diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 004051f5b19..8dcf826595d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -89,6 +89,8 @@ jobs:
           scripts/test-mobile-release-candidate-publisher.sh
       - name: Mobile worktree identity contract
         run: scripts/test-mobile-worktree-overrides.sh
+      - name: Desktop dev command contract
+        run: scripts/test-desktop-dev-command-contract.sh
       - name: Codex security review contract
         run: just security-review-check
       - name: Rust cache contract
diff --git a/desktop/src-tauri/tauri.conf.json b/desktop/src-tauri/tauri.conf.json
index 05dc5553397..fb1c42a8ac4 100644
--- a/desktop/src-tauri/tauri.conf.json
+++ b/desktop/src-tauri/tauri.conf.json
@@ -5,7 +5,7 @@
   "identifier": "xyz.block.buzz.app",
   "build": {
     "beforeDevCommand": {
-      "script": "exec ./node_modules/.bin/vite",
+      "script": "pnpm exec vite",
       "cwd": "..",
       "wait": false
     },
diff --git a/scripts/instance-env.sh b/scripts/instance-env.sh
index bc185d98f18..f67b2b0791c 100755
--- a/scripts/instance-env.sh
+++ b/scripts/instance-env.sh
@@ -25,7 +25,16 @@ if [[ "${BUZZ_RESET_WEBVIEW_STATE:-0}" == "1" ]]; then
     DEV_URL="${DEV_URL}?resetDevState=1"
 fi
 
-BUZZ_TAURI_CONFIG="{\"build\":{\"devUrl\":\"${DEV_URL}\",\"beforeDevCommand\":\"exec ./node_modules/.bin/vite --port ${BUZZ_VITE_PORT} --strictPort\"},\"identifier\":\"xyz.block.buzz.app.dev\",\"productName\":\"Buzz Dev\"}"
+# Tauri runs this through `cmd /C` on Windows, which has no `exec` and cannot
+# execute the extensionless `.bin/vite` shim. `pnpm exec` resolves the local
+# Vite binary on every platform; elsewhere `exec` still hands the shell's
+# process slot to pnpm so Tauri's Ctrl+C reaches the launched command.
+case "${BUZZ_TEST_PLATFORM:-$(uname -s)}" in
+    MINGW*|MSYS*|CYGWIN*) VITE_LAUNCH="pnpm exec vite" ;;
+    *) VITE_LAUNCH="exec pnpm exec vite" ;;
+esac
+
+BUZZ_TAURI_CONFIG="{\"build\":{\"devUrl\":\"${DEV_URL}\",\"beforeDevCommand\":{\"script\":\"${VITE_LAUNCH} --port ${BUZZ_VITE_PORT} --strictPort\",\"cwd\":\"..\",\"wait\":false}},\"identifier\":\"xyz.block.buzz.app.dev\",\"productName\":\"Buzz Dev\"}"
 unset VITE_DEV_BRANCH
 
 # In worktrees, extract a label from the branch name and derive a unique app
@@ -86,10 +95,10 @@ if git rev-parse --is-inside-work-tree &>/dev/null; then
         GENERATE_DEV_ICON="$WORKTREE_ROOT/scripts/generate-dev-icon.swift"
         BASE_ICON="$WORKTREE_ROOT/desktop/src-tauri/icons/icon.icns"
 
