docs(architecture): record OQ-09 — slim-crate model under discussion

New open question capturing the doors-as-family-infrastructure
direction: alkssh (planned) becomes the ssh door for git, git is a
payload service exposed by downstream doors (alkhttp, alkssh, alknet),
and the crate set may slim to protocol crates + http adapter (kept in
alkgit, Slim-A, or promoted to an alkhttp git feature, Slim-B).

OQ-09 carries the three sub-decisions (alkgit-ssh deletion vs
temporary russh scaffolding; http adapter home; alkgitd consumption
path) and cross-references ADR-006 (now flagged as possibly superseded
before finalization) and OQ-01. Deferred summary table updated.

docs/architecture/README.md

@@ -52,8 +52,9 @@ Note: ADR-001's crate table and ssh.md record the v1 ssh-door decision
 
 All unresolved questions are tracked in [open-questions.md](open-questions.md)
 with stable OQ-IDs, priorities, and cross-references. Highest-priority opens:
-OQ-01 (http adapter home / composability, blocks ADR-006 finalization),
+OQ-09 (slim-crate model: doors as family infrastructure — may supersede
-OQ-06 (metadata store backing), OQ-08 (identity sources per front door).
+ADR-006/001 shape), OQ-04 (receive-pack validation), OQ-06 (metadata store
+backing), OQ-08 (identity sources per front door).
 
 ## Document Lifecycle
 

docs/architecture/decisions/006-http-adapter-composition.md

@@ -1,7 +1,9 @@
 # ADR-006: HTTP adapter composition — router factory in alkgit-http
 
 ## Status
-Proposed (recommendation recorded; final call pending user review — OQ-01)
+Proposed (recommendation recorded; final call pending user review — OQ-01,
+and now also OQ-09, whose slim-crate model may supersede this ADR's
+shape entirely)
 
 ## Context
 
@@ -84,8 +86,8 @@ hatch here is enough.
   reconciliation path).
 
 ## References
-- `docs/research/poc3-findings.md` §"alkhttp fit" (with_extra_routes surface), follow-up 1
+- `poc3-findings.md` §"alkhttp fit" (with_extra_routes surface), follow-up 1
 - `docs/research/vision.md` §"ALPN as a service", §"Sub-crate shape"
 - alkcall ADR-027 (precedent and its limits)
 - ADR-001 (crate decomposition), ADR-002 (session boundary), ADR-007/008/009
-- http.md, OQ-01, OQ-08
+- http.md, OQ-01, OQ-08, OQ-09 (may supersede this ADR)

docs/architecture/open-questions.md

@@ -23,6 +23,7 @@ when their impacts say so; it records how careful the resolution must be.
 
 | OQ | Status | Blocked on / investigation |
 |---|---|---|
+| OQ-09 | open (discussion) | slim-crate model: doors as family infrastructure; subsumes OQ-01 if Slim-B |
 | OQ-04 | deferred(unclear) | receive-pack walkthrough (capabilities, shallow, thin-pack, CAS timing) + push POC |
 | OQ-06 | deferred(scope) | concrete metadata-scale requirements (feeders: OQ-07, OQ-08 outputs) |
 | OQ-05 | deferred(scope) | ecosystem need for sha256 |
@@ -176,3 +177,39 @@ when their impacts say so; it records how careful the resolution must be.
 - **Resolution path**: one dedicated session once OQ-08's identity model
   exists (the ops' shapes depend on what identities/credentials mean).
 - **Cross-references**: ADR-007, OQ-08, alkgitd.md §admin API
+
+### OQ-09: Slim-crate model — doors as family infrastructure, git as a payload service
+
+- **Origin**: user session (2026-09-21); ADR-006, ADR-001, ssh.md
+- **Status**: open — under discussion, no commitment
+- **Door type**: one-way once anything is published (crate deletion and
+  feature-promotion are wire/registry-visible to dependents)
+- **Priority**: high
+- **Impacts**: blocks ADR-006 finalization (OQ-01 is subsumed by this if
+  Slim-B is chosen); reshapes ADR-001 (crate set), ssh.md (delete or
+  defer), OQ-08 (narrows: git consumes door identity), alkgitd's assembly
+  surface, and publish sequencing (alkhttp `git` feature requires
+  alkgit-transport on crates.io first).
+- **Context**: the alk family shares doors — alkhttp exists, alkssh is
+  planned (after alksocks), alknet rewrite coming. Doors wrap alkcall
+  producer/consumer in their wire protocol; services (git, tty, tunnels,
+  socks) are payloads doors optionally expose. git should be a service
+  exposed by downstream consumers rather than owning its own doors:
+  candidate end-state is protocol crates (core + transport) + http adapter
+  either in alkgit or as an alkhttp `git` feature (Slim-B) or kept as
+  alkgit-http (Slim-A). alkssh is where git-over-ssh belongs when it
+  exists — the temporary russh-in-alkgitd decision (ssh.md) is scaffolding
+  either way.
+- **Sub-decisions**: (1) delete `alkgit-ssh` now and defer git-over-ssh to
+  alkssh, or keep temporary russh scaffolding in alkgitd until then
+  (hinges on whether our deployment needs git-over-ssh before alkssh
+  lands); (2) http adapter home — Slim-A (keep alkgit-http, ADR-006
+  Option A as written) vs Slim-B (alkhttp 0.6 `git` feature; requires
+  alkgit published first); (3) if Slim-B, whether `alkgitd` keeps an
+  internal factory consumption path or consumes the alkhttp feature like
+  any downstream.
+- **Resolution path**: dedicated discussion session; decide the three
+  sub-decisions, then rewrite ADR-001/006 and ssh.md (a new ADR superseding
+  the affected parts, per ADR stability rules), and re-scope OQ-08.
+- **Cross-references**: OQ-01, OQ-03, OQ-08, ADR-001, ADR-006, ssh.md,
+  alkgitd.md