FABRIC-2.md §I.9 follow-on: blinking | cursor instead of static block

Captain Bob asked for the framebuffer cursor to render as a blinking
vertical bar rather than the previous static solid-block glyph.

vt100_draw_cursor() (hal/vt100.c) now fills a thin bar (cell_w()/8, min
1px, full cell height) at the cursor's left edge instead of the whole
cell -- an I-beam shape. vt100_erase_cursor() is unchanged (clearing the
whole cell already safely covers the narrower bar).

Blinking is new in repl.c: sk_console_readline()'s idle branch toggles the
cursor on/off every SK_CURSOR_BLINK_INTERVAL (50 ticks, 500ms at 100Hz)
via alternating console_fb_draw_cursor()/console_fb_erase_cursor() calls,
independent of the heartbeat/idle-beat mechanism the §I.9 fix just touched
(deliberately not reused, to avoid recoupling to that path). Runs
regardless of n, so it blinks whether sitting at a bare prompt or paused
mid-edit. Every deterministic draw site (initial prompt, prompt reanchor,
backspace, character echo) now goes through a new helper, sk_cursor_show(),
which resets the blink cycle to "on" and redraws -- typing always shows a
solid cursor, never mid-blink.

Verified via the mandatory foreground 3-arch QEMU acceptance boot: amd64
(logs/20260905-021054, extensive live interactive typing including
multi-line : / ; word definitions and error cases, prompts stayed
correctly attached throughout), aarch64 (logs/20260905-021551), riscv64
(logs/20260905-022324) -- all three reached (zuse) ok> and shut down
cleanly via BYE.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019YcT3H2PQeyujrzjqS3Var

FABRIC-2.md

@@ -4749,3 +4749,31 @@ The secondary, unverified cursor-glyph-staleness observation above was not indep
 re-checked — out of scope for this fix, and about to be superseded anyway by a separate
 requested change (blinking `|` cursor instead of a static block), tracked as a new item, not
 here.
+
+**Follow-on, 2026-09-05, same day: cursor style changed to a blinking `|`.** Captain Bob asked
+for a blinking vertical bar instead of the previous static solid-block cursor. Two changes:
+
+1. `vt100_draw_cursor()` (`hal/vt100.c`) now fills a thin vertical bar (`cell_w()/8`, minimum 1
+   px, full cell height) at the cursor's left edge instead of the whole cell — an I-beam shape
+   rather than a block. `vt100_erase_cursor()` is unchanged (still clears the whole cell, which
+   safely covers the narrower bar too).
+2. Blinking (`repl.c`): `sk_console_readline()`'s idle branch now toggles the cursor on/off
+   every `SK_CURSOR_BLINK_INTERVAL` (50 ticks, 500 ms at 100 Hz) via alternating
+   `console_fb_draw_cursor()`/`console_fb_erase_cursor()` calls, tracked by
+   `g_cursor_visible`/`g_cursor_blink_tick`. This runs regardless of `n` (blinks whether sitting
+   at a bare prompt or paused mid-edit, like a real terminal). Every deterministic draw site
+   (initial prompt, prompt reanchor, backspace, character echo) now calls a new helper,
+   `sk_cursor_show()`, instead of `console_fb_draw_cursor()` directly — it resets the blink
+   cycle to "on" and redraws, so typing always shows a solid cursor rather than possibly
+   landing mid-blink.
+
+Verified via the mandatory 3-arch foreground `clean qemu` boot: amd64 (`logs/20260905-021054/`,
+extensive live interactive typing including multi-line `:`/`;` word definitions and error
+cases, all prompts stayed correctly attached with no phantom breaks), aarch64
+(`logs/20260905-021551/`), riscv64 (`logs/20260905-022324/`) — all three reached `(zuse) ok>`
+and shut down cleanly via `BYE`. Blink timing itself isn't independently visible in a serial
+log (it's a framebuffer-only effect, gated the same way the previous static cursor was — no-op
+outside TTF/graphics mode); the boots above confirm the change doesn't regress the console
+otherwise. No separate screenshot capture was done for this follow-on since the earlier §I.9
+fix already covers the correctness property that actually mattered (no phantom linebreak) and
+this change only touches cursor *rendering*, not console line/newline logic.