diff --git a/src/desktop/single-instance.js b/src/desktop/single-instance.js
index 2e6c92d..005894b 100644
--- a/src/desktop/single-instance.js
+++ b/src/desktop/single-instance.js
@@ -1,5 +1,8 @@
-const PROTOCOL_PREFIX = 'farmcontrol://'
-const SINGLE_INSTANCE_HOST = '127.0.0.1'
+import { mkdirSync, readFileSync, unlinkSync, writeFileSync, existsSync } from 'node:fs'
+import { join } from 'node:path'
+import { getWindowsLaunchSources } from './windows-launch-args.js'
+
+const SINGLE_INSTANCE_HOSTS = ['127.0.0.1', 'localhost']
 const SINGLE_INSTANCE_PATH = '/farmcontrol-instance'
 
 // Keep below Electrobun's RPC server range (50000+).
@@ -14,6 +17,21 @@ function getSingleInstancePort() {
   return 30000 + (Math.abs(hash) % 10000)
 }
 
+function getInstanceDir() {
+  if (process.platform === 'win32') {
+    const localAppData = process.env.LOCALAPPDATA || process.env.APPDATA
+    if (localAppData) {
+      return join(localAppData, 'com.tombutcher.farmcontrol', 'instance')
+    }
+  }
+
+  return join(process.env.TMPDIR || '/tmp', 'com.tombutcher.farmcontrol', 'instance')
+}
+
+function getPendingDeeplinkPath() {
+  return join(getInstanceDir(), 'pending-deeplink.json')
+}
+
 export function findProtocolUrl(args) {
   const sources = args.filter((arg) => typeof arg === 'string')
 
@@ -42,11 +60,75 @@ export function findProtocolUrl(args) {
   return undefined
 }
 
+function collectLaunchSources() {
+  const sources = [...process.argv]
+
+  if (process.platform === 'win32') {
+    sources.push(...getWindowsLaunchSources())
+  }
+
+  return sources
+}
+
+function getLaunchProtocolUrl() {
+  return findProtocolUrl(collectLaunchSources())
+}
+
 function buildSecondInstanceMessage() {
-  const url = findProtocolUrl(process.argv)
+  const sources = collectLaunchSources()
+  const url = findProtocolUrl(sources)
+
   return url
-    ? { type: 'deeplink', url, argv: process.argv }
-    : { type: 'focus', argv: process.argv }
+    ? { type: 'deeplink', url, argv: sources }
+    : { type: 'focus', argv: sources }
+}
+
+function stagePendingDeeplink(message) {
+  const url = message?.url || findProtocolUrl(message?.argv || [])
+  if (!url) return
+
+  try {
+    mkdirSync(getInstanceDir(), { recursive: true })
+    writeFileSync(
+      getPendingDeeplinkPath(),
+      JSON.stringify({ url, timestamp: Date.now() }),
+      'utf8'
+    )
+  } catch (error) {
+    console.warn('Failed to stage pending deeplink:', error)
+  }
+}
+
+function clearPendingDeeplinkFile() {
+  const filePath = getPendingDeeplinkPath()
+  if (!existsSync(filePath)) return
+
+  try {
+    unlinkSync(filePath)
+  } catch {
+    // Ignore cleanup failures.
+  }
+}
+
+function consumePendingDeeplinkFile() {
+  const filePath = getPendingDeeplinkPath()
+  if (!existsSync(filePath)) return null
+
+  try {
+    const data = JSON.parse(readFileSync(filePath, 'utf8'))
+    clearPendingDeeplinkFile()
+    return data?.url || null
+  } catch {
+    clearPendingDeeplinkFile()
+    return null
+  }
+}
+
+function processPendingDeeplinkFile() {
+  const url = consumePendingDeeplinkFile()
+  if (url) {
+    dispatchMessage({ type: 'deeplink', url })
+  }
 }
 
 function resolveIncomingMessage(message) {
@@ -89,25 +171,36 @@ function dispatchMessage(message) {
   }
 }
 
-function getSingleInstanceUrl() {
-  return `http://${SINGLE_INSTANCE_HOST}:${getSingleInstancePort()}${SINGLE_INSTANCE_PATH}`
+function getSingleInstanceUrl(host) {
+  return `http://${host}:${getSingleInstancePort()}${SINGLE_INSTANCE_PATH}`
 }
 
-async function forwardToPrimaryInstance(message) {
-  const response = await fetch(getSingleInstanceUrl(), {
-    method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify(message)
-  })
+async function tryForwardToPrimaryInstance(message) {
+  const body = JSON.stringify(message)
 
