diagnose

name	diagnose
description	Diagnosis-only investigation of a failure with unknown cause — reproduce, localize, reduce, deliver root cause with evidence. Read-only; an explicit fix request routes by target and tier instead, never here.

diagnose

Find the cause; change nothing.

1. Reproduce. Capture the exact failing command or input and its output. No reproduction → say so and stop; do not guess from symptoms.
2. Localize. Bisect the surface: which layer, module, commit, or input feature flips the behavior. Prefer evidence — logs, minimal harnesses, git bisect — over reading and speculating.
3. Reduce. Shrink to the smallest input or state that still fails.
4. Deliver. Root cause plus its evidence chain, the reduced reproduction, and the smallest fix direction — into NOTES.md when a bundle exists, otherwise the conversation.

Discipline

• Every probe follows a written hypothesis — "I believe X causes this because Y" — then the minimal test that can falsify it. No hypothesis, no probe.
• Three refuted hypotheses in a row: stop treating this as a local bug. Question the architecture — a structural cause or an unsettled design decision is scout work (grill or model), not a fourth probe.
• Red flags that mean return to step 1: proposing a fix before the cause is known, changing several things at once, "probably X" without a check.

Diagnosis is read-only toward production code: instrumentation and harnesses live outside production paths or are reverted before delivery.

An explicit fix request routes by target and tier — production Full-tier scope is implement work (diagnosis becomes its first phase), a small production fix proceeds directly under tier Light, a prototype fix belongs to explore; never downgrade a requested fix to analysis.