ask-matt: map the full skill set, add router maintenance rule

Ask Matt was missing five skills that now exist and are user-reachable:
tdd (the red-green engine implement drives), diagnosing-bugs (there was
no route for "something's broken"), domain-modeling and codebase-design
(the two vocabulary references), and grilling (the shared primitive).

- SKILL.md: add a "Something's broken" on-ramp for diagnosing-bugs, a
  "Vocabulary underneath" section for domain-modeling/codebase-design,
  weave tdd into the main flow, flesh out prototype, broaden the
  description from "user-invoked skills" to "the skills".
- docs/engineering/ask-matt.md: re-sync the framing to match.
- CLAUDE.md: add a maintenance rule so any future skill change triggers
  an Ask Matt re-check, beside the existing docs-page re-sync rule.

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

skills/engineering/ask-matt/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: ask-matt
-description: Ask which skill or flow fits your situation. A router over the user-invoked skills in this repo.
+description: Ask which skill or flow fits your situation. A router over the skills in this repo.
 disable-model-invocation: true
 ---
 
@@ -8,13 +8,13 @@ disable-model-invocation: true
 
 You don't remember every skill, so ask.
 
-A **flow** is a path through the skills. Most paths run along one **main flow**, and two **on-ramps** merge onto it. Everything else is standalone.
+A **flow** is a path through the skills. Most paths run along one **main flow**, and two **on-ramps** merge onto it. Everything else is standalone, or a vocabulary layer that runs underneath.
 
 ## The main flow: idea → ship
 
 The route most work travels. You have an idea and want it built.
 
-1. **`/grill-with-docs`** — sharpen the idea by interview. Start here when you **have a codebase**: it's stateful, retaining what it learns in `CONTEXT.md` and ADRs. (No codebase? Use `/grill-me` — see Standalone.)
+1. **`/grill-with-docs`** — sharpen the idea by interview. Start here when you **have a codebase**: it's stateful, retaining what it learns in `CONTEXT.md` and ADRs. (No codebase? Use `/grill-me` — see Standalone. Both run the same `/grilling` primitive; `grill-with-docs` is the one that leaves a paper trail.)
 2. **Branch — can you settle every question in conversation?** If a question needs a runnable answer (state, business logic, a UI you have to see), detour through a prototype, bridged by **`/handoff`** in both directions (see Crossing sessions):
    - **`/handoff`** out, then open a fresh session against that file,
    - **`/prototype`** to answer the question with throwaway code,
@@ -23,7 +23,7 @@ The route most work travels. You have an idea and want it built.
    - **Yes** → **`/to-prd`** (turn the thread into a PRD) → **`/to-issues`** (split the PRD into independently-grabbable issues). Because the issues are independent, **clear context between each one**: start a fresh session per issue and kick off **`/implement`** by passing it the PRD and the single issue to work on.
    - **No** → **`/implement`** right here, in the same context window.
 
-   Either way, `/implement` closes out by running **`/code-review`** — a two-axis review (Standards + Spec) of the diff — before committing. Reach for **`/code-review`** on its own whenever you want to review a branch or PR against a fixed point.
+   Either way, **`/implement`** builds each issue by driving **`/tdd`** internally — one red-green slice at a time — then closes out by running **`/code-review`**, a two-axis review (Standards + Spec) of the diff, before committing. Reach for **`/tdd`** on its own when you just want to build a concrete behaviour test-first without a full spec, and **`/code-review`** on its own whenever you want to review a branch or PR against a fixed point.
 
 ### Context hygiene
 
@@ -39,11 +39,20 @@ A starting situation that generates work, then merges onto the main flow.
 
   Triage is only for issues **you didn't create** — bug reports, incoming feature requests, anything that arrives raw. Issues that `/to-issues` produced are already agent-ready, so **don't triage them**.
 
+- **Something's broken** → **`/diagnosing-bugs`**. For the hard ones: the bug that resists a first glance, the intermittent flake, the regression that crept in between two known-good states. It refuses to theorise until it has a **tight feedback loop** — one command that already goes red on *this* bug — then fixes with a regression test. Its post-mortem hands off to **`/improve-codebase-architecture`** when the real finding is that there's no good seam to lock the bug down.
+
 ## Codebase health
 
 Not feature work — upkeep.
 
-- **`/improve-codebase-architecture`** — run whenever you have a spare moment to keep the codebase good for agents to operate in. It surfaces deepening opportunities; picking one _generates an idea_ you can take into the main flow at `/grill-with-docs`.
+- **`/improve-codebase-architecture`** — run whenever you have a spare moment to keep the codebase good for agents to operate in. It surfaces **deepening opportunities**; picking one _generates an idea_ you can take into the main flow at `/grill-with-docs`. It's the survey that finds the candidates; **`/codebase-design`** (below) is the bench you design the chosen one on.
+
+## Vocabulary underneath
+
+Two model-invoked references that run *beneath* the other skills — each the single source of truth for its vocabulary. Reach for them directly when the **words**, not the process, are the problem; or let the skills above pull them in.
+
+- **`/domain-modeling`** — sharpen the project's *domain* language: challenge a fuzzy term, resolve an overloaded word ("account" doing three jobs), record a hard-to-reverse decision as an ADR. It's the active discipline `/grill-with-docs` drives to keep `CONTEXT.md` a clean glossary.
+- **`/codebase-design`** — the deep-module vocabulary (module, interface, depth, seam, adapter, leverage, locality) for designing a module's *shape*: a lot of behaviour behind a small interface at a clean seam. `/tdd` and `/improve-codebase-architecture` both speak it.
 
 ## Crossing sessions
 
@@ -55,6 +64,7 @@ Not feature work — upkeep.
 Off the main flow entirely.
 
 - **`/grill-me`** — the same relentless interview as `/grill-with-docs`, but for when you have **no codebase**. Stateless: it saves nothing locally, builds no `CONTEXT.md`. Reach for it to sharpen any plan or design that doesn't live in a repo.
+- **`/prototype`** — a small, throwaway program that answers one design question: does this state model feel right, or what should this UI look like. Throwaway from day one — keep the answer, delete the code. It's the detour in step 2 of the main flow, but reach for it any time a design question is hard to settle on paper.
 - **`/teach`** — learn a concept over multiple sessions, using the current directory as a stateful workspace.
 - **`/writing-great-skills`** — reference for writing and editing skills well.