-  if (!response.ok) {
-    throw new Error(`Forward failed with status ${response.status}`)
+  for (const host of SINGLE_INSTANCE_HOSTS) {
+    try {
+      const response = await fetch(getSingleInstanceUrl(host), {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body,
+        signal: AbortSignal.timeout(1000)
+      })
+
+      if (response.ok) {
+        return true
+      }
+    } catch {
+      // Try the next host.
+    }
   }
+
+  return false
 }
 
 function startPrimaryInstanceServer() {
   server = Bun.serve({
-    hostname: SINGLE_INSTANCE_HOST,
+    hostname: '127.0.0.1',
     port: getSingleInstancePort(),
     fetch: async (req) => {
       const { pathname } = new URL(req.url)
@@ -124,6 +217,14 @@ function startPrimaryInstanceServer() {
       }
 
       dispatchMessage(message)
+
+      const resolved = resolveIncomingMessage(message)
+      if (resolved?.type === 'deeplink' && resolved.url) {
+        clearPendingDeeplinkFile()
+      } else {
+        processPendingDeeplinkFile()
+      }
+
       return new Response('ok')
     }
   })
@@ -134,22 +235,25 @@ export async function ensureSingleInstanceLock() {
     return true
   }
 
+  const message = buildSecondInstanceMessage()
+  stagePendingDeeplink(message)
+
+  if (await tryForwardToPrimaryInstance(message)) {
+    return false
+  }
+
   try {
     startPrimaryInstanceServer()
     return true
   } catch (error) {
-    if (error?.code !== 'EADDRINUSE') {
-      console.warn('Single instance lock failed:', error)
-      return true
+    if (error?.code === 'EADDRINUSE') {
+      if (await tryForwardToPrimaryInstance(message)) {
+        return false
+      }
     }
 
-    try {
-      await forwardToPrimaryInstance(buildSecondInstanceMessage())
-    } catch (forwardError) {
-      console.warn('Failed to forward to running instance:', forwardError)
-    }
-
-    return false
+    console.warn('Single instance lock failed:', error)
+    return true
   }
 }
 
@@ -159,6 +263,8 @@ export function setSingleInstanceHandlers({ onDeepLink, onFocus }) {
   while (pendingMessages.length > 0) {
     dispatchMessage(pendingMessages.shift())
   }
+
+  processPendingDeeplinkFile()
 }
 
 export function closeSingleInstanceServer() {
diff --git a/src/desktop/window.js b/src/desktop/window.js
index 8ce50d0..9ad7888 100644
--- a/src/desktop/window.js
+++ b/src/desktop/window.js
@@ -11,6 +11,7 @@ const isMacOS = process.platform === 'darwin'
 const DEV_SERVER_PORT = 5780
 const DEV_SERVER_URL = `http://localhost:${DEV_SERVER_PORT}`
 import { findProtocolUrl } from './single-instance.js'
+import { getWindowsLaunchSources } from './windows-launch-args.js'
 
 let mainWindow = null
 let webviewDomReady = false
@@ -84,7 +85,13 @@ export function handleDeepLink(url) {
 
 export function handleDeepLinkFromArgv() {
   if (process.platform === 'darwin') return
-  const url = findProtocolUrl(process.argv)
+
+  const sources = [...process.argv]
+  if (process.platform === 'win32') {
+    sources.push(...getWindowsLaunchSources())
+  }
+
+  const url = findProtocolUrl(sources)
   if (url) handleDeepLink(url)
 }
 
diff --git a/src/desktop/windows-launch-args.js b/src/desktop/windows-launch-args.js
new file mode 100644
index 0000000..424708d
--- /dev/null
+++ b/src/desktop/windows-launch-args.js
@@ -0,0 +1,39 @@
+export function getWindowsLaunchSources() {
+  if (process.platform !== 'win32') {
+    return []
+  }
+
+  try {
+    const proc = Bun.spawnSync({
+      cmd: [
+        'powershell.exe',
+        '-NoProfile',
+        '-NonInteractive',
+        '-Command',
+        `$pid = $PID
+for ($i = 0; $i -lt 6; $i++) {
+  $proc = Get-CimInstance Win32_Process -Filter "ProcessId=$pid" -ErrorAction SilentlyContinue
+  if (-not $proc) { break }
+  if ($proc.CommandLine) { $proc.CommandLine }
+  if ($proc.CommandLine -match 'farmcontrol://') { break }
+  if (-not $proc.ParentProcessId) { break }
+  $pid = $proc.ParentProcessId
+}`
+      ],
+      stdout: 'pipe',
+      stderr: 'pipe'
+    })
+
+    if (proc.exitCode !== 0) {
+      return []
+    }
+
+    return proc.stdout
+      .toString()
+      .split(/\r?\n/)
+      .map((line) => line.trim())
+      .filter(Boolean)
+  } catch {
+    return []
+  }
+}