fed-sx-m1: Step 8c-art — GET /artifacts/{cid} route reusing match_prefix + 9 tests

plans/fed-sx-milestone-1.md

@@ -511,7 +511,7 @@ publish(ActorId, ActivityRequest) ->
 - [ ] **8b-start** — `start/1(Port)` spawns an Erlang process hosting `http:listen/2`, requires the dict↔proplist marshaling bridge in the BIF wrapper.
 - [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.
 - [x] **8c-actors-doc** — `match_prefix/2` byte-level path-prefix matcher + GET `/actors/{id}` route returning an `actor: <id>` stub body. `/actors/{id}/outbox` deferred (needs path-segment splitting). `next/tests/http_actors.sh` (13 cases).
-- [ ] **8c-art** — Route `/artifacts/{cid}` (also path-prefix matching).
+- [x] **8c-art** — Route GET `/artifacts/{cid}` via `match_prefix`. Stub body echoes the cid (`artifact: <cid>\n`); real content store lookup deferred. `next/tests/http_artifacts.sh` (9 cases).
 - [ ] **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.
@@ -988,6 +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-art: GET `/artifacts/{cid}` route added on top of `match_prefix`. Single GET dispatch clause now tries `actors_prefix` first, falls through to `artifacts_prefix` — no path collision (different leading bytes). Stub body echoes the CID with `artifact: ` prefix; real artifact-store lookup deferred to later (will key into the registry / genesis bundle). `next/tests/http_artifacts.sh` 9/9 covers happy path, empty-cid 404, POST 404, actor/artifact non-collision, static-route regression. Erlang conformance 729/729.
 - **2026-05-28** — Step 8c-actors-doc: `http_server` extended with `match_prefix/2` — pure byte-level prefix matcher built on Erlang binary pattern matching (`<<B, _/binary>>`-style head/tail walk). Empty prefix returns `{ok, FullPath}`; non-match returns `nomatch`; exact match returns `{ok, <<>>}`. Wired into a new GET `/actors/{id}` clause that extracts the id suffix and returns it as the body of `actor_doc_response/1` (stub: `actor: <id>\n`). Empty id falls into 404. `/actors/{id}/outbox` deferred to a later step (needs segment splitting beyond prefix). `next/tests/http_actors.sh` 13/13. Erlang conformance 729/729.
 - **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.