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/995_self_rebuild.c

@@ -1,18 +1,13 @@
 /*
- * 995_self_rebuild — the wwstage rebuilds itself.
- *
- * Drives ww_ww (the ww-side driver, which shells to w6c_ww/w6a_ww/w6l_ww)
- * over each wwstage tool's source and diffs the result byte-for-byte
- * against the cstage-built binary in $BIN. A green run means the
- * toolchain can recompile itself without touching cc, modulo the
- * cold-start binary — which is the v1.0 lock from PLAN.md.
+ * A green run means the toolchain can recompile itself without
+ * touching cc, modulo the cold-start binary — which is the v1.0 lock
+ * from PLAN.md.
  *
  * This is stricter than `make bootstrap`: that loop only proves the
  * wwdump cgen self-stabilises; this proves every wwstage tool round-
  * trips through the wwstage pipeline.
  *
- * The five tool builds run concurrently: fork() per tool, parent
- * collects each pid with waitpid() and then byte-compares. Wall drops
+ * The five tool builds run concurrently (fork() per tool): wall drops
  * from sum(builds) to max(builds).
  */
 #include <stdio.h>
@@ -84,8 +79,8 @@ struct buildjob {
 	pid_t pid;
 };
 
-/* Fork a child that runs the `ww_ww build` for this tool. The child
- * inherits no concurrent siblings — system() spawns a fresh /bin/sh -c.
+/* The child inherits no concurrent siblings — system() spawns a fresh
+ * /bin/sh -c.
  * stderr lands in <workdir>/build.err so concurrent builds don't merge
  * their diagnostics. `-o <workdir>/main` (T3) makes the driver write its
  * intermediates (main.{s,o} and the sepwork tree) beside the output in <workdir>
@@ -137,8 +132,6 @@ spawn_build(const char *bin, const char *cwd, struct buildjob *j)
 	return 0;
 }
 
-/* Reap one job, byte-diff rebuilt vs canonical, replay captured stderr
- * on build failure, rm workdir. Returns 0 on byte-match, -1 otherwise. */
 static int
 collect_build(const char *bin, struct buildjob *j)
 {