docs(architecture): resolve OQ-06/07/08 — per-repo authz, registry backing, CRUD ops

ADR-011 (resolves OQ-08): per-repo authorization — grants live in repo
records keyed on the stable logical identity id (alkcall ADR-025,
referenced); policy is alkgit-core's authorize() function (public+read
anonymous-first-class, write always authenticated+granted); alkgit
stores no identity records; vault placement resolved as nothing to
place in v1.

ADR-012 (resolves OQ-06/OQ-07): registry backing + write surface —
GitRegistryStore write supertrait (alknet ADR-035 read/write split
shape); registry-file default (per-repo record files + in-memory
index, config-seeded, op-mutable, no gitoxide); git/repo/* CRUD ops
shipped External with scope+ownership ACL (create mints ownership and
seeds creator grants; ownership never implies git access); the
two-op-kind classification recorded (open op + call ops from one
crate, per alkcall ADR-047); recorded split trigger for a downstream
platform crate.

Doc sync: backend.md (five-trait family, feature model split,
two-op-kinds), doors.md + overview.md (authorize policy, dual-kind
crate map), open-questions.md (OQ-06/07/08 resolved), README (ADR
table, current state), oq-06 tracker task closed (resolved early).

Verification: cargo test (default + --no-default-features), clippy
-D warnings, fmt --check.

tasks/architecture/oq-06-metadata-backing.md

@@ -1,37 +1,41 @@
 ---
 id: architecture/oq-06-metadata-backing
 name: OQ-06 unblock — metadata-scale requirements arrive
-status: pending
+status: done
 depends_on: []
 scope: narrow
 risk: trivial
 impact: component
 level: research
-tags: [external-trigger, deferred-oq]
+tags: [external-trigger, deferred-oq, resolved-early]
 ---
 
 ## Description
 
 Tracker for OQ-06 (`deferred(scope)`): registry/metadata backing store.
-This task is not actionable work — it tracks whether the blocking
-condition has arrived: concrete metadata-scale requirements (repo count,
-metadata fields beyond id/root/visibility/ACL scope, alkcall-hub
-integration scope). When they exist, mark completed; OQ-06 transitions to
-`open`.
+**Resolved early (2026-09-21, ADR-012)** before the blocking condition
+arrived: the deferral's premise was wrong — the deferred "metadata-scale
+requirements" only ever gated a *persistence adapter* (future, separate,
+additive), never the default backing. The default (`registry-file`
+feature: per-repo record files + in-memory index, config-seeded,
+op-mutable) is file-scale by design under the alknet repo/adapter
+pattern. Marking done closes the tracker.
 
 ## Work
 
-None by default. On trigger: set OQ-06 to `open` and schedule the backing
-decision session.
+None. OQ-06 is resolved by
+`docs/architecture/decisions/012-registry-backing-and-ops.md` (§1–2, §4).
 
 ## Verification
 
-- OQ-06 status matches `docs/architecture/open-questions.md`.
+- OQ-06 status matches `docs/architecture/open-questions.md` (resolved).
 
 ## Out of scope
 
-- Choosing the backing store.
+- Building a persistence adapter (gated on a real deployment need —
+  additive, no tracker needed until then).
 
 ## Summary
 
-> Filled on completion.
+Resolved early via ADR-012: the repo/adapter pattern made the default
+independent of scale requirements; the deferral dissolved.