Imported from 2389-research/thrifty (skills/thrifty-plan/SKILL.md). Install upstream with npx skills add 2389-research/thrifty --skill thrifty-plan. Copyright stays with the author.

thrifty-plan — the architect's planning discipline

Your job here is to produce a plan detailed enough that cheap executors (Haiku) can do the work to ~90% with no further decisions, and a checker (Sonnet) can verify each piece objectively. You make every cross-unit decision once, here, so no executor ever has to.

Work in this order. Persist everything to docs/thrifty/<task-slug>/.

0. First: is this even an thrifty job?

thrifty's machinery (contract + briefs + ledger) exists only to keep multiple units consistent. Before planning, check the shape of the work:

• One indivisible artifact, no tiering wanted → don't use thrifty. Just do it.
• One artifact, but you want the cost/quality tiering → run a degenerate plan: skip CONTRACT.md (there are no cross-unit seams to pin), write a single briefs/UNIT-001.md with acceptance criteria, dispatch one Haiku executor, one Sonnet checker. You still get "Haiku drafts, Sonnet verifies" without orchestration.
• Multiple units → continue below.

1. Choose a decomposition mode

"One unit = one file" is only one way to split work. Pick the mode by asking how cohesive the final artifact must be — how seamlessly the pieces must read as one.

Default to partition when pieces are separable. Reach for relay or layered when parallel fragment-writing would produce seams — drifting voice, broken continuity, a committee-written feel. You can also mix: partition a document into chapters, then relay within a chapter.

A good unit, in any mode:

• produces one coherent contribution (a region, the next segment, or one pass),
• can be executed by reading only the contract + its own brief (+ in relay/layered, the current artifact state),
• is small enough for one Haiku pass.

Identify the dependencies. In partition, independent units run in parallel. In relay and layered, the graph is fully linear (each unit depends on the previous and operates on the same artifact). Record the chosen mode in CONTRACT.md.

Prefer fewer, well-bounded units over many tiny ones — each dispatch has overhead.

1b. Choose a planning tier (direct vs split)

Independently of the decomposition mode, decide who writes the per-unit briefs. This trades the architect's own output + context against an extra tier + a translation boundary.

• direct — you (the architect) write the contract AND every brief (this skill, steps 2–5 below). One translation boundary (you → executor). Best for few units, subtle/high-coupling briefs, or correctness-critical work where your judgment must reach the brief intact.
• split — you (the architect / director) write the contract + a terse unit spec per unit, then stop. The orchestrator dispatches parallel Sonnet thrifty-brief writers (one per unit) to expand each spec into a full brief. The bulky brief-writing runs in parallel and your context stays lean. Best for many units (≳ 6) with mechanical / well-trodden briefs, or when running at scale.

You may also go hybrid: write the 1–2 subtle units' briefs yourself and leave the routine ones to the split tier. Record the chosen tier in CONTRACT.md.

In split tier, you do steps 2 + 3-split + 5 below and STOP (the contract, the terse unit specs, and the ledger — not the full briefs). In direct tier you do all of steps 2–5.

2. Write CONTRACT.md

Use ../thrifty/templates/CONTRACT.template.md. This is the cross-unit surface.

The specificity rule — the one test for every line:

Would two different executors, working independently, have to agree on this for their outputs to fit together?

• Yes → it's a seam. Pin it in the contract.
• No (it only affects one unit's interior) → leave it out; it goes in that unit's brief, at the depth Haiku needs.

Calibrate to the executor — and Haiku is strong

This is the governing principle, and it controls your token budget. The exhaustiveness of a contract should scale inversely with the executor's strength:

• local_code_gen writes 600-line, byte-pinned contracts (every field, a cross-module test on every edge, "what fails without this" on every convention) because its executor is a tiny local model (qwen3.6 / gemma) that infers nothing.
• thrifty's executor is Haiku — far stronger. Haiku fills obvious fields, follows idiom, and handles ordinary ambiguity on its own. So pin only what is both cross-unit AND genuinely ambiguous — the few decisions where two capable units would otherwise diverge. Everything Haiku can reasonably infer, leave out.

Because the architect's and checker's (Sonnet) output tokens are the expensive part, terseness is the goal, not thoroughness. When in doubt, write less and let the acceptance criteria catch the rare miss — a cheap checker catch beats expensive over-specification on every unit.

