# Agent Note: Documentation structure, tiers, and budgets

Status: implemented

English | [中文](2026-07-04-doc-tiers-and-budgets.zh.md)

## Problem

Standing docs accumulated repeated rules, retold incidents, duplicated package maps, and stale Agent Note summaries despite existing writing guidance. That guidance also did not define how a document's place in the hierarchy limits its scope or how ordered teaching differs from lookup-oriented material. Because review alone did not prevent that growth, the repository needed a mechanical budget alongside its documentation taxonomy.

## Decision

- **Structure follows the documentation tree.** [docs/AGENTS.md](../../../../docs/AGENTS.md) is the documentation standard: a document owns detail about its subject, summarizes only the purpose, responsibility, and high-level behavior of direct children, and links to deeper owners. [Agent Notes](../../README.md) remain outside this structural contract. Every human-facing document is a tutorial with an ordered outcome or a reference with an explicit lookup scope; a [postmortem](../../../../docs/postmortem/README.md) is an incident-scoped reference whose chronology records evidence. Tutorials introduce concepts in prerequisite order for the reader's starting knowledge.
- **A tier taxonomy with one home per fact.** The standard assigns every Markdown tier one job, forbids restating a fact outside its home tier, and carries the slop checklist used when writing or reviewing any doc.
- **A narrow, hard budget gate.** [scripts/verify-doc-budgets.ts](../../../../scripts/verify-doc-budgets.ts) joins `doc-sync`: every doc listed in [scripts/doc-budgets.manifest.json](../../../../scripts/doc-budgets.manifest.json) must stay under its word ceiling (`wc -w` semantics, whole file), and a budgeted file that is missing fails the gate so a rename cannot silently orphan its budget. Scope is deliberately only the accretion-prone standing docs — the root and subtree `AGENTS.md` files, `architecture.md`, `packages/README.md`, and the standing policy docs they evict content into (`docs/testing.md`, `docs/defensive-patterns.md`). Reference docs, Agent Notes, and package READMEs are unbudgeted: length is legitimate there when every row is a fact, and review plus the slop checklist govern them.
- **Ceilings are an enforcement frontier that ratchets.** A doc at or below its target keeps at least 5% headroom as its ceiling ratchets down; a doc above target keeps a frozen ceiling that prevents growth until it reaches the target (root `AGENTS.md` ≤ 1,600 words; `architecture.md` ≤ 1,800; subtree `AGENTS.md` ≤ 600 except `packages/AGENTS.md` ≤ 650 and `docs/AGENTS.md` ≤ 1,250; `packages/README.md` ≤ 600). When the gate goes red, relocate or condense; raise a ceiling only with explicit PR justification.
- **A thin workflow skill, contracts in docs.** [.agents/skills/dsh-doc-standards](../../../skills/dsh-doc-standards/SKILL.md) carries the placement/audit/red-gate workflow and defers to the standard as its source of truth, the same split as [dsh-translate-docs](../../../skills/dsh-translate-docs/SKILL.md) over the i18n contract.

## Alternatives considered

- **Skill and review discipline without a gate** — rejected: the accretion above happened while the current-state rule and reviewer attention already existed; a prose rule with no mechanical backstop demonstrably does not hold here, and this repo's own [quality-gates stance](2026-06-11-quality-gates.md) says invariants worth keeping are worth encoding.
- **A broad gate over every doc tier** — rejected: a blanket ceiling punishes exactly the right kind of long doc (a feature matrix or type catalog where every row is a fact) and generates per-file override churn that trains contributors to rubber-stamp raises.
- **Housing the standard inside the skill** — rejected: contracts live in docs and workflows in skills; a standard packed into SKILL.md is invisible to an agent that edits docs without invoking the skill, and `docs/AGENTS.md` already loads as subtree instructions for anyone working under `docs/`.

## Consequences

- Adding to a budgeted doc requires displacement: relocate the addition to its taxonomy home with a pointer, or condense existing prose to pay for it. Growth without pruning fails CI.
- Structural review starts with ownership and document form before sentence-level editing, so lower-level detail moves to its owner instead of being polished in the wrong place.
- Budgeted docs that remain above target cannot grow; reaching the target restores the 5% working headroom.
- Word count is a crude proxy accepted deliberately: it cannot judge quality, but it forces the relocation decision at exactly the moment content is being added, which is when the author has the context to place it correctly.
