Merge pull request #750 from mattpocock/worktree-phase-boundaries

feat: give ask-matt the phase boundary decision tree

.changeset/ask-matt-phase-boundaries.md

@@ -0,0 +1,13 @@
+---
+"mattpocock-skills": patch
+---
+
+Give `/ask-matt` the **phase boundary** decision tree, replacing the two-bullet `Crossing sessions` section.
+
+A **phase** is a chunk of work inside a session — the grilling, the implementation, the QA — and the boundary between two of them is where you decide what to do with the context you've built. The router now carries all five options in order (**continue**, `/clear`, `/handoff`, **subagent**, `/compact`), with the ordered tree and its reasoning disclosed in a new `PHASE-BOUNDARIES.md`. Three fixes come with it:
+
+- **`/handoff` was oversold.** It read as the general bridge between context windows. It's narrow: you need it only when something has to *travel* — a new harness, a new directory, a colleague, or a side task forked mid-phase. What it buys is portability.
+- **`/compact` is the default, not the first reach.** It sits at the bottom of the tree, after the four cheaper or more precise questions above it. Starting there produces a session that's confidently wrong about whatever the summary flattened.
+- **Two branches were missing entirely.** **Continue** is the one to rule out first — it's the only move that keeps the conversation as a primary source rather than a summary of one — and a **subagent** handles anything scoped tightly enough to run AFK.
+
+Context hygiene's escape hatch now says `/compact` rather than `/handoff` (same harness, same directory, at a boundary — the handoff clause doesn't apply), and the smart zone figure is updated from ~120k to ~150k tokens.

docs/engineering/ask-matt.md

@@ -26,6 +26,10 @@ Reach for it whenever you're unsure which skill or flow a situation calls for: y
 
 The idea `ask-matt` gives you to think with is the **flow** — a path *through* the skills rather than a single one. Most work runs along one **main flow** (idea → ship: grill → spec → tickets → implement → review), two **on-ramps** merge onto it (a triage lane for incoming bugs and requests; a codebase-health lane that generates ideas), and everything else is a **standalone** you reach for on its own. Ask a question and you get placed on the right flow, at the right step — not just handed a tool.
 
+## Phase boundaries
+
+The other idea it hands you is the **phase boundary**. A **phase** is a chunk of work inside a session — the grilling, the implementation, the QA — and the boundary between two of them is where you decide what to do with the context you've built up. You have five options: **continue**, **`/clear`**, **`/handoff`**, a **subagent**, or **`/compact`**. `ask-matt` carries the decision tree that orders them, and the two corrections most people need: `/handoff` is narrow — it earns its keep only when something has to *travel* (a new harness, a new directory, a colleague, a side task forked mid-phase) — and `/compact` is the tree's default at the bottom, not its first reach. Reach for the tree at a boundary; mid-phase there's nothing to decide.
+
 ## Where it fits
 
 `ask-matt` is the **router** — the standalone map that sits over the whole set. It is the node every other docs page links back to as [ask-matt](https://aihero.dev/skills-ask-matt), so it never sits *in* a chain; it points *into* every chain. From here you'll most often land on [grill-with-docs](https://aihero.dev/skills-grill-with-docs), the head of the main flow, or [triage](https://aihero.dev/skills-triage), the on-ramp for work you didn't create. When even the router's own picture is stale, its [Source](https://github.com/mattpocock/skills/tree/main/skills/engineering/ask-matt) is the map of record.

skills/engineering/ask-matt/PHASE-BOUNDARIES.md

@@ -0,0 +1,55 @@
+# Phase boundaries
+
+A **phase** is a chunk of work inside a session — the grilling, the implementation, the QA. The definition is fuzzy on purpose: a phase ends when you think *"ok, we're done with that"*.
+
+The **phase boundary** is the gap between two phases, and it is the only place this decision belongs. Mid-phase there is no decision to make — continue, or split the work that's left into subagents. Compacting mid-phase makes the agent lose the thread.
+
+## The five options
+
+| Option       | What it does                                                    |
+| ------------ | --------------------------------------------------------------- |
+| **Continue** | Stay in the session. No context switch at all.                    |
+| **`/clear`** | Empty the context window and start from nothing.                  |
+| **`/handoff`** | Write a portable markdown file and seed a session anywhere with it. |
+| **Subagent** | Send the task to its own context window and get a report back.     |
+| **`/compact`** | Compress this context and seed a fresh session with the summary.  |
+
+## The tree
+
+Work top to bottom at the boundary. The first **yes** wins.
+
+**1. Can you continue in this session?** Two things make the answer yes: the next phase needs this phase as a **primary source**, or you have enough [smart zone](https://www.aihero.dev/ai-coding-dictionary/smart-zone) left (~150k tokens) for the next phase to fit. Grilling → implementation is the standard yes: the implementation wants the reasoning verbatim, not a summary of it. Continue costs nothing and loses nothing, so rule it out before anything else.
+
+**2. Is the context irrelevant to what comes next?** Is everything in this session — the exploration, the decisions, the dead ends — disposable? If so, **`/clear`**. It is the cheapest move on the board: it takes no time and hands back the whole window. `/clear` also isn't terminal — the old session stays resumable.
+
+The cost of getting this wrong is one-way. Clear a *relevant* context and you lose the **why** behind what you built, and no amount of reading the diff back gets it returned.
+
+**3. Do you need to hand off?** `/handoff` is narrow. You need it only when you are:
+
+- swapping to a **new harness** (Claude → Codex),
+- moving to a **new directory** or repo,
+- sending the work to a **colleague**,
+- or forking a side task you found **mid-phase** without derailing what you're doing.
+
+That list is the whole clause. What `/handoff` buys is **portability** — a file that travels. If nothing is travelling, you don't need it.
+
+**4. Can the task be done AFK?** Is it scoped tightly enough to run with you away from the keyboard, no steering? Then send it to a **subagent** and leave this session untouched. Automated review is the standard case: the agent reads the diff and reports, and you aren't needed while it does.
+
+**5. Otherwise, `/compact`.** Relevant context, same harness, same directory, and you need to stay in the loop — this is where the tree lands, and it lands here often. Pass it an instruction (`/compact we're going to QA this area`) so the summary keeps what the next phase needs.
+
+`/compact` is the **default, not the first reach**. It sits at the bottom because the four questions above it are all cheaper or more precise. The failure mode when people start here is a fresh session that is confidently wrong about a decision the summary flattened.
+
+## Primary and secondary sources
+
+Every move except **Continue** turns a **primary source** into a **secondary source** — the session as it happened, replaced by a summary of it. The trade is always the same shape:
+
+| Source                            | Information | Noise | Room to move |
+| --------------------------------- | ----------- | ----- | ------------ |
+| Primary (Continue)                | Full        | Lots  | Little       |
+| Secondary (`/compact`, `/handoff`) | Lossy       | Less  | Lots         |
+
+This is why question 1 comes first. You only pay the lossiness when staying costs more than it saves.
+
+## These are judgement calls
+
+The questions are not objective — each has taste in it, and the same boundary can go two ways on two days. The value is in asking them **in order**, at the boundary rather than in the middle of the work.

