---
name: writing-plans
description: The spec-to-plan bridge. Routed to by /feature once the brainstormed spec is approved, and by /sprint before execution. Decomposes the spec into 2–5 minute tasks, each carrying its exact file path(s) and a concrete verification step that maps to a tdd obligation. Writes the plan to .codearbiter/plans/<slug>.md, ordered with dependencies flagged and an MVP slice identifiable. Nothing executes until every task has a path and a verification and the task set covers every acceptance criterion.
disable-model-invocation: true
---

# writing-plans

Turn an approved spec into an executable plan. Routed to by `/feature` (after spec approval) and `/sprint`.

## Pre-flight

Read these, or STOP and surface the gap — never plan against an unapproved or missing spec:

- `{{PROJECT_DIR}}/.codearbiter/specs/<slug>.md` — the approved brainstorming spec. The single source of acceptance criteria. Absent or unapproved → STOP and route back to `/feature`.
- `{{PROJECT_DIR}}/.codearbiter/CONTEXT.md` — the `stage:` frontmatter (the maturity value) and project context.
- `{{PROJECT_DIR}}/.codearbiter/tech-stack.md` — file layout, build/test/lint invocations. A verification step cites a real command from here, never a guess.
- `{{PROJECT_DIR}}/.codearbiter/coding-standards.md` — structure and naming, so a task names the right path.

**If `--farm` was requested:** check that `FARM_API_KEY` is set in the environment{{IF:pi}} of the Pi parent process{{ELSE}} (or `.env` at `{{PLUGIN_ROOT}}/tools/.env`){{END}}. If absent, BLOCK immediately — cite `{{PLUGIN_ROOT}}/includes/farm.md` for setup instructions. Do not proceed; the farm dispatcher cannot run without an API key. Model selection happens later (at dispatch time in `subagent-driven-development`), so no model research is needed here.

## Phase 1 — Criterion extraction · gate: BLOCK

Lift every acceptance criterion from the spec verbatim and assign each a stable ID (`AC-01`,
`AC-02`, …). This list is the coverage ledger for the whole plan — Phase 4 checks the task set
against it.

A criterion the spec leaves ambiguous is a `[CONFIRM-NN]` against
`{{PROJECT_DIR}}/.codearbiter/open-questions.md` — surface it, do not invent the intent.

**Backstop the ledger against the spec's own stated intent, mechanically, before trusting it — this
runs even when `brainstorming` already ran the same check, because a hole that survived Phase 3
survives Phase 4's bijection too, silently** (#566): run `"$PY" "{{PLUGIN_ROOT}}/hooks/_intentlib.py"
uncovered-intent {{PROJECT_DIR}}/.codearbiter/specs/<slug>.md [--issue-body <scratch-file>]` —
`<scratch-file>` holds the linked issue's body when one exists (`gh issue view <N> --json body -q
.body > <scratch-file>`, written outside the working tree), omitted when none does. A non-empty
result names an in-scope bullet or an acceptance checkbox the criteria never cited — BLOCK and route
back to `brainstorming` (`{{PLUGIN_ROOT}}/skills/brainstorming/SKILL.md`) to add the missing criterion or record a `[CONFIRM-NN]`; never paper over a
missing criterion by authoring a task for it here instead. This is the LAST point before a hole gets
laundered through Phase 4's bijection, which only checks the ledger against itself and cannot see
past it.

Then ask the half this tool cannot mechanize: **if every `AC-NN` passed and nothing else changed,
what would still be broken?** A real answer names a criterion the ledger is missing even though
every scope bullet and checkbox is technically cited — judgment, not mechanizable, and not satisfied
by a rhetorical "nothing." Finding nothing broken is a reportable result, stated in one line, never a
silent skip.

Gate: every acceptance criterion in the spec captured as a numbered `AC-NN`; the `uncovered_intent`
backstop above returns empty or every finding is resolved; and the negative question has been asked
and answered. A partial ledger does not pass.

## Phase 2 — Task decomposition · gate: BLOCK

Break the work into the smallest honest units. Each **task** is ~2–5 minutes of work and carries:

- **id** — `T-01`, `T-02`, … stable.
- **path(s)** — the exact file(s) the task touches, resolved against `coding-standards.md`. "Some files" is not a path.
- **verification** — one concrete command or observable that proves the task done (e.g., `<test cmd> -k test_token_expiry passes`, `endpoint returns 401 on missing header`). It cites a real `tech-stack.md` invocation or a directly observable behavior — never "looks right".
- **maps-to** — the `tdd` obligation this verification corresponds to. The verification *maps to* a tdd obligation; it does NOT replace tdd's own gates. `tdd` Phase 1 still derives and Phase 4 still verifies obligations against passing tests.
- **covers** — the `AC-NN`(s) this task advances.

