Channel table + common channel, inert (B1) -- FABRIC-3.6.md task 3.2

Adds SkHermesChannel: a channel is an index into a boot-time,
stadium_max_vm_count()-sized table (same sizing pattern task 3.1
established for the switch table -- no separate numeric rule was ruled
for this table, so task 3.1's bound is extended directly, flagged as
such rather than restated as a new ruling). No name field, mirroring
messaging.4th's own nameless CH-ARENA.

The common channel (index 0) is created at boot and permanent. Hera
subscribes explicitly in kernel_main.c (she is the one VM never born
through capsule_birth_baby()); every other VM -- Tripod fleet and
future WIREBIND identities alike -- subscribes inside
capsule_birth_baby() itself, the single choke point every other birth
already passes through.

Inert: no publish, no dispatch, no ACK/NACK, no ACL hook (tasks 3.3,
3.6, 3.7). Verified live on all three architectures: channel table
sized to 50/202/50 slots (matching switch-signal's own per-arch
sizing), common-channel fleet self-test confirms all four Tripod
members are members, and a synthetic create/subscribe/unsubscribe/
destroy round-trip against a private topic passes, including refusing
to destroy the common channel.

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

include/starkernel/vm/kernel_hermes.h

@@ -279,6 +279,101 @@ uint64_t sk_hermes_audit_failure_count(void);
 uint64_t sk_hermes_scan_held(size_t *live_count);
 int sk_hermes_scan_check(void);
 
+/*
+ * Channel table (FABRIC-3.6.md task 3.2, B1 / FABRIC-3.5.md SXLV.1): B1
+ * overrules SXXXIII.5's single flat broadcast list -- messaging is
+ * publish/subscribe, one permanent common channel every VM joins at
+ * birth, private channels created by request/grant/deny (task 3.6, not
+ * this one). SkHermesMembership (task 2.1) becomes per-channel: one
+ * instance per SkHermesChannel table entry instead of one global list.
+ *
+ * INERT, same posture as task 2.1: this task wires channel existence and
+ * membership bookkeeping only. No publish, no dispatch, no ACK/NACK, no
+ * ACL hook (tasks 3.3, 3.6, 3.7) -- creating/destroying/subscribing a
+ * channel here changes no VM's dictionary and delivers no message.
+ *
+ * Sizing: SXLV.1 says the channel table has "no fixed channel maximum,
+ * same reasoning as SXLV.2" -- SXLV.2/task 3.1's own ruling is boot-time,
+ * RAM-derived sizing (Stadium's stadium_max_vm_count_val pattern), not a
+ * literal unbounded/growable table. No separate numeric sizing rule was
+ * ruled for the channel table specifically (task 3.0's five sub-items
+ * covered ACK cadence/ACL-hook-location/switch-table-sizing/chunk-
+ * framing/drain-cadence, not this). Extending task 3.1's already-ruled
+ * pattern directly -- same stadium_max_vm_count() bound, same
+ * kmalloc-at-boot shape -- is the smallest choice consistent with what
+ * was ruled, flagged here as an engineering extrapolation, not restated
+ * as a separate Captain Bob ruling.
+ */
+
+/* SK_HERMES_CHANNEL_COMMON - the permanent common channel's fixed index.
+ * Exists (in_use, empty membership) from sk_hermes_channels_boot_init()
+ * itself, before any VM is born -- every VM joins it at birth (task 3.2's
+ * own kernel_main.c/capsule_birth.c wiring), never destroyed. */
+#define SK_HERMES_CHANNEL_COMMON 0
+
+/*
+ * SkHermesChannel - one channel/topic: its membership plus an occupancy
+ * flag for the dynamic table below. No name field -- messaging.4th's own
+ * channel abstraction (CH-ARENA) has none either; a channel is identified
+ * by its table index, the same way a Stadium quota slot or a switch-
+ * signal slot is identified by index, not by string.
+ */
+typedef struct {
+    SkHermesMembership membership;
+    int                 in_use;
+} SkHermesChannel;
+
+/* Boot-time allocation: kmalloc's the channel table to
+ * stadium_max_vm_count() entries (see this section's own sizing note
+ * above) and creates the common channel (index SK_HERMES_CHANNEL_COMMON,
+ * in_use, empty membership -- members join at birth, not pre-populated
+ * here). Must run after stadium_boot_init() (that bound is 0, and this
+ * fails, until Stadium has computed it). Soft failure -- returns -1 and
+ * leaves the table unallocated (capacity 0, so every call below simply
+ * refuses) rather than halting boot, same posture as
+ * stadium_boot_init()/session_boot_init()/sk_vm_switch_signal_boot_init().
+ * Idempotent-unsafe: calling twice leaks the first allocation, so callers
+ * must call it exactly once. */
+int sk_hermes_channels_boot_init(void);
+
+/* sk_hermes_channel_create - allocate a new, empty, inert channel.
+ * Returns its table index, or -1 if the table is full or
+ * sk_hermes_channels_boot_init() was never called/failed. */
+int sk_hermes_channel_create(void);
+
+/* sk_hermes_channel_destroy - tear down a channel created by
+ * sk_hermes_channel_create(). Refuses (-1, no effect) if channel_id is
+ * SK_HERMES_CHANNEL_COMMON (the common channel is permanent, SXLV.1),
+ * out of range, or not in use. Clears membership. */
+int sk_hermes_channel_destroy(int channel_id);
+
+/* sk_hermes_channel_subscribe - add vm_id to channel_id's membership.
+ * Refuses (-1, no effect) if channel_id is invalid/not in use, vm_id is
+ * already a member, or the channel's membership is already at
+ * SK_HERMES_MEMBER_MAX. Idempotent in effect (a second call with the
+ * same args refuses rather than duplicating), not in return value. */
+int sk_hermes_channel_subscribe(int channel_id, VMUuid vm_id);
+
+/* sk_hermes_channel_unsubscribe - remove vm_id from channel_id's
+ * membership (compacts the list, same shape as
+ * sk_vm_switch_signal_unregister()). Refuses (-1, no effect) if
+ * channel_id is invalid/not in use or vm_id is not a member. */
+int sk_hermes_channel_unsubscribe(int channel_id, VMUuid vm_id);
+
+/* sk_hermes_channel_is_member - nonzero iff vm_id is currently a member
+ * of channel_id. Zero (not an error signal) if channel_id is invalid/not
+ * in use. */
+int sk_hermes_channel_is_member(int channel_id, VMUuid vm_id);
+
+/* sk_hermes_channel_member_count - current membership size of channel_id,
+ * or -1 if channel_id is invalid/not in use. */
+int sk_hermes_channel_member_count(int channel_id);
+
+/* sk_hermes_channel_capacity - the table's boot-time-computed capacity
+ * (0 if sk_hermes_channels_boot_init() was never called or failed) --
+ * DoE/test observability, mirrors sk_vm_switch_signal_slot_capacity(). */
+int sk_hermes_channel_capacity(void);
+
 #endif /* __STARKERNEL__ */
 
 #endif /* STARKERNEL_VM_KERNEL_HERMES_H */