diff --git a/packages/shade-sdk/tests/broadcast.test.ts b/packages/shade-sdk/tests/broadcast.test.ts
index 0105e8a..91049c6 100644
--- a/packages/shade-sdk/tests/broadcast.test.ts
+++ b/packages/shade-sdk/tests/broadcast.test.ts
@@ -14,8 +14,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     store: new MemoryPrekeyStore(),
     disableRateLimit: true,
   });
-  const port = 19500 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
diff --git a/packages/shade-sdk/tests/gates.test.ts b/packages/shade-sdk/tests/gates.test.ts
index 34ca154..e092313 100644
--- a/packages/shade-sdk/tests/gates.test.ts
+++ b/packages/shade-sdk/tests/gates.test.ts
@@ -12,8 +12,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     store: new MemoryPrekeyStore(),
     disableRateLimit: true,
   });
-  const port = 19500 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
diff --git a/packages/shade-sdk/tests/profile.test.ts b/packages/shade-sdk/tests/profile.test.ts
index 017751c..a4769a3 100644
--- a/packages/shade-sdk/tests/profile.test.ts
+++ b/packages/shade-sdk/tests/profile.test.ts
@@ -36,8 +36,12 @@ async function startServer(): Promise<ServerHandle> {
     blobStore: new MemoryBlobStore(),
     disableRateLimit: true,
   });
-  const port = 19000 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: app.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: app.fetch });
+  const port = handle.port;
   return {
     url: `http://localhost:${port}`,
     stop: () => handle.stop(true),
diff --git a/packages/shade-sdk/tests/sdk.test.ts b/packages/shade-sdk/tests/sdk.test.ts
index db4e20e..37ad6ee 100644
--- a/packages/shade-sdk/tests/sdk.test.ts
+++ b/packages/shade-sdk/tests/sdk.test.ts
@@ -25,8 +25,12 @@ async function startPrekeyServer(): Promise<{
     disableRateLimit: true,
     events,
   });
-  const port = 19500 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return {
     url: `http://localhost:${port}`,
     stop: () => handle.stop(),
diff --git a/packages/shade-sdk/tests/streams-integration.test.ts b/packages/shade-sdk/tests/streams-integration.test.ts
index 52269da..c3bff57 100644
--- a/packages/shade-sdk/tests/streams-integration.test.ts
+++ b/packages/shade-sdk/tests/streams-integration.test.ts
@@ -26,8 +26,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     disableRateLimit: true,
     events,
   });
-  const port = 21000 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
@@ -46,8 +50,12 @@ async function setupRig(): Promise<TestRig> {
 
   // Spin up Bob's HTTP transfer endpoint.
   const bobApp = await bob.transferRoute();
-  const port = 21500 + Math.floor(Math.random() * 500);
-  const bobServer = Bun.serve({ port, fetch: bobApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const bobServer = Bun.serve({ port: 0, fetch: bobApp.fetch });
+  const port = bobServer.port;
   const bobBaseUrl = `http://localhost:${port}`;
 
   // Wire up Alice's outgoing transfer routing.
diff --git a/packages/shade-sdk/tests/thumbnail.test.ts b/packages/shade-sdk/tests/thumbnail.test.ts
index 50661da..b396407 100644
--- a/packages/shade-sdk/tests/thumbnail.test.ts
+++ b/packages/shade-sdk/tests/thumbnail.test.ts
@@ -33,8 +33,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     disableRateLimit: true,
     events,
   });
-  const port = 22000 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
@@ -49,8 +53,12 @@ async function setupRig(): Promise<TestRig> {
     },
   });
   const bobApp = await bob.transferRoute();
-  const port = 22500 + Math.floor(Math.random() * 500);
-  const bobServer = Bun.serve({ port, fetch: bobApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const bobServer = Bun.serve({ port: 0, fetch: bobApp.fetch });
+  const port = bobServer.port;
   const bobBaseUrl = `http://localhost:${port}`;
 
   alice.configureTransfers({
diff --git a/packages/shade-sdk/tests/webrtc-failover.test.ts b/packages/shade-sdk/tests/webrtc-failover.test.ts
index e3c117f..a3bfc1f 100644
--- a/packages/shade-sdk/tests/webrtc-failover.test.ts
+++ b/packages/shade-sdk/tests/webrtc-failover.test.ts
@@ -103,8 +103,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     disableRateLimit: true,
     events,
   });
-  const port = 23000 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
@@ -127,13 +131,21 @@ async function setupRig(connectTimeoutMs: number): Promise<Rig> {
   bob.configureWebRTC({ factory: broken, connectTimeoutMs });
 
