diff --git a/docs/agent-playbooks/known-surprises.md b/docs/agent-playbooks/known-surprises.md
index bcc0bb42..c70bea4f 100644
--- a/docs/agent-playbooks/known-surprises.md
+++ b/docs/agent-playbooks/known-surprises.md
@@ -75,5 +75,5 @@ If uncertain, ask the developer before adding an entry.
 - **Context:** Starting `yarn start` in one 5chan worktree while another 5chan worktree was already serving through Portless
 - **What was surprising:** Using the literal Portless app name `5chan` in every worktree makes the route itself collide, even when the backing ports are different, so the second process fails with `"5chan.localhost" is already registered`.
 - **Impact:** Parallel 5chan branches can block each other even though Portless is meant to let them coexist safely.
-- **Mitigation:** Keep Portless startup behind `scripts/start-dev.js`, which now uses a branch-scoped `*.5chan.localhost:1355` route outside the canonical case and falls back to a branch-scoped route when the bare `5chan.localhost` name is already occupied.
+- **Mitigation:** Keep Portless startup behind `scripts/start-dev.js`, which now uses a branch-scoped `*.5chan.localhost:1355` route outside the canonical case and automatically increments a `-2`, `-3`, ... suffix when that branch-scoped route is already occupied.
 - **Status:** confirmed
diff --git a/scripts/start-dev.js b/scripts/start-dev.js
index 0ca4679b..27f2e32b 100644
--- a/scripts/start-dev.js
+++ b/scripts/start-dev.js
@@ -36,7 +36,7 @@ function getCurrentBranch() {
   return branch || null;
 }
 
-function isCanonicalRouteBusy() {
+function getActivePortlessRoutes() {
   const result = spawnSync(portlessBin, ['list'], {
     cwd: process.cwd(),
     encoding: 'utf8',
@@ -44,13 +44,19 @@ function isCanonicalRouteBusy() {
   });
 
   if (result.status !== 0) {
-    return false;
+    return new Set();
   }
 
-  return result.stdout.includes('http://5chan.localhost:1355');
+  const matches = result.stdout.match(/http:\/\/[a-z0-9.-]+\.localhost:1355/g) || [];
+
+  return new Set(matches);
 }
 
-function getPortlessAppName() {
+function isRouteBusy(activeRoutes, appName) {
+  return activeRoutes.has(`http://${appName}.localhost:1355`);
+}
+
+function getPreferredPortlessAppName(activeRoutes) {
   const branch = getCurrentBranch();
   const branchLabel = sanitizeLabel(branch || 'current');
 
@@ -58,13 +64,32 @@ function getPortlessAppName() {
     return `${branchLabel}.5chan`;
   }
 
-  if (isCanonicalRouteBusy()) {
+  if (isRouteBusy(activeRoutes, '5chan')) {
     return `${branchLabel}.5chan`;
   }
 
   return '5chan';
 }
 
+function getPortlessAppName() {
+  const activeRoutes = getActivePortlessRoutes();
+  const preferredAppName = getPreferredPortlessAppName(activeRoutes);
+
+  if (!isRouteBusy(activeRoutes, preferredAppName)) {
+    return preferredAppName;
+  }
+
+  for (let suffix = 2; suffix < 1000; suffix += 1) {
+    const candidate = `${preferredAppName}-${suffix}`;
+
+    if (!isRouteBusy(activeRoutes, candidate)) {
+      return candidate;
+    }
+  }
+
+  return `${preferredAppName}-${Date.now()}`;
+}
+
 const command = usePortless && existsSync(portlessBin) ? portlessBin : viteBin;
 let args;
 let publicUrl = null;