starkernel: item 3.8 -- VM identifiers as UUID/GUID

Punch list §25 item 3.8 complete. Added after starting item 4.1
surfaced the need to thread a vm_id into stadium_admit()'s new quota
parameter; Captain Bob ruled UUID/GUID rather than keeping the
narrower uint32_t.

New VMUuid type (vm_uuid.h/vm_uuid.c): two uint64_t halves, RFC-4122-
shaped for logging. Not real randomness -- checked directly against
QEMU 10.2.1's actual CPU feature set: amd64 RDRAND and riscv64 Zkr are
both real, available features here; aarch64 has no RNG property on any
CPU model including "max" (verified exhaustively via QMP
query-cpu-model-expansion). Captain Bob ruled a uniform fallback
across all three ISAs rather than a per-architecture split.

Fallback is a deterministic PRNG (splitmix64) seeded from the Mama
capsule's content hash, pre-filling a 16-entry FIFO pool at boot and
refilling with another batch of the same stream when exhausted --
exactly the shape requested. Same capsule booted twice produces the
same id sequence, preserving the dict_hash reproducibility this
session has relied on throughout.

Hera keeps a fixed, reserved all-zero id, not drawn from the pool --
capsule_birth.c uses vm_id == 0 as a load-bearing sentinel in three
places (KILL protection x2, fleet heat-fanout parent-chain
terminator), found by reading before writing any code.

Two real sentinel-collision bugs caught before shipping, same class as
STADIUM_CONTAINS_NONE: vm_uuid_none() (all-ones, not all-zero) for
"not yet assigned"/"no VM" placeholders; confirmed item 3.7's quota
table already used an in_use boolean rather than a vm_id sentinel, so
no second collision was actually possible there -- the dead,
never-referenced STADIUM_QUOTA_SLOT_EMPTY macro was removed.

Blast radius larger than first scoped, flagged mid-work rather than
silently absorbed: capsule_vm_physics.c/.h (the fleet heat-transfer
layer item 2.1 modified earlier this session) has its own vm_id-keyed
node table and walks parent_vm_id chains through the same identity
space, so it needed the same change, plus its callers in
mama_forth_words.c and sk_vm_bootstrap.c.

One live FORTH word contract changed, by explicit ruling: CAPSULE-BIRTH
was ( capsule-id -- vm-id ), a single cell -- can't hold 128 bits.
Captain Bob picked pushing two cells ("there is doubles support in the
FORTH std word set anyway"): ( capsule-id -- vm-id-hi vm-id-lo ).
MAMA-VM-ID changed the same way: ( -- 0 0 ).

Verified: full (not standalone-file) kernel rebuild to catch cross-file
breakage given the size of this change -- it surfaced the
capsule_vm_physics.c blast radius a narrower check would have missed.
Three-architecture boot (amd64, aarch64, riscv64), all reaching ok>
with identical dict_hash=0x3d4e1daf289da94f matching the item-3.7
baseline.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

include/starkernel/vm/stadium.h

@@ -37,6 +37,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include "starforth_config.h" /* STADIUM_CONTAINS_DEPTH_MAX, STADIUM_CAPACITY_TICK, STADIUM_MEMORY_PERCENT */
+#include "starkernel/vm_uuid.h" /* VMUuid -- FABRIC.md item 3.8 */
 
 #define STADIUM_CELL_BYTES 64
 
@@ -272,19 +273,15 @@ int stadium_evict(size_t cell_index);
 /*
  * StadiumVMQuota - per-VM ownership of a subset of the global cell array
  * (FABRIC.md §22.3, item 3.7: "each VM holds its own free-list head index
- * into the global array"). A small table, linearly searched by vm_id --
- * capsule_birth.c's vm_id is monotonic and never reused (next_vm_id only
- * increments, even across VM death), so it cannot index this table
- * directly, and STADIUM_MAX_VM_COUNT is small enough (default 4) that a
- * linear scan costs nothing. Not exposed outside stadium.c: nothing outside
- * needs to inspect quota state directly yet.
+ * into the global array"). A small table, linearly searched by vm_id -- a
+ * VMUuid (item 3.8) can't be used as a direct array index anyway, and
+ * STADIUM_MAX_VM_COUNT is small enough (default 4) that a linear scan costs
+ * nothing. Not exposed outside stadium.c: nothing outside needs to inspect
+ * quota state directly yet. Slot emptiness is tracked by an internal
+ * `in_use` flag, not a vm_id sentinel value -- there is no unused vm_id bit
+ * pattern to reserve for it.
  */
 
-/* Sentinel meaning "no VM owns this slot yet." Distinct from a real vm_id
- * (capsule_birth.c reserves 0 for Hera, so 0 cannot double as "unused" here
- * either -- same shape of mistake STADIUM_CONTAINS_NONE was fixed for). */
-#define STADIUM_QUOTA_SLOT_EMPTY ((uint32_t)-1)
-
 /*
  * stadium_admit - Place a candidate patron header into the Stadium, scoped
  * to vm_id's quota (FABRIC.md §19.3, §22.3, item 3.7).
@@ -301,9 +298,9 @@ int stadium_evict(size_t cell_index);
  * -- the item-3.6 rule that patron zero (Hera) must never actually be
  * selected is a separate, later check at the eviction site.
  *
- * REFUSES if vm_id has no quota granted (only Hera, vm_id 0, has one today
- * -- granted the entire array at stadium_boot_init(), since she is the only
- * VM that exists per item 0.1). Granting quota to additional VMs, and
+ * REFUSES if vm_id has no quota granted (only Hera, vm_uuid_hera(), has one
+ * today -- granted the entire array at stadium_boot_init(), since she is the
+ * only VM that exists per item 0.1). Granting quota to additional VMs, and
  * transferring capacity between them, is capacity ARBITRATION -- item 1.3
  * left "how much capacity moves per eligible transfer" explicitly open, so
  * this item does not invent it. Only the boot-time all-to-Hera grant exists.
@@ -336,7 +333,7 @@ int stadium_evict(size_t cell_index);
  *         quota full and candidate not denser than its least-dense
  *         evictable resident, or it has no evictable resident at all).
  */
-size_t stadium_admit(uint32_t vm_id, const StadiumPatronHeader *candidate);
+size_t stadium_admit(VMUuid vm_id, const StadiumPatronHeader *candidate);
 
 #endif /* __STARKERNEL__ */