feat(wasm): add browser QEMU build

ROADMAP.md

@@ -19,7 +19,7 @@ running in-browser from static files. The endgame merges those two.
 
 ## Status
 
-**Phase 1 (native foundation) is done for X3 and X4 selection.** Unmodified
+**The native foundation and WASM compile phase are done.** Unmodified
 [canonical firmware](https://github.com/crosspoint-reader/crosspoint-reader)
 auto-detects `xteink,variant=x3` through its real I²C fingerprint and boots the
 X3 home screen with SD support. `variant=x4` omits those chips, so the same
@@ -35,6 +35,8 @@ make run VARIANT=x4       # X4 detection + blank panel stub
 
 QMP screenshots confirmed the X3 home screen and 528×792 orientation; captured
 X4 SPI traffic confirmed the firmware selected its SSD1677 driver.
+`make qemu-wasm` produces the Emscripten module, WASM binary, and pthread worker
+under `dist/wasm/`; a Node smoke check confirms `xteink` is registered.
 
 ### Device selection (X3 vs X4)
 
@@ -80,11 +82,9 @@ reuses unchanged — no bespoke abstraction layer:
 
 ## Remaining phases
 
-1. **Compile the patched fork to WASM** — combine Espressif's SoC models with
-   qemu-wasm's WASM TCG/TCI backend; build `qemu-system-riscv32` with Emscripten.
-2. **Browser front-end (static)** — uploaded flash, canvas, physical buttons,
+1. **Browser front-end (static)** — uploaded flash, canvas, physical buttons,
    SD block backend, and pre-boot X3/X4 picker. Fully airgapped.
-3. **Full X4 panel** — implement SSD1677 RAM/window/update commands when visible
+2. **Full X4 panel** — implement SSD1677 RAM/window/update commands when visible
    X4 rendering is needed; the selection, dimensions, wiring, and stub exist.
 
 ## Repo layout
@@ -94,7 +94,9 @@ reuses unchanged — no bespoke abstraction layer:
 | `flake.nix` | espressif-qemu release pkg (`nix run .#run-upstream`) + full QEMU build devShell |
 | `Makefile` | `qemu` (source build), `firmware`, `sdimage`, `run`, `chip` |
 | `scripts/build-qemu.sh` | clone pinned espressif/qemu, apply patch, build riscv32-softmmu |
-| `qemu/patches/` | xteink machine + device models (applied onto the pinned QEMU commit) |
+| `qemu/patches/` | xteink devices plus the qemu-wasm host port, applied onto pinned Espressif QEMU |
+| `qemu/wasm/Dockerfile` | Minimal pinned Emscripten dependency environment |
+| `scripts/build-qemu-wasm.sh` | X3/X4-only WASM build → `dist/wasm/` |
 | `chip/eink-x3.chip.c` | legacy Wokwi model — the reverse-engineered X3 e-ink protocol reference |
 | `web/` | (phase 3) static front-end: upload + canvas + buttons |