RIOv4_3rc1 candidate: wedge fix + E0 threshold + check-display repaint; archive prior images

New edit 6 (--checkrepaint, requires --e0thresh): hooks the CheckRequest
handler's final notify ($C5E4) through a 10-byte cave at $E020 that
repaints F0000000 after the self-test and re-renders the E0 readout only
when a counter is at/over threshold — no more stale 04000000 after
status checks. Candidate = 9600 native-game-compatible base + edits
1-2/5/6, 68 bytes vs stock, disassembly-verified, awaiting burn; on
verification it will be christened RIO 4.3.

All prior patched generations (wedge-only, 31250/31250v2, 62500/125000
science builds, e0t5 pair) moved to rio-firmware/archive/ with their
disassemblies; RIOv4_2.bin stays at top level as the pristine patch
source.

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

README.md

@@ -41,22 +41,37 @@ the SCI state machine (protocol constants FC=ACK FD=NAK FE=RESTART
 FF=IDLE, idle-reload-4 patterns), patch the early-ACK/error wedge path or
 widen its window, burn a new EPROM, keep this original safe.
 
-## Patched images (built by make_patch.py; see RIOv4_2-ANALYSIS.md)
+## Current work candidate — `RIOv4_3rc1.bin`
 
-- **`RIOv4_2_patched.bin`** — the reply-latch wedge fix, 23 bytes changed.
-  sha256 `3fc8170caf60e2580641724ff995176c93c4f2e706f31487beded8233142493f`.
-- **`RIOv4_2_patched_31250.bin`** (`make_patch.py --baud31250`) — wedge fix
-  + SCI retuned 9600 → 31250 baud (one more byte, `$D62B: 30→02`).
-  sha256 `9f866cf353d04906e1d3e3847b6375eaae251c987b656f68f093e61ba1bd545b`.
-  Bench/RIOJoy-only until the native games get baud patches; needs an
-  FTDI-class adapter (16550s can't make 31250). Test tools take `--baud 31250`.
-- **Speed-ladder variants** (`_31250v2`, `_62500`, `_125000`) and bench
-  verdicts: see RIOv4_2-ANALYSIS.md — 31250v2 is the certified FastRIO
-  build; 62500/125000 were science runs (CPU is the wall).
-- **`RIOv4_2_patched_e0t5.bin` / `RIOv4_2_patched_31250v2_e0t5.bin`**
-  (`--e0thresh=5`) — adds a threshold to the cockpit display's `E0`
-  serial-error readout, which stock firmware paints on the *first*
-  counter event (`E0000001` forever after one benign give-up). Display
-  stays `F0000000` until any error counter reaches 5; counters still
-  accumulate. 30-byte cave at `$E000`, disassembly-verified, **not yet
-  burned/bench-verified**. Details in RIOv4_2-ANALYSIS.md.
+Built by `make_patch.py --e0thresh=5 --checkrepaint RIOv4_2.bin
+RIOv4_3rc1.bin`; sha256
+`dc59bd51cae34781cf42f338e44a020b249a4030acc3c584af916aee9ca881e3`
+(68 bytes changed vs stock). 9600 baud, native-game compatible. On the
+stock v4.2 base it carries:
+
+1. **Reply-latch wedge fix** (edits 1-2) — bench-certified.
+2. **E0-display threshold, N=5** (edit 5) — bench-certified 2026-07-19
+   (held `F0000000` sub-threshold, flipped to `E0000105` at the 5th
+   teardown; mash regression clean).
+3. **Check self-test display repaint** (edit 6, NEW) — the CheckRequest
+   handler previously left a stale `04000000` frame on the display; a
+   10-byte cave at `$E020` now repaints `F0000000` after every check,
+   then re-renders the `E0` readout only if a counter is at/over
+   threshold. **Needs on-hardware verification**: after a burn, any
+   version+check exchange (tray connect, monitor, mash start) must
+   leave the display reading `F0000000`, not `04000000`; then re-run
+   `--e0test` (expect the certified behavior unchanged) and a mash
+   spot-check.
+
+Once edit 6 is verified on the cockpit, this image is christened
+**RIO 4.3**.
+
+## Archive
+
+All prior generations live in [`archive/`](archive/) with their
+disassemblies: `RIOv4_2_patched` (wedge fix only), `_31250`/`_31250v2`
+(FastRIO speed builds), `_62500`/`_125000` (speed-ladder science runs),
+and the `_e0t5` pair (threshold without check-repaint; the 9600 one is
+in the socket as of 2026-07-19 until rc1 is burned). Bench verdicts and
+per-edit history: RIOv4_2-ANALYSIS.md. The pristine dump `RIOv4_2.bin`
+stays at top level — it is the source every patch builds from.