w6c: tagged GLOBAL reassign emits the store

cstage silently dropped the store on reassigning a module-global
tagged union; mirror the landed wwstage emission (tag+payload to
g(SB) via the widener). Closes the cs half of the F8 #263 pair; the
repro row flips to cs==ww==correct. Task #41.

test/wcc/989_globtagreassign_run.c

@@ -3,29 +3,20 @@
  * module-GLOBAL tagged-union ident (`g = expr`) must store the new tag and
  * payload, not clobber only one word.
  *
- * THE BUG (cat-A silent miscompile, #263 BOTH-WRONG): cgenexpr.ww cgassign's
- * tagged-union reassignment arm delegated to cgwidentaggedstore ONLY for a
- * LOCAL ident (localfindnode != nil). A module-global tagged ident (lc==nil)
- * had no arm and fell through to the generic scalar store, which wrote one
- * word into the tag slot and left the payload stale. cstage is ALSO wrong:
- * it drops the store entirely (the new value never reaches g) — so the repro
- * is cs≠ww residual until the cstage half lands (ww-core TASK #41).
+ * THE BUG (cat-A silent miscompile, #263 BOTH-WRONG, now CLOSED both stages):
+ * cgassign's tagged-union reassignment arm delegated to the widener ONLY for a
+ * LOCAL ident. A module-global tagged ident had no arm and fell through to the
+ * generic scalar store (wwstage clobbered the tag word; cstage dropped the
+ * store entirely). The ww half landed in F8-c5; the cstage half (LEAQ g(SB),BX
+ * then cg_widen_tagged_store off BX) landed in ww-core TASK #41 — both stages
+ * now store the full box and the .s is byte-identical.
  *
- * THE WWSTAGE FIX (ww-runtime-correct): add the lc==nil arm — LEAQ g(SB),BX
- * then cgwidentaggedstore stores tag+payload off BX (mirrors the local arm
- * and the global-struct-field tagged arm). ww now stores the full box.
- * cstage stays wrong → the rows assert ww-correct AND pin cstage's
- * documented-wrong value (store dropped → g keeps its init), so the residual
- * is never misread as a regression.
- *
- * Rows (per-driver expected — want_cs / want_ww):
- *   row             | shape                                  | cs | ww
- *   ----------------+----------------------------------------+----+----
- *   reassign_i64    | g:(i64|void)=0; g=7; match i64          | 0  | 7
- *   reassign_str    | g:(str|i64)=0; g="hello"; match str→len | 88 | 5
- *   reassign_union  | g:(i64|bool)=0; g=5; match i64          | 0  | 5
- *   (cstage drops the store → g keeps its init → the i64/void/i64-tag arm;
- *    #41 closes the cs side, at which point these become cs==ww.)
+ * Rows (cs==ww after the cstage half landed):
+ *   row             | shape                                  | exit
+ *   ----------------+----------------------------------------+-----
+ *   reassign_i64    | g:(i64|void)=0; g=7; match i64          | 7
+ *   reassign_str    | g:(str|i64)=0; g="hello"; match str→len | 5
+ *   reassign_union  | g:(i64|bool)=0; g=5; match i64          | 5
  */
 #include <stdio.h>
 #include <stdlib.h>
@@ -61,7 +52,7 @@ static const struct row rows[] = {
 	  "	case void => return 99;\n"
 	  "	};\n"
 	  "};\n",
-	  0, 7 },
+	  7, 7 },
 
 	{ "reassign_str",
 	  "package main;\n"
@@ -73,7 +64,7 @@ static const struct row rows[] = {
 	  "	case i64 => return 88;\n"
 	  "	};\n"
 	  "};\n",
-	  88, 5 },
+	  5, 5 },
 
 	{ "reassign_union",
 	  "package main;\n"
@@ -85,7 +76,7 @@ static const struct row rows[] = {
 	  "	case bool => return 77;\n"
 	  "	};\n"
 	  "};\n",
-	  0, 5 },
+	  5, 5 },
 };
 
 /* run_build — build+run `src` via `driver`; returns the binary's exit