wwstage: accept module-level const/let slice-from-arrlit (#28)

wwstage rejected a module-level `const/let []T = [arrlit]` global with "let: not assignable"; cstage accepts (textbook Hare, ref/hare/path/stack.ha:30). The arrlit->slice admission in checkletassign was gated local-only; lift it to module scope too, aligning wwstage UP to cstage's arrlit_init_fits (check.c:3406-3409, slice arm 519-520). cstage unchanged.

Two guards the un-gating requires: the n.rhs.lhs=arr stash stays local-only (a module decl keeps its raw N_ARRLIT for DATA emit, so stashing would leave an untyped count node for the pass-3 asserttyped walker); and tuple-element slice globals are excluded at module scope, because the synthesis delegates element checks to isassignable which lacks a strict tuple arm (#38) -- a [](str,*fn) table would over-accept a sig-mismatched &fn that cstage's strict type_assignable rejects (#124) -- so they stay on the existing typeeqast path.

Closes two divergences 944_alias_emit_b7 pinned: Group A (cstage-runs/ww-rejects) migrates to test/lang/slice_global_arg_test.ww (promoted from _runonly, now cs==ww byte-id); Group B converges to a shared emit_slice_data reject with the identical diagnostic.

test/wcc/944_alias_emit_b7_run.c

@@ -4,19 +4,24 @@
  * symmetric K_BUILDERR rejects (slcstr_plain_ctl, slcslc_2lvl) to
  * test/wcc/data/alias_{slcstr_plain,slcslc}/case.ww runww //ww:error.
  *
- * What survives here are the 4 IRREDUCIBLE per-stage rows neither in-language
- * surface can host (ken's emit_slice_data observation cells — load-bearing
- * codegen pins, MUST NOT move):
- *   • slc_2lvl / slc_plain_ctl (Group A): cstage builds+RUNS exit 0; wwstage
- *     LOUD-REJECTS at the let checker ("let: not assignable"). cstage emits the
- *     []my64b / []i64 slice-literal global DATA and runs; the ww checker
- *     rejects every slice-literal global (the #120/#29-kin acceptance
- *     divergence, ken-d2-oracle; pre-slim #66-R2/#29). @test needs ww to
- *     build, //ww:error needs cs to fail — neither fits.
- *   • slcstr_2lvl / slctag_2lvl (Group B): BOTH reject but with DIFFERENT
- *     diagnostics (cs at emit_slice_data 3-way "static-init unsupported"; ww at
- *     the let checker "not assignable") — a held cs!=ww divergence; the two
- *     messages ARE the pin, so each stage's own substring is asserted.
+ * What survives here are the 2 IRREDUCIBLE both-stage emit-reject rows neither
+ * in-language surface can host (ken's emit_slice_data observation cells —
+ * load-bearing codegen pins, MUST NOT move):
+ *   • slcstr_2lvl / slctag_2lvl: a slice-of-{str,tagged} literal GLOBAL is
+ *     admitted by BOTH checkers and then LOUD-REJECTED at emit_slice_data
+ *     ("slice-of-{str,slice,tagged} literal static-init unsupported", a rule-7
+ *     deferred #10 follow-up) in BOTH stages with the IDENTICAL message. @test
+ *     needs a build, runww //ww:error drives one path — a dual-stage emit
+ *     reject fits neither, so each stage's reject is asserted directly here.
+ *
+ * HISTORY (#28): Group A (slc_2lvl []my64b / slc_plain_ctl []i64, cstage-runs /
+ * wwstage-checker-rejects) and Group B's old wwstage HALF (the ww checker
+ * rejected EVERY slice-literal global at "let: not assignable") were both that
+ * pre-#28 divergence. Once the module-scope slice-from-arrlit admission landed
+ * (selfhost check.ww checkletassign), wwstage admits these globals at the
+ * checker exactly as cstage does: Group A converged to cs==ww build+run and
+ * migrated to test/lang/slice_global_arg_test.ww; Group B converged to the
+ * shared emit_slice_data reject below.
  */
 #include <stdio.h>
 #include <stdlib.h>
@@ -105,24 +110,6 @@ run_row(const char *bin, const struct row *r, int i)
 }
 
 static const struct row rows[] = {
-	{ "slc_2lvl",
-	  "package main;\n"
-	  "type my64 = i64;\n"
-	  "type my64b = my64;\n"
-	  "let G: []my64b = [5, 6, 7];\n"
-	  "export fn main() i32 = {\n"
-	  "	if (G[0] + G[1] + G[2] != 18) { return 1; };\n"
-	  "	if (len(G) != 3) { return 2; };\n"
-	  "	return 0;\n"
-	  "};\n", M_CSRUN_WWERR, NULL, "let: not assignable" },
-	{ "slc_plain_ctl",
-	  "package main;\n"
-	  "let G: []i64 = [5, 6, 7];\n"
-	  "export fn main() i32 = {\n"
-	  "	if (G[0] + G[1] + G[2] != 18) { return 1; };\n"
-	  "	if (len(G) != 3) { return 2; };\n"
-	  "	return 0;\n"
-	  "};\n", M_CSRUN_WWERR, NULL, "let: not assignable" },
 	{ "slcstr_2lvl",
 	  "package main;\n"
 	  "type ms0 = str;\n"
@@ -133,7 +120,7 @@ static const struct row rows[] = {
 	  "	return 0;\n"
 	  "};\n", M_BOTHERR,
 	  "slice-of-{str,slice,tagged} literal static-init unsupported",
-	  "let: not assignable" },
+	  "slice-of-{str,slice,tagged} literal static-init unsupported" },
 	{ "slctag_2lvl",
 	  "package main;\n"
 	  "type u0 = (void | i64);\n"
@@ -144,7 +131,7 @@ static const struct row rows[] = {
 	  "	return 0;\n"
 	  "};\n", M_BOTHERR,
 	  "slice-of-{str,slice,tagged} literal static-init unsupported",
-	  "let: not assignable" },
+	  "slice-of-{str,slice,tagged} literal static-init unsupported" },
 };
 
 int