docs(arch): review-001 doc batch — A-4, D-2, D-3, N-1, N-2

Amendment batch (no new decisions, all doc-level):

- A-4: done-round boundary set is the recognized subset — request
  haves filtered through common_haves, the same honest-boundary rule
  as the ack rounds (never honor an unverified have); amendment clause
  in ADR-014 §2, same rule restated in transport.md §fetch.
- D-2: amendment note on ADR-007 step 3 — the per-repo check is
  ADR-011's authorize policy function (static ACL engine fails closed
  on None identity); step order unchanged.
- D-3: authorized-repo marker added to both substrate input tuples in
  transport.md and to backend.md's public-API list (ADR-007's
  type-level enforcement promise is now findable from the transport
  spec).
- N-1: advertisement ref cap is fail-closed (breach is an error, never
  a silent truncation) — transport.md §Limits.
- N-2: RegistryError::NotFound and authorization failure collapse to
  the same wire error at the variant→wire mapping — transport.md
  §error taxonomy.
- review 001: A-4/D-2/D-3/N-1/N-2 marked resolved.

Verification: cargo doc --no-deps, cargo test — clean.

docs/architecture/transport.md

@@ -22,12 +22,16 @@ full decision (what each substrate owns and why); the surface is:
 
 - **Duplex session** (the `alk/git` ALPN producer, channels-opened git
   sessions, embedder stream doors) — input: (peer identity, resolved repo
-  id, duplex stream, `Limits`). Encapsulates the split/compat/packetline
+  id, authorized-repo marker, duplex stream, `Limits`). The marker is a
+  type the door/adapter constructs only after the ADR-007 check passes
+  (skipping the check is a type error — ADR-007; D-3). Encapsulates the
+  split/compat/packetline
   bridge, the request reader (delim-aware parsing, `reset()` discipline,
   break-on-error), and the sideband writer.
 - **Stateless session** (smart-http doors, e.g. alkhttp's future `git`
-  feature) — input: (peer identity, resolved repo id, request-reader,
-  response-writer, `Limits`) per http POST; adds the http-framing rules
+  feature) — input: (peer identity, resolved repo id, authorized-repo
+  marker, request-reader, response-writer, `Limits`) per http POST; adds
+  the http-framing rules
   (capability-dump skip, flush-only responses, probe handling). IO-abstract:
   the door supplies reader/writer; see [doors.md](doors.md) for the
   mounting.
@@ -66,7 +70,10 @@ substrate property (per-request state), not a protocol fork.
   get an `acknowledgments` section (`ACK <oid>` per recognized have via
   the backend's `common_haves`, `NAK` when none, flush; never `ready`),
   the `done` round generates closure(wants) − closure(haves) via
-  `GitPackGen`. No cross-round state on either substrate (the client
+  `GitPackGen`, with the boundary set the *recognized* subset (request
+  haves filtered through `common_haves` — the same honest-boundary rule
+  as the ack rounds; never honor an unverified have; ADR-014 §2). No
+  cross-round state on either substrate (the client
   re-sends wants + commons each round — negotiation-captures.md).
   Advertisement text is unchanged: `fetch=wait-for-done`.
 - Pack generation via `GitPackGen` (ADR-004), streamed over sideband on
@@ -118,12 +125,21 @@ grammar-inferred.
 - io errors are terminal (session ends); protocol errors map to pkt-line
   error bands (duplex) or http status + body (stateless). Substrate-level
   `thiserror` enum; no panics in library code (convention 2).
+- At the wire-mapping point (review 001 N-2), `RegistryError::NotFound`
+  and an authorization failure collapse to the same wire error — the
+  unknown-repo ≡ unauthorized indistinguishability rule (ADR-007/ADR-008)
+  holds at the variant→wire mapping, so no variant leaks an existence
+  oracle to the client.
 
 ## Limits
 
 Every session carries `Limits` (ADR-009): negotiation rounds, haves per
 round, receive-pack max size, wall clock, sideband chunk size (fixed
 65000), advertisement ref cap. Missing `Limits` is a type-level error.
+The advertisement ref cap is fail-closed like every other budget
+(review 001 N-1): breach is a session error, never a silent truncation —
+a partial ref list is the worst failure mode an advertisement can have
+(clones appear to succeed).
 
 ## Public API surface (v1)