feat(doc-standards): documentation tiers, budgets, and the ceiling gate

Standing docs accrete a paragraph per PR with nothing pushing back; the
root AGENTS.md reached 8,130 words in 50 commits with the same rule
stated two and three times. This encodes the counter-pressure:

- docs/AGENTS.md becomes the documentation standard: the tier taxonomy
  (one home per fact), target word budgets, and the slop checklist.
- verify-doc-budgets joins doc-sync: word ceilings for the six
  accretion-prone standing docs, manifest-driven, frozen at current
  sizes and ratcheted down as each doc is brought to target.
- .agents/skills/dsh-doc-standards: the thin placement/audit/red-gate
  workflow over the standard, mirroring the dsh-translate-docs split.
- RFC (implemented/process) records the decision, alternatives, and
  the first audit cycle's deferred work list.

The gate's first catch was the standard itself (1,057 > 1,000); it
ships condensed to 984 words rather than with a raised ceiling.

docs/rfc/implemented/process/2026-07-04-doc-tiers-and-budgets.md

@@ -0,0 +1,36 @@
+# Documentation tiers, budgets, and the ceiling gate
+
+## Context
+
+The repo's standing docs accrete. Root `AGENTS.md` reached 8,130 words through 50 commits in two and a half weeks — each PR appending its own lesson, none displacing anything — until the same rule was stated two or three times inside one file (the pushed-branch rewrite ban ~600 words across two sections; the with-key e2e policy ~400 words across two), an incident already recorded in [postmortem 0001](../../../postmortem/0001-acp-default-export-drops-inject.md) was retold inline at ~750 words, and the per-package one-liner map existed in five places. [architecture.md](../../../architecture.md) grew the same way: paragraph walls re-narrating RFCs it already links, plus implementation-status annotations that were stale the week after they were written. The writing rules that forbid this (document current state, never history) predate the drift and sat in the very file violating them — prose rules alone do not hold against accretion pressure. The repo's standing answer to an invariant of this kind is a mechanical check ([quality gates](2026-06-11-quality-gates.md), [doc-sync enforcement](2026-06-11-doc-sync-enforcement.md)).
+
+## Decision
+
+- **A tier taxonomy with one home per fact.** [docs/AGENTS.md](../../../AGENTS.md) is the documentation standard: it assigns every Markdown tier a single job (standing orders, system map, type catalog, decision records, incident stories, how-tos, per-package contracts, generated catalogs, workflows), forbids restating a fact outside its home tier (link instead), 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`. Reference docs, RFCs, 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 ceiling starts at the doc's current size, freezing growth from day one, and ratchets down as the doc is brought to its target budget (root `AGENTS.md` ≤ 1,500 words; `architecture.md` ≤ 1,800; subtree `AGENTS.md` ≤ 600; `packages/README.md` ≤ 600) — the same rollout mechanism as the [translation-pairing `required` list](2026-07-02-bilingual-docs-and-pairing-gate.md). When the gate goes red the fix is to relocate or condense per the taxonomy; raising a ceiling is permitted only with explicit justification in the PR description, the manifest diff being the reviewable act.
+- **A thin workflow skill, contracts in docs.** [.agents/skills/dsh-doc-standards](../../../../.agents/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](../../../../.agents/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, e.g. `packages/ui/acp/acp-feature-support.md`) 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 now 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.
+- The bring-under-target rewrites land as stacked follow-ups that ratchet the manifest down as they merge; until each lands, its doc's frozen ceiling only prevents further growth.
+- 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.
+
+## Deferred work
+
+The first audit cycle under the standard, in rough priority order (evidence gathered in the survey that motivated this RFC):
+
+- Root `AGENTS.md` rewrite to the ≤ 1,500-word target: rules stay as one-liners plus links; situational clusters move to `docs/testing.md`, `docs/defensive-patterns.md`, and a cookbook guide for responding to review across a stacked PR chain; doc-authoring rules consolidate into `docs/AGENTS.md`.
+- `architecture.md` rewrite to the ≤ 1,800-word target: seam narration compressed to pointers, the MVP feature-to-mechanism checklist moved de-statused into [the extension cookbook](../../../cookbook/extension-cookbook.md), the stale layering-diagram row fixed.
+- `packages/README.md` reduced to the group table plus the dependency rule; the hand-maintained ASCII dependency graph yields to the generated [module-graph.md](../../../module-graph.md); group READMEs become the canonical per-package map.
+- Package README trims where generated catalogs or JSDoc are restated or history is narrated: `packages/ui/acp`, `packages/core/tools`, `packages/bash/tool-bash`, `packages/core/session`, `packages/compact/compact-basic`, `packages/session-persistence/session-persistence`.
+- [The web capability seam RFC](../architecture/2026-06-24-web-capability-seam.md) converted from spec-speak to shipped reality (drop the migration plan and test enumeration, "should" → "is").
+- `docs/core-data-structures/core.md`: drop the JSDoc walls from the `Agent`/`GenerateOptions` type-equiv pastes per that page's own stated rule.
+- [Postmortem 0001](../../../postmortem/0001-acp-default-export-drops-inject.md): merge the overlapping Executive summary and Summary sections.