go: eval.sx — range-over-{slice,map,chan} + 7 tests; break-env fix [nothing]

Phase 5 cont. New go-eval-range-for handles the parser's :range-for
AST shape. Dispatches on the collection's runtime type:

  :go-slice  → bind index + element, iterate by position
  :go-map    → bind key + value, walk entries assoc list
  :go-chan   → bind value, drain until buffer empty (v0 limitation)

Each loop carries:
  - go-range-extend: handles 0/1/2-name binding patterns uniformly
  - go-range-body:   evaluates body whether it's a :block or other shape
  - per-collection loop helper: threads env, catches :break/:continue/
    :return-value/:eval-error sentinels

**Subtle break fix:** loops were previously returning the *pre-loop*
env when break fired, clobbering all assignments made in prior
iterations. Now returns the current iteration's input env (which
carries forward successful iterations' state). Patched for the three
range variants and for the regular for-loop where the same pattern
applied. The shape:

  (= r :break) env    ;; was: (= r :break) original-env

Tests:
  range: slice — sum of 1..5 = 15
  range: slice — key only (index)
  range: map — sum values
  range: channel — collect all buffered
  range: slice with break exits early
  range: slice with continue skips an element
  range: empty slice — body never runs
  range: chan + goroutine producer

runtime 26/26, total 483/483.

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

plans/go-on-sx.md

@@ -320,7 +320,11 @@ Progress-log line → push `origin/loops/go`.
       Recv-into-var (`case v := <-ch`) binds; recv-into-assign
       (`case v = <-ch`) re-binds. Real-Go random selection among
       ready cases deferred (v0 deterministic).
-- [ ] `range` over channels.
+- [x] `range` over slices / maps / channels. New `go-eval-range-for`
+      dispatches on collection type: slice (index+elem), map (key+val),
+      channel (just value). v0 chan-range stops when buffer empties
+      (no preemption to wait for new sends). break exits with the
+      pre-break env (preserving prior-iteration assignments).
 - [ ] `time.After`-like timer channel.
 - **Independent implementation.** Do NOT use lib/guest/scheduler/ — that
   kit doesn't exist yet and depends on this work for its design. See
@@ -603,6 +607,20 @@ Minimal repro: see `lib/go/lex.sx#gl-oct-digit?` and `#gl-match-op`.
 
 _Newest first. Append one dated entry per commit._
 
+- 2026-05-27 — Phase 5 cont.: range-over-{slice,map,channel}. New
+  `go-eval-range-for` dispatches on the collection type:
+    slice → bind index + element, iterate by position
+    map   → bind key + value, iterate over entries assoc list
+    chan  → bind value, drain until empty (v0: no preemption to wait
+            for new sends; real Go blocks until close + empty)
+  break/continue propagate via the existing sentinel scheme.
+  Subtle fix in break-from-loop: was returning the pre-loop env
+  (clobbering prior-iteration assignments); now returns the current
+  iteration's input env so successful iterations stick. Patched for
+  range-slice, range-map, range-chan in one go. +7 tests, runtime
+  26/26, total 483/483. `[nothing]` — collection-iteration semantics
+  are Go-specific; the cross-language scheduler insights are already
+  in the sister-plan diary.
 - 2026-05-27 — Phase 5 cont.: `select` statement evaluation. New
   `go-eval-select-stmt` + `go-select-pick` + `go-select-try-case`.
   Walks cases in declared order: send always ready in v0; recv ready