docs(architecture): resolve OQ-04 — receive-pack state machine (ADR-013)

- ADR-013: V0-framed push machine grounded in real git 2.43.0 captures
  (file://, git://, smart-http mock, raw stdio into real receive-pack):
  V0-shaped ref advertisement (caps on first ref line, capabilities^{}
  sentinel only for empty repos), served capability set, shallow requests
  rejected for v1, thin packs accepted with server-odb bases (no
  capability involved; push.thin default), ingestion bound to
  Bundle::write_to_directory_eagerly + gix-fsck + one gix-ref transaction
  per push (.keep-guarded), unpack-first CAS timing with observed
  upstream order, band-1 pkt-line-framed status report, http framing
  (probe/Content-Length/chunked), v1 update policy (CAS only; deletes
  and force-push allowed)
- docs/research/push-captures.md: the normative push wire record
- transport.md/backend.md/doors.md: receive-pack sections rewritten to
  the decided shapes; backend.md ingestion composition bound; stale
  OQ-04 references resolved
- ADR-003 amended: V2-only governs fetch; push is V0-framed by upstream
  design (fixes the V2-only contradiction found in review)
- ADR-009 amended: haves default reconciled with the client's stateless
  ceiling (16384); blocking-pipeline budget covers generation+ingestion
- OQ-04 resolved; tracker task closed; CAS-fail-fast optimization
  tracked (tasks/architecture/oq-13-cas-failfast.md)
- research index: poc findings + capture docs listed

Verification: cargo test / clippy -D warnings / fmt --check / doc pass

docs/architecture/README.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-09-21
+last_updated: 2026-09-25
 ---
 
 # alkgit Architecture
@@ -14,12 +14,14 @@ to a POC finding or research doc, or is flagged as an open question.
 ## Current State
 
 Phase 1, architecture committed to the pure-protocol-crate shape (ADR-010;
-OQ-09 resolved). All docs below are `draft` except the superseded ADRs.
-POC-1/2/3 validated the git protocol half end-to-end against real git
-2.43. This cycle settled the auth/backend theme: per-repo authorization
-(ADR-011, OQ-08), registry backing + write surface + CRUD ops (ADR-012,
-OQ-06/OQ-07). The remaining design work is the receive-pack state machine
-(OQ-04) and V2 multi-round negotiation (OQ-02).
+OQ-09 resolved). POC-1/2/3 validated the git protocol half end-to-end
+against real git 2.43. Previous cycles settled the auth/backend theme
+(ADR-011, ADR-012). This cycle settled the wire surface against
+real-client captures: the receive-pack push state machine (ADR-013,
+OQ-04) and the V2 multi-round negotiation ack loop (ADR-014, OQ-02). All
+wire-layer design is now capture-grounded; the remaining open questions
+are the publish-freeze timing (OQ-03, a release decision) and sha256
+policy (OQ-05, deferred on ecosystem need).
 
 ## Architecture Documents
 
@@ -47,14 +49,16 @@ OQ-06/OQ-07). The remaining design work is the receive-pack state machine
 | [010](decisions/010-pure-protocol-crate.md) | Pure protocol crate (alktty/alktunnels template) | Accepted |
 | [011](decisions/011-per-repo-authorization.md) | Per-repo authorization (grants in records, policy in core) | Accepted |
 | [012](decisions/012-registry-backing-and-ops.md) | Registry backing, write surface, CRUD ops, feature split | Accepted |
+| [013](decisions/013-receive-pack-state-machine.md) | receive-pack state machine (V0-framed push, thin-pack, unpack-first CAS) | Accepted |
+| [014](decisions/014-v2-negotiation-ack-loop.md) | V2 negotiation ack loop (no `ready`, wait-for-done stays) | Accepted |
 
 ## Open Questions
 
 All unresolved questions are tracked in [open-questions.md](open-questions.md)
-with stable OQ-IDs, priorities, and cross-references. Highest-priority
-open: OQ-04 (receive-pack validation). Also open: OQ-02 (multi-round
-negotiation), OQ-03 (publish freeze inventory), OQ-05 (sha256,
-deferred).
+with stable OQ-IDs, priorities, and cross-references. Remaining: OQ-03
+(publish freeze inventory — partially resolved, blocked on first-publish
+timing) and OQ-05 (sha256, deferred on ecosystem need). The wire-layer
+questions (OQ-02, OQ-04) resolved this cycle with ADR-014/ADR-013.
 
 ## Document Lifecycle