host: Phase 1 — router + handler + GET /feed endpoint on Dream, 28/28

First migrated endpoint onto the SX host. lib/host is a thin wiring layer:
a host handler is a Dream handler (request->response) that calls a subsystem
public API and serialises via a shared JSON envelope.

- handler.sx: host/ok, host/ok-status, host/error, host/json-status (Dream's
  dream-json is 200-only), host/query-int
- router.sx: host/make-app assembles per-domain route groups + /health probe
  into one dream-router (reuses dr/flatten-routes)
- feed.sx: GET /feed reads feed/all + stream combinators, recent-first, with
  ?actor= filter and ?limit= cap
- 3 test suites incl. a golden test (body == subsystem recent stream + envelope)
- conformance.sh mirrors lib/dream's runner

Builds on dream-on-sx (merged, gate green 480/480) rather than a throwaway
native request model; collapses most of plan Phase 4 into Phase 1.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/host/tests/feed.sx

@@ -0,0 +1,98 @@
+;; lib/host/tests/feed.sx — the first migrated endpoint, GET /feed. Includes a
+;; golden test: the host response body must equal the feed subsystem's own
+;; recent-first stream wrapped in the standard envelope — the endpoint adds the
+;; HTTP/JSON shell and nothing else.
+
+(define host-fd-pass 0)
+(define host-fd-fail 0)
+(define host-fd-fails (list))
+
+(define
+  host-fd-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! host-fd-pass (+ host-fd-pass 1))
+      (begin
+        (set! host-fd-fail (+ host-fd-fail 1))
+        (append! host-fd-fails {:name name :actual actual :expected expected})))))
+
+(define
+  host-fd-req
+  (fn (target) (dream-request "GET" target {} "")))
+
+(define
+  host-fd-app
+  (host/make-app (list host/feed-routes)))
+
+;; ── empty feed ─────────────────────────────────────────────────────
+(feed/reset!)
+(host-fd-test
+  "empty feed 200"
+  (dream-status (host-fd-app (host-fd-req "/feed")))
+  200)
+(host-fd-test
+  "empty feed data:[]"
+  (contains? (dream-resp-body (host-fd-app (host-fd-req "/feed"))) "\"data\":[]")
+  true)
+
+;; ── seeded feed ────────────────────────────────────────────────────
+(feed/reset!)
+(feed/post {:actor "alice" :verb "post" :object "p1" :at 1})
+(feed/post {:actor "bob" :verb "post" :object "p2" :at 2})
+(feed/post {:actor "alice" :verb "like" :object "p2" :at 3})
+
+;; recent-first: newest activity (at 3) leads, so its object p2 appears before p1.
+(host-fd-test
+  "timeline recent-first"
+  (let ((body (dream-resp-body (host-fd-app (host-fd-req "/feed")))))
+    (< (index-of body "\"at\":3") (index-of body "\"at\":1")))
+  true)
+
+;; actor filter: only alice's two activities.
+(host-fd-test
+  "actor filter count"
+  (feed/count
+    (feed/by-actor (feed/recent (feed/all)) "alice"))
+  2)
+(host-fd-test
+  "actor filter excludes bob"
+  (contains?
+    (dream-resp-body (host-fd-app (host-fd-req "/feed?actor=alice")))
+    "bob")
+  false)
+
+;; limit: cap to a single activity (the most recent).
+(host-fd-test
+  "limit caps results"
+  (contains?
+    (dream-resp-body (host-fd-app (host-fd-req "/feed?limit=1")))
+    "\"at\":1")
+  false)
+
+;; ── golden: endpoint = subsystem recent stream + envelope ───────────
+(host-fd-test
+  "golden full timeline"
+  (dream-resp-body (host-fd-app (host-fd-req "/feed")))
+  (str
+    "{\"ok\":true,\"data\":"
+    (dream-json-encode (feed/items (feed/recent (feed/all))))
+    "}"))
+(host-fd-test
+  "golden actor-filtered"
+  (dream-resp-body (host-fd-app (host-fd-req "/feed?actor=alice")))
+  (str
+    "{\"ok\":true,\"data\":"
+    (dream-json-encode
+      (feed/items (feed/by-actor (feed/recent (feed/all)) "alice")))
+    "}"))
+
+(define
+  host-fd-tests-run!
+  (fn
+    ()
+    {:total (+ host-fd-pass host-fd-fail)
+     :passed host-fd-pass
+     :failed host-fd-fail
+     :fails host-fd-fails}))