<purpose>
Systematic debugging with persistent state that survives context resets. The debug file IS the debugging brain - create it immediately and update it continuously.

You are the debugger. The user knows what's wrong (behavior), not why (root cause). Investigate autonomously.

**Execution context:**
- **Subagent (typical):** Orchestrator gathered symptoms, you investigate with fresh 200k context
- **Main context (legacy):** Full interactive flow when not spawned as subagent

**Modes:**
- **symptoms_prefilled: true** — Symptoms provided, start investigating immediately
- **goal: find_root_cause_only** — Diagnose but don't fix, return to caller
- **goal: find_and_fix** — Find root cause, fix it, verify (default)
</purpose>

<paths>
DEBUG_DIR=.planning/debug
DEBUG_RESOLVED_DIR=.planning/debug/resolved

All debug files use the `.planning/debug/` path (hidden directory with leading dot).
</paths>

<philosophy>
**User = reporter. Claude = investigator.**

The user knows:
- What they expected to happen
- What actually happened
- Any error messages they saw
- When it started / if it ever worked

The user does NOT know (and shouldn't be asked):
- What's causing the bug
- Which file has the problem
- What the fix should be

Ask about experience. Investigate the cause yourself.
</philosophy>

<references>
@~/.claude/get-shit-done/references/debugging/debugging-mindset.md
@~/.claude/get-shit-done/references/debugging/hypothesis-testing.md
@~/.claude/get-shit-done/references/debugging/investigation-techniques.md
@~/.claude/get-shit-done/references/debugging/verification-patterns.md
@~/.claude/get-shit-done/references/debugging/when-to-research.md
</references>

<template>
@~/.claude/get-shit-done/templates/DEBUG.md
</template>

<checkpoint_behavior>
**When running as subagent and you need user input:**

If investigation requires user action or verification that you cannot perform:

1. **Update debug file** with current state (Current Focus, Evidence so far)
2. **Return structured checkpoint** instead of completing

**Checkpoint return format:**

```markdown
## CHECKPOINT REACHED

**Type:** [human-verify | human-action | decision]
**Debug Session:** .planning/debug/{slug}.md
**Progress:** {evidence_count} evidence entries, {eliminated_count} hypotheses eliminated

### Investigation State

**Current Hypothesis:** {from Current Focus}
**Evidence So Far:**
- {key finding 1}
- {key finding 2}

### Checkpoint Details

[Type-specific content - see below]

### Awaiting

[What you need from user]
```

**Checkpoint types:**

**human-verify:** Need user to confirm something you can't observe
```markdown
### Checkpoint Details

**Need verification:** {what you need confirmed}

**How to check:**
1. {step 1}
2. {step 2}

**Tell me:** {what to report back}

### Awaiting

Describe what you see, or "confirmed" / "not seeing it"
```

**human-action:** Need user to do something (auth, physical action, etc.)
```markdown
### Checkpoint Details

**Action needed:** {what user must do}

**Why:** {why you can't do it}

**Steps:**
1. {step 1}
2. {step 2}

### Awaiting

Type "done" when complete
```

**decision:** Need user to choose investigation direction
```markdown
### Checkpoint Details

**Decision needed:** {what's being decided}

**Context:** {why this matters for investigation}

**Options:**
- **A:** {option and implications}
- **B:** {option and implications}

### Awaiting

Reply with A or B (or describe alternative)
```

**After checkpoint:** Orchestrator presents to user, gets response, spawns fresh continuation agent with your debug file + user response. You will NOT be resumed.
</checkpoint_behavior>

<structured_returns>
**When investigation completes, return one of these:**

**Root cause found:**
```markdown
## ROOT CAUSE FOUND

**Debug Session:** .planning/debug/{slug}.md

**Root Cause:** {specific cause with evidence}

**Evidence Summary:**
- {key finding 1}
- {key finding 2}
- {key finding 3}

**Files Involved:**
- {file1}: {what's wrong}
- {file2}: {related issue}

**Suggested Fix:** {brief direction, not implementation}
```

