feat(v4): the screen and the keyboards

The stick, increment 1, task 2 (plan 2026-10-26-stick-1-screen-and-keyboard;
docs/v4.0.0/STICK.md 2, 5.3, 5.4). On the v4 path:
- the framebuffer is brought up after POST, cleared and dark: console text
  goes to serial only ("splash only, log on serial") until Zuse logs in;
  then the screen is the console (TTF, a blinking cursor, as v3's), and
  when she logs out it is cleared and dark again (console_fb_mirror(),
  console_fb_clear(); the mirror is on by default, so v3 is unchanged);
- the line editor and the node's KEY read every keyboard -- PS/2, USB, the
  virtio keyboard -- through the shared bridge (sk_input_getc()); the
  headless wait drops keyboard input as well as serial bytes;
- an EMERGENCY_CONSOLE_ENABLED build has the screen from the start.
The framebuffer setup is one helper both paths call (kernel_main.c).

Red (before): screen_dark_until_login 153051 (10835 lit), console/keys
153309, logout 153609, kbd_typeahead 153918, virtio_kbd aarch64 154245
and riscv64 154718; no_framebuffer 155546 passed before and after.
Green: 155926 (0 lit), 160156, 160409 (0 lit after logout), 160630,
virtio_kbd 161414 and 161820, no_framebuffer 161206; usb_kbd with the USB
keyboard the only one (-machine i8042=off) 164548, v3 control 164757;
the identity gate's sessions 162245-163802 all pass; v3 typed by keyboard
164009, 164115. (usb_kbd 160857 and 164313 failed in the harness:
input-send-event's device names a display, not a keyboard.)
Accepted: suite EXIT 0; three clean qemu boots, POST 538/538, dict_hash
0xfec8c47cfc6f437f unchanged (174704, 174911, 175315); test-32, 39
modules, 0 failures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

kernel/src/v4/sk_v4.c

@@ -22,6 +22,7 @@
  */
 #include "starkernel/v4/sk_v4.h"
 #include "starkernel/v4/sk_v4_identity.h"
+#include "starkernel/kbd_input.h"
 #include "starkernel/console.h"
 #include "starkernel/arch.h"
 #include "starkernel/timer.h"
@@ -52,10 +53,11 @@ static void sk_v4_out(const char *text, unsigned len)
     for (i = 0; i < len; i++) console_putc(text[i]);
 }
 
-/* a character for a line that reads the keyboard, when there is one */
+/* a character for a line that reads the keyboard, when there is one: the
+ * serial line or any keyboard (docs/v4.0.0/STICK.md 5.4) */
 static int sk_v4_key(void)
 {
-    int c = console_getc();
+    int c = sk_input_getc();
     return c < 0 ? V4_BOOT_KEY_NONE : c;
 }
 
@@ -81,12 +83,25 @@ static void sk_v4_serve(v4_node *node, unsigned request)
  * (not in a build with EMERGENCY_CONSOLE_ENABLED, whose console needs no
  * login: v3's sk_console_readline() the same).  While nothing is typed the
  * idle beat runs, as v3's. */
+#define SK_V4_CURSOR_BLINK 50u           /* ticks between blinks, as v3's (500 ms at 100 Hz) */
+
 static int sk_v4_readline(void)
 {
     int len = 0;
+    int cursor_on = 1;
+    uint64_t blink = heartbeat_ticks();
+
+    console_fb_draw_cursor();
     for (;;) {
-        int c = console_getc();
+        int c = sk_input_getc();
         if (c < 0) {
+            uint64_t now = heartbeat_ticks();
+            if (now - blink >= SK_V4_CURSOR_BLINK) {
+                blink = now;
+                cursor_on = !cursor_on;
+                if (cursor_on) console_fb_draw_cursor();
+                else           console_fb_erase_cursor();
+            }
             if (len == 0) {
                 sk_v4_identity_beat();
 #if !EMERGENCY_CONSOLE_ENABLED
@@ -98,13 +113,16 @@ static int sk_v4_readline(void)
             arch_relax();
             continue;
         }
-        if (c == '\r' || c == '\n') { console_putc('\n'); return len; }
+        if (c == '\r' || c == '\n') { console_fb_erase_cursor(); console_putc('\n'); return len; }
         if (c == 8 || c == 127) {
             if (len > 0) { len--; console_putc(8); console_putc(' '); console_putc(8); }
         } else if (c >= 32 && c < 127 && len < (int)SK_V4_LINE) {
             sk_v4_text[len++] = (char)c;
             console_putc((char)c);
         }
+        cursor_on = 1;                           /* typing shows a solid cursor, as v3's */
+        blink = heartbeat_ticks();
+        console_fb_draw_cursor();
     }
 }
 
@@ -132,6 +150,11 @@ void sk_v4_run(void (*chain)(void))
         }
     }
     sk_v4_identity_boot();
+#if EMERGENCY_CONSOLE_ENABLED
+    /* a console that needs no login has the screen from the start */
+    console_fb_mirror(1);
+    console_fb_enable_ttf();
+#endif
 
     /* The prompt is the host's: read a line, hand it to the node, say how it
      * ended. */