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/rejected/architecture/2026-06-11-immutable-public-surfaces.md

@@ -2,8 +2,6 @@
 
 Status: rejected — the pervasive `DeepReadonly<T>` type flip was rejected in favor of an always-on `deriveMessages` clone plus dev-mode `Object.freeze` + invariants. The immutability *goal* shipped via that alternative; see [dev-mode invariants](../../implemented/architecture/2026-06-11-dev-invariants-over-deep-readonly.md).
 
-<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
-
 ## Problem
 
 The session log is append-only by contract, but `session.events` returns `readonly SessionEvent[]` whose *elements* are mutable: a plugin can reach in and rewrite history (`events[0].data.content.push(...)`), silently breaking replay equivalence and the derived-history guarantee. The same applies to derived messages and prompt assemblies passed through waterfalls — mutation is sometimes the intended idiom (waterfall middleware mutates the request) and sometimes corruption (mutating a *logged* event), and the types don't distinguish.
@@ -26,3 +24,5 @@ Introduce `DeepReadonly`, flip the session read paths, fix resulting compile err
 ## Risks
 
 `DeepReadonly` types can produce noisy errors at waterfall boundaries where mutation IS the API — keep the mutable/readonly boundary exactly at "logged vs in-flight" and document it in the session README.
+
+<!-- rfc-format: alternatives-not-recorded (pre-format RFC) -->

docs/rfc/rejected/architecture/2026-06-20-providerless-example-base.md

@@ -25,3 +25,5 @@ The shared base should contain only provider-neutral services and tools: `llm`,
 ## What we give up
 
 Real demos lose one layer of convenience: each must opt into the adapter. That is the right default for examples, because adapter choice is the variable part and providerless wiring is the shared product core.
+
+<!-- rfc-format: alternatives-not-recorded (pre-format RFC) -->