fed-sx-m1: Step 8c-cap — GET /.well-known/sx-capabilities route + 8 tests

plans/fed-sx-milestone-1.md

@@ -509,7 +509,11 @@ publish(ActorId, ActivityRequest) ->
 - [x] **8a** — `http:listen/2` BIF wrapper in `lib/erlang/runtime.sx` (the briefing's allowed exception). Validates args, bridges Erlang handler funs to SX-callable lambdas via `er-of-sx`/`er-to-sx`, delegates to the native `http-listen` primitive in `bin/sx_server.ml`. Tests verify registration + arg validation (not the blocking listen loop). `next/tests/http_listen_bif.sh` (5 cases).
 - [x] **8b-route** — `next/kernel/http_server.erl`: pure `route/1` dispatch + `ok_response/1`, `not_found_response/0`, `welcome_body/0`. GET / returns welcome; everything else returns 404 (graceful for missing fields). `next/tests/http_route.sh` (11 cases).
 - [ ] **8b-start** — `start/1(Port)` spawns an Erlang process hosting `http:listen/2`, requires the dict↔proplist marshaling bridge in the BIF wrapper.
-- [ ] **8c** — `route/1`: dispatch table for GET /actors/{id}, /outbox, /artifacts/{cid}, /projections, POST /activity (Step 6e auth via bearer token), /.well-known/sx-capabilities, /.well-known/webfinger.
+- [x] **8c-cap** — Route GET `/.well-known/sx-capabilities` (static doc: kernel/version/verbs lines). `next/tests/http_capabilities.sh` (8 cases). Other concrete routes follow.
+- [ ] **8c-actors** — Routes for `/actors/{id}` + `/actors/{id}/outbox` (needs path-prefix matching since `{id}` is dynamic).
+- [ ] **8c-art** — Route `/artifacts/{cid}` (also path-prefix matching).
+- [ ] **8c-proj** — Routes `/projections` (list) + `/projections/{name}` (state).
+- [ ] **8c-post** — POST `/activity` glue: parse body → call `outbox:publish` with bearer-token auth (env var `NEXT_PUBLISH_TOKEN`).
 - [ ] **8d** — Content negotiation by Accept header: application/activity+json (default), application/cbor, application/json, application/sx.
 
 **Deliverables:**
@@ -984,6 +988,7 @@ A few things still under-specified; resolve as work begins.
 Newest first. One line per sub-deliverable commit. Erlang conformance gate
 (`bash lib/erlang/conformance.sh`) must remain 729/729 on every entry.
 
+- **2026-05-28** — Step 8c-cap: GET `/.well-known/sx-capabilities` route + `capabilities_body/0` + `capabilities_path/0` exposed for tests. Body is a small plain-text descriptor with `kernel: fed-sx-m1`, `version: 0.0.1`, `verbs: Create Update Delete` (hand-spelled as integer-segment binary; string-literal segments unusable in this port). `next/tests/http_capabilities.sh` 8/8 covers method+path matching, body content, the existing GET / regression-free. Step 8c split into cap (done) + actors / art / proj / post — the rest need path-prefix matching helpers since `{id}` and `{cid}` are dynamic. Erlang conformance 729/729.
 - **2026-05-28** — Step 8b-route: `next/kernel/http_server.erl` — pure `route/1` request→response dispatch. Request shape `[{method, Bin}, {path, Bin}, ...]`; response `[{status, N}, {headers, []}, {body, Bin}]`. GET / returns 200 with hand-spelled "fed-sx kernel m1" body; everything else returns 404 with "not found" body. Method/path binaries spelled byte-by-byte (string-literal segments would truncate). Split former 8b into 8b-route (done) + 8b-start (needs dict↔proplist marshaling bridge in the BIF wrapper before the spawned `http:listen` call gets useful request fields). `next/tests/http_route.sh` 11/11. Erlang conformance 729/729.
 - **2026-05-28** — Step 8a: `http:listen/2` BIF wrapper added to `lib/erlang/runtime.sx` (the briefing's single allowed scope exception). The BIF takes `(Port, Handler)`, validates Port is an integer and Handler is an Erlang fun (else `badarg`), then builds an SX-callable bridge lambda that marshals request dict↔Erlang term via `er-of-sx`/`er-to-sx` and calls `er-apply-fun` on the handler. Delegates to the native `http-listen` primitive (registered in `bin/sx_server.ml`, native-only). Tests verify registration + arg validation paths (the blocking listen loop itself is not exercised — production callers spawn an Erlang process to host the call). `next/tests/http_listen_bif.sh` 5/5; Erlang conformance preserved at 729/729 despite the runtime.sx edit. Step 8 broken into 8a–8d on the plan.
 - **2026-05-28** — Step 7c: `outbox:publish` now broadcasts the signed activity to every projection process named in `Context`'s `:projections` entry — fired immediately after `log:append`, via `projection:async_fold`. Missing/nil/empty list is a no-op (preserves the Step 6d-publish contract). Stage halts (replay duplicate, sig failure) suppress the broadcast — projection state stays at zero while the activity is rejected. `next/tests/outbox_broadcast.sh` 14/14 covers single + multi projection fan-out, three-publish accumulation, replay-skip, sig-skip, and the projection receiving the post-sign Signed envelope (not the pre-sign skeleton). Erlang conformance 729/729.