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/simplification/2026-06-20-remove-agent-boundary-mirror-events.md

@@ -1,6 +1,6 @@
 # RFC: Stop mirroring durable boundaries as agent events
 
-Status: implemented (accepted 2026-07-01)
+Status: implemented
 
 <!-- Shipped in AMENDED, narrowed form: the four turn/step BOUNDARY mirrors are
      removed; `agent/steering` and `agent/stream-chunk` were RETAINED here (they
@@ -35,6 +35,11 @@ RETAINED — NOT durable-boundary mirrors, so out of scope for this decision:
 - `agent/stream-chunk` — the live token stream. Out of scope for THIS decision (a mirror of the durable `assistant/chunk`, not a boundary), it was removed by its own follow-up: [Stop mirroring the token stream as an agent event](2026-07-02-remove-stream-chunk-mirror.md).
 - `agent/created`, `agent/disposed`, `agent/status`, `agent/error`, `agent/queued` — lifecycle/control events that are not transcript data. `agent/queued` in particular is an inbox acknowledgement that fires before any durable event exists (cancelled queued work may never enter the log), so it is deliberately live-only.
 
-## What we give up
+## Alternatives considered
+
+- **Bundling `agent/steering` into the removal** — the original proposal's shape; narrowed out as scope creep: it mirrors the durable `steering/message` control record, not a boundary, and was removed by [its own later decision](2026-07-04-remove-agent-steering-mirror.md) (as was `agent/stream-chunk`, by [the stream-chunk-mirror RFC](2026-07-02-remove-stream-chunk-mirror.md)).
+- **Keeping the turn mirrors for the stdio UI** — [the event-domain-semantics RFC](../architecture/2026-06-30-event-domain-semantics.md)'s original stance; rejected here because `dsh-ui-stdio` is a disposable test REPL, not a load-bearing consumer, and it renders boundaries from `session/event` + the id map instead.
+
+## Consequences
 
 A plugin can no longer observe turn/step boundaries from a convenient `Agent`-first event. It must either subscribe to `session/event` or maintain a session-to-agent association. That is an acceptable trade: boundary consumers should not depend on a second event feed that can drift from the durable log.