go: after(d) timer stub + 13 pattern tests → runtime 40/40, Phase 5 closed [shapes-scheduler]

Acceptance bar hit (40 runtime, 497 total). Tests: timer ready,
select-with-timeout, fan-in (3 producers), worker queue, pipeline,
fan-out-then-fan-in, select source-order, fallback case, default,
producer-consumer, two-stage pipeline, channel-counter, after+default,
tick-collector.

Shape chiselled: timer collapses "after duration" into
"channel ready immediately" — select needs only ready? from each
case. Real time is when the flip happens, not what the protocol is.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/go/eval.sx

@@ -23,7 +23,8 @@
     (list "append" (list :go-builtin "append"))
     (list "print"  (list :go-builtin "print"))
     (list "make"   (list :go-builtin "make"))
-    (list "close"  (list :go-builtin "close"))))
+    (list "close"  (list :go-builtin "close"))
+    (list "after"  (list :go-builtin "after"))))
 
 (define
   go-env-lookup
@@ -395,6 +396,12 @@
           (not (go-chan? (first vals)))
           (list :eval-error :close-not-chan (first vals))
           :else (do (go-chan-close! (first vals)) nil))
+        (= name "after")
+        ;; v0 stub for time.After: returns a channel already holding a
+        ;; ready value (the duration arg is ignored). Lets `select`
+        ;; with-timeout patterns express the intent even though we
+        ;; don't model real time yet.
+        (let ((ch (go-make-chan))) (go-chan-send! ch :tick) ch)
         :else (list :eval-error :unknown-builtin name)))))
 
 (define