diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
new file mode 100644
index 0000000..0123801
--- /dev/null
+++ b/.github/workflows/windows.yml
@@ -0,0 +1,142 @@
+name: Windows
+
+# Fast Windows-only build + publish. The full Release workflow waits on every
+# matrix leg (Linux/macOS), and the tty visual test can hang on Linux for the
+# full 20m step timeout before pages can deploy. This workflow builds only the
+# Windows binary and publishes it to the Pages site so a single platform fix
+# can be live-tested in minutes.
+#
+# Trigger manually:
+#   gh workflow run windows.yml --ref main
+# Or it fires on push to main alongside Release.
+#
+# The workflow file must exist on the branch you dispatch from (--ref main),
+# so merge this to main before the first manual run.
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [main]
+    paths:
+      - '.github/workflows/windows.yml'
+      - 'src/**'
+      - 'tests/**'
+      - '*.nimble'
+      - 'config.nims'
+
+jobs:
+  build:
+    runs-on: windows-latest
+
+    # git-bash on the Windows runner. The Windows default (pwsh) does not
+    # propagate non-zero exit codes from native exes like nimble, so a failed
+    # build/test is swallowed and the job runs on into packaging, which then
+    # fails for a misleading reason (missing artifact). Same workaround as
+    # release.yml.
+    defaults:
+      run:
+        shell: bash
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: jiro4989/setup-nim-action@v2
+        with:
+          nim-version: stable
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Install dependencies
+        run: |
+          nimble install -y --depsOnly
+          nimble setup -y
+          echo '--path:"src"' >> nimble.paths
+
+      - name: Compute build flags
+        run: |
+          if [[ "${GITHUB_REF}" == refs/tags/* ]]; then
+            echo "BUILD_FLAGS=-d:autoUpdate" >> "$GITHUB_ENV"
+          else
+            echo "BUILD_FLAGS=-d:versionSuffix=-main-${GITHUB_SHA:0:8}" >> "$GITHUB_ENV"
+          fi
+
+      - name: Build
+        run: nimble build -y -d:release ${{ env.BUILD_FLAGS }}
+
+      - name: Run tests
+        # The `when defined(windows):` suite in tests/test_streamexec.nim
+        # asserts the no-bundled-bash contract (resolveBash() == "" and
+        # runStreamingBash returns 127 on a clean runner, since no installer
+        # has staged MSYS2 into the bundle path). The POSIX suites guard the
+        # shared launcher logic both platforms use.
+        run: nimble test
+        timeout-minutes: 20
+
+      - name: Package (Windows) - bundle OpenSSL DLLs alongside .exe
+        shell: pwsh
+        run: |
+          New-Item -ItemType Directory -Path 3code-windows-amd64 | Out-Null
+          Copy-Item 3code.exe 3code-windows-amd64/
+          Copy-Item README.md, LICENSE 3code-windows-amd64/
+          # Stock Windows ships no OpenSSL. Nim's std/net dlopens libssl /
+          # libcrypto by hardcoded names; without these DLLs alongside
+          # 3code.exe, any TLS code path dies with
+          #   could not load: (libcrypto-1_1-x64|libeay64).dll
+          # Use the canonical Nim Windows DLL bundle from nim-lang.org;
+          # it also ships a cacert.pem that we point SSL_CERT_FILE at.
+          Invoke-WebRequest -Uri https://nim-lang.org/download/dlls.zip -OutFile dlls.zip
+          Expand-Archive -Path dlls.zip -DestinationPath dlls
+          Copy-Item dlls/libssl-1_1-x64.dll, dlls/libcrypto-1_1-x64.dll, dlls/cacert.pem 3code-windows-amd64/
+          Compress-Archive -Path 3code-windows-amd64 -DestinationPath 3code-windows-amd64.zip
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: 3code-windows-amd64
+          path: 3code-windows-amd64.zip
+
+  pages:
+    # Deploy on a manual workflow_dispatch (fast Windows-only publish for
+    # live testing). On push, the full Release workflow owns the site.
