feat(kernel): v4 boots in the kernel's boot -- the Stadium, its checks, the opcode patrons

#189, ENGINE step 4, Phase 1 (plan 2026-11-13-engine-step4-phase1), Tasks
1-4. Captain Bob, 2026-11-13: Q1 "A new node key", Q2 "Per heartbeat
tick", Q3 "All of v3's", Q4 "In Phase 1" / "Full births now", who runs
next "Hera by compudynamics now" (Task 5, to come).

- stadium.c/.h: stadium_node_key(node) ("NODE" | number),
  stadium_boot_init_for(first), stadium_birth_node(key, name);
  stadium_boot_init() and stadium_birth_hera() are them for Hera's key, so
  v3's path is as it was (only an impossible panic's words changed).
- kernel_main.c: the system is chosen and said first, then the Stadium,
  sessions, switch-signal and kernel-Hermes tables for both systems in
  v3's order; v4: Hera, node 10, patron zero under her node key, the word,
  block and opcode layers. The quota self-test and the heartbeat's line
  are functions now, called by both systems.
- sk_v4.c/.h: sk_v4_run() goes -- sk_v4_boot() returns, the kernel's
  checks after POST (opcodes, words, conservation, quota, heartbeat), then
  sk_v4_prompt(). sk_v4_charge_opcodes() at the heartbeat's service points
  (the key wait, after each line) and once after POST.
- stadium_ops.c/.h: a node's 32 opcodes as Stadium patrons (HEAT-OP's
  feed, "Both"): retirements charged as the word layer's dispatches, a
  quantum each, the reservoir's floor kept, shared by retirements when
  short; cooling per tick as words. ~0.5 us a charge on the host: kept.
- qemu_session.py: a v4 acceptance boot fails without "Stadium: N cells",
  "Stadium conservation: CONSERVED" and the heartbeat's ticks (#189).

Tests first (logs/20261113-122142): the physics check failed on the v4
boot; test_stadium_node, test_stadium_ops (and its share case, after a
real boot showed ";" taking all the heat) failed before. Now: kernel host
tests all pass; amd64 v4 boot passes, POST 539/539, dict_hash unchanged,
"Stadium opcodes: 30 resident, hottest opcode 8", CONSERVED; a system=v3
boot prints its Stadium lines as on 2026-11-06.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017RzZgrf7V7Zk2iczBXDRbm

kernel/include/starkernel/v4/sk_v4.h

@@ -10,13 +10,27 @@
 
 #include "uefi.h"   /* BootDisk */
 
-/* Start one StarForth v4 host node from the capsule image linked into the
- * kernel, with its console on the kernel's console, and run it.  Does not
- * return. */
-/* `chain` sets the kernel's block chain up.  It is called when the node has
- * booted and passed POST, before the prompt: as on the v3 path, POST runs
- * against block RAM of its own and the chain comes after it.  `boot_disk` is
- * the loader's: which disk it booted from (sk_v4_identity_boot()). */
-void sk_v4_run(void (*chain)(void), const BootDisk *boot_disk);
+/* Hera's node number: the first node the kernel brings up, as the hosted mesh numbers her
+ * (v4/tests/test_host_unit.c: "it is told it is 10"). The Stadium is keyed by it (#189). */
+#define SK_V4_HERA_NODE 10u
+
+/* Bring one StarForth v4 host node up from the capsule image linked into the
+ * kernel, with its console on the kernel's console: the node, POST, the
+ * blocks, the identity.  It returns; a node that does not start stops the
+ * machine.  `chain` sets the kernel's block chain up: it is called when the
+ * node has booted and passed POST, before the prompt -- as on the v3 path,
+ * POST runs against block RAM of its own and the chain comes after it.
+ * `boot_disk` is the loader's: which disk it booted from
+ * (sk_v4_identity_boot()). */
+void sk_v4_boot(void (*chain)(void), const BootDisk *boot_disk);
+
+/* The prompt: read a line, hand it to the node, say how it ended.  Does not
+ * return.  The kernel calls it after sk_v4_boot() and its own checks (#189,
+ * ENGINE.md step 4, Phase 1: sk_v4_run() went). */
+void sk_v4_prompt(void);
+
+/* Charge the node's opcode counts to its opcode patrons in the Stadium (#189; stadium_ops.h). The
+ * prompt does it as it waits and after each line; the kernel once after sk_v4_boot(). */
+void sk_v4_charge_opcodes(void);
 
 #endif /* STARKERNEL_V4_SK_V4_H */