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

selfhost/, cmd/, internal/ join the tree-wide sweep: every section
banner dies (91 selfhost + the cmd C-style dividers -> 0); narration
and stale contracts deleted (pre-#22 bundler notes, retired
single-PT_LOAD and no-archive claims, superseded ABI tables); every
ref/harec/qbe cite, task cite, encoding/ELF contract, and rule-10
twin pointer kept; lost lifetime/rationale lines restored where the
sweep over-cut (elf_globals ownership, kwtab linear-scan). Comment-
only proven: all five wwstage tool binaries byte-identical across
the sweep; test-commit, test-byteid (161+1399, 0 pinned-divergent),
and test-bootstrap (fixed point + 991-995 byte-id) all exit 0.
The read-through banked 66 latent-bug leads (checkpoint).

cmd/wcc/mem.c

@@ -1,11 +1,8 @@
 /*
- * mem.c — arena allocator. No free per allocation; freearena releases
- * the whole chain. Aligned to 16 so structs with 8-byte fields and
- * doubles are happy.
- *
- * Hot allocations in the compiler land in arenas: tokens, AST nodes,
- * symbols, types. The chunk size doubles up to a cap so we don't
- * fragment on huge inputs.
+ * No free per allocation; freearena releases the whole chain.
+ * Aligned to 16 so structs with 8-byte fields and doubles are happy.
+ * The chunk size doubles up to a cap so we don't fragment on huge
+ * inputs.
  */
 #include "ww.h"
 #include <stdlib.h>
@@ -43,7 +40,6 @@ grow(Arena *a, u64 need)
 	if (ncap < need)
 		ncap = roundup(need, ALIGN);
 
-	/* push current chunk onto chain, allocate fresh head */
 	Arena *old = malloc(sizeof *old);
 	if (old == NULL)
 		fatal("arena: oom");