-        if swift "$GENERATE_DEV_ICON" "$BASE_ICON" "$DEV_ICON" "$BUZZ_WORKTREE_LABEL"; then
+        if [[ "$(uname -s)" == Darwin ]] && command -v swift &>/dev/null && swift "$GENERATE_DEV_ICON" "$BASE_ICON" "$DEV_ICON" "$BUZZ_WORKTREE_LABEL"; then
             echo "🌳 Worktree: ${BUZZ_WORKTREE_LABEL}"
             export VITE_DEV_BRANCH="$BUZZ_WORKTREE_LABEL"
-            BUZZ_TAURI_CONFIG="{\"build\":{\"devUrl\":\"${DEV_URL}\",\"beforeDevCommand\":\"exec ./node_modules/.bin/vite --port ${BUZZ_VITE_PORT} --strictPort\"},\"identifier\":\"xyz.block.buzz.app.dev.${BUZZ_INSTANCE_SLUG}\",\"productName\":\"Buzz Dev (${BUZZ_WORKTREE_LABEL})\",\"bundle\":{\"icon\":[\"$DEV_ICON\"]}}"
+            BUZZ_TAURI_CONFIG="{\"build\":{\"devUrl\":\"${DEV_URL}\",\"beforeDevCommand\":{\"script\":\"${VITE_LAUNCH} --port ${BUZZ_VITE_PORT} --strictPort\",\"cwd\":\"..\",\"wait\":false}},\"identifier\":\"xyz.block.buzz.app.dev.${BUZZ_INSTANCE_SLUG}\",\"productName\":\"Buzz Dev (${BUZZ_WORKTREE_LABEL})\",\"bundle\":{\"icon\":[\"$DEV_ICON\"]}}"
         fi
     fi
 fi
diff --git a/scripts/test-desktop-dev-command-contract.sh b/scripts/test-desktop-dev-command-contract.sh
new file mode 100755
index 00000000000..fa5922b523b
--- /dev/null
+++ b/scripts/test-desktop-dev-command-contract.sh
@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
+
+assert_dev_command() {
+    node -e '
+        const config = JSON.parse(process.argv[1]);
+        const expectedScript = process.argv[2];
+        const command = config.build.beforeDevCommand;
+        if (
+          typeof command !== "object" ||
+          command.script !== expectedScript ||
+          command.cwd !== ".." ||
+          command.wait !== false
+        ) {
+          console.error("unexpected beforeDevCommand:", JSON.stringify(command));
+          process.exit(1);
+        }
+    ' "$1" "$2"
+}
+
+config_for_platform() {
+    local platform=$1
+    (
+        cd "$repo_root/desktop"
+        export BUZZ_TEST_PLATFORM="$platform"
+        source ../scripts/instance-env.sh >/dev/null 2>&1
+        printf '%s' "$BUZZ_TAURI_CONFIG"
+    )
+}
+
+port_from_json() {
+    node -e '
+        const config = JSON.parse(process.argv[1]);
+        process.stdout.write(new URL(config.build.devUrl).port);
+    ' "$1"
+}
+
+base_config=$(cat "$repo_root/desktop/src-tauri/tauri.conf.json")
+assert_dev_command "$base_config" "pnpm exec vite"
+
+windows_config=$(config_for_platform MINGW64_NT-10.0)
+windows_port=$(port_from_json "$windows_config")
+assert_dev_command "$windows_config" "pnpm exec vite --port ${windows_port} --strictPort"
+
+unix_config=$(config_for_platform Darwin)
+unix_port=$(port_from_json "$unix_config")
+assert_dev_command "$unix_config" "exec pnpm exec vite --port ${unix_port} --strictPort"
+
+tmp=$(mktemp -d)
+trap 'rm -rf "$tmp"' EXIT
+mkdir -p "$tmp/bin"
+cat > "$tmp/bin/git" <<'MOCK_GIT'
+#!/usr/bin/env bash
+case "$*" in
+    "rev-parse --show-toplevel") printf '%s\n' "$TEST_REPO_ROOT" ;;
+    "rev-parse --is-inside-work-tree") printf '%s\n' true ;;
+    "rev-parse --git-dir") printf '%s\n' "$TEST_REPO_ROOT/.git/worktrees/windows-test" ;;
+    "rev-parse --git-common-dir") printf '%s\n' "$TEST_REPO_ROOT/.git" ;;
+    "rev-parse --abbrev-ref HEAD") printf '%s\n' feature/windows-test ;;
+    *) exit 1 ;;
+esac
+MOCK_GIT
+cat > "$tmp/bin/uname" <<'MOCK_UNAME'
+#!/usr/bin/env bash
+printf '%s\n' MINGW64_NT-10.0
+MOCK_UNAME
+cat > "$tmp/bin/swift" <<'MOCK_SWIFT'
+#!/usr/bin/env bash
+touch "$SWIFT_CALLED_MARKER"
+exit 1
+MOCK_SWIFT
+chmod +x "$tmp/bin/git" "$tmp/bin/uname" "$tmp/bin/swift"
+
+export TEST_REPO_ROOT="$repo_root"
+export SWIFT_CALLED_MARKER="$tmp/swift-called"
+(
+    export PATH="$tmp/bin:$PATH"
+    cd "$repo_root/desktop"
+    source ../scripts/instance-env.sh >/dev/null 2>&1
+)
+if [[ -e "$SWIFT_CALLED_MARKER" ]]; then
+    echo "expected Windows desktop setup to skip the macOS Swift icon generator" >&2
+    exit 1
+fi
+
+echo "desktop dev command contract test passed"