diff --git a/docs/guide/deploying.md b/docs/guide/deploying.md
index 81536e1..b2e3f7b 100644
--- a/docs/guide/deploying.md
+++ b/docs/guide/deploying.md
@@ -41,6 +41,17 @@ To install Browser or Voice from Settings:
 
 Follow [Docker add-ons](/guide/add-ons) for installation, controls, storage and cleanup.
 
+## Resuming container sessions
+
+The container executor automatically removes completed runners. Before starting
+a session, it also removes a leftover stopped runner with the same name, but
+only when its ownership labels match that session.
+
+A running runner is left alone. Wait for its current task to finish before
+resuming. If an unrelated container uses the same name, the portal reports the
+collision; inspect that container and rename or remove it yourself once you
+have identified it. The portal does not force-delete it.
+
 ## Updating
 
 ```bash
diff --git a/server/src/executors/index.ts b/server/src/executors/index.ts
index 5773959..a368012 100644
--- a/server/src/executors/index.ts
+++ b/server/src/executors/index.ts
@@ -1,5 +1,6 @@
 import { spawn } from "node:child_process";
 import path from "node:path";
+import { removeStoppedRunner } from "./stale-container.js";
 import { PiRpcClient } from "../pi/rpc-client.js";
 import { SdkPiClient } from "../pi/sdk-client.js";
 import type { PiClient } from "../pi/types.js";
@@ -147,6 +148,7 @@ export class ContainerExecutor implements Executor {
       ...piArgs({ ...opts }, "/sessions"),
     ];
 
+    await removeStoppedRunner(opts.sessionId);
     const child = spawn("docker", args, { stdio: ["pipe", "pipe", "pipe"] });
     return new PiRpcClient(child);
   }
diff --git a/server/src/executors/stale-container.ts b/server/src/executors/stale-container.ts
new file mode 100644
index 0000000..ae41646
--- /dev/null
+++ b/server/src/executors/stale-container.ts
@@ -0,0 +1,30 @@
+import { execFile } from 'node:child_process';
+import { promisify } from 'node:util';
+
+const exec = promisify(execFile);
+type DockerCommand = (args: string[]) => Promise<string>;
+const docker: DockerCommand = async (args) => (await exec('docker', args)).stdout;
+
+/** Reclaim an old session name without killing a live or unrelated container. */
+export async function removeStoppedRunner(sessionId: string, run: DockerCommand = docker): Promise<void> {
+  const name = `pithagoras-${sessionId}`;
+  let output: string;
+  try {
+    output = await run(['container', 'inspect', name]);
+  } catch (error) {
+    const stderr = (error as {stderr?: string}).stderr ?? '';
+    if (/No such (?:object|container):/i.test(stderr)) return;
+    throw error;
+  }
+  const [container] = JSON.parse(output);
+  const labels = container?.Config?.Labels;
+  if (labels?.['pithagoras.managed'] !== 'true' || labels?.['pithagoras.session'] !== sessionId) {
+    throw new Error(`Container ${name} is not owned by this session; remove or rename it manually.`);
+  }
+  if (!['created', 'exited', 'dead'].includes(container.State?.Status)) {
+    throw new Error(`Container ${name} is still active; wait for it to stop before resuming.`);
+  }
+  // Use the inspected ID, never force removal: a container that starts between
+  // inspect and rm remains protected by Docker's running-container check.
+  await run(['container', 'rm', container.Id]);
+}
diff --git a/tests/stale-container.test.mts b/tests/stale-container.test.mts
new file mode 100644
index 0000000..7f34340
--- /dev/null
+++ b/tests/stale-container.test.mts
@@ -0,0 +1,24 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {removeStoppedRunner} from '../server/src/executors/stale-container.ts';
+const fixture=(status='exited',managed='true')=>JSON.stringify([{Id:'immutable-container-id',Config:{Labels:{'pithagoras.managed':managed,'pithagoras.session':'test'}},State:{Status:status}}]);
+test('only stopped managed runners are removed, by ID without force',async()=>{
+ for(const status of ['created','exited','dead']){
+  const calls:string[][]=[];
+  await removeStoppedRunner('test',async args=>{calls.push(args);return calls.length===1?fixture(status):''});
+  assert.deepEqual(calls,[['container','inspect','pithagoras-test'],['container','rm','immutable-container-id']]);
+ }
+});
+test('running or unrelated containers are never removed',async()=>{
+ for(const output of [fixture('running'),fixture('paused'),fixture('restarting'),fixture('exited','false')]){
+  let calls=0;
+  await assert.rejects(removeStoppedRunner('test',async()=>{calls++;return output}));
+  assert.equal(calls,1);
+ }
+});
+test('missing container is normal; daemon and removal failures propagate',async()=>{
+ await removeStoppedRunner('test',async()=>{throw Object.assign(new Error(),{stderr:'Error: No such container: pithagoras-test'})});
+ await assert.rejects(removeStoppedRunner('test',async()=>{throw Object.assign(new Error('daemon unavailable'),{stderr:'Cannot connect to Docker daemon'})}),/daemon unavailable/);
+ let calls=0;
+ await assert.rejects(removeStoppedRunner('test',async()=>{if(++calls===1)return fixture();throw new Error('container is running')}),/container is running/);
+});