§H.12 step 2: session-slot table, session_find/session_register

src/starkernel/vm/session.c: kmalloc'd-at-boot slot table sized from
stadium_max_vm_count() (mirrors stadium.c's own StadiumVMQuota, not a
fixed compile-time array as originally planned -- that table was already
moved off a fixed array for the same "population isn't knowable in
advance" reason). session_boot_init()/session_find()/session_register()
implemented for real, no stubs; session_register() zeroes identity and
leaves pinned=0, matching VMIdentity's own documented default and
deferring pin policy to callers. Added session.c to Makefile.starkernel's
explicit source lists. No callers yet.

Verified 3-arch boot to ok> (amd64/aarch64/riscv64).

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

include/starkernel/session.h

@@ -76,6 +76,54 @@ typedef struct {
     VMIdentity identity;                 /* embedded, not referenced -- see vm_identity.h */
 } Session;
 
+/*
+ * session_boot_init - Boot-time allocation, mirroring stadium_boot_init()'s
+ * own kmalloc-sized-from-budget shape rather than a fixed compile-time
+ * array (stadium.c's own StadiumVMQuota table was moved off a fixed array
+ * for the same reason -- population isn't knowable in advance). Must run
+ * after stadium_boot_init() (session slot count is sized from
+ * stadium_max_vm_count()) and before the first session is registered.
+ * No callers yet (§H.12 step 2) -- wiring into the boot sequence happens
+ * in a later punch-list step.
+ *
+ * @return 0 on success, -1 if kmalloc failed or stadium_max_vm_count() is 0
+ *         (Stadium not yet initialized).
+ */
+int session_boot_init(void);
+
+/*
+ * session_find - Look up a session by the VMUuid of the patron it
+ * references. Linear scan, same shape as stadium.c's own
+ * quota_slot_for_vm() -- the population this searches is small (one entry
+ * per VM, not per word/block).
+ *
+ * @return Pointer to the live session, or NULL if none is registered for
+ *         vm_id.
+ */
+Session *session_find(VMUuid vm_id);
+
+/*
+ * session_register - Register a new session for vm_id. identity starts
+ * zeroed (VMIdentity's own documented default: installed=0, "no lock,
+ * allow freely" -- §H.12 Correction 2). pinned starts 0 (unpinned); use
+ * session_set_pinned() separately to pin, keeping this function's job to
+ * "create the session record" only, not "create and also decide pin
+ * policy" -- callers (e.g. the capsule-birth admission path, §H.12 phase 2)
+ * decide pinning themselves.
+ *
+ * @param vm_id   The patron this session references. Must not already have
+ *                a registered session (session_find(vm_id) must be NULL).
+ * @param parent  Who birthed this session (vm_uuid_hera() for Hera's own
+ *                self-registration -- self-referential, matching the
+ *                existing parent_vm_id convention documented in
+ *                capsule_run.h).
+ * @param name    Copied into the new session's name buffer, truncated to
+ *                SESSION_NAME_BUF - 1 if longer.
+ * @return Pointer to the new session, or NULL if the slot table is full,
+ *         not yet initialized, or vm_id is already registered.
+ */
+Session *session_register(VMUuid vm_id, VMUuid parent, const char *name);
+
 #endif /* __STARKERNEL__ */
 
 #endif /* STARKERNEL_SESSION_H */