FORTH: KEY-EVENT unified keyboard interface, closes 4.3.5-4.3.5f (item 4.3.5f)

Punch list §25 item 4.3.5f complete. Keyboard-input slice done.

New KEY-EVENT ( -- keycode pressed -1 | 0 ) converges amd64's i8042,
riscv64's and aarch64's virtio-keyboard-pci behind one shape. Translation
needed is minimal: XT Set-1 make codes and Linux input keycodes are
numerically identical across the standard 84-key block (a documented
historical property of the Linux input subsystem, confirmed against this
host's own headers and this tree's own prior live observations), so amd64
needs two lines, riscv64/aarch64 need none. Verified live with a real
keypress on all three architectures: identical "-1 1 30" output everywhere.
Three-arch acceptance boot clean.

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

FABRIC.md

@@ -4323,7 +4323,7 @@ document and committing that amendment as its own item.*
   > (`logs/20260808-122743/riscv64/`, unaffected — this item's riscv64-side changes were
   > doc-comment-only).
 
-- [ ] **4.3.5f — Checkpoint: one keyboard abstraction, three architectures, no polling.**
+- [x] **4.3.5f — Checkpoint: one keyboard abstraction, three architectures, no polling.**
   Converge 4.3.5/4.3.5c/4.3.5e behind a single scancode/keycode interface so the REPL
   keyboard-input work (M8, outside Stadium) has one thing to call, not three. Stop and
   review here — same posture as 4.3.4 — before scoping REPL wiring.
@@ -4333,6 +4333,39 @@ document and committing that amendment as its own item.*
   three-arch QEMU boot, logs committed.
   *Refs:* §27.5.
 
+  > **Done, 2026-08-08. Keyboard-input slice (4.3.5–4.3.5f) complete.** New `KEY-EVENT
+  > ( -- keycode pressed -1 | 0 )` in `keyboard_words.c`, alongside (not replacing) the
+  > existing per-device diagnostics `KBD-SCAN`/`VKBD-EVENT`. `keycode` uses the Linux input
+  > keycode namespace; `pressed` is 1 or 0.
+  >
+  > **The convergence needed almost no translation, for a reason worth recording rather than
+  > just asserting.** Comparing this build host's own `/usr/include/linux/input-event-codes.h`
+  > against 4.3.5's already-documented live scancode observations (`sendkey a` → 30,
+  > `sendkey b` → 48) showed `KEY_A=30`/`KEY_B=48` match those XT Set-1 make codes exactly —
+  > checked systematically across the full standard 84-key block (`KEY_ESC=1` through
+  > `KEY_F10=68`), all identical to the historical XT/AT Set-1 numbering. Not a coincidence:
+  > documented historical property of how Linux's input keycode namespace was originally
+  > defined. So amd64's translation is two lines (`keycode = sc & 0x7F`, `pressed = !(sc &
+  > 0x80)`) covering the entire non-extended key range, not a lookup table — riscv64/aarch64
+  > need no translation at all, `virtio_input_pop_event()`'s `code`/`value` already live in
+  > the same namespace. Explicitly out of scope, matching this checkpoint's "one shared shape
+  > proven live," not full coverage: extended (`0xE0`-prefixed) i8042 scancodes, virtio-input
+  > autorepeat (`value=2`, folded into "still pressed" here) — deferred to the REPL wiring
+  > item (M8) this checkpoint unblocks.
+  >
+  > Verified live on all three architectures with a real `sendkey a`, same technique as
+  > 4.3.5/4.3.5c/4.3.5e — identical output shape everywhere, `-1 1 30` (flag, pressed,
+  > keycode): amd64 (`logs/20260808-123405/amd64/qemu-amd64-20260808-123405-keyevent-
+  > verify.log`), riscv64 (`logs/20260808-124059/riscv64/qemu-riscv64-20260808-124059-
+  > keyevent-verify.log`), aarch64 (`logs/20260808-124207/aarch64/qemu-aarch64-20260808-
+  > 124207-keyevent-verify.log`) — the exact "same shape of event... confirmed with a live
+  > keypress test per architecture" this item's acceptance requires. Three-architecture
+  > standard acceptance boot clean, zero exceptions: amd64 (`logs/20260808-124331/amd64/`),
+  > aarch64 (`logs/20260808-124418/aarch64/`), riscv64 (`logs/20260808-124524/riscv64/`).
+  >
+  > This closes the keyboard-input slice opened at 4.3.5. Next per the 2026-08-07 sequencing
+  > note below: glyph rendering (stroke-based font capsules), not yet scoped.
+
   > **Sequencing noted 2026-08-07, not yet scoped:** keyboard input (4.3.5–4.3.5f) →
   > glyph rendering (stroke-based font capsules) → REPL — in that order, before the 4.4
   > Artemis boundary. Recorded so the order is not lost between sessions; neither glyph