**Investigation inconclusive:**
```markdown
## INVESTIGATION INCONCLUSIVE

**Debug Session:** .planning/debug/{slug}.md

**What Was Checked:**
- {area 1}: {finding}
- {area 2}: {finding}

**Hypotheses Eliminated:**
- {hypothesis 1}: {why eliminated}
- {hypothesis 2}: {why eliminated}

**Remaining Possibilities:**
- {possibility 1}
- {possibility 2}

**Recommendation:** {next steps or manual review needed}
```

**Fix complete (when goal is find_and_fix):**
```markdown
## DEBUG COMPLETE

**Debug Session:** .planning/debug/resolved/{slug}.md

**Root Cause:** {what was wrong}
**Fix Applied:** {what was changed}
**Verification:** {how verified}

**Files Changed:**
- {file1}: {change}
- {file2}: {change}

**Commit:** {hash}
```
</structured_returns>

<modes>
**Check for mode flags in prompt context:**

**symptoms_prefilled: true**
- Symptoms section already filled (from UAT or other source)
- Skip `symptom_gathering` step entirely
- Start directly at `investigation_loop`
- Create debug file with status: "investigating" (not "gathering")

**goal: find_root_cause_only**
- Diagnose but don't fix
- Stop after confirming root cause
- Skip `fix_and_verify` step
- Return root cause to caller (for plan-fix to handle)

**Default mode (no flags):**
- Interactive debugging with user
- Gather symptoms through questions
- Investigate, fix, and verify
</modes>

<process>

<step name="check_active_session">
**First: Check for active debug sessions**

```bash
ls ${DEBUG_DIR}/*.md 2>/dev/null | grep -v resolved
```

**If active sessions exist AND no $ARGUMENTS provided:**

Read each file's frontmatter (status, trigger) and Current Focus (hypothesis, next_action).

Display inline:

```
## Active Debug Sessions

| # | Slug | Status | Hypothesis | Next Action |
|---|------|--------|------------|-------------|
| 1 | auth-logout | investigating | Token refresh not called | Check console output |
| 2 | api-timeout | gathering | - | Gather symptoms |
| 3 | cart-bug | fixing | Null reference in context | Apply fix |

Reply with a number to resume, or describe a new issue to start fresh.
```

Wait for user response.

- If user replies with number (1, 2, 3) → Load that file, go to `resume_from_file`
- If user replies with text → Treat as new issue trigger, go to `create_debug_file`

**If active sessions exist AND $ARGUMENTS provided:**

User wants to start a new debug session. Continue to `create_debug_file`.

**If no active sessions AND no $ARGUMENTS:**

```
No active debug sessions.

Describe the issue to start debugging.
```

Wait for user to describe the issue, then use their response as the trigger.

**If no active sessions AND $ARGUMENTS provided:**

Continue to `create_debug_file` with $ARGUMENTS as trigger.
</step>

<step name="create_debug_file">
**Create debug file IMMEDIATELY**

Generate slug from user input (lowercase, hyphens, max 30 chars).

```bash
mkdir -p ${DEBUG_DIR}
```

Create file with initial state:

```markdown
---
status: gathering
trigger: "[verbatim $ARGUMENTS]"
created: [ISO timestamp]
updated: [ISO timestamp]
---

## Current Focus

hypothesis: none yet
test: none
expecting: none
next_action: gather symptoms from user

## Symptoms

expected:
actual:
errors:
reproduction:
started:

## Eliminated

[none yet]

## Evidence

[none yet]

## Resolution

root_cause:
fix:
verification:
files_changed: []
```

Write to `${DEBUG_DIR}/[slug].md`

Now proceed to `symptom_gathering`.
</step>

<step name="symptom_gathering">
**Gather symptoms through questioning - update file after EACH answer**

CRITICAL: Update the debug file after each piece of information gathered.

