test: banner purge + WHY-only comment sweep (rule 8)

Every section banner dies (103 -> 0) across test/lang, the observer
suites, the C carriers, and the five comment-heavy corpus fixtures;
banner provenance (#N cites, carrier numbers, repair-cluster labels)
folded into headers or adjacent WHY comments. Narration deleted; row
provenance, ref cites, divergence pins, and layout contracts kept
(fwd-ref decl-order guards and bootstrap-gate corpus rationale
restored where the sweep over-cut). Comment-only proven: all 3742
wwbuild workdir .s byte-identical before/after; test-commit and
test-byteid (161 lang + 1399 data, 0 pinned-divergent) green.

test/wcc/300_check.c

@@ -1,9 +1,3 @@
-/*
- * 300_check — type-checker tests.
- *
- * Each row is (src, expect) where expect is "ok" (no errors) or a
- * substring that must appear in the captured stderr.
- */
 #include "ww.h"
 #include <stdio.h>
 #include <string.h>
@@ -54,7 +48,6 @@ runrow(const char *src, const char *expect)
 struct row { const char *src, *expect; };
 
 static const struct row rows[] = {
-	/* OK cases */
 	{ "fn main() void = {};", "ok" },
 	{ "fn id(x: i32) i32 = { return x; };", "ok" },
 	{ "fn add(a: i32, b: i32) i32 = { return a + b; };", "ok" },
@@ -81,14 +74,12 @@ static const struct row rows[] = {
 	  "type point = struct { x: i32 };", "ok" },
 	{ "fn loops() void = { for () { break; }; for () { continue; }; };", "ok" },
 
-	/* multi-return tuples */
 	{ "fn divmod(a: i64, b: i64) (i64, i64) = { return a / b, a % b; };", "ok" },
 	{ "fn dm(a: i64, b: i64) (i64, i64) = { return a, b; };\n"
 	  "fn caller() i64 = { let q, r = dm(10, 3); return q + r; };", "ok" },
 	{ "fn dm() (i64, i64) = { return 1, 2; };\n"
 	  "fn ass() void = { let q: i64 = 0; let r: i64 = 0; q, r = dm(); };", "ok" },
 
-	/* error cases */
 	{ "fn f() void = { return 1; };", "return value in void" },
 	{ "fn f() i32 = { return; };", "not assignable" },
 	{ "fn f() void = { x = 1; };", "undefined" },
@@ -111,7 +102,6 @@ static const struct row rows[] = {
 	  "not enough arguments" },
 	{ "fn f() void = { if (1) { }; };", "if condition" },
 
-	/* tagged-union normalization & exhaustiveness */
 	{ "fn f() (i32 | never) = { return 7; }; "
 	  "fn g() i32 = { return f(); };", "ok" },	/* (T|never) → T */
 	{ "fn f() (i32 | i32) = { return 5; }; "
@@ -130,7 +120,6 @@ static const struct row rows[] = {
 	{ "fn die() never = { for (true) { let _: i32 = 1; }; }; "
 	  "fn f() i32 = { die(); };", "ok" },	/* never assignable to anything */
 
-	/* ? error-subset propagation typecheck */
 	{ "fn inner() (i32 | str) = { return 1; }; "
 	  "fn outer() i32 = { let v: i32 = inner()?; return v; };",
 	  "enclosing function must return a tagged union" },
@@ -155,7 +144,6 @@ static const struct row rows[] = {
 	{ "fn lookup(p: *i32) (*i32 | void) = { return p; };", "ok" },
 	{ "fn lookup() (*i32 | void) = { return; };", "ok" },	/* bare return → null */
 
-	/* `case T` must name a variant of the scrutinee */
 	{ "fn pick() (i32 | str) = { return 1; }; "
 	  "fn caller() void = { let v: (i32 | str) = pick(); "
 	  "match (v) { case let n: i32 => { }; case let s: str => { }; "
@@ -168,7 +156,6 @@ static const struct row rows[] = {
 	  "return 0; };",
 	  "case: f64 is not a variant" },
 
-	/* enum types */
 	{ "type color = enum { RED, GREEN, BLUE };\n"
 	  "fn f() i32 = { return color.GREEN as i32; };", "ok" },
 	{ "type mode = enum u8 { R = 1, W = 2, RW = R | W };\n"