docs(rfc): define and enforce a uniform RFC format; adopt it across the corpus

Define the in-file RFC contract in docs/rfc/README.md § The file format:
the header block (`# RFC: <title>` plus a dateless Status enum
cross-checked against the lifecycle folder), the per-lifecycle body
skeleton (a Problem opener everywhere; Proposal/Alternatives considered/
Acceptance criteria/Risks in proposed/; present-tense Decision/
Consequences with proposal-era headings banned in implemented/; the
frozen proposal shape in rejected/), and a mandatory Alternatives
considered section with a date-fenced grandfather comment for pre-format
RFCs whose alternatives are not reconstructible from the record.

Enforce it with a new doc-sync gate, scripts/verify-rfc-format.ts, and
normalize all 112 RFCs to it: ~15 Status-line spellings collapse to the
enum, 29 Context openers become Problem, the 39 legacy-format XXX debt
markers are resolved and banned from reappearing, proposal-era sections
in implemented RFCs are rewritten to shipped reality (including the
web/fs/subagent seam RFCs' migration plans and test checklists, closing
the doc-tiers deferred-work item on the web seam), every RFC gains an
Alternatives considered section or the grandfather comment, and the
bilingual pair is re-mirrored and re-recorded.

Move the generated index tables out of README.md into a fully generated
docs/rfc/INDEX.md — gen-rfc-index now writes the whole file, and
verify-rfc-classification checks its freshness and rejects index-shaped
rows in the curated README — which makes room for the format contract to
live in the README front door instead of a separate FORMAT.md.

The decision record, and the first RFC written in the new format, is
docs/rfc/implemented/process/2026-07-05-uniform-rfc-format.md.

docs/rfc/implemented/process/2026-06-18-markdown-cross-link-lint.md

@@ -1,8 +1,8 @@
 # RFC: Markdown cross-link validity linting
 
-Status: implemented (proposed 2026-06-18, accepted 2026-06-18)
+Status: implemented
 
-## Context
+## Problem
 
 Docs in this repo link to each other by relative path — `[topic](../implemented/2026-…-….md)`, `[the cookbook](adding-a-tool.md)`, `[architecture.md](../../architecture.md)`. Nothing verified those targets exist. A rename or a move silently breaks every inbound link, and the break is invisible until a reader clicks it. [Doc-sync enforcement](2026-06-11-doc-sync-enforcement.md) already mechanized two classes of doc drift (uncompilable code blocks, a stale event-taxonomy table) and [verify-md-wrap](2026-06-11-doc-sync-enforcement.md) a third (hard-wrapped prose) — but a dead cross-link is a fourth, equally mechanical class that was still verified by eyeball.
 
@@ -18,11 +18,14 @@ A fourth `doc-sync` gate, `verify-md-links` (`scripts/verify-md-links.ts`), mirr
 
 Scope matches the other gates plus the AGENTS.md pair and the repo-authored agent-skill Markdown under `.agents/skills/` (those skill files cross-link into the docs tree, so this reorg rewrote links in them too): `README.md`, `docs/**/*.md`, `packages/*/README.md`, `AGENTS.md`, `packages/AGENTS.md`, `.agents/skills/**/*.md`, deduped by real path (the `CLAUDE.md` symlinks resolve onto the AGENTS.md files). It is wired into the `doc-sync` script that the lefthook pre-push hook and CI both run, so a broken link fails locally before a push — consistent with [mechanical quality gates](2026-06-11-quality-gates.md).
 
-This gate checks *existence*, not anchor validity: a link to a real file with a `#wrong-heading` fragment still passes (the file resolves; the fragment is stripped). Anchor-level checking is a heavier, lower-value follow-up — file-level dead links are the failure that actually bit us.
+This gate checks *existence*, not anchor validity: a link to a real file with a `#wrong-heading` fragment still passes (the file resolves; the fragment is stripped).
+
+## Alternatives considered
+
+**Anchor-level validity checking** — heavier and lower-value; file-level dead links are the failure that actually bit. The scope cut is deliberate: authors verify `#fragment` anchors themselves when linking to one.
 
 ## Consequences
 
 - Renames and moves that orphan a cross-link now fail the pre-push hook and CI instead of waiting for a reader to click a dead link. This made the RFC reorganization that introduced the gate self-verifying: the same PR that rewrote forty links also added the check that proves none dangle.
 - One more fast tsx script in the `doc-sync` chain; no new dependency (the mdast/GFM stack is already in devDependencies for `verify-md-wrap`).
-- Fragment/anchor validity remains unchecked — a known, deliberate scope cut.
 - The convention this enforces — cross-reference docs by machine-checkable relative link, never by bare prose or a number — is documented in [docs/AGENTS.md](../../../AGENTS.md) so authors know the gate exists and why.