Windows dev setup fails: postinstall requires bash, ensure-phrocs rejects Windows

[trippyogi]

Fresh clone on Windows 11 fails twice before reaching a dev environment.
With workarounds, everything else works: full build (7/7), signed
win-unpacked app, app runs. The toolchain already targets Windows
(win32 map in download-binaries.mjs, conpty signing, codex.exe/rg.exe
fetch fine), so these look like gaps, not an unsupported platform.

Env: Windows 11 (26200), Node 22.12.0, pnpm 10.23.0, Git for Windows,
WSL launcher present but no distro.

1. pnpm install: postinstall hard-requires bash. apps/code runs
bash scripts/postinstall.sh; on stock Windows, bash is the System32
WSL stub:
<3>WSL (9 - Relay) ERROR: execvpe(/bin/bash) failed: No such file or directory

Workaround: point bash at Git Bash (PATH or pnpm script-shell). The
script is Windows-safe once a real bash runs it. Suggested fix: convert
to a Node script with the plist step gated on darwin. Four of five steps
are already Node calls. Happy to PR this.

2. pnpm dev: ensure-phrocs.sh whitelists darwin|linux and exits
(Unsupported OS: mingw64_nt-10.0-26200). No Windows phrocs binary is
published, and the dev:mprocs fallback assumes mprocs is installed.
Workaround: run pnpm dev:agent and pnpm dev:code in two terminals.
Suggested fix: publish a windows binary, or have pnpm dev print the
two-terminal fallback instead of hard-exiting. Can PR the script side.

3. Docs have no Windows section; a few lines covering both points
above would prevent this issue. Can fold into the postinstall PR.

(Cosmetic: fresh installs warn Failed to create bin ... agent-server ...bin.cjs.EXE until the workspace package first builds.)

Failure 1: pnpm install postinstall (WSL bash stub)

Scope: all 21 workspace projects
Lockfile is up to date, resolution step is skipped
Packages: +2550
Progress: resolved 0, reused 2329, downloaded 17, added 2550, done
node_modules/@parcel/watcher: Running install script, done in 123ms
node_modules/node-pty: Running install script, done in 143ms
node_modules/esbuild: Running postinstall script, done in 268ms
node_modules/better-sqlite3: Running install script, done in 705ms
[additional install scripts trimmed]
 WARN  Failed to create bin at C:\dev\code\packages\api-client\node_modules\.bin\agent-server. ENOENT: no such file or directory, stat 'C:\dev\code\packages\api-client\node_modules\@posthog\agent\dist\server\bin.cjs.EXE'
 WARN  3 other warnings

╭ Warning ──────────────────────────────────────────────────────────────────╮
│   Ignored build scripts: @google/genai, koffi.                            │
│   Run "pnpm approve-builds" to pick which dependencies should be allowed  │
╰───────────────────────────────────────────────────────────────────────────╯

. preinstall$ node scripts/enforce-pnpm.mjs
└─ Done in 101ms
. prepare$ husky
└─ Done in 189ms
apps/code postinstall$ bash scripts/postinstall.sh
│ <3>WSL (9 - Relay) ERROR: CreateProcessCommon:640: execvpe(/bin/bash) failed: No such file or directory
└─ Failed in 4.8s at C:\dev\code\apps\code
 ELIFECYCLE  Command failed with exit code 1.

Failure 2: pnpm dev (ensure-phrocs rejects Windows)

> posthog-code@0.0.0 dev C:\dev\code
> pnpm build:deps && bash scripts/ensure-phrocs.sh && bin/phrocs --config mprocs.yaml

[full turbo build output trimmed: all packages built, electron-builder
packaged and signed out\win-unpacked\PostHog Code.exe successfully]

 Tasks:    7 successful, 7 total
Cached:    0 cached, 7 total
  Time:    3m5.536s

phrocs not found, downloading...
Unsupported OS: mingw64_nt-10.0-26200
 ELIFECYCLE  Command failed with exit code 1.