fed-sx-m1: Step 8d-dispatch-cap — capabilities_body_for + Accept-aware route + 13 tests

next/kernel/http_server.erl

@@ -10,7 +10,8 @@
          post_activity_response/0,
          validation_failed_response/0,
          cid_response/1,
-         accept_format/1, accept_format_from/1]).
+         accept_format/1, accept_format_from/1,
+         capabilities_body_for/1]).
 
 %% HTTP request router per design §16.1.
 %%
@@ -43,6 +44,11 @@ route(Req, Cfg) ->
     case {M, P} of
         {<<80,79,83,84>>, <<47,97,99,116,105,118,105,116,121>>} ->
             handle_post_activity(Req, Cfg);
+        {<<71,69,84>>,
+         <<47,46,119,101,108,108,45,107,110,111,119,110,
+           47,115,120,45,99,97,112,97,98,105,108,105,116,105,101,115>>} ->
+            F = accept_format_from(Req),
+            ok_response(capabilities_body_for(F));
         _ ->
             dispatch(M, P)
     end.
@@ -356,3 +362,30 @@ accept_format_from(Req) ->
                 not_found -> text
             end
     end.
+
+%% capabilities_body_for/1 — content-negotiated capability bodies.
+%% Each format returns a distinct byte sequence so dispatch can be
+%% observed end-to-end. Real serialisation (JSON-LD, dag-cbor, etc.)
+%% lands once the corresponding encoder BIFs are wired; v1 uses
+%% tagged stubs that are syntactically the right shape.
+capabilities_body_for(text) ->
+    capabilities_body();
+%% `{"caps":"fed-sx-m1"}\n` — 21 bytes
+capabilities_body_for(json) ->
+    <<123,34,99,97,112,115,34,58,34,
+      102,101,100,45,115,120,45,109,49,34,125,10>>;
+capabilities_body_for(activity_json) ->
+    %% Same payload as :json — the difference is the Content-Type
+    %% header (Step 8d-content-type follow-up); body shape matches.
+    capabilities_body_for(json);
+%% `(caps "fed-sx-m1")\n` — 19 bytes
+capabilities_body_for(sx) ->
+    <<40,99,97,112,115,32,34,
+      102,101,100,45,115,120,45,109,49,34,41,10>>;
+%% A minimal CBOR map: 0xA1 0x64 "caps" 0x69 "fed-sx-m1"
+%% A1 = map(1); 64 = text(4) "caps"; 69 = text(9) "fed-sx-m1"
+capabilities_body_for(cbor) ->
+    <<161,100,99,97,112,115,105,
+      102,101,100,45,115,120,45,109,49>>;
+capabilities_body_for(_) ->
+    capabilities_body().