Dynamic switch table (B2) -- FABRIC-3.6.md task 3.1

Replaces the fixed SK_SWITCH_MAX_SLOTS=16 compile-time array with a
boot-time, RAM-derived allocation via a new sk_vm_switch_signal_boot_init(),
kmalloc'd to stadium_max_vm_count() entries -- the same pattern
session_boot_init() already established for Stadium-derived sizing.
Every switch-signal participant is a Stadium VM, so this reuses that
bound directly rather than deriving a separate one.

Verified live on all three architectures: switch table sized to 50
slots (amd64), 202 slots (aarch64), 50 slots (riscv64) -- all well
past the old fixed cap. All three boot to [zuse@Hera] ok> cleanly;
dict_hash for Hermes/Hestia identical across architectures, unmoved
from pre-task values.

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

include/starkernel/capsule_vm_switch_signal.h

@@ -49,6 +49,15 @@
  * participants (Hera/Hermes/Artemis) -- extending participation later
  * (Stage 4+) is another sk_vm_switch_signal_register() call, not a
  * redesign.
+ *
+ * FABRIC-3.6.md task 3.1 (2026-09-21, ruled B2 / FABRIC-3.5.md §XLV.2): the
+ * slot table is no longer a fixed SK_SWITCH_MAX_SLOTS=16 compile-time array.
+ * It is kmalloc'd at boot by sk_vm_switch_signal_boot_init(), sized from
+ * stadium_max_vm_count() -- the same RAM-derived population bound Stadium
+ * and session.c already use (session_boot_init() is the direct precedent
+ * mirrored here). Every switch-signal participant is a Stadium VM, so
+ * reusing that bound directly (rather than re-deriving a separate RAM
+ * budget) needs no new sizing formula.
  */
 
 #ifndef STARKERNEL_CAPSULE_VM_SWITCH_SIGNAL_H
@@ -59,17 +68,29 @@
 #include <stdint.h>
 #include "starkernel/vm_uuid.h"
 
+/* Boot-time allocation (FABRIC-3.6.md task 3.1, 2026-09-21): kmalloc's the
+ * slot table to stadium_max_vm_count() entries. Must run after
+ * stadium_boot_init() (that bound is 0, and this fails, until Stadium has
+ * computed it) and before the first sk_vm_switch_signal_register() call.
+ * Soft failure -- returns -1 and leaves the table unallocated (capacity 0,
+ * so register() below simply refuses every registration) rather than
+ * halting boot, same posture as stadium_boot_init()/session_boot_init().
+ * Idempotent-unsafe: calling twice leaks the first allocation, so callers
+ * must call it exactly once. */
+int sk_vm_switch_signal_boot_init(void);
+
 /* Register a VM as a switch-signal participant. Returns its slot index,
- * or -1 if the slot table is full. Call once per participating VM,
- * after that VM is fully born (never mid-birth -- this stage has no
- * critical-section protection against being switched away mid-setup). */
+ * or -1 if the slot table is full (or sk_vm_switch_signal_boot_init() was
+ * never called / failed). Call once per participating VM, after that VM is
+ * fully born (never mid-birth -- this stage has no critical-section
+ * protection against being switched away mid-setup). */
 int sk_vm_switch_signal_register(VMUuid vm_id);
 
 /* Remove a switch-signal participant (FABRIC-3.md §XXVIII Stage 4,
  * 2026-09-14) -- Tripod VMs never need this (they live forever), but
  * WIREBIND-birthed identity VMs cycle through attach/detach repeatedly
  * and must free their slot for reuse, or the bounded table exhausts
- * after SK_SWITCH_MAX_SLOTS attach/detach cycles. Compacts the table
+ * after sk_vm_switch_signal_slot_capacity() attach/detach cycles. Compacts the table
  * (small, bounded, mutated only at attach/detach -- not a hot path).
  * Clears a pending switch targeting this VM, if any, so the checkpoint
  * never attempts to switch into a no-longer-registered participant.
@@ -115,6 +136,12 @@ int      sk_vm_switch_signal_slot_count(void);
 uint32_t sk_vm_switch_signal_readiness(int slot);      /* 0 if slot out of range */
 uint32_t sk_vm_switch_signal_readiness_of(VMUuid vm_id); /* 0 if not registered */
 
+/* FABRIC-3.6.md task 3.1 (2026-09-21): the table's boot-time-computed
+ * capacity (0 if sk_vm_switch_signal_boot_init() was never called or
+ * failed) -- the dynamic replacement for the old compile-time
+ * SK_SWITCH_MAX_SLOTS=16. */
+int      sk_vm_switch_signal_slot_capacity(void);
+
 #endif /* __STARKERNEL__ */
 
 #endif /* STARKERNEL_CAPSULE_VM_SWITCH_SIGNAL_H */