skills/engineering/ask-matt/SKILL.md

@@ -15,12 +15,12 @@ A **flow** is a path through the skills. Most paths run along one **main flow**,
 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. 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):
+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 (a prototype lives in its own directory, which is exactly what `/handoff` is for — see Phase boundaries):
    - **`/handoff`** out, then open a fresh session against that file,
    - **`/prototype`** to answer the question with throwaway code,
    - **`/handoff`** back what you learned, and reference it from the original idea thread.
 3. **Branch — is this a multi-session build?**
-   - **Yes** → **`/to-spec`** (turn the thread into a spec), then **`/to-tickets`** to split it into tracer-bullet tickets, each declaring its **blocking edges**. On a local tracker that's one file per ticket under `.scratch/<feature>/issues/`, worked blockers-first by hand; on a real tracker the edges become native blocking links, so any ticket whose blockers are done can be grabbed — kick off **`/implement`** per ticket, **clearing context between each one**.
+   - **Yes** → **`/to-spec`** (turn the thread into a spec), then **`/to-tickets`** to split it into tracer-bullet tickets, each declaring its **blocking edges**. On a local tracker that's one file per ticket under `.scratch/<feature>/issues/`, worked blockers-first by hand; on a real tracker the edges become native blocking links, so any ticket whose blockers are done can be grabbed — kick off **`/implement`** per ticket, **`/clear`ing context between each one**. Each ticket is self-contained, so the last one's context is disposable.
    - **No** → **`/implement`** right here, in the same context window.
 
    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.
@@ -29,7 +29,7 @@ The route most work travels. You have an idea and want it built.
 
 Keep steps 1–3 in **one unbroken context window** — don't compact or clear until after `/to-tickets` — so the grilling, spec, and tickets all build on the same thinking. Each `/implement` then starts fresh, working from the ticket.
 
-The limit on this is the **[smart zone](https://www.aihero.dev/ai-coding-dictionary/smart-zone)**: the window (~120k tokens on state-of-the-art models) within which the model still reasons sharply. If a session approaches it before `/to-tickets`, don't push on degraded — `/handoff` and continue in a fresh thread.
+The limit on this is the **[smart zone](https://www.aihero.dev/ai-coding-dictionary/smart-zone)**: the window (~150k tokens on state-of-the-art models) within which the model still reasons sharply. If a session approaches it before `/to-tickets`, don't push on degraded — `/compact` at the nearest phase boundary and carry on (see Phase boundaries).
 
 ## On-ramps
 
@@ -58,10 +58,17 @@ Two model-invoked references that run *beneath* the other skills — each the si
 - **`/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
+## Phase boundaries
 
-- **`/handoff`** — when a thread is full or you need to branch off (e.g. into a `/prototype` session), this compacts the conversation into a markdown file. You don't continue in place — you **open a new session and reference that file** to carry the context across. It's the bridge between context windows, in either direction. Use it when you want a **fresh session** but need the **current conversation preserved**.
+A **phase** is a chunk of work inside a session — the grilling, the implementation, the QA. At the **boundary** between two of them you have five options, and picking between them is the fuzziest decision in this whole map:
-- **`/compact`** (built-in) — stay in the **same conversation**, letting the earlier turns be summarized. Use it at **intentional breaks between phases**, when you don't mind losing the verbatim history. Don't compact mid-phase — the agent can lose its way. `/handoff` forks; `/compact` continues.
+
+- **Continue** — stay put. Costs nothing, loses nothing.
+- **`/clear`** — empty the window, when nothing here matters to what's next.
+- **`/handoff`** — write a portable markdown file. Narrow: only for a **new harness**, a **new directory**, a **colleague**, or forking a side task **mid-phase**. What it buys is portability.
+- **Subagent** — send a tightly-scoped task to its own window and get a report back.
+- **`/compact`** — compress this context and seed a fresh session with it. The **default**, at the bottom of the tree rather than the first reach.
+
+Read [PHASE-BOUNDARIES.md](PHASE-BOUNDARIES.md) for the ordered tree — the five questions, the reasoning behind each branch, and why the primary-source cost makes **Continue** the one to rule out first. Make the decision **at** a boundary; mid-phase, continue or split the rest into subagents.
 
 ## Standalone