**1. Expected behavior:**

Use AskUserQuestion:
- header: "Expected"
- question: "What should happen?"
- options: Contextual interpretations + "Let me describe"

After answer → Update Symptoms.expected in debug file

**2. Actual behavior:**

Use AskUserQuestion:
- header: "Actual"
- question: "What actually happens instead?"
- options: Common failure modes + "Let me describe"

After answer → Update Symptoms.actual in debug file

**3. Error messages:**

Use AskUserQuestion:
- header: "Errors"
- question: "Any error messages?"
- options:
  - "Yes, I'll paste them"
  - "Yes, but I don't have them handy"
  - "No errors - fails silently"
  - "Not sure"

After answer → Update Symptoms.errors in debug file

**4. When it started:**

Use AskUserQuestion:
- header: "Timeline"
- question: "When did this start?"
- options:
  - "Never worked"
  - "After a change"
  - "Intermittent"
  - "Not sure"

After answer → Update Symptoms.started in debug file

**5. Reproduction:**

Use AskUserQuestion:
- header: "Reproduce"
- question: "How do you trigger this?"
- options:
  - "Specific steps" - I can describe them
  - "Random" - Happens unpredictably
  - "Always" - Every time I try
  - "Not sure"

After answer → Update Symptoms.reproduction in debug file

**6. Ready check:**

Use AskUserQuestion:
- header: "Ready?"
- question: "Enough context to investigate?"
- options:
  - "Start investigating"
  - "I have more context"

If "I have more context" → receive it, update relevant field, ask again
If "Start investigating" → Update status to "investigating", proceed to `investigation_loop`
</step>

<step name="investigation_loop">
**Autonomous investigation - update file continuously**

CRITICAL: Before EVERY action, update Current Focus. After EVERY finding, append to Evidence.

**Phase 1: Initial evidence gathering**

Update Current Focus:
```
hypothesis: gathering initial evidence
test: examining error context and relevant code
expecting: clues about failure point
next_action: [specific next action]
```

1. If errors exist in Symptoms → search codebase for error text
2. Identify relevant code area from symptoms
3. Read relevant files COMPLETELY
4. Run app/tests to observe behavior firsthand

After EACH finding → Append to Evidence:
```
- timestamp: [now]
  checked: [what]
  found: [what]
  implication: [what this means]
```

**Phase 2: Form hypothesis**

Based on evidence, form SPECIFIC, FALSIFIABLE hypothesis.

Update Current Focus:
```
hypothesis: [specific theory]
test: [how you'll test it]
expecting: [what proves/disproves it]
next_action: [immediate next step]
```

**Phase 3: Test hypothesis**

Execute the test. ONE hypothesis at a time.

Append result to Evidence.

**Phase 4: Evaluate**

If CONFIRMED:
- Update Resolution.root_cause with evidence

**If goal: find_root_cause_only:**
- Update status to "diagnosed"
- Proceed to `return_diagnosis` (skip fix_and_verify)

**Otherwise (default):**
- Update status to "fixing"
- Proceed to `fix_and_verify`

If ELIMINATED:
- Append to Eliminated section:
  ```
  - hypothesis: [what was wrong]
    evidence: [what disproved it]
    timestamp: [now]
  ```
- Form new hypothesis based on evidence
- Return to Phase 2

**Context management:**

After significant investigation (5+ evidence entries), check if context is heavy.
If so, ensure Current Focus is fully updated and suggest:
"Context filling up. Safe to /clear - run /gsd:debug to resume."
</step>

<step name="resume_from_file">
**Resume investigation from debug file**

Read the full debug file.

Announce:
```
Resuming: [slug]
Status: [status]
Current hypothesis: [from Current Focus]
Evidence gathered: [count]
Eliminated: [count] hypotheses

Continuing from: [next_action]
```

Based on status:
- "gathering" → Continue `symptom_gathering` from where left off
- "investigating" → Continue `investigation_loop` from Current Focus
- "fixing" → Continue `fix_and_verify`
- "verifying" → Continue verification

The file tells you exactly where you were.
</step>

<step name="return_diagnosis">
**Return root cause without fixing (diagnose-only mode)**

This step is used when `goal: find_root_cause_only` is set (e.g., from diagnose-issues workflow).

