investigate

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## When to invoke this skill

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 invoke this skill (do NOT debug directly) when the user reports
errors, 500 errors, stack traces, unexpected behavior, "it was working
yesterday", or is troubleshooting why something stopped working.

## Preamble (run first)

```bash
_SS="$HOME/.claude/skills/gstack/bin/gstack-skill-start"
[ -x "$_SS" ] || _SS=".claude/skills/gstack/bin/gstack-skill-start"
"$_SS" --skill "investigate" --model "claude" --parent-pid "$PPID" \
  || echo "SKILL_START: unavailable — stale install; run ./setup or /gstack-upgrade (preamble degraded, continue the user's task)"
```

Read the echoed `KEY: value` STATUS lines — they drive every preamble rule
below. **Degraded mode:** if `SKILL_START_PROTO: 1` is missing from the output
(script absent, stale install, or a different protocol number), apply safe
…