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Brummel 6410732943 feat: debug RED stage requires minimal, autonomous fixture

Phase 3 previously said only "smallest possible reproducer" — a
passive property an agent can satisfy by name while still asserting
against the full reproducing fixture. Sharpen it into an explicit
two-step discipline: minimize the trigger (delta-reduce until one
more cut makes the symptom vanish) and make the fixture autonomous
(inline input, no shared fixtures/DB seeds/clocks/server boots
unless the bug is genuinely at that integration boundary).

- Iron Law gains: an un-minimized repro is not a RED test
- Phase 3 rewritten with explicit Minimize + Autonomous steps
- 3 rationalization rows + 4 red flags for the "full fixture
  reproduces deterministically, ship it" failure mode
- SKILL.md overview/handoff mirrored at orchestrator altitude

Baseline (writing-skills RED-first): 6 subagent runs showed the old
wording usually steered right but relied on agent instinct; GREEN:
2 runs under the targeted full-fixture pressure now reduce to the
minimal trigger and cite the contract verbatim.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

2026-05-30 10:19:15 +02:00

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name, description

name	description
debug	Use when a bug surfaces — failing test, segfault, wrong stdout, panic, or any observable misbehaviour. Bug fixes are RED-first TDD; no fix is attempted before the failing test exists in the working tree. Mandatory for any bug, including ones that look trivial.

debug — RED-first bug diagnoser

Violating the letter of these rules is violating the spirit.

Overview

Bugs are diagnosed and fixed by a two-stage handoff: this skill produces the RED test and the cause analysis; the implement skill then drives the fix to GREEN. Skipping the RED stage — even for "trivial" bugs — produces fixes that don't stick and tests that don't exist to catch the next regression.

The substantive process — root cause investigation → pattern analysis → minimal, autonomous RED test → handoff, plus the Phase 4.5 architecture-question trigger after three failed hypotheses — lives in agents/debugger.md. The RED stage is not "any failing test": Phase 3 reduces the reproducer to the smallest autonomous trigger before the test counts. That file is the single source of truth for the discipline; this skill file only governs trigger, dispatch, and handoff.

When to Use / Skipping

Trigger this skill on:

a failing run of the project's test command (configured under commands.test in the profile)
wrong stdout from running a project artefact
a segfault from a built binary
a panic / unhandled exception in the toolchain
a structured diagnostic from bencher or architect that names a concrete misbehaviour

Never skipped. A bug without a regression test is a code change, not a fix. Ad-hoc judgement that a bug is "too small for TDD" is the exact failure mode this skill exists to prevent.

The Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST
NO FIX WITHOUT A FAILING TEST FIRST

Both clauses are non-negotiable.

Dispatch

Dispatch debugger with:

Carrier field	Content
`symptom`	Exact error message, stack trace, wrong output, or repro command
`repro_known`	One-line repro if known, otherwise the agent finds one
`recent_iter`	Iteration that last touched the suspected area (often `git log` tail)

The agent writes the RED test to the working tree (uncommitted) and reports the handoff carrier for implement mini-mode. The agent does NOT commit anything, and does NOT write the fix — splitting RED (this skill) and GREEN (implement mini-mode) across two dispatches keeps the diagnosis honest. The orchestrator decides whether to commit the RED test as a separate audit-trail commit before dispatching implement mini-mode, or to hand the dirty working tree directly to mini-mode (the mini-mode orchestrator's Phase-0 clean-tree check will refuse the latter — so for an audit-trail-preserving flow the orchestrator commits the RED test first; for a streamlined-fix flow the orchestrator commits the combined RED+GREEN at the end of mini-mode).

Handoff Contract

debug produces, for implement mini-mode:

Field	Content
`red_test_path`	absolute path to the failing test file — minimal and autonomous (Phase 3)
`cause_summary`	1-2 sentences naming the file + function + why
`constraint`	`"minimal fix, no surrounding cleanup"`

Anything else (broader refactor, doc rewrite, new feature) is OUT of scope for the bug-fix iteration and gets queued for a separate one.

Cross-references

Agent dispatched: agents/debugger.md — carries the four-phase process, the Phase 4.5 escalation rule, the Common Rationalisations table, and the Red Flags list. The orchestrator does not execute these phases directly.
Hand-off target: ../implement/SKILL.md — runs the GREEN side after the orchestrator has decided whether to commit the RED test separately or as part of the final fix commit.

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