playbook/skills/thirdparty/ask-matt/PHASE-BOUNDARIES.md

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 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.