parse: enforce strict-package — reject package-less files (#24a)

Flip the soft-default to a hard "missing package clause" error symmetrically in
both stages (cmd/wcc/parse.c + lib/ww/syntax/parse.ww): the first real decl of a
primary section with empty pathmod/resetmod and no seen clause is now rejected.
Closes the documented soft-default divergence (the 63-wrapper carve-out).

The gate flip can't be split from the migration it breaks, so this is one atomic
commit: ~80 test/wcc wrappers gain `package main;` via a shared wwtestpkg.h
helper, 6 data fixtures plus 17 asm-grep assertions update for the bare->main.<leaf>
root-helper mangle shift, and rt/ declares `package rt;` with @symbol pinning the
bare rt_ensure/rt_malloc linker names.

Root mangling narrows: the executable entry `main` stays bare (existing
carve-out), but root helper symbols become main.X. The #84 cluster is rewritten
to assert main.run distinct from aa.run/test.run; its cgen fix and bare machinery
are retained — still load-bearing for package-less module-reset deps. New
table-driven test 782_strict_package.c (6 rows, both stages).

Retiring //ww:module-reset is deferred to #24b: it is load-bearing (clears the
.wwi pathmod so the body's package clause asserts), not a vestige; fusing its
removal here would be a silent mismatch.

All byte-id gates green; full make test reports "all 335 tests passed".

test/wcc/wwtestpkg.h

@@ -0,0 +1,61 @@
+/*
+ * wwtestpkg.h — strict-package (#24a) test support.
+ *
+ * Inline ww test fixtures historically omitted the `package main;` clause
+ * that the parser now requires (a missing clause is a hard error). These
+ * helpers inject it transparently so the fixtures stay terse, WITHOUT
+ * disturbing fixtures that already declare their own module identity.
+ *
+ * wwtest_fputs is a drop-in for fputs(src, f): it prepends `package main;`
+ * only when writing at the START of a fresh file (ftell == 0) AND the
+ * fixture does not already open with its own `package`/`//ww:module`
+ * directive. The ftell guard keeps multi-part writes and writes to
+ * non-seekable streams (stderr) behaving exactly like plain fputs.
+ */
+#ifndef WWTESTPKG_H
+#define WWTESTPKG_H
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static inline int
+wwtest_has_module(const char *s)
+{
+	const char *p = s;
+	while (p != NULL) {
+		while (*p == ' ' || *p == '\t')
+			p++;
+		if (strncmp(p, "package ", 8) == 0
+		    || strncmp(p, "package\t", 8) == 0
+		    || strncmp(p, "//ww:module", 11) == 0)
+			return 1;
+		p = strchr(p, '\n');
+		if (p != NULL)
+			p++;
+	}
+	return 0;
+}
+
+static inline void
+wwtest_fputs(const char *src, FILE *f)
+{
+	if (ftell(f) == 0 && !wwtest_has_module(src))
+		fputs("package main;\n", f);
+	fputs(src, f);
+}
+
+/* In-process variant: a malloc'd copy of src with the clause prefixed
+ * (unless src declares its own module). Caller frees. */
+static inline char *
+wwtest_wrap(const char *src)
+{
+	const char *pfx = wwtest_has_module(src) ? "" : "package main;\n";
+	size_t np = strlen(pfx), ns = strlen(src);
+	char *b = malloc(np + ns + 1);
+	memcpy(b, pfx, np);
+	memcpy(b + np, src, ns + 1);
+	return b;
+}
+
+#endif