fed-sx-m1: Step 8c-post-publish-http — POST /activity wires through nx_kernel:publish + 10 tests

plans/fed-sx-milestone-1.md

@@ -516,7 +516,7 @@ publish(ActorId, ActivityRequest) ->
 - [x] **8c-post-auth** — `route/2(Req, Cfg)` adds POST `/activity` with bearer-token check. Cfg `:publish_token` is the expected token; missing / wrong / malformed Authorization all return 401. Authorized requests get a stub 200 ("published (stub)"). `next/tests/http_post_activity.sh` (13 cases).
 - [x] **8c-post-publish-pure** — `next/kernel/nx_kernel.erl` — pure-functional kernel orchestrator. `new/3(ActorId, KeySpec, ActorState)` builds the runtime state; `publish/2(Request, State)` calls `outbox:publish` with a Context derived from state, advances log + next_published on success. `next/tests/nx_kernel_pure.sh` (12 cases).
 - [x] **8c-post-publish-srv** — gen_server wrapper around nx_kernel: `start_link/3`, named-process `publish/1`, `query/0`, `log_tip/0`, `with_projections/1`, `stop/0`. `next/tests/nx_kernel_server.sh` (11 cases). HTTP layer integration follows.
-- [ ] **8c-post-publish-http** — Wire the gen-server-backed `nx_kernel:publish/1` into `http_server` POST `/activity` handler.
+- [x] **8c-post-publish-http** — POST `/activity` handler now calls `nx_kernel:publish/1` when the kernel process is registered; falls back to the existing stub when not. Success → 200 with `cid: <cid>\n` body via `cid_response/1`; sig/replay failures → 422 via `validation_failed_response/0`. `next/tests/http_publish.sh` (10 cases).
 - [ ] **8d** — Content negotiation by Accept header: application/activity+json (default), application/cbor, application/json, application/sx.
 
 **Deliverables:**
@@ -991,6 +991,7 @@ 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-post-publish-http: POST `/activity` handler now bridges into `nx_kernel:publish/1` when the kernel gen_server is registered (`erlang:whereis(nx_kernel) =/= undefined`). On success the response carries the canonical CID via `cid_response/1`; on pipeline failure the response is 422 via `validation_failed_response/0`. When the kernel isn't registered, the handler falls through to the existing 200 stub — preserves backwards compatibility for the auth-only tests in `http_post_activity.sh`. Distinct POSTs produce distinct CIDs (next_published counter in nx_kernel state). Unauthorized POSTs never reach the kernel — log tip stays at 0. `next/tests/http_publish.sh` 10/10. The POST `/activity` → publish → fold loop is now functional end-to-end through the kernel. Erlang conformance 729/729.
 - **2026-05-28** — Step 8c-post-publish-srv: `nx_kernel.erl` extended with gen_server callbacks + named-process API. `start_link/3(ActorId, KeySpec, ActorState)` spawns the worker and registers under the literal `nx_kernel` atom; `publish/1(Request)` calls into `handle_call({publish, Request}, ...)` which delegates to the pure `publish/2` and reflects the new state back into the server. `query/0` returns the full state proplist; `log_tip/0` is a direct accessor; `with_projections/1` mutates the projections list. Same port quirks as Step 5b/7b documented (raw Pid return, no `?MODULE`, processes don't persist across separate `erlang-eval-ast` calls — tests inline start_link with operations). `next/tests/nx_kernel_server.sh` 11/11. Erlang conformance 729/729.
 - **2026-05-28** — Step 8c-post-publish-pure: `next/kernel/nx_kernel.erl` — pure-functional kernel orchestrator that wraps `outbox:publish/2` with a long-lived runtime state. `new/3(ActorId, KeySpec, ActorState)` initialises state with an empty log + monotonic `:next_published` counter. `publish/2(Request, State)` builds the publish Context from state, calls outbox:publish, and on success advances `:log` and increments `:next_published`. The counter solves the "same Request published twice" replay collision — each call gets a distinct `:published` timestamp, so the canonical-bytes CID differs and stage_replay doesn't halt. On failure (e.g. bad key), state is returned unchanged. Step 8c-post-publish split into pure (done) + srv (gen_server wrapper) sub-deliverables. `next/tests/nx_kernel_pure.sh` 12/12. Erlang conformance 729/729.
 - **2026-05-28** — Step 8c-post-auth: POST `/activity` route + bearer-token auth via new `route/2(Req, Cfg)` variant. Cfg's `:publish_token` is the expected bearer; mismatched / missing / malformed (no "Bearer " prefix) / empty-token Authorization all surface as 401 `unauthorized_response/0`. `route/1` is a backwards-compatible wrapper with empty Cfg — any POST `/activity` over `route/1` is 401 by design (no token configured). `Bearer ` prefix stripped via the same `match_prefix` helper used elsewhere. Real publish wiring deferred to `8c-post-publish` (needs the kernel orchestrator that holds logs / actor keys / projection list). `next/tests/http_post_activity.sh` 13/13. Erlang conformance 729/729.