+    needs: build
+    if: github.event_name == 'workflow_dispatch' && github.ref == 'refs/heads/main'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deploy.outputs.page_url }}
+
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          name: 3code-windows-amd64
+          path: dl
+
+      - name: Assemble site
+        run: |
+          mkdir -p site/main
+          cp dl/3code-windows-amd64.zip site/main/ 2>/dev/null || true
+          cat > site/index.html <<EOF
+          <!doctype html><meta charset=utf-8><title>3code main builds</title>
+          <h1>3code main builds</h1>
+          <p>Per-commit builds from <code>main</code> (commit ${GITHUB_SHA}).</p>
+          <ul>
+          EOF
+          for f in site/main/*; do
+            [ -f "$f" ] || continue
+            b=$(basename "$f")
+            echo "            <li><a href=\"main/$b\">$b</a></li>" >> site/index.html
+          done
+          cat >> site/index.html <<EOF
+          </ul>
+          EOF
+
+      - uses: actions/configure-pages@v5
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: site
+
+      - id: deploy
+        uses: actions/deploy-pages@v4
diff --git a/config.example b/config.example
index 7b6c834..809639d 100644
--- a/config.example
+++ b/config.example
@@ -15,6 +15,7 @@ current = "baseten.glm5"
 ; SERP, so swap only for a Startpage-compatible mirror.
 ; search-url = "https://www.startpage.com/do/search?cat=web&q="
 ; notify = on  ; fire a desktop notification when a turn ends (off by default)
+; bash_path = "C:\\tools\\msys64\\usr\\bin\\bash.exe"  ; Windows only: override bash detection
 
 [provider]
 name = "baseten"
diff --git a/docs/gitcmd.md b/docs/gitcmd.md
new file mode 100644
index 0000000..567c56e
--- /dev/null
+++ b/docs/gitcmd.md
@@ -0,0 +1,137 @@
+.. title:: 3code - bash and unix tools on Windows for coding agents
+
+## bash + unix tools on Windows
+
+This research note covers how a coding agent gets a real bash and the usual
+unix toolset on Windows — the equivalent of 3code's
+``irm https://3code.capocasa.dev/install.ps1 | iex`` formula, but for the
+shell layer rather than the agent itself. Two questions answered: is there a
+turnkey one-command install, and does any of this disturb WSL.
+
+### Short answer
+
+There is no single official ``irm ... | iex`` one-liner that drops a complete
+bash+unix-tools bundle the way the 3code installer does. But there is a
+de facto procedure the agent community has converged on, and the substrate
+for it is a private, bundled MinGit/PortableGit. The community-built agents
+that already do this well are Hermes (Nous Research) and, to a lesser
+extent, mise — both pin their bash via an env var.
+
+### The substrates
+
+Three real options, ranked by suitability for a coding agent.
+
+**MSYS2** — the most complete bundle: full bash, ``pacman``, ripgrep,
+coreutils, git. This is the setup OpenAI's Codex Windows guide recommends
+(`openai/codex#3580 <https://github.com/openai/codex/discussions/3580>`_).
+Strictly better than Git Bash for agent use because the toolset is complete
+and ``pacman``-upgradeable.
+
+Not a piped one-liner, but the installer is fully scriptable. Closest
+equivalent::
+
+    # GUI installer, silent CLI mode -> C:\msys64
+    .\msys2-x86_64-latest.exe in --confirm-command --accept-messages --root C:/msys64
+
+    # Or the self-extracting archive (no GUI integration, functionally identical):
+    .\msys2-base-x86_64-latest.sfx.exe -y -oC:\
+
+Then ``pacman -Syu`` and ``pacman -S mingw-w64-ucrt-x86_64-ripgrep`` etc.
