FABRIC.md item 4.4z: draw the scroll box's visible border

draw_box_border() (vt100.c) strokes four 1px edges around the 640x480
CANVAS box, reusing the same border-gray constant the REPL strip's
border lines use (renamed VT100_STRIP_BORDER_GRAY -> VT100_BORDER_GRAY
since it's now shared -- one pinned color decision, 4.4w, not two).
Called from erase_display()'s box-scoped branch so the border survives
every box clear (the initial one and any later ESC[2J), not just the
first.

Verified: three-arch clean QEMU boot + logs, amd64 screendump showing a
full rectangle outline around the box, visually distinct from the strip
below it.

Punch list §25 item 4.4z complete.

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

FABRIC.md

@@ -6028,7 +6028,7 @@ document and committing that amendment as its own item.*
   > **DECIDED 2026-08-12 — Ctrl+TAB.** Chosen by Captain Bob directly. 4.4v's interception
   > code intercepts this specific combination, not bare TAB.
 
-- [ ] **4.4z — Draw the scroll box's visible border.** 4.4t confined REPL text to the 640×480
+- [x] **4.4z — Draw the scroll box's visible border.** 4.4t confined REPL text to the 640×480
   box's coordinate space but never stroked a visible rectangle outline on it — the box's edges
   are implicit (where text stops), not drawn. 4.4u step 6 calls for "an actual stroked
   rectangle outline." Small, separable from 4.4v/4.4r — a single `fb_fill_rect()`-based
@@ -6039,6 +6039,18 @@ document and committing that amendment as its own item.*
   locks in (see 4.4w); three-arch QEMU boot + logs per CLAUDE.md.
   *Refs:* §27.8, 4.4t, 4.4u, 4.4w.
 
+  > **DONE 2026-08-12.** `draw_box_border()` (`vt100.c`) strokes four 1px edges around the box
+  > using the same `VT100_BORDER_GRAY` constant the strip's border lines use (renamed from
+  > `VT100_STRIP_BORDER_GRAY` since it's now shared by both — one pinned color decision,
+  > 4.4w, not two). Called from `erase_display()`'s box-scoped branch (`mode==2`, TTF mode),
+  > right after the box-clear fill — this covers both the initial clear at
+  > `vt100_enable_ttf()` time and any later `ESC[2J`, so the border survives every box clear,
+  > not just the first, per this item's own done-when. Three-arch QEMU boot + logs clean
+  > (`logs/20260812-150341/amd64`, `logs/20260812-150426/aarch64`,
+  > `logs/20260812-150540/riscv64`); amd64 screendump
+  > (`logs/screendump-4.4z/amd64-border.png`) shows a full rectangle outline around the box,
+  > visually distinct from the strip below it.
+
 - [ ] **4.5 — URGENT, flagged by Captain Bob 2026-08-11: the kernel build has never used any
   compiler optimization.** **Blocking priority, set by Captain Bob 2026-08-11: no other
   punch-list item is worked until 4.5a–4.5f are done**, ahead of whatever would otherwise

logs/screendump-4.4z/qemu-stdout.log

@@ -0,0 +1 @@
+qemu: terminating on signal 15 from pid 102222 (/bin/bash)

src/starkernel/hal/vt100.c

@@ -113,7 +113,10 @@ static ttf_raster_cache_t  g_ttf_cache;
  * --------------------------------------------------------------------- */
 #define VT100_STRIP_GAP_PX      15u  /* baseline-to-border-line gap, both sides, mirrored */
 #define VT100_STRIP_BOX_GAP_PX   8u  /* gap between the strip's top border and the box's bottom edge */
-#define VT100_STRIP_BORDER_GRAY  FB_RGB(0xAA, 0xAA, 0xAA)  /* FB_ANSI_PALETTE[7] */
+#define VT100_BORDER_GRAY        FB_RGB(0xAA, 0xAA, 0xAA)  /* FB_ANSI_PALETTE[7]; shared by the
+                                                              strip's border lines (4.4x) and
+                                                              the box's own border (4.4z) --
+                                                              same pinned decision (4.4w) */
 #define VT100_STRIP_TEXT_WHITE   FB_RGB(0xFF, 0xFF, 0xFF)
 #define VT100_STRIP_LEFT_MARGIN_PX(fbw) (((fbw) - VT100_BOX_W) / 2u)  /* aligned under the box */
 
@@ -344,8 +347,8 @@ void vt100_strip_draw(const char *text)
                              VT100_STRIP_TEXT_WHITE, VT100_DEFAULT_BG);
     }
 
-    fb_fill_rect(0, top_line_y,    fbw, 1u, VT100_STRIP_BORDER_GRAY);
-    fb_fill_rect(0, bottom_line_y, fbw, 1u, VT100_STRIP_BORDER_GRAY);
+    fb_fill_rect(0, top_line_y,    fbw, 1u, VT100_BORDER_GRAY);
+    fb_fill_rect(0, bottom_line_y, fbw, 1u, VT100_BORDER_GRAY);
 }
 
 static void draw_cursor_glyph(uint8_t ch)
@@ -679,6 +682,26 @@ static void erase_line_range(uint32_t row, uint32_t c0, uint32_t c1)
     fb_fill_rect(px_of(c0), py_of(row), (c1 - c0) * cell_w(), cell_h(), g_vt.bg);
 }
 
+/* FABRIC.md item 4.4z: stroke the scroll box's own visible border. 4.4t
+ * confined text to the box's coordinate space but never drew a rectangle
+ * outline on it -- the edges were implicit (where text stops), not
+ * drawn. Four thin edges, 1px each, same gray as the strip's border
+ * lines (4.4x/4.4w -- one shared color, one design decision). Called
+ * from erase_display()'s box-scoped branch below, so the border survives
+ * every box clear (the initial one at vt100_enable_ttf() time and any
+ * later ESC[2J), not just the first. */
+static void draw_box_border(void)
+{
+    fb_fill_rect(g_origin_x,                    g_origin_y,
+                 VT100_BOX_W, 1u,                                  VT100_BORDER_GRAY);
+    fb_fill_rect(g_origin_x,                    g_origin_y + VT100_BOX_H - 1u,
+                 VT100_BOX_W, 1u,                                  VT100_BORDER_GRAY);
+    fb_fill_rect(g_origin_x,                    g_origin_y,
+                 1u, VT100_BOX_H,                                  VT100_BORDER_GRAY);
+    fb_fill_rect(g_origin_x + VT100_BOX_W - 1u, g_origin_y,
+                 1u, VT100_BOX_H,                                  VT100_BORDER_GRAY);
+}
+
 static void erase_display(int mode)
 {
     if (mode == 0) {
@@ -701,6 +724,7 @@ static void erase_display(int mode)
          * full-screen in bitmap mode as before (boot/POST unaffected). */
         if (g_glyph_mode == VT_GLYPH_TTF) {
             fb_fill_rect(g_origin_x, g_origin_y, VT100_BOX_W, VT100_BOX_H, g_vt.def_bg);
+            draw_box_border();
         } else {
             fb_fill_rect(0, 0, fb_width(), fb_height(), g_vt.def_bg);
         }