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>

debug/SKILL.md

@@ -16,9 +16,11 @@ 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 → RED test → handoff, plus the Phase 4.5 architecture-
-question trigger after three failed hypotheses — lives in
-`agents/debugger.md`. That file is the single source of truth
+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.
 
@@ -77,7 +79,7 @@ RED+GREEN at the end of mini-mode).
 
 | Field | Content |
 |-------|---------|
-| `red_test_path` | absolute path to the failing test file |
+| `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"` |