+The sfx archive lives on the msys2-installer GitHub releases, so it's one
+PowerShell line away from being a ``irm | iex`` — you'd just be the one
+hosting it. There is no off-the-shelf equivalent to copy.
+
+**Git for Windows / Git Bash** — one command via winget::
+
+    winget install --id Git.Git -e --source winget
+
+Git Bash is a stripped-down MSYS2 fork: enough bash + git + a minimal set of
+coreutils to work, but intentionally lean — no ``pacman``, manual installs
+for things like ripgrep via scoop/choco separately. The Codex thread also
+notes Git Bash has caused load failures in some IDE agent plugins without
+clear errors, where MSYS2 hasn't. For a coding agent, MSYS2 beats Git Bash.
+
+**Private bundled MinGit** — the actual pattern mature agents use. See
+below.
+
+### The procedure agents actually use
+
+The pattern, documented explicitly by Hermes and noted as "the same strategy
+Claude Code uses": **don't install the full Git-for-Windows or MSYS2 into the
+system. Bundle a trimmed PortableGit/MinGit into a private directory and pin
+it with an env var.**
+
+Hermes's ``irm | iex`` installer does this, step by step:
+
+1. Downloads the official **MinGit** zip (~45 MB, from git-for-windows
+   releases) into ``%LOCALAPPDATA%\hermes\git\PortableGit``. No admin, no
+   registry, no Windows installer.
+2. Sets ``HERMES_GIT_BASH_PATH`` to ``...\git\usr\bin\bash.exe`` so fresh
+   shells find it deterministically.
+3. Resolution order on the agent side: env var → its own bundled PortableGit
+   → system Git for Windows → MSYS2/Cygwin → anything on PATH as last
+   resort.
+
+That env var is the whole trick. It sidesteps the classic footgun where
+``C:\Windows\System32\bash.exe`` (the WSL launcher) wins ``bash`` resolution
+and the agent ends up running inside WSL by accident.
+
+Two gotchas the Hermes docs call out, both worth baking into a custom
+``install.ps1``:
+
+- Use the **non-busybox** MinGit (``MinGit-*-64-bit.zip``, not
+  ``*-busybox*``). The busybox build ships ``ash``, not ``bash``, and
+  coreutils are missing.
+- In MinGit's layout, bash lives at ``usr\bin\bash.exe``, **not**
+  ``bin\bash.exe``. Check both.
+
+For the 3code formula this is the cleanest substrate: one PowerShell line,
+~45 MB, self-contained, and the bash path is controlled via an env var
+rather than fighting system PATH ordering. MSYS2 is more powerful (full
+``pacman``, ripgrep, etc.) but heavier and has no turnkey ``irm | iex`` —
+that bootstrap would have to be written by hand.
+
+### Does it disturb WSL?
+
+No. They coexist cleanly.
+
+- Git for Windows / MSYS2 install into their own directories (``C:\msys64``,
+  ``C:\Program Files\Git``, or a private ``%LOCALAPPDATA%\...\git``). They
+  do not touch the WSL distro, the WSL VM, or ``/mnt/c`` interop. Hermes
+  explicitly documents that native and WSL2 installs "coexist cleanly" with
+  data in separate roots.
+- No admin rights, no registry mutation for the portable variant, no PATH
+  clobbering of the WSL launcher.
+
+The one real interaction — not damage, just ambiguity — is ``bash``
+resolution: ``C:\Windows\System32\bash.exe`` is the WSL launcher, and if an
+agent naively calls ``bash`` it can land in WSL instead of the bundled Git
+Bash. That is exactly what the ``*_GIT_BASH_PATH`` env-var pin solves. mise
+documents the same problem and the same fix (``MISE_BASH_PATH``). So: install
+is harmless to WSL; the only thing to get right is making sure the agent
+resolves the *right* bash.
+
+If hard isolation is ever wanted, disable WSL's PATH-interop in
+``/etc/wsl.conf``::
+
+    [interop]
+    appendWindowsPath = false
+
+That's only relevant if a tool (like mise's shim mode) actually leaks
+Windows shims into WSL. For a Git Bash install, not needed.
+
+### Sources
+
+- `MSYS2 installer docs <https://www.msys2.org/docs/installer/>`_ — silent
+  CLI install forms, sfx archive.
+- `openai/codex#3580 <https://github.com/openai/codex/discussions/3580>`_ —
+  the Codex Windows MSYS2 setup guide; also flags the Git Bash plugin-load
+  failures and the ``System32\bash.exe`` WSL collision.
+- `Hermes Windows (Native) Guide
+  <https://hermes-agent.nousresearch.com/docs/user-guide/windows-native>`_ —
+  the private PortableGit + env-var-pin procedure, the MinGit layout and
+  busybox gotchas, the WSL coexistence statement.
+- `mise troubleshooting
+  <https://mise.jdx.dev/troubleshooting.html>`_ — same ``bash``-resolution
+  footgun, ``MISE_BASH_PATH`` fix, the WSL interop ``appendWindowsPath``
+  lever.
diff --git a/src/threecode.nim b/src/threecode.nim
index 1fb9bb2..757ff42 100644
--- a/src/threecode.nim
+++ b/src/threecode.nim
@@ -32,6 +32,8 @@ when defined(posix):
 import threecode/[types, util, prompts, shell, session, compact,
                   config, actions, api, display, ui, update, fatprompt,
                   toolstream, turns, transcript]
+when defined(windows):
+  import threecode/streamexec  # for resolveBash, used by ensureBash
 import tinotify
 import threecode/minline
 export types, util, prompts, shell, session, compact,
@@ -70,6 +72,19 @@ proc refuseRoot() =
         "Run as your normal user. (override: THREECODE_ALLOW_ROOT=1)"
       quit ExitUsage
 
+proc ensureBash() =
+  ## Windows startup guard: 3code depends on bash, and the supported source
+  ## is the MSYS2 tree the installer drops into the 3code app dir
+  ## (`%LOCALAPPDATA%\3code\msys64`). Hard-fail if it is missing — the one
+  ## fix is to (re)run the installer, which also bootstraps MSYS2. POSIX
+  ## always has /bin/sh so this is a no-op there.
+  when defined(windows):
+    let b = resolveBash()
+    if b.len == 0:
+      stderr.writeLine "3code: bash not found. Re-run the installer to set it up:"
+      stderr.writeLine "  irm https://3code.capocasa.dev/install.ps1 | iex"
+      quit ExitUsage
+
 proc setupTlsEnv() =
   ## macOS: stock LibreSSL at `/usr/lib/libssl.dylib` fails handshakes
   ## against most modern endpoints, so we ship Homebrew OpenSSL 3 dylibs
@@ -177,6 +192,7 @@ proc main() =
   setupTlsEnv()
   cleanupStaleBinaries()
   refuseRoot()
+  ensureBash()
   # Internal flag for the detached background worker. Run silently and
   # exit before any other startup work (skill extraction, config load).
   let cl = commandLineParams()
diff --git a/src/threecode/config.nim b/src/threecode/config.nim
index 7d10d8f..ef1e772 100644
--- a/src/threecode/config.nim
+++ b/src/threecode/config.nim
@@ -75,6 +75,11 @@ var notifyEnabled*: bool = false
   ## Resolved at config load. Set true by `[settings]` `notify = on`.
   ## When true, a native desktop notification fires when a turn ends.
 
+var bashPathOverride*: string
+  ## Windows-only. `[settings]` `bash_path = "..."` overrides MSYS2
+  ## detection in `streamexec.resolveBash` for users with bash at a
+  ## non-standard location. Empty on POSIX (where /bin/sh is always used).
+
 proc gateExperimental*(p: Profile): bool =
   ## True if the profile is allowed to run a turn under current policy:
   ## empty profile (caller handles that), known-good model, or the
@@ -228,6 +233,8 @@ proc parseConfigFile*(path: string): (string, string, seq[ProviderRec]) =
           of "on", "true", "yes", "1": streamingEnabled = true
           of "off", "false", "no", "0": streamingEnabled = false
           else: discard
+        of "bash_path", "bash-path":
+          bashPathOverride = v
         else: discard
       of "provider":
         case e.key
diff --git a/src/threecode/streamexec.nim b/src/threecode/streamexec.nim
index f542741..9ced77d 100644
--- a/src/threecode/streamexec.nim
+++ b/src/threecode/streamexec.nim
@@ -14,6 +14,33 @@ else:
   import std/streams
 import types, util, shell
 
+when defined(windows):
+  var cachedBash* {.threadvar.}: string
+
+  proc bundledMsys2Bash(): string =
+    ## The installer drops an MSYS2 tree into the 3code app dir
+    ## (`%LOCALAPPDATA%\3code\msys64`), so 3code owns its bash + unix
+    ## toolset regardless of what else is on the system. No probing of
+    ## system MSYS2 roots or PATH: a single deterministic location.
+    result = getEnv("LOCALAPPDATA") & r"\3code\msys64\usr\bin\bash.exe"
+
+  proc resolveBash*(): string =
+    ## Windows bash resolution. Order: the 3code-owned bundled MSYS2
+    ## (the supported, always-present source), then an explicit config
+    ## override (`bash_path`) for hyper-users, then nothing (hard-fail
+    ## at the startup guard). We never fall back to a system or PATH
+    ## bash: the bundled toolset is the whole point.
+    if cachedBash.len > 0: return cachedBash
+    let bundled = bundledMsys2Bash()
+    if fileExists(bundled):
+      cachedBash = bundled
+      return bundled
+    when declared(bashPathOverride):
+      if bashPathOverride.len > 0 and fileExists(bashPathOverride):
+        cachedBash = bashPathOverride
+        return bashPathOverride
+    return ""
+
 const PartialLineFlushMs = 700
 
 proc emitCompleteLine(rawOut: var string; lineBuf: var string;
@@ -299,7 +326,10 @@ export DEBIAN_FRONTEND=noninteractive
         startProcess("/bin/sh", args = ["-c", wrapped],
                      options = {poStdErrToStdOut, poUsePath})
     else:
-      startProcess("/bin/sh", args = ["-c", wrapped],
+      let b = resolveBash()
+      if b == "":
+        return ("bash not found", 127, cap)
+      startProcess(b, args = ["-c", wrapped],
                    options = {poStdErrToStdOut, poUsePath})
   startToolCancelWatcher(p.processID)
   startToolTimeoutWatcher(cap)
diff --git a/tests/test_streamexec.nim b/tests/test_streamexec.nim
index 108cdea..87e75c7 100644
--- a/tests/test_streamexec.nim
+++ b/tests/test_streamexec.nim
@@ -330,3 +330,19 @@ suite "streamexec: no external timeout dependency":
     check code == 124
     check elapsed < 6.0
     check "timed out" in o
+
+when defined(windows):
+  suite "streamexec: Windows bash resolution":
+    # On a clean CI runner no installer has run, so the bundled MSYS2 is
+    # absent and resolveBash() returns "". That is the documented contract
+    # (the startup guard hard-fails on it); assert it here rather than
+    # depending on the runner shipping bash at the bundle path.
+    test "resolveBash returns empty when no bundled bash":
+      cachedBash = ""  # defeat the threadvar cache
+      check resolveBash() == ""
+
+    test "runStreamingBash fails cleanly when no bundled bash":
+      cachedBash = ""
+      let act = Action(kind: akBash, body: "echo hello")
+      let (_, code, _) = runStreamingBash(act, nil, nil)
+      check code == 127