Change Map

Change Map (pre- and post-implementation)

The artifact that answers "where in the codebase does this task live?" — asked twice, on purpose:

• Planned — before a line is written, from the missions: which modules the task expects to add, change, or brush against.
• Actual — after the missions are green and the reviewers have passed, from the real diff: which modules it did.
• Drift — the difference between them. Drift is the deliverable; the two maps exist so it can be computed at all.

Where the other post-implementation skills judge the change — ../review-implementation/SKILL.md asks "is this good code?", ../sync-architecture/SKILL.md asks "do the docs know about it?" — this one only describes its shape. It never reviews code, never edits code, never edits the architecture docs.

Reduction is the point. A task that touched 40 files gets 6 rows; the cap is 10. A map that reads as an inventory of the diff has failed — the tracker's mission summaries already list the files. The map exists to be understood in seconds, months later, by someone who will not read the diff.

ALWAYS check .ab-method/structure/index.yaml FIRST for where tasks and the architecture/domain docs live — paths are user-configurable. The rendering rules, the line types, and a full worked file live in DIAGRAM-FORMAT.md; read it before drawing either pass.

What counts as a module here

Not "a directory". The map partitions the codebase the way this project partitions it, in this order:

1. CONTEXT.md / CONTEXT-MAP.md — the bounded contexts, named in the project's own ubiquitous language. Best source by far: the map then speaks the domain, and a row nobody predicted reads as a context boundary being crossed, not as "another folder changed".
2. docs/architecture/* — documented entry points, layers, and pattern groupings.
3. The source tree — top-level source directories, one level deeper where a directory is large.

A module is a module in the ../codebase-design/SKILL.md sense — an interface with an implementation hidden behind it — and rows are named the way the docs already name it. Never invent a taxonomy the project doesn't use; a map in private vocabulary is unreadable to everyone but the session that drew it.

Pass 1 — the planned map

When: /create-task § 7.6 (after critique-plan, before the user validates the plan) and /extend-task (appended for the new missions). It is drawn from the plan, never from code you wrote.

Inputs: the drafted missions, the grill's constraints and existing-code anchors, the architecture + domain docs, and enough of a read of the named modules to tell [NEW] from [extended].

• One row per module the missions touch, with the missions that touch it in the right-hand column (M2 · M4).
• + lines list only interfaces the plan actually commits to — an endpoint the mission names, a function the grill agreed on, a type the tracker records. If the plan names none, omit the line. A predicted symbol nobody promised is the single thing that makes the later drift meaningless: it turns a prediction into a guess, and drift against a guess measures nothing.
• Seam lines (└ will use, ▲ will be called by) only where a mission genuinely crosses them.
• The → line — one sentence on what this module will do that it doesn't today — is mandatory. A row with an unwritten → is not publishable.

If drawing the map forces you to invent a module, the plan is wrong — not the map. This pass is a second read on the missions: a module you can't attribute to a mission, or a mission whose row you can't place anywhere, is a planning gap critique-plan didn't catch. Say so out loud and fix the missions before the user validates them. That is most of this pass's value; the picture is the by-product.

The planned map is shown to the user in /create-task § 8 alongside the mission list — they are validating the blast radius, not just the sentences.

Pass 2 — the actual map

When: after review-implementation and sync-architecture have run, before the task's status is set to Completed. Not earlier: the reviewers apply safe fixes and commit append-only doc additions, so a map drawn before them describes a diff that no longer exists.

Derive it from the task's commit range, never the working tree:

git diff --name-status -M <base>..<head>   # what changed, and how
git diff --numstat    -M <base>..<head>    # how much, for the verdicts

<base>..<head> is the task's own range — the parent of its first mission commit through the last commit the task made (including the review and doc-sync commits). If the working tree is dirty, say so and commit first; a map of uncommitted work is not reproducible.

Verdicts here are derived, not judged (thresholds in DIAGRAM-FORMAT.md). The + / − lines are exported symbols that exist at head but not base, or the reverse — re-exports and export default are skipped, because a barrel forwarding a symbol is not new logic. A − line is often the most informative thing on the page: it is where the task removed a concept.

Generated and vendored files (lockfiles, migration snapshots, generated route trees, i18n catalogs, build output) are excluded from ranking, so a 9,000-line generated file can't push the real change off the map. They still appear in the also touched: tail.

Write each → line after reading the module — never paraphrased from the symbol names. Names say what moved; only the sentence says what it now does.

Pass 3 — drift

Three findings, in a table (format in DIAGRAM-FORMAT.md):

• Unplanned — in Actual, absent from Planned. The blast radius was wider than the plan said. State why in one clause, citing the mission that reached it. This is the most valuable row on the page.
• Predicted, untouched — in Planned, absent from Actual. Either the plan over-drew the scope (fine — note it and move on) or a mission claimed that module and didn't deliver it (not fine — re-read that mission's summary in the tracker and say so before the task is closed).
• Escalated — the same module, at a heavier verdict than planned ([touched] → [rewritten], [extended] → [NEW] siblings). The plan under-read the work.

A task that landed where its plan said gets exactly one line — No drift — the change landed where the plan said it would. — and that is the good, common outcome for a well-grilled task. Never manufacture drift to look thorough.

What drift is actually for. It routes; it never fixes:

Output — change-map.md

Written next to progress-tracker.md, at docs/tasks/<task>/change-map.md.

• The planned pass creates the file with ## Planned only.
• The actual pass appends ## Actual and ## Drift.

The actual pass never rewrites ## Planned. The planned map is a record of what you believed before you knew, and it stays wrong on the page — editing it to match reality destroys the only thing the file is for.

Modes

Interactive (/create-task, /resume-task, /extend-task, standalone): show the map inline. On the actual pass, walk the drift findings with the user before closing the task.

Autonomous (/start-task, /start-roadmap): write the file, commit it as docs(<task>): change map (repo convention), and put the drift lines in the run's final report. Never prompt — an afk user must not discover a wider-than-planned blast radius by accident.

When there is no planned map

A task created before this skill existed, or one you're mapping standalone, has no ## Planned section. Draw ## Actual and record Drift: no planned map — nothing to compare.

Never back-fill a planned map from the diff. A prediction reverse-engineered from the answer is a lie, and every drift computation that reads the file afterwards inherits it.

What this skill does NOT do

It does not review the change (that's review-implementation), does not update the architecture or domain docs (that's sync-architecture / /update-architecture), and does not edit code. It only describes shape. Keep it that way: judgment living in two places drifts, and a map that argues stops being a map.

Key Principles

• Drift is the deliverable — the two maps are the instrument, not the product.
• Reduction over inventory — 10 rows maximum, siblings collapsed; the mission summaries already list files.
• Predict only what the plan commits to — an invented symbol or module makes the drift measure nothing.
• The planned map is immutable once written — it records a belief, and being wrong is its whole value.
• Never back-fill a prediction from the answer — a task with no planned map has no drift, and that's fine.
• Speak the project's language — rows come from CONTEXT.md and the architecture docs, never a taxonomy you made up.
• Report, never fix — drift routes to /improve-codebase-architecture, /domain-model, or a re-read of a mission.

Remember

• Check .ab-method/structure/index.yaml for paths; read DIAGRAM-FORMAT.md before drawing.
• The planned pass runs after critique-plan (missions may still change) and before the user validates.
• The actual pass runs after review-implementation and sync-architecture — their commits are part of the diff it maps.
• Map the commit range, not the working tree; a dirty tree means commit first.
• Every → is written by you, after reading the module. A map shipped with an unfilled → advertises that nobody read the change.
• The ## Actual block plus its also touched: line is exactly what goes at the top of this task's PR body.