/pasteurize

A discipline for hard bugs. Skip phases only when explicitly justified.

When exploring the codebase, use /cheez-search to orient and check .cheese/specs/ for any spec or design notes that touch the failing seam.

Phase 1 — Build a feedback loop

This is the skill. Everything else is mechanical. If you have a fast, deterministic, agent-runnable pass/fail signal for the bug, you will find the cause — bisection, hypothesis-testing, and instrumentation all just consume that signal. If you don't have one, no amount of staring at code will save you.

Spend disproportionate effort here. Be aggressive. Be creative. Refuse to give up.

Ways to construct one — try them in roughly this order

1. Failing test at whatever seam reaches the bug — unit, integration, e2e.
2. Curl / HTTP script against a running dev server.
3. CLI invocation with a fixture input, diffing stdout against a known-good snapshot.
4. Headless browser script (Playwright / Puppeteer) — drives the UI, asserts on DOM/console/network.
5. Replay a captured trace. Save a real network request / payload / event log to disk; replay it through the code path in isolation.
6. Throwaway harness. Spin up a minimal subset of the system (one service, mocked deps) that exercises the bug code path with a single function call.
7. Property / fuzz loop. If the bug is "sometimes wrong output", run 1000 random inputs and look for the failure mode.
8. Bisection harness. If the bug appeared between two known states (commit, dataset, version), automate "boot at state X, check, repeat" so you can git bisect run it.
9. Differential loop. Run the same input through old-version vs new-version (or two configs) and diff outputs.
10. HITL bash script. Last resort. If a human must click, drive them with a structured loop so output still feeds back to you.

Build the right feedback loop, and the bug is 90% fixed.

Iterate on the loop itself

Treat the loop as a product. Once you have a loop, ask:

• Can I make it faster? (Cache setup, skip unrelated init, narrow the test scope.)
• Can I make the signal sharper? (Assert on the specific symptom, not "didn't crash".)
• Can I make it more deterministic? (Pin time, seed RNG, isolate filesystem, freeze network.)

A 30-second flaky loop is barely better than no loop. A 2-second deterministic loop is a debugging superpower.

Non-deterministic bugs

The goal is not a clean repro but a higher reproduction rate. Loop the trigger 100×, parallelise, add stress, narrow timing windows, inject sleeps. A 50%-flake bug is debuggable; 1% is not — keep raising the rate until it's debuggable.

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. Write a status: halt handoff slug (see below) and stop.

Do not proceed to Phase 2 until you have a loop you believe in.

Phase 2 — Reproduce

Run the loop. Watch the bug appear.

Confirm:

• The loop produces the failure mode the user described — not a different failure that happens to be nearby. Wrong bug = wrong fix.
• The failure is reproducible across multiple runs (or, for non-deterministic bugs, reproducible at a high enough rate to debug against).
• You have captured the exact symptom (error message, wrong output, slow timing) so later phases can verify the fix actually addresses it.

Do not proceed until you reproduce the bug.

Phase 3 — Hypothesise

Generate 3–5 ranked hypotheses before testing any of them. Single-hypothesis generation anchors on the first plausible idea.

Each hypothesis must be falsifiable: state the prediction it makes.

Format: "If <X> is the cause, then <changing Y> will make the bug disappear / <changing Z> will make it worse."

If you cannot state the prediction, the hypothesis is a vibe — discard or sharpen it.

Show the ranked list to the user via AskUserQuestion before testing. They often have domain knowledge that re-ranks instantly ("we just deployed a change to #3"), or know hypotheses they've already ruled out. Cheap checkpoint, big time saver. Don't block on it — proceed with your ranking if the user is AFK or running --auto.

Phase 4 — Instrument

Each probe must map to a specific prediction from Phase 3. Change one variable at a time.

Tool preference:

1. Debugger / REPL inspection if the env supports it. One breakpoint beats ten logs.
2. Targeted logs at the boundaries that distinguish hypotheses.
3. Never "log everything and search".

Tag every debug log with a unique prefix, e.g. [DEBUG-a4f2]. Cleanup at the end becomes a single /cheez-search content query. Untagged logs survive; tagged logs die.

Perf branch. For performance regressions, logs are usually wrong. Instead: establish a baseline measurement (timing harness, performance.now(), profiler, query plan), then bisect. Measure first, fix second.

Use /cheez-write for any instrumentation edits — never the host Edit / Write tools.

Phase 5 — Fix + regression test

Write the regression test before the fix — but only if there is a correct seam for it.

A correct seam is one where the test exercises the real bug pattern as it occurs at the call site. If the only available seam is too shallow (single-caller test when the bug needs multiple callers, unit test that can't replicate the chain that triggered the bug), a regression test there gives false confidence.

If no correct seam exists, that itself is the finding. Note it in the handoff slug as an architectural follow-up. The codebase is preventing the bug from being locked down. Skip the test write; do not paper over it. Phase 6's "what would have prevented this bug?" retrospective still applies.

If a correct seam exists:

1. Turn the minimised repro into a failing test at that seam — write it via /cheez-write.
2. Watch it fail.
3. Apply the smallest production change that makes the test pass — also via /cheez-write. No scope creep, no "while I'm here" cleanup.
4. Watch the test pass.
5. Re-run the Phase 1 feedback loop against the original (un-minimised) scenario to confirm the symptom is gone, not just the test seam.

All edits go through /cheez-write — never the host Edit / Write tools.

Broader implementation (related cleanup, follow-on changes, anything beyond the minimal fix) is not pasteurize's job. Note it in the slug and let /cook --auto pick it up in Phase 6's handoff.

