fix: stop the router and READMEs describing the old prototype behaviour

ask-matt still told the agent to 'keep the answer, delete the code',
which prototype-primary-source made false — the prototype is kept on a
prototype/<name> branch and pointed at from the implementation issue.
Both READMEs still called the logic artifact a runnable terminal app;
it is a single shareable HTML file.

README.md

@@ -204,7 +204,7 @@ Skills I use daily for code work.
 
 **Model-invoked**
 
-- **[prototype](./skills/engineering/prototype/SKILL.md)** — Build a throwaway prototype to answer a design question — a runnable terminal app for state/logic questions, or several radically different UI variations toggleable from one route.
+- **[prototype](./skills/engineering/prototype/SKILL.md)** — Build a throwaway prototype to answer a design question — a single shareable HTML file for state/logic questions, or several radically different UI variations toggleable from one route.
 - **[diagnosing-bugs](./skills/engineering/diagnosing-bugs/SKILL.md)** — Disciplined diagnosis loop for hard bugs and performance regressions: reproduce → minimise → hypothesise → instrument → fix → regression-test.
 - **[research](./skills/engineering/research/SKILL.md)** — Investigate a question against high-trust primary sources and capture the findings as a cited Markdown file in the repo, run as a background agent.
 - **[tdd](./skills/engineering/tdd/SKILL.md)** — Test-driven development with a red-green-refactor loop. Builds features or fixes bugs one vertical slice at a time.

skills/engineering/README.md

@@ -21,7 +21,7 @@ Reachable only when you type them (Claude Code: `disable-model-invocation: true`
 
 Model- or user-reachable (rich trigger phrasing so the model can reach for them).
 
-- **[prototype](./prototype/SKILL.md)** — Build a throwaway prototype to answer a design question: a runnable terminal app for state/logic, or several toggleable UI variations.
+- **[prototype](./prototype/SKILL.md)** — Build a throwaway prototype to answer a design question: a single shareable HTML file for state/logic, or several toggleable UI variations.
 
 - **[diagnosing-bugs](./diagnosing-bugs/SKILL.md)** — Disciplined diagnosis loop for hard bugs and performance regressions: reproduce → minimise → hypothesise → instrument → fix → regression-test.
 - **[research](./research/SKILL.md)** — Investigate a question against high-trust primary sources and capture the findings as a cited Markdown file in the repo, run as a background agent.

skills/engineering/ask-matt/SKILL.md

@@ -75,7 +75,7 @@ Read [PHASE-BOUNDARIES.md](PHASE-BOUNDARIES.md) for the ordered tree — the fiv
 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.
+- **`/prototype`** — a small, throwaway program that answers one design question: does this state model feel right, or what should this UI look like. Throwaway is a constraint on how the code is written, not a promise to destroy it: the answer folds into the real code, and the prototype itself is kept as a **primary source** on a `prototype/<name>` branch out of main, pointed at from the implementation issue. 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.
 - **`/research`** — delegate reading legwork to a **background agent**: it investigates a question against **primary sources**, then leaves a cited Markdown file in the repo. Keep working while it reads. The file it produces is something to take *into* the main flow at `/grill-with-docs` — research feeds the thinking, it doesn't replace it.
 - **`/to-questionnaire`** — when the thing blocking you isn't in your head or the codebase but in **someone else's**, this writes them a questionnaire to fill in. It's the inverse of `/grill-me`: instead of interviewing you about the subject, it interviews you about the **send** — who it's going to, what you need back — and aims the questions at the gap. What comes back is material for `/grill-with-docs` or `/to-spec`.
 - **`/wizard`** — for the steps only a **human** can take: clicking through a third-party dashboard, running a one-off migration, moving the project from state A to state B. It generates an interactive bash script that opens each URL, captures each value, and writes it into `.env` and GitHub secrets — so the procedure stops being something you re-explain to an agent every time. If the agent could just do it itself, it should; reach for this only where a human is genuinely in the loop.