diff --git a/electron/main/process-runner-worker-exit.test.mjs b/electron/main/process-runner-worker-exit.test.mjs
new file mode 100644
index 00000000..068ccc7e
--- /dev/null
+++ b/electron/main/process-runner-worker-exit.test.mjs
@@ -0,0 +1,83 @@
+/**
+ * A JS process extension runs in a worker thread that is kept warm between
+ * runs. If that worker dies mid-run -- an uncaught error outside the awaited
+ * processor call, running out of memory on a large mesh, process.exit() -- it
+ * never posts 'done' or 'error'. The run must settle with an error instead of
+ * leaving the workflow waiting forever, and the next run must get a fresh
+ * worker rather than posting into the dead one.
+ */
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { buildSync } from 'esbuild'
+import { createRequire } from 'node:module'
+import { mkdtempSync, mkdirSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join, resolve } from 'node:path'
+
+function loadModule() {
+  const outfile = join(mkdtempSync(join(tmpdir(), 'modly-worker-exit-test-')), 'process-runner.cjs')
+  const require = createRequire(import.meta.url)
+  const result = buildSync({
+    entryPoints: [resolve('electron/main/process-runner.ts')],
+    bundle: true,
+    platform: 'node',
+    format: 'cjs',
+    write: false,
+  })
+  writeFileSync(outfile, result.outputFiles[0].text, 'utf8')
+  return require(outfile)
+}
+
+// Behaves according to params.mode; `runs` counts runs served by this worker,
+// so a fresh worker starts again from 1.
+function makeRunner() {
+  const { ProcessRunner } = loadModule()
+  const root = mkdtempSync(join(tmpdir(), 'modly-worker-exit-'))
+  const extDir = join(root, 'ext')
+  mkdirSync(extDir, { recursive: true })
+  writeFileSync(join(extDir, 'processor.js'), [
+    'let runs = 0',
+    'module.exports = async (input, params) => {',
+    '  runs += 1',
+    "  if (params.mode === 'throw') throw new Error('bad input')",
+    "  if (params.mode === 'crash') {",
+    "    setTimeout(() => { throw new Error('worker blew up') }, 0)",
+    '    return new Promise(() => {})',
+    '  }',
+    "  if (params.mode === 'exit') process.exit(3)",
+    '  return { text: String(runs) }',
+    '}',
+    '',
+  ].join('\n'))
+  return new ProcessRunner(extDir, 'processor.js', join(root, 'workspace'), root)
+}
+
+test('a run whose worker crashes rejects instead of hanging', { timeout: 5000 }, async () => {
+  const runner = makeRunner()
+  try {
+    await assert.rejects(runner.run({}, { mode: 'crash' }), /worker blew up/)
+  } finally {
+    runner.terminate()
+  }
+})
+
+test('after its worker exits, the runner starts a fresh one for the next run', { timeout: 5000 }, async () => {
+  const runner = makeRunner()
+  try {
+    await assert.rejects(runner.run({}, { mode: 'exit' }), /exited with code 3/)
+    assert.deepEqual(await runner.run({}, { mode: 'ok' }), { text: '1' })
+  } finally {
+    runner.terminate()
+  }
+})
+
+test('an error thrown by the processor still rejects with its message and keeps the warm worker', { timeout: 5000 }, async () => {
+  const runner = makeRunner()
+  try {
+    await assert.rejects(runner.run({}, { mode: 'throw' }), { message: 'Error: bad input' })
+    // Same worker thread: its run counter carried over instead of restarting.
+    assert.deepEqual(await runner.run({}, { mode: 'ok' }), { text: '2' })
+  } finally {
+    runner.terminate()
+  }
+})
diff --git a/electron/main/process-runner.ts b/electron/main/process-runner.ts
index 758f62d2..d12a7eec 100644
--- a/electron/main/process-runner.ts
+++ b/electron/main/process-runner.ts
@@ -127,25 +127,52 @@ export class ProcessRunner implements IProcessRunner {
     const worker = this.worker!
 
     return new Promise((resolve, reject) => {
+      const settle = () => {
+        worker.off('message', handler)
+        worker.off('error', onError)
+        worker.off('exit', onExit)
+      }
       const handler = (msg: { type: string; result?: ProcessResult; message?: string; percent?: number; label?: string }) => {
         if (msg.type === 'progress') {
           onProgress?.(msg.percent ?? 0, msg.label ?? '')
         } else if (msg.type === 'log') {
           onLog?.(msg.message ?? '')
         } else if (msg.type === 'done') {
-          worker.off('message', handler)
+          settle()
           resolve(msg.result ?? {})
         } else if (msg.type === 'error') {
-          worker.off('message', handler)
+          settle()
           reject(new Error(msg.message))
         