Phase 6 — Cleanup + hand off

Before writing the handoff slug, confirm:

• Original repro no longer reproduces (re-run the Phase 1 loop).
• Regression test passes (or absence of seam is documented in the slug).
• All [DEBUG-...] instrumentation removed — run a /cheez-search content query for the prefix and verify zero hits.
• Throwaway harnesses / prototypes deleted (or moved to a clearly-marked debug location and called out in the slug).
• The confirmed hypothesis is captured in the slug so the commit message downstream can reference it.

Then ask: what would have prevented this bug? If the answer involves architectural change (no good test seam, tangled callers, hidden coupling), note it in the slug under an architectural-follow-up line. The chain still runs; the user can pick up the architectural work via /mold after the fix lands. Make the recommendation after the fix is in, not before — you have more information now than when you started.

Once the checklist is green and the slug is on disk, hand off to /cook <slug> --auto (default). Cook --auto picks up the post-fix state, runs its taste-test against the applied diff for spec drift / readability / scope creep, produces its package-ready report, and triggers the autonomous /press → /age → /cure chain. Pasteurize itself does not commit, open PRs, or drive the chain — cook owns that.

Preferred tools and fallbacks

Need	Prefer	Fallback
Code search / blast radius	/cheez-search (tilth MCP)	flag the gap; do not fall back to host grep
Reading code	/cheez-read (tilth MCP)	flag the gap; do not fall back to host cat/Read
Editing instrumentation	/cheez-write (tilth MCP)	flag the gap; do not fall back to host Edit/Write
Diff visualization	delta	plain git diff
GitHub context	gh	local git history or user-provided links
External sanity check	/briesearch	clearly mark as an assumption

Missing optional tools should not interrupt diagnosis. Keep tool use proportional to the bug.

Output

Return a short report covering:

• The named cause (one sentence, with <certain> / <speculating> / <don't know> calibration).
• The feedback loop (command, observed vs expected).
• Hypotheses considered and which one held.
• The regression test path and the fix's file:line footprint.
• Cleanup status ([DEBUG-...] removed, harnesses deleted or relocated).
• Suggested next skill — /cook <slug> --auto for the autonomous chain forward.

Handoff slug

Write a minimum-shape handoff slug to .cheese/pasteurize/<slug>.md so /cook (and any orchestrator) can resume without re-reading the full report. Schema:

status: ok | halt: <one-line reason>
next: cook | mold | done
artifact: <path-to-richer-report-if-any>
cause: <one-sentence named cause>
loop: <command or repro path>
seam: <regression-test path:line, or "none — architectural follow-up">
fix: <production diff footprint, e.g. "src/foo.ts:42">
follow_up: <architectural follow-up note, or "none">
<one-line orientation: what pasteurize converged on>

status: ok when the regression test is green, the original repro no longer reproduces, and cleanup is done. status: halt: <reason> when Phase 1 failed (cannot build a loop, missing environment access, missing artifact), or Phase 3 exhausted both hypothesis rounds without a confirmed cause. next: is cook for the standard chain, mold if the diagnosis itself recommends an architectural spec instead of a per-bug fix, or done if the bug was caused outside the repo and no follow-up is needed.

Handoff

Pipeline: cheese (debug) → [pasteurize] → cook --auto → press → age → cure → ship

After the report is printed and the handoff slug is on disk, ask via AskUserQuestion which downstream to run. Lead each option with the verb (what the user wants to do next):

• Validate and chain forward (recommended when status: ok) — /cook <slug> --auto.
• Validate without auto chain — /cook <slug> (cook runs taste-test, then the user picks each subsequent step).
• Spec the architectural follow-up first — /mold <slug> (when seam: none — architectural follow-up).
• Stop — fix is in tree; defer the chain.

Pre-select Validate and chain forward when status: ok. The chain default is --auto because pasteurize already wrote and verified the fix; the work left for cook → press → age → cure is mechanical validation, not new authoring. Never auto-invoke; the user must still select.

When invoked with --auto, skip this AskUserQuestion entirely and invoke /cook <slug> --auto directly.

Auto mode

--auto is the autonomous-pipeline switch. Propagated from upstream skills (/cheese --auto) or invoked directly with --auto.

What auto mode does:

1. Phase 3's "show the user the ranked hypothesis list" gate is skipped — proceed with the model's ranking.
2. Phase 4–5 still run in full; the auto signal does not loosen the discipline.
3. After Phase 6 cleanup, invoke /cook <slug> --auto directly.
4. From there, cook's own auto-mode contract takes over (press → age → cure cycle).

Auto mode stops early when:

• Phase 1 fails (status: halt written, no loop achievable).
• Phase 3 disproves all hypotheses across two rounds (cap at two Phase 3 rounds, then halt).
• Phase 5's seam check finds no correct seam — write status: halt: no correct regression-test seam and route to /mold instead of /cook.
• The fix breaks an unrelated test that pasteurize cannot reconcile within scope.

In every early-stop case, write the halt slug and surface the report. Do not silently downgrade to "best guess".

Rules

• Do not skip Phase 1. The feedback loop is the skill; everything else is mechanical.
• Do not hypothesise without a reproducing loop.
• Phase 5 writes only the regression test and the minimal production change. Broader implementation — related cleanup, follow-on features, refactors the bug suggests — belongs in /cook, not pasteurize.
• Do not leave [DEBUG-...] tags in the tree — clean them before the handoff slug is written.
• Do not claim "shipped". Pasteurize claims "cause named, regression green, fix in tree, ready for chain". The chain (cook → press → age → cure) claims shipped.
• If the bug exposes an architectural gap (no correct regression-test seam), say so in the slug. Do not silently paper over it.