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/vm/stadium.h

@@ -180,6 +180,21 @@ typedef char stadium_capacity_tick_configured_check[(STADIUM_CAPACITY_TICK > 0)
  */
 int stadium_boot_init(void);
 
+/*
+ * The Stadium keyed by a v4 node's number (#189; Captain Bob, 2026-11-13: "A new node key").
+ * stadium_node_key(node) -- a node's key: "NODE" in the high word, the node's number in the low; never
+ *   Hera's all-zero key or none's all-ones, and the same each time.
+ * stadium_boot_init_for(first) -- stadium_boot_init(), with `first`'s key in the first quota where
+ *   stadium_boot_init() puts Hera's (it is stadium_boot_init_for(vm_uuid_hera())).
+ * stadium_birth_node(key, name) -- stadium_birth_hera() for any key: the node is patron zero, on cell
+ *   0, its session registered under `name` and pinned. 0, or -1 as stadium_birth_hera().
+ * v3's path keeps vm_uuid_hera() and stadium_birth_hera() (docs/v4.0.0/MACHINE.md 7, item 3).
+ */
+#define STADIUM_NODE_KEY_HI 0x4E4F444500000000ULL     /* "NODE" */
+VMUuid stadium_node_key(uint32_t node);
+int    stadium_boot_init_for(VMUuid first);
+int    stadium_birth_node(VMUuid key, const char *name);
+
 /* stadium_is_initialized - Whether stadium_boot_init() has succeeded. */
 int stadium_is_initialized(void);