Stage I: strip dead code -- pump drain loop, SWITCH-MARK-WORK, global interpret depth, native_switch_back_to (FABRIC-3.8 §4 row I)

Each shown dead three ways (FABRIC-3.5 §XXII): the pump loop by its
condition, by construction (birth cap == switch table capacity, every birth
registers) and at run time (probe silent through boot, G interleave, an
8-worker DoE trial and the relay); SWITCH-MARK-WORK by callers, capsules
(source and baked), experiments/tools/logs; the depth counter and back_to
field by having no readers.

Kept: Hera's own pump drain (last timer-paced delivery, Hera only) and the
always-0 readiness CSV columns (a DoE schema call). Acceptance on amd64/
aarch64/riscv64: G interleave unchanged, cfg-0 trial fail=0 2/2 dead,
relay 3, idle growth 0; dict_hash set changed by the removed word
(word_count 531) and identical across ISAs. FABRIC-3.8 stages A-I done.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

include/starkernel/vm/kernel_hermes.h

@@ -543,7 +543,9 @@ typedef struct VM VM;
  * one message per checkpoint, ruled 2026-09-21). Called from
  * execute_colon_word()'s existing cooperative checkpoint in vm_core.c,
  * gated the same way the switch-signal checkpoint already is
- * (sk_vm_at_outermost_interpret()).
+ * (sk_vm_at_outermost_interpret() then; since FABRIC-3.8.md Stage A the
+ * per-VM sk_vm_owns_outermost_frame(), and the global counter is removed,
+ * Stage I).
  *
  * AMENDS SXLIII.5's own claim: "recursive drain is prevented for free"
  * via g_vm_interpret_depth is true (the SAME message cannot drain twice),