   const bobApp = await bob.transferRoute();
-  const bobPort = 23500 + Math.floor(Math.random() * 500);
-  const bobServer = Bun.serve({ port: bobPort, fetch: bobApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const bobServer = Bun.serve({ port: 0, fetch: bobApp.fetch });
+  const bobPort = bobServer.port;
   baseUrls.set('bob', `http://localhost:${bobPort}`);
 
   const aliceApp = await alice.transferRoute();
-  const alicePort = 24000 + Math.floor(Math.random() * 500);
-  const aliceServer = Bun.serve({ port: alicePort, fetch: aliceApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const aliceServer = Bun.serve({ port: 0, fetch: aliceApp.fetch });
+  const alicePort = aliceServer.port;
   baseUrls.set('alice', `http://localhost:${alicePort}`);
 
   return {
@@ -145,12 +157,18 @@ async function setupRig(connectTimeoutMs: number): Promise<Rig> {
   };
 }
 
-async function teardownRig(rig: Rig): Promise<void> {
-  await rig.alice.shutdown();
-  await rig.bob.shutdown();
-  rig.bobServerStop();
-  rig.aliceServerStop();
-  rig.prekeyStop();
+async function teardownRig(rig: Rig | undefined): Promise<void> {
+  // Tolerates a rig that never finished being built. When setupRig threw —
+  // EADDRINUSE, before ports stopped being guessed — this ran anyway and died
+  // on `rig.alice`, so one failure became two and the second one, a TypeError
+  // in teardown, is what you saw first. Cleanup must never be the loudest
+  // thing in a failing test.
+  if (!rig) return;
+  await rig.alice?.shutdown().catch(() => {});
+  await rig.bob?.shutdown().catch(() => {});
+  try { rig.bobServerStop?.(); } catch { /* already gone */ }
+  try { rig.aliceServerStop?.(); } catch { /* already gone */ }
+  try { rig.prekeyStop?.(); } catch { /* already gone */ }
 }
 
 function hex(b: Uint8Array): string {
diff --git a/packages/shade-sdk/tests/webrtc-integration.test.ts b/packages/shade-sdk/tests/webrtc-integration.test.ts
index aebe0b6..f5a1bad 100644
--- a/packages/shade-sdk/tests/webrtc-integration.test.ts
+++ b/packages/shade-sdk/tests/webrtc-integration.test.ts
@@ -40,8 +40,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     disableRateLimit: true,
     events,
   });
-  const port = 22000 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
@@ -70,13 +74,21 @@ async function setupRig(): Promise<Rig> {
   bob.configureWebRTC({ factory, connectTimeoutMs: 10_000 });
 
   const bobApp = await bob.transferRoute();
-  const bobPort = 22500 + Math.floor(Math.random() * 500);
-  const bobServer = Bun.serve({ port: bobPort, fetch: bobApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const bobServer = Bun.serve({ port: 0, fetch: bobApp.fetch });
+  const bobPort = bobServer.port;
   const bobBaseUrl = `http://localhost:${bobPort}`;
 
   const aliceApp = await alice.transferRoute();
-  const alicePort = 22000 + Math.floor(Math.random() * 500);
-  const aliceServer = Bun.serve({ port: alicePort, fetch: aliceApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const aliceServer = Bun.serve({ port: 0, fetch: aliceApp.fetch });
+  const alicePort = aliceServer.port;
   const aliceBaseUrl = `http://localhost:${alicePort}`;
 
   baseUrls.set('alice', aliceBaseUrl);
diff --git a/packages/shade-sdk/tests/webrtc-throughput.test.ts b/packages/shade-sdk/tests/webrtc-throughput.test.ts
index cab8dcd..bb9b023 100644
--- a/packages/shade-sdk/tests/webrtc-throughput.test.ts
+++ b/packages/shade-sdk/tests/webrtc-throughput.test.ts
@@ -44,8 +44,12 @@ async function startPrekeyServer(): Promise<{ url: string; stop: () => void }> {
     disableRateLimit: true,
     events,
   });
-  const port = 24500 + Math.floor(Math.random() * 500);
-  const handle = Bun.serve({ port, fetch: server.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const handle = Bun.serve({ port: 0, fetch: server.fetch });
+  const port = handle.port;
   return { url: `http://localhost:${port}`, stop: () => handle.stop() };
 }
 
