fix: make diagnosing-bugs redact secrets

A Snyk audit (W007, HIGH) flagged the skill for insecure credential
handling: it tells the agent to "paste the invocation and its output",
builds curl loops, and collects artifacts — three paths by which a live
token can end up reproduced in the agent's response.

Add a Redact section making redaction the first move on each, and point
the two call sites at it. Warn in the HITL template that `capture`
prints its value back to the terminal, where the agent reads it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.changeset/diagnosing-bugs-redact-secrets.md

@@ -0,0 +1,9 @@
+---
+"mattpocock-skills": patch
+---
+
+Make `diagnosing-bugs` redact secrets.
+
+- Add a **Redact** section to `SKILL.md`. The skill has the agent show commands, outputs and captured artifacts; the section makes redaction the first move on each — write `<REDACTED>`, show a command's shape (`Bearer $API_TOKEN`) rather than its credential, build loops against env vars, and redact HAR files, log dumps and payloads before quoting them.
+- The Phase 1 completion criterion said "paste the invocation and its output". It now says show it redacted, and Phase 1 asks the user for a **redacted** captured artifact.
+- Note in `scripts/hitl-loop.template.sh` that `capture` prints its value back to the terminal, so it takes observations while signing in stays a `step`.

skills/engineering/diagnosing-bugs/SKILL.md

@@ -9,6 +9,16 @@ A discipline for hard bugs. Skip phases only when explicitly justified.
 
 When exploring the codebase, read `CONTEXT.md` (if it exists) to get a clear mental model of the relevant modules, and check ADRs in the area you're touching.
 
+## Redact
+
+This skill has you show commands, outputs and captured artifacts. **Redact every secret first** — API keys, tokens, passwords, cookies, session IDs, connection strings, signed URLs. Write `<REDACTED>` in its place.
+
+- **Show a command's shape, not its credential**: `curl -H "Authorization: Bearer $API_TOKEN" …`. The env var reference is the redacted form, and it still runs.
+- **Build loops against env vars**, so the credential stays in the environment rather than in the file you write or the output you quote.
+- **Redact captured artifacts** — HAR files, log dumps and request payloads carry auth headers. Quote only the lines that carry the signal.
+
+If the redacted output is not enough to diagnose the bug, say so and ask the user.
+
 ## Phase 1 — Build a feedback loop
 
 **This is the skill.** Everything else is mechanical. If you have a **tight** pass/fail signal for the bug — one that goes red on _this_ bug — you will find the cause; bisection, hypothesis-testing, and instrumentation all just consume it. If you don't have one, no amount of staring at code will save you.
@@ -46,11 +56,11 @@ The goal is not a clean repro but a **higher reproduction rate**. Loop the trigg
 
 ### When you genuinely cannot build a loop
 
-Stop and say so explicitly. List what you tried. Ask the user for: (a) access to whatever environment reproduces it, (b) a captured artifact (HAR file, log dump, core dump, screen recording with timestamps), or (c) permission to add temporary production instrumentation. Do **not** proceed to hypothesise without a loop.
+Stop and say so explicitly. List what you tried. Ask the user for: (a) access to whatever environment reproduces it, (b) a redacted captured artifact (HAR file, log dump, core dump, screen recording with timestamps), or (c) permission to add temporary production instrumentation. Do **not** proceed to hypothesise without a loop.
 
 ### Completion criterion — a tight loop that goes red
 
-Phase 1 is done when the loop is **tight** and **red-capable**: you can name **one command** — a script path, a test invocation, a curl — that you have **already run at least once** (paste the invocation and its output), and that is:
+Phase 1 is done when the loop is **tight** and **red-capable**: you can name **one command** — a script path, a test invocation, a curl — that you have **already run at least once** (show the invocation and its output, redacted), and that is:
 
 - [ ] **Red-capable** — it drives the actual bug code path and asserts the **user's exact symptom**, so it can go red on this bug and green once fixed. Not "runs without erroring" — it must be able to _catch this specific bug_.
 - [ ] **Deterministic** — same verdict every run (flaky bugs: a pinned, high reproduction rate, per above).

skills/engineering/diagnosing-bugs/scripts/hitl-loop.template.sh

@@ -11,6 +11,9 @@
 #   capture VAR "<question>"      → show question, read response into VAR
 #
 # At the end, captured values are printed as KEY=VALUE for the agent to parse.
+#
+# `capture` prints its value back to the terminal, where the agent reads it — so
+# capture observations, and leave signing in to the user as a `step`.
 
 set -euo pipefail