Unify console prompt to [user@VM]; fix real personality-block truncation; correct §XXV's wrong lockdown conclusion (FABRIC-3.md §XXVI)

Investigating the std79 lockdown finding from FABRIC-3.md §XXV led
to a real discovery: WIREBIND births TWO VMs per identity, a console
proxy under the plain username and the actual restricted identity
under <username>~user (capsule_wirebind.c). Every test in §XXV
targeted the console proxy, which was never locked down at all.
Retested against the correct target (rajames~user): the lockdown
works exactly as designed. §XXV's "lockdown never engages" conclusion
was wrong -- corrected here, not deleted, since the mistake and how
it was caught are worth keeping (see the new feedback memory:
confirm which specific VM a name resolves to before concluding
anything, when a subsystem is known to birth more than one VM per
identity).

Two real, separate things found along the way are kept regardless
of that correction:

- capsule_runcap.c: the reserved personality devblock was read in
  full (mostly zero-padding after a short ~200-byte string) with no
  terminator, producing "WARN: block 4998 exceeds 1KB, truncating"
  on every std79-locked identity's birth, universal, since at least
  2026-09-10. Fixed by trimming to the first NUL byte actually found
  -- real, but harmless to execution (real content sat in the
  truncated block's surviving head); it mattered for capsule_id/
  content_hash being computed over padding instead of real content.

- console.h/console.c/repl.c: unified the prompt from a separately-
  computed "[VMName] (user)" into a single "[user@VMName]" line
  prefix -- exactly the ambiguity that caused the original
  misdiagnosis (the prompt showed only the WIREBIND username,
  identical whether USE had targeted the console proxy or the real
  ~user identity). Implemented as a registered callback
  (console_set_user_prefix_provider()) rather than console.c calling
  into WIREBIND/session logic directly, since console.c is a clean
  HAL module with no prior dependency on capsule-level subsystems.

Verified: clean build on all 3 architectures, zero new warnings,
identical dict_hash/capsule_hash to every prior boot this session
(console/prompt-only change). Full 9-identity messaging campaign
re-run end to end: 202s, zero faults, all 8 identities at 99/99
tokens, zero regression.

Also surfaced, not yet acted on: the full campaign's own console
tags now visibly show which VM each identity's tests actually
reached ([zuse@rajames], not [zuse@rajames~user]) -- messaging.4th's
VM-NAMES-INIT registers identities by plain username, so std79-doe.
fth's turn-attractor has been dispatching to each identity's console
proxy, not the actual locked-down identity, since the messaging
rewrite. Flagged for a deliberate decision, not investigated further.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EXieurDfDSsDFdnSyusuWo

src/starkernel/hal/console.c

@@ -195,6 +195,18 @@ const char *console_get_vm_name(void) {
     return g_active_vm_name;
 }
 
+/* FABRIC-3.md SXXV follow-up: see console.h's own doc comment on
+ * console_set_user_prefix_provider() for why this is a registered
+ * callback rather than console.c calling into capsule/WIREBIND logic
+ * directly. NULL (the default, until repl.c registers one at boot) means
+ * "no provider yet" -- emit_prefix() falls back to the bare "[VMName] "
+ * form, identical to today's behavior. */
+static console_user_prefix_fn g_user_prefix_fn = (void *)0;
+
+void console_set_user_prefix_provider(console_user_prefix_fn fn) {
+    g_user_prefix_fn = fn;
+}
+
 void console_save_vm_name(char *out, size_t cap) {
     if (!out || cap == 0) return;
     size_t i = 0;
@@ -239,10 +251,19 @@ static void emit_prefix(void) {
     int fb = fb_is_available();
     static const char *color_on  = "\x1b[38;2;255;165;0m";
     static const char *color_off = "\x1b[39m";
+    const char *user = g_user_prefix_fn ? g_user_prefix_fn() : (void *)0;
 
     for (p = color_on; *p; p++) { raw_putc(*p); if (fb) vt100_putc(*p); }
     raw_putc('[');
     if (fb) vt100_putc('[');
+    if (user && user[0]) {
+        for (p = user; *p; p++) {
+            raw_putc(*p);
+            if (fb) vt100_putc(*p);
+        }
+        raw_putc('@');
+        if (fb) vt100_putc('@');
+    }
     for (p = g_active_vm_name; *p; p++) {
         raw_putc(*p);
         if (fb) vt100_putc(*p);