§H.12 step 1: add Session struct (type only)

include/starkernel/session.h: vm_id (VMUuid), pinned (int, authoritative
over Stadium's STADIUM_FLAG_PIN per H.10), parent (VMUuid), name (fixed
64-byte buffer), identity (embedded VMIdentity, reusing the existing
type rather than inventing a new one). No logic yet, no callers -- next
step wires the session-slot array and register/find functions.

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

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

include/starkernel/session.h

@@ -0,0 +1,81 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  This file is part of the StarForth project.
+
+  Licensed under the StarForth License, Version 1.0 (the "License");
+  you may not use this file except in compliance with the License.
+
+  You may obtain a copy of the License at:
+      https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
+
+  This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  express or implied, including but not limited to the warranties of
+  merchantability, fitness for a particular purpose, and noninfringement.
+
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ */
+
+/**
+ * session.h - Per-VM session (FABRIC-3.md §H, decided 2026-09-02/03)
+ *
+ * A session is a Stadium patron (FABRIC-3.md §H.1) -- registering a session
+ * IS admitting a patron to the Stadium, not a new parallel bookkeeping
+ * structure. This struct is the piece that sits ALONGSIDE the patron,
+ * referencing it by VMUuid rather than being indexed by Stadium cell index
+ * or grown as inline fields on StadiumPatronHeader/struct VM (deliberately
+ * its own header, mirroring VMUuid's/VMIdentity's own precedent -- standing
+ * instruction: give real-shaped data its own header and integrate as a
+ * field, don't grow existing structs ad hoc).
+ *
+ * Fields (FABRIC-3.md §H.2, all five confirmed 2026-09-02/03):
+ *   vm_id    -- the patron this session references.
+ *   pinned   -- session is AUTHORITATIVE over Stadium's STADIUM_FLAG_PIN
+ *               bit (§H.10): the sole read/write path for pin state is
+ *               session_set_pinned()/session_is_pinned() below, nothing
+ *               else (including existing Stadium code) may touch
+ *               STADIUM_FLAG_PIN directly.
+ *   parent   -- who birthed this session (Hera -> Hermes/Artemis, etc).
+ *   name     -- canonical human-readable name; feeds console.c's
+ *               g_active_vm_name prefix, does not replace the
+ *               console-binding mechanism itself.
+ *   identity -- embedded VMIdentity (FABRIC-3.md §H.4's VM card is
+ *               effectively VMIdentity's existing ownership check; reused
+ *               directly here, not reinvented).
+ *
+ * Explicit user framing (2026-09-02), still true: "we're gonna be
+ * revisiting this part of it around and around for a while" -- treat this
+ * shape as a live working draft, not permanently locked.
+ */
+
+#ifndef STARKERNEL_SESSION_H
+#define STARKERNEL_SESSION_H
+
+#ifdef __STARKERNEL__
+
+#include <stdint.h>
+
+#include "starkernel/vm_uuid.h"
+#include "starkernel/vm_identity.h"
+
+/* Matches console.c's CONSOLE_VM_NAME_BUF precedent -- same order of
+ * magnitude for the same kind of data (a short human-readable VM name). */
+#define SESSION_NAME_BUF 64
+
+typedef struct {
+    VMUuid     vm_id;                    /* the patron this session references */
+    int        pinned;                   /* authoritative over STADIUM_FLAG_PIN; see
+                                           * session_set_pinned()/session_is_pinned() */
+    VMUuid     parent;                   /* who birthed this session */
+    char       name[SESSION_NAME_BUF];   /* canonical human-readable name */
+    VMIdentity identity;                 /* embedded, not referenced -- see vm_identity.h */
+} Session;
+
+#endif /* __STARKERNEL__ */
+
+#endif /* STARKERNEL_SESSION_H */