@@ -70,13 +74,21 @@ async function setupRig(opts: { withWebRTC: boolean }): Promise<Rig> {
   }
 
   const bobApp = await bob.transferRoute();
-  const bobPort = 25000 + Math.floor(Math.random() * 500);
-  const bobServer = Bun.serve({ port: bobPort, fetch: bobApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const bobServer = Bun.serve({ port: 0, fetch: bobApp.fetch });
+  const bobPort = bobServer.port;
   baseUrls.set('bob', `http://localhost:${bobPort}`);
 
   const aliceApp = await alice.transferRoute();
-  const alicePort = 25500 + Math.floor(Math.random() * 500);
-  const aliceServer = Bun.serve({ port: alicePort, fetch: aliceApp.fetch });
+  // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+  // range and hoped — and several files here guessed inside the SAME range,
+  // so with test files serving in parallel the collision arrived about a
+  // quarter of the time as EADDRINUSE.
+  const aliceServer = Bun.serve({ port: 0, fetch: aliceApp.fetch });
+  const alicePort = aliceServer.port;
   baseUrls.set('alice', `http://localhost:${alicePort}`);
 
   return {
diff --git a/packages/shade-transfer/tests/resume.test.ts b/packages/shade-transfer/tests/resume.test.ts
index 76ac562..325ad13 100644
--- a/packages/shade-transfer/tests/resume.test.ts
+++ b/packages/shade-transfer/tests/resume.test.ts
@@ -41,8 +41,12 @@ describe('Resume protocol — kill-restart-verify', () => {
       myAddress: 'bob',
     });
     const receiverApp = await createTransferRoutes(receiverEngine);
-    const port = 22000 + Math.floor(Math.random() * 500);
-    const server = Bun.serve({ port, fetch: receiverApp.fetch });
+    // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+    // range and hoped — and several files here guessed inside the SAME range,
+    // so with test files serving in parallel the collision arrived about a
+    // quarter of the time as EADDRINUSE.
+    const server = Bun.serve({ port: 0, fetch: receiverApp.fetch });
+    const port = server.port;
     const baseUrl = `http://localhost:${port}`;
 
     // Receiver accepts incoming.
diff --git a/packages/shade-transfer/tests/ws-fallback.test.ts b/packages/shade-transfer/tests/ws-fallback.test.ts
index 3f0f153..befbca4 100644
--- a/packages/shade-transfer/tests/ws-fallback.test.ts
+++ b/packages/shade-transfer/tests/ws-fallback.test.ts
@@ -39,8 +39,12 @@ describe('WS opt-in transport with HTTP fallback', () => {
       myAddress: 'bob',
     });
     const httpApp = await createTransferRoutes(receiverEngine);
-    const httpPort = 23000 + Math.floor(Math.random() * 500);
-    const httpServer = Bun.serve({ port: httpPort, fetch: httpApp.fetch });
+    // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+    // range and hoped — and several files here guessed inside the SAME range,
+    // so with test files serving in parallel the collision arrived about a
+    // quarter of the time as EADDRINUSE.
+    const httpServer = Bun.serve({ port: 0, fetch: httpApp.fetch });
+    const httpPort = httpServer.port;
     const httpBaseUrl = `http://localhost:${httpPort}`;
     cleanups.push(() => httpServer.stop());
 
diff --git a/packages/shade-transport/tests/kt-transport.test.ts b/packages/shade-transport/tests/kt-transport.test.ts
index 8ebfdac..4910596 100644
--- a/packages/shade-transport/tests/kt-transport.test.ts
+++ b/packages/shade-transport/tests/kt-transport.test.ts
@@ -31,8 +31,12 @@ describe('ShadeFetchTransport with KT verifier', () => {
       },
     });
 
-    const port = 20100 + Math.floor(Math.random() * 500);
-    const handle = Bun.serve({ port, fetch: app.fetch });
+    // Port 0 lets the OS hand out a free one. This guessed inside a 500-wide
+    // range and hoped — and several files here guessed inside the SAME range,
+    // so with test files serving in parallel the collision arrived about a
+    // quarter of the time as EADDRINUSE.
+    const handle = Bun.serve({ port: 0, fetch: app.fetch });
+    const port = handle.port;
     try {
       const baseUrl = `http://localhost:${port}`;