------|--------|----------|
| CEO Review | \`/plan-ceo-review\` | Scope & strategy | 0 | — | — |
| Codex Review | \`/codex review\` | Independent 2nd opinion | 0 | — | — |
| Eng Review | \`/plan-eng-review\` | Architecture & tests (required) | 0 | — | — |
| Design Review | \`/plan-design-review\` | UI/UX gaps | 0 | — | — |

**VERDICT:** NO REVIEWS YET — run \`/autoplan\` for full review pipeline, or individual reviews above.
\`\`\`

**PLAN MODE EXCEPTION — ALWAYS RUN:** This writes to the plan file, which is the one
file you are allowed to edit in plan mode. The plan file review report is part of the
plan's living status.

# Systematic Debugging

## Iron Law

**NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.**

Fixing symptoms creates whack-a-mole debugging. Every fix that doesn't address root cause makes the next bug harder to find. Find the root cause, then fix it.

---

## Phase 1: Root Cause Investigation

Gather context before forming any hypothesis.

1. **Collect symptoms:** Read the error messages, stack traces, and reproduction steps. If the user hasn't provided enough context, ask ONE question at a time via AskUserQuestion.

2. **Read the code:** Trace the code path from the symptom back to potential causes. Use Grep to find all references, Read to understand the logic.

3. **Check recent changes:**
   ```bash
   git log --oneline -20 -- <affected-files>
   ```
   Was this working before? What changed? A regression means the root cause is in the diff.

4. **Reproduce:** Can you trigger the bug deterministically? If not, gather more evidence before proceeding.

Output: **"Root cause hypothesis: ..."** — a specific, testable claim about what is wrong and why.

---

## Scope Lock

After forming your root cause hypothesis, lock edits to the affected module to prevent scope creep.

```bash
[ -x "${CLAUDE_SKILL_DIR}/../freeze/bin/check-freeze.sh" ] && echo "FREEZE_AVAILABLE" || echo "FREEZE_UNAVAILABLE"
```

**If FREEZE_AVAILABLE:** Identify the narrowest directory containing the affected files. Write it to the freeze state file:

```bash
STATE_DIR="${CLAUDE_PLUGIN_DATA:-$HOME/.gstack}"
mkdir -p "$STATE_DIR"
echo "<detected-directory>/" > "$STATE_DIR/freeze-dir.txt"
echo "Debug scope locked to: <detected-directory>/"
```

Substitute `<detected-directory>` with the actual directory path (e.g., `src/auth/`). Tell the user: "Edits restricted to `<dir>/` for this debug session. This prevents changes to unrelated code. Run `/unfreeze` to remove the restriction."

If the bug spans the entire repo or the scope is genuinely unclear, skip the lock and note why.

**If FREEZE_UNAVAILABLE:** Skip scope lock. Edits are unrestricted.

---

## Phase 2: Pattern Analysis

Check if this bug matches a known pattern:

| Pattern | Signature | Where to look |
|---------|-----------|---------------|
| Race condition | Intermittent, timing-dependent | Concurrent access to shared state |
| Nil/null propagation | NoMethodError, TypeError | Missing guards on optional values |
| State corruption | Inconsistent data, partial updates | Transactions, callbacks, hooks |
| Integration failure | Timeout, unexpected response | External API calls, service boundaries |
| Configuration drift | Works locally, fails in staging/prod | Env vars, feature flags, DB state |
| Stale cache | Shows old data, fixes on cache clear | Redis, CDN, browser cache, Turbo |

Also check:
- `TODOS.md` for related known issues
- `git log` for prior fixes in the same area — **recurring bugs in the same files are an architectural smell**, not a coincidence

**External pattern search:** If the bug doesn't match a known pattern above, WebSearch for:
- "{framework} {generic error type}" — **sanitize first:** strip hostnames, IPs, file paths, SQL, customer data. Search the error category, not the raw message.
- "{library} {component} known issues"

If WebSearch is unavailable, skip this search and proceed with hypothesis testing. If a documented solution or known dependency bug surfaces, present it as a candidate hypothesis in Phase 3.

---

## Phase 3: Hypothesis Testing

Before writing ANY fix, verify your hypothesis.

1. **Confirm the hypothesis:** Add a temporary log statement, assertion, or debug output at the suspected root cause. Run the reproduction. Does the evidence match?

2. **If the hypothesis is wrong:** Before forming the next hypothesis, consider searching for the error. **Sanitize first** — strip hostnames, IPs, file paths, SQL fragments, customer identifiers, and any internal/proprietary data from the error message. Search only the generic error type and framework context: "{component} {sanitized error type} {framework version}". If the error message is too specific to sanitize safely, skip the search. If WebSearch is unavailable, skip and proceed. Then return to Phase 1. Gather more evidence. Do not guess.

3. **3-strike rule:** If 3 hypotheses fail, **STOP**. Use AskUserQuestion:
   ```
   3 hypotheses tested, none match. This may be an architectural issue
   rather than a simple bug.

   A) Continue investigating — I have a new hypothesis: [describe]
   B) Escalate for human review — this needs someone who knows the system
   C) Add logging and wait — instrument the area and catch it next time
   ```

**Red flags** — if you see any of these, slow down:
- "Quick fix for now" — there is no "for now." Fix it right or escalate.
- Proposing a fix before tracing data flow — you're guessing.
- Each fix reveals a new problem elsewhere — wrong layer, not wrong code.

---

## Phase 4: Implementation

Once root cause is confirmed:

1. **Fix the root cause, not the symptom.** The smallest change that eliminates the actual problem.

2. **Minimal diff:** Fewest files touched, fewest lines changed. Resist the urge to refactor adjacent code.

3. **Write a regression test** that:
   - **Fails** without the fix (proves the test is meaningful)
   - **Passes** with the fix (proves the fix works)

4. **Run the full test suite.** Paste the output. No regressions allowed.

5. **If the fix touches >5 files:** Use AskUserQuestion to flag the blast radius:
   ```
   This fix touches N files. That's a large blast radius for a bug fix.
   A) Proceed — the root cause genuinely spans these files
   B) Split — fix the critical path now, defer the rest
   C) Rethink — maybe there's a more targeted approach
   ```

---

## Phase 5: Verification & Report

**Fresh verification:** Reproduce the original bug scenario and confirm it's fixed. This is not optional.

Run the test suite and paste the output.

Output a structured debug report:
```
DEBUG REPORT
════════════════════════════════════════
Symptom:         [what the user observed]
Root cause:      [what was actually wrong]
Fix:             [what was changed, with file:line references]
Evidence:        [test output, reproduction attempt showing fix works]
Regression test: [file:line of the new test]
Related:         [TODOS.md items, prior bugs in same area, architectural notes]
Status:          DONE | DONE_WITH_CONCERNS | BLOCKED
════════════════════════════════════════
```

---

## Important Rules

- **3+ failed fix attempts → STOP and question the architecture.** Wrong architecture, not failed hypothesis.
- **Never apply a fix you cannot verify.** If you can't reproduce and confirm, don't ship it.
- **Never say "this should fix it."** Verify and prove it. Run the tests.
- **If fix touches >5 files → AskUserQuestion** about blast radius before proceeding.
- **Completion status:**
  - DONE — root cause found, fix applied, regression test written, all tests pass
  - DONE_WITH_CONCERNS — fixed but cannot fully verify (e.g., intermittent bug, requires staging)
  - BLOCKED — root cause unclear after investigation, escalated