Split anything that won't fit ~5 minutes or touches unrelated paths. Reject the trap of one
monolithic "implement the feature" task — that defeats the plan.

Gate: every task has at least one path AND a verification AND a `maps-to`. A task missing any of the
three blocks the plan.

## Phase 3 — Order & MVP slice · gate: BLOCK

Order tasks so each runs only after what it depends on. Flag every dependency explicitly
(`T-07 depends on T-03`). A cycle is a decomposition error — return to Phase 2 and split.

Group the ordered tasks so the **MVP slice** is identifiable: the minimal contiguous task set that
satisfies the spec's core acceptance criteria and is shippable on its own. Everything past the slice
is incremental.

Gate: a complete dependency order with no cycle, and an explicitly marked MVP slice.

## Phase 4 — Bijection proof & write · gate: BLOCK

Cross the ledger against the task set, both directions. **This proves the plan and the ledger AGREE
with each other — it does not prove the ledger itself is COMPLETE relative to the spec's stated
intent.** A criterion missing from the ledger entirely was never a candidate for either check below;
that completeness gap is caught earlier, by Phase 1's `uncovered_intent` backstop (and by
`brainstorming` Phase 3 before that) — never re-derived here, and never implied by this phase's name
(#566: a prior version of this gate read "coverage proof", which a bijective check does not earn).

- Every `AC-NN` is covered by at least one task's `covers`. An uncovered criterion blocks — author the missing task.
- Every task advances at least one `AC-NN`. A task that covers nothing is scope creep — cut it or surface it.

Then write the plan to `{{PROJECT_DIR}}/.codearbiter/plans/<slug>.md` — `<slug>` matching the
spec — with the `AC-NN` ledger, the ordered task table (id · path(s) · verification · maps-to ·
covers · depends-on · **status**, initialized `PENDING`), the marked MVP slice, and any out-of-scope
item tagged inline `[NEEDS-TRIAGE]`.

The status column is the pipeline's resume ledger: `subagent-driven-development` flips a task to
`ACCEPTED` the moment it accepts it, so an interrupted run (crash, compaction, closed session) is
re-entered by `/feature` at the first non-`ACCEPTED` task instead of restarted from brainstorming.

Gate: bijection proven between the plan and the ledger — no criterion without a task, no task without
a criterion — and the plan written to disk. This proves the two are mutually consistent, nothing more;
completeness of the ledger itself was Phase 1's gate, not this one. This clears the path to execution:
`executing-plans` (checkpointed, via `/feature`) or `subagent-driven-development` (autonomous, via
`/sprint`) — each routes every task through `tdd`. The plan never hands off to `tdd` directly.

### Phase 4-farm extension (only when `--farm` was requested)

When `--farm` was requested, after the bijective coverage gate passes and the `.md` plan is written,
produce the farm artifact (`plan.json`) — **one MVP slice at a time** — per
`{{PLUGIN_ROOT}}/skills/writing-plans/references/farm-plan.md`. Load that leaf and follow it;
it owns the per-task failing-test + schema-valid `plan.json` procedure.

Gate: all failing tests written and confirmed failing; `plan.json` written and schema-valid. Both
artifacts exist before handing off to `subagent-driven-development` (`{{PLUGIN_ROOT}}/skills/subagent-driven-development/SKILL.md`).

## Hard rules

- MUST NOT plan against an absent or unapproved spec — STOP and route back to `/feature`.
- MUST NOT emit a task without an exact path AND a concrete verification step.
- MUST NOT let a task's verification stand in for a `tdd` gate — it maps to a tdd obligation, it does not replace one.
- MUST NOT write the plan while any acceptance criterion is uncovered or any task covers nothing.
- MUST NOT guess a verification command — cite `tech-stack.md` or STOP.
- MUST NOT resolve an ambiguous criterion by guessing — raise a `[CONFIRM-NN]`.
- MUST run the `uncovered_intent` backstop and ask the negative-judgment question in Phase 1, and MUST NOT treat Phase 4's bijection proof as a substitute — bijection proves the plan and the ledger agree with each other, never that the ledger is complete (#566).
- MUST NOT emit `plan.json` in `--farm` mode without writing and confirming each failing test first.
- MUST NOT set `meta.model` or `meta.apiBaseUrl` in `plan.json` — these belong to the dispatch step.
- MUST NOT proceed with `--farm` if `FARM_API_KEY` is absent — cite `{{PLUGIN_ROOT}}/includes/farm.md` and BLOCK.
- MUST, at exit, run the follow-up harvest (`{{PLUGIN_ROOT}}/includes/harvest.md`) over any `[NEEDS-TRIAGE]` out-of-scope items — batch-confirm promoting them to `open-tasks.md` (work) or `open-questions.md` (decisions) so they don't die in the plan file.