fed-sx-m1: Step 8d-accept — Accept header parsing (accept_format/1 + accept_format_from/1) + 13 tests

plans/fed-sx-milestone-1.md

@@ -517,7 +517,8 @@ publish(ActorId, ActivityRequest) ->
 - [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.
 - [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.
+- [x] **8d-accept** — `accept_format/1` + `accept_format_from/1` parse the Accept header into `:activity_json | :json | :sx | :cbor | :text`. Priority: activity+json > json > sx > cbor; everything else falls to text. `next/tests/http_accept.sh` (13 cases).
+- [ ] **8d-dispatch** — Wire format dispatch into responses (e.g., the `cid_response`/`actor_doc_response`/etc. emit body shapes matching the chosen format).
 
 **Deliverables:**
 
@@ -996,6 +997,7 @@ 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 8d-accept: `accept_format/1` + `accept_format_from/1` parse the Accept header into a content-negotiation atom. Priority order via successive `match_prefix` checks: application/activity+json → `activity_json`; application/json → `json`; application/sx → `sx`; application/cbor → `cbor`; everything else (including nil / empty / non-binary) → `text`. Comma-separated lists with activity+json first still resolve to activity_json — leading-prefix match is sufficient for v1 envelopes. Step 8d split into 8d-accept (done) + 8d-dispatch (wire into response bodies). `next/tests/http_accept.sh` 13/13. Erlang conformance 729/729.
 - **2026-05-28** — Step 5c-populate: `bootstrap:populate_registry/0` walks `read_genesis` output and calls `registry:register/3` (gen_server API) for each entry. Total return is 31 = 3 + 10 + 7 + 3 + 3 + 2 + 3 across the seven kinds, matching the manifest authored in Step 4. `next/tests/bootstrap_populate.sh` 14/14 verifies per-kind counts + lookups against known names (`activity_types/create`, `object_types/define-activity`, `validators/envelope-shape`). Erlang conformance 729/729.
 - **2026-05-28** — Step 9-pre-fold: in-process integration test proving the full POST → publish → broadcast → projection-fold chain. With `projection:start_link` + `nx_kernel:start_link` + `nx_kernel:with_projections([p_count, p_collect])`, three authorized POST `/activity` calls advance both projections to 3 — and the kernel's log to 3 entries — and the projection's collected activity carries the POST body as `:object`. Unauthorized or sig-failed POSTs leave projection state unchanged. Step 9a/b proper (curl-driven smoke tests) wait on Step 8b-start (TCP) + Define\* SX-source eval bridge, but the structural chain is already verified end-to-end. `next/tests/http_publish_fold.sh` 10/10. Erlang conformance 729/729. Step 9 split into 9-pre-fold (done) + 9a + 9b.
 - **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.