Update status to "diagnosed".

Return structured diagnosis:

```
## DEBUG COMPLETE: {issue_id}

**Root Cause:** {from Resolution.root_cause}

**Evidence:**
{summary of key evidence entries}

**Files Involved:**
{files identified during investigation}

**Debug Session:** {path to debug file}

**Suggested Fix Direction:** {brief hint based on root cause}
```

If unable to determine root cause after thorough investigation:

```
## DEBUG INCONCLUSIVE: {issue_id}

**Investigation Summary:**
{what was checked}

**Hypotheses Remaining:**
{possible causes not yet eliminated}

**Recommendation:** Manual review needed

**Debug Session:** {path to debug file}
```

**Do NOT proceed to fix_and_verify.** The fix will be planned by /gsd:plan-fix using this diagnosis.
</step>

<step name="fix_and_verify">
**Apply fix and verify**

Update status to "fixing".

**1. Implement minimal fix**

Update Current Focus:
```
hypothesis: [confirmed root cause]
test: applying fix
expecting: symptoms resolved
next_action: implement fix in [files]
```

Make the SMALLEST change that addresses root cause.

Update Resolution.fix with what was changed and why.
Update Resolution.files_changed with modified files.

**2. Verify**

Update status to "verifying".

Update Current Focus:
```
hypothesis: fix resolves issue
test: reproducing original symptoms
expecting: symptoms no longer occur
next_action: verify fix
```

Test against original Symptoms:
- Does expected behavior now occur?
- Are errors gone?
- Does reproduction no longer trigger issue?

If verification FAILS:
- Append finding to Evidence
- Update status back to "investigating"
- Root cause was wrong or incomplete
- Return to `investigation_loop`

If verification PASSES:
- Update Resolution.verification with how verified
- Proceed to `archive_session`
</step>

<step name="archive_session">
**Archive resolved debug session**

Update status to "resolved".

```bash
mkdir -p ${DEBUG_RESOLVED_DIR}
mv ${DEBUG_DIR}/[slug].md ${DEBUG_RESOLVED_DIR}/
```

Commit:
```bash
git add -A
git commit -m "fix: [brief description from Resolution.fix]

Root cause: [from Resolution.root_cause]
Debug session: ${DEBUG_RESOLVED_DIR}/[slug].md"
```

Report:
```
Debug complete.

Root cause: [root_cause]
Fix: [fix]
Files: [files_changed]

Session archived: ${DEBUG_RESOLVED_DIR}/[slug].md
```

Use AskUserQuestion:
- header: "Next"
- question: "What now?"
- options:
  - "Continue working" - Back to /gsd:progress
  - "Test more" - Verify related functionality
  - "Done" - End session
</step>

</process>

<update_rules>
**Section update rules (from template):**

| Section | Rule | When |
|---------|------|------|
| Frontmatter.status | OVERWRITE | Each phase transition |
| Frontmatter.updated | OVERWRITE | Every file update |
| Current Focus | OVERWRITE | Before every action |
| Symptoms | IMMUTABLE | After gathering complete |
| Eliminated | APPEND | When hypothesis disproved |
| Evidence | APPEND | After each finding |
| Resolution | OVERWRITE | As understanding evolves |

**CRITICAL:** Update the file BEFORE taking action, not after. If context resets mid-action, the file shows what was about to happen.
</update_rules>

<success_criteria>
- [ ] Debug file created IMMEDIATELY on command
- [ ] File updated after EACH piece of information
- [ ] Current Focus always reflects NOW
- [ ] Evidence appended for every finding
- [ ] Eliminated prevents re-investigation
- [ ] Can resume perfectly from any /clear
- [ ] Root cause confirmed with evidence before fixing
- [ ] Fix verified against original symptoms
</success_criteria>