docs: record Windows spike failure, document WSL2 path, update plan status

- ADR §6: spike evidence (Swift 6.3.3 on windows-latest cannot compile
  hello-world; DLL split across install trees); native Windows deferred
  behind a revisit trigger; WSL2/Docker stays the supported path
- README: concrete WSL2 + Docker Desktop instructions for Windows users
- PLAN.md: step statuses updated

Author: yashranaway

PLAN.md

@@ -49,6 +49,17 @@ Linux host already uses. So Windows becomes a third engine adapter, not a rewrit
 We still test the ground truth first, with a spike (step 1 below). If the spike fails,
 we port only the shared core to Rust, never the whole product.
 
+## Status
+
+- Step 0: release #45 prepared (tag pushed; publish blocked only on Apple/npm
+  secrets). Docs debt #53 closed.
+- Step 1: spike ran on real Windows runners and **failed** — Swift-for-Windows
+  cannot even compile hello-world today. Evidence in architecture decision §6.
+- Step 2: adapter is off the table. Native Windows is deferred behind a
+  revisit trigger; WSL2/Docker is the supported Windows path.
+- Step 3: WSL2 install documented in README; macOS/Linux packaging already
+  shipped in the E-series work.
+
 ## The plan
 
 ```

README.md

@@ -218,6 +218,25 @@ installer that checks Chromium and FFmpeg before copying the binaries. The
 Docker image is the supported self-contained Linux runtime and uses Debian's
 Chromium binary at `/usr/lib/chromium/chromium`.
 
+### Windows (WSL2)
+
+There is no native Windows build; the Swift toolchain cannot currently compile
+the core for Windows (see architecture decision §6). Run Headless inside
+WSL2 instead:
+
+```powershell
+wsl --install -d Ubuntu
+```
+
+Then, inside WSL2, follow the Linux install above. Chromium and FFmpeg come
+from `apt` (`sudo apt install chromium ffmpeg`). Alternatively, run the
+published GHCR image under Docker Desktop:
+
+```sh
+docker run --shm-size=1g ghcr.io/lockintime/headless:latest headless --version
+```
+
+
 ### npm / npx
 
 JavaScript-based agent harnesses can run the verified launcher without a

docs/roadmap/architecture-decisions.md

@@ -159,6 +159,31 @@ the only remote story. A hosted service is out of scope for this roadmap
 - **Interim answer (Phase 3):** published Docker image + WSL2 documented as
   the supported Windows path.
 
+**Update — 2026-08-22, Swift-for-Windows spike failed.** Per PLAN.md step 1,
+we attempted to build the shared core with Swift 6.3.3 for
+x86_64-unknown-windows-msvc on a real `windows-latest` runner
+(workflow: `.github/workflows/windows-spike.yml`, branch
+`spike/windows-core`; run logs preserved there). Findings:
+
+1. Cross-compilation from Linux is not possible; Swift SDK bundles target
+   Linux and WebAssembly only.
+2. The winget toolchain is broken out of the box: runtime DLLs are split
+   across two install trees (`Toolchains\6.3.3+Asserts\usr` and
+   `Runtimes\6.3.3\usr`). `swift.exe` exits `STATUS_DLL_NOT_FOUND` until the
+   trees are merged by hand.
+3. After repair, no Swift code compiles: even `swiftc hello.swift` fails with
+   "unable to load standard library for target x86_64-unknown-windows-msvc",
+   both via SPM and direct `swiftc`. Suspected cause is the `+Asserts`
+   toolchain packaged against a non-asserts runtime, or missing stdlib
+   modules in the package.
+
+Consequence: the "portable already" claim above does not hold on today's
+toolchain, so a Windows engine adapter written in Swift is not viable.
+WSL2/Docker remains the only supported Windows path. A native Windows host
+requires either a materially better Swift-for-Windows toolchain or a scoped
+Rust port of the shared core; revisit only when native Windows becomes an
+actual product requirement, and record a new decision entry first.
+
 ## 7. macOS engine: keep WKWebView as the visible-browser experience
 
 **Decision:** keep the WKWebView host as macOS's default engine. It is the
@@ -422,7 +447,7 @@ credentials.
 | 1   | Keep Swift core; Rust only via revisit trigger              | Decided           | 2026-08-04 |
 | 3   | Extract HostCore + BrowserEngine, typed errors              | Implemented       | 2026-08-10 |
 | 5   | Remote stays SSH-only; no cloud offering                    | Decided (owner)   | 2026-08-04 |
-| 6   | Windows = stretch via Chromium engine; WSL2/Docker interim  | Decided (owner)   | 2026-08-04 |
+| 6   | Windows = stretch via Chromium engine; WSL2/Docker interim  | Decided (owner); spike failed 2026-08-22, native deferred | 2026-08-04 |
 | 8   | Real CDP input on Linux as capability upgrade               | Implemented       | 2026-08-13 |
 | 12  | Version unification on git tag                              | Implemented       | 2026-08-04 |
 | 14  | Run one conformance scenario against every engine           | Implemented       | 2026-08-10 |