Two cheap habits worth keeping (they remove ambiguity without bulk):

• Make the call on genuine forks. Where a cross-unit decision is truly ambiguous, commit to one answer rather than "X or Y" — but only for decisions that actually cross a boundary. Don't adjudicate within-unit trivia.
• Name shared shapes once. Give a shared type/interface once so units agree on it; you need not enumerate every obvious field — Haiku fills those. Spell a field set out only when getting it wrong would silently break a consumer.

Cross-module tests are an opt-in tool, not a mandate. For most edges, pinning the shared interface is enough for Haiku. Reach for a required cross-module test (a named test in the consumer that feeds a real upstream value through the API) only on a genuinely fragile seam — one where signature drift would slip past unit-level tests. One or two across a whole project, not one per edge.

3-split (split tier only): Write terse UNIT-SPECS, then stop

If you chose the split tier, do NOT write full briefs. Instead write UNIT-SPECS.md — one terse block per unit (the analog of local_code_gen's sprint_descriptions.jsonl) that a Sonnet brief-writer will expand. Each block:

• id + title + objective (1–2 sentences) and owned files/outputs + deps.
• Symbols it defines — by NAME (reference shared shapes in the contract; don't restate them).
• Consumes — the upstream symbols/sections it depends on.
• Criteria-intent — what "done" means at a high level, and any validation command. The brief-writer turns this into concrete tagged criteria.
• (only if the contract pins a cross-module test for an incoming edge) note it so the brief-writer surfaces it. Most units won't have one.

Keep these terse — a few lines each. The point of split tier is that you write little and Sonnet expands; don't pre-write the brief here.

Use ../thrifty/templates/UNIT-SPEC.template.md. Then go to step 5 (ledger) and stop — the orchestrator dispatches the Sonnet brief-writers. Steps 3–4 below are the brief-writers' job in split tier (they run thrifty-brief); they are YOUR job only in direct tier.

3. Write one BRIEF per unit (direct tier)

Use ../thrifty/templates/BRIEF.template.md. Each brief is self-contained: an executor reads the contract + this brief and nothing else.

• Approach at the level Haiku needs — describe what to do, not every keystroke. Pseudocode only where a precise sequence is genuinely load-bearing.
• Name the exact inputs (paths, upstream symbols/sections) the unit consumes.
• State constraints an executor might otherwise get wrong.

4. Set acceptance criteria (the trust contract)

Every brief ends with concrete, checkable acceptance criteria. This is the generalization of "tests as the source of truth" — the checker scores against this list, never against vibes.

Discipline (from simmer-setup): inspect → infer → propose → confirm. You do the thinking; the user validates. Never ask the user to describe what you can read.

1. Infer the criteria for each unit from the task and context.
2. Make each concrete — "what done looks like," not "make it good."
3. Classify each criterion:
   • runnable (preferred when available, especially code) — a command/test the checker executes: pytest passes, curl returns 200, build succeeds.
   • assertional (non-code) — a concrete checklist item: "covers all 5 sources; no claim uncited; under 800 words."
4. Propose + confirm — present the inferred criteria to the user in one message; let them adjust or override.
5. Sufficiency-check skip — if the user already stated the criteria, skip the proposal and use them. The user is never forced to author criteria, but always gets to veto.

Bad criterion: "the CSV export works well." Good criteria: "(runnable) pytest tests/test_csv_export.py passes" + "(assertional) output has a header row and CRLF line endings" + "(assertional) unknown id → 404 ApiError, not a raw dict."

5. Initialize the LEDGER

Use ../thrifty/templates/LEDGER.template.md. One row per unit, all pending, counters at 0, with the dependency column filled from the graph.

Output of this step

In docs/thrifty/<task-slug>/:

• CONTRACT.md with the dependency graph and the chosen modes/tier,
• LEDGER.md initialized,
• direct tier: briefs/UNIT-NNN.md … one per unit, each with acceptance criteria (you wrote them); confirm criteria with the user unless pre-specified.
• split tier: UNIT-SPECS.md with one terse block per unit (you wrote these); the briefs do not exist yet — the orchestrator dispatches Sonnet thrifty-brief writers to produce them, and criteria are confirmed after that.

Return control to the orchestrator for the dispatch phase.