diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2efdffa..ec391fc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,11 +10,20 @@ jobs:
   test:
     name: Test
     runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental == true }}
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest]
         go-version: ['1.24', '1.25', '1.26']
+        include:
+          # One Windows test job: before #139 Windows only built, never ran
+          # tests, so a whole platform's correctness was asserted by a build.
+          # Informational until #214 (124 pre-existing Windows failures,
+          # grouped by cause there) is empty; it still reports on every PR.
+          - os: windows-latest
+            go-version: '1.26'
+            experimental: true
 
     steps:
       - uses: actions/checkout@v4
@@ -30,6 +39,8 @@ jobs:
             pip install ast-grep-cli
           elif [ "$RUNNER_OS" = "macOS" ]; then
             brew install ast-grep
+          elif [ "$RUNNER_OS" = "Windows" ]; then
+            pip install ast-grep-cli
           fi
         shell: bash
 
diff --git a/mcp/main.go b/mcp/main.go
index 86cf9d6..6e435bf 100644
--- a/mcp/main.go
+++ b/mcp/main.go
@@ -399,9 +399,27 @@ func mustSchemaFor[T any]() *jsonschema.Schema {
 	return schema
 }
 
+// expandHome resolves a leading "~" against the user's home directory.
+// os.UserHomeDir reads USERPROFILE on Windows, where HOME is normally unset;
+// joining os.Getenv("HOME") there produced a relative path that filepath.Abs
+// resolved against the server's cwd, so "~/proj" could silently analyse the
+// wrong project. When no home is known the caller gets an error naming the
+// path instead of a guess.
+func expandHome(path string) (string, error) {
+	if path != "~" && !strings.HasPrefix(path, "~/") && !strings.HasPrefix(path, `~\`) {
+		return path, nil
+	}
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("cannot expand %q: %w", path, err)
+	}
+	return filepath.Join(home, strings.TrimLeft(path[1:], `/\`)), nil
+}
+
 func validateProjectPath(path string) (string, *mcp.CallToolResult) {
-	if strings.HasPrefix(path, "~/") {
-		path = filepath.Join(os.Getenv("HOME"), path[2:])
+	path, err := expandHome(path)
+	if err != nil {
+		return "", errorResult("Invalid path: " + err.Error())
 	}
 	absPath, err := filepath.Abs(path)
 	if err != nil {
@@ -642,7 +660,7 @@ type EmptyInput struct{}
 
 func handleStatus(ctx context.Context, req *mcp.CallToolRequest, input EmptyInput) (*mcp.CallToolResult, any, error) {
 	cwd, _ := os.Getwd()
-	home := os.Getenv("HOME")
+	home, _ := os.UserHomeDir()
 
 	// Check active watchers
 	watchersMu.RLock()
@@ -693,14 +711,7 @@ func handleListProjects(ctx context.Context, req *mcp.CallToolRequest, input Lis
 	if cancelled := cancellationResult(ctx, "Project discovery"); cancelled != nil {
 		return cancelled, nil, nil
 	}
-	// Expand ~ to home directory
-	path := input.Path
-	if strings.HasPrefix(path, "~/") {
-		home := os.Getenv("HOME")
-		path = filepath.Join(home, path[2:])
-	}
-
-	absPath, invalid := validateProjectPath(path)
+	absPath, invalid := validateProjectPath(input.Path)
 	if invalid != nil {
 		return invalid, nil, nil
 	}
diff --git a/mcp/main_test.go b/mcp/main_test.go
index f696555..d13317c 100644
--- a/mcp/main_test.go
+++ b/mcp/main_test.go
@@ -579,9 +579,41 @@ func resultText(t *testing.T, res *mcp.CallToolResult) string {
 	return text.Text
 }
 
+// setHome points os.UserHomeDir at dir on every OS: HOME on Unix, USERPROFILE
+// on Windows. Tests that set only HOME passed on Windows by supplying the
+// variable Windows would not have, which is how #139 stayed invisible.
+func setHome(t *testing.T, dir string) {
+	t.Helper()
+	t.Setenv("HOME", dir)
+	t.Setenv("USERPROFILE", dir)
+}
+
+func TestExpandHome(t *testing.T) {
+	home := t.TempDir()
+	setHome(t, home)
+	for _, in := range []string{"~/x", `~\x`} {
+		got, err := expandHome(in)
+		if err != nil || got != filepath.Join(home, "x") {
+			t.Fatalf("expandHome(%q) = %q, %v; want %q", in, got, err, filepath.Join(home, "x"))
+		}
+	}
+	if got, err := expandHome("~"); err != nil || got != home {
+		t.Fatalf("expandHome(~) = %q, %v; want %q", got, err, home)
+	}
+	if got, err := expandHome("plain/x"); err != nil || got != "plain/x" {
+		t.Fatalf("expandHome(plain/x) = %q, %v; want unchanged", got, err)
+	}
+	// No home at all: an error naming the path, never a cwd-relative guess.
+	t.Setenv("HOME", "")
+	t.Setenv("USERPROFILE", "")
+	if got, err := expandHome("~/x"); err == nil || !strings.Contains(err.Error(), "~/x") {
+		t.Fatalf("expandHome without home = %q, %v; want error naming the path", got, err)
+	}
+}
+
 func TestValidateProjectPathExpandsHomeAndRejectsInvalidRoots(t *testing.T) {
 	home := t.TempDir()
-	t.Setenv("HOME", home)
+	setHome(t, home)
 	proj := filepath.Join(home, "proj")
 	if err := os.MkdirAll(filepath.Join(proj, ".git"), 0o755); err != nil {
 		t.Fatal(err)
diff --git a/mcp/surface_hygiene_test.go b/mcp/surface_hygiene_test.go
index f4ab382..a49dd15 100644
--- a/mcp/surface_hygiene_test.go
+++ b/mcp/surface_hygiene_test.go
@@ -262,7 +262,7 @@ func TestFileContextUsesNativeKeysAndKeepsProjectRootsRequestLocal(t *testing.T)
 
 func TestFindFileResolvesHomeAndKeepsConfigRootsRequestLocal(t *testing.T) {
 	home := t.TempDir()
-	t.Setenv("HOME", home)
+	setHome(t, home)
 	alpha := filepath.Join(home, "alpha")
 	beta := filepath.Join(home, "beta")
 	writeFindProject(t, alpha, `{"only":["go"]}`)
@@ -471,7 +471,7 @@ func TestValidateProjectPathRejectsInaccessiblePath(t *testing.T) {
 		t.Fatalf("unexpected rejection: %q", resultText(t, result))
 	}
 	home := t.TempDir()
-	t.Setenv("HOME", home)
+	setHome(t, home)
 	if err := os.MkdirAll(filepath.Join(home, "proj"), 0o755); err != nil {
 		t.Fatal(err)
 	}
diff --git a/mcp/topology.go b/mcp/topology.go
index d5dfefe..6ec24a1 100644
--- a/mcp/topology.go
+++ b/mcp/topology.go
@@ -3,10 +3,8 @@ package codemapmcp
 import (
 	"context"
 	"encoding/json"
-	"os"
 	"path/filepath"
 	"sort"
-	"strings"
 
 	"codemap/internal/projectpath"
 	"codemap/limits"
@@ -145,8 +143,9 @@ func handleGetModuleContext(ctx context.Context, req *mcp.CallToolRequest, input
 }
 
 func topologyProjectRoot(path string) (string, error) {
-	if strings.HasPrefix(path, "~/") {
-		path = filepath.Join(os.Getenv("HOME"), path[2:])
+	path, err := expandHome(path)
+	if err != nil {
+		return "", err
 	}
 	selection, err := projectpath.Select(path)
 	if err != nil {