go: goroutine-panic propagation + 8 corner tests → eval 100/100, Phase 6 acceptance cleared [shapes-scheduler]

Wired panic through :go stmt (v0 sync surfaces back to spawner —
matches real Go's "crash whole program" end-effect) and through
go-eval-for (was swallowing panic at the loop boundary).

8 tests added: goroutine-panic-surfaces, goroutine-recover-via-
spawner-defer, multi-defer-LIFO-with-recover, defer-fires-on-panic-
path, panic(nil), panic-in-loop, defer-still-runs-in-panicking-fn,
args-eager-on-panic-path. 20 Phase-6 tests total; +20 acceptance
bar cleared (eval/ 80 → 100).

Shape: 4 control-flow sites now repeat the same sentinel dispatch
arm (return-value, break, continue, eval-error, go-panic). The
scheduler kit should bake in a single propagates? helper rather
than have each guest evaluator list every sentinel inline — diary
documents the cross-cutting abstraction.

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

lib/go/eval.sx

@@ -914,6 +914,8 @@
                 :else (go-for-loop env1 cnd post body)))
             (go-eval-error? r)
             r
+            (go-panic? r)
+            r
             :else (let
               ((env1 (cond (= post nil) r :else (go-eval-stmt r post))))
               (cond
@@ -972,9 +974,16 @@
       (and (list? stmt) (= (first stmt) :defer))
       (go-eval-defer-stmt env stmt)
       (and (list? stmt) (= (first stmt) :go))
+      ;; v0: synchronous spawn. A panic from the spawned expression
+      ;; that the goroutine didn't recover propagates here — real
+      ;; Go would crash the whole program; the sync model surfaces
+      ;; it back to the spawner which has the same end-effect.
       (let
         ((v (go-eval env (nth stmt 1))))
-        (cond (go-eval-error? v) v :else env))
+        (cond
+          (go-eval-error? v) v
+          (go-panic? v) v
+          :else env))
       (and (list? stmt) (= (first stmt) :select))
       (let
         ((r (go-eval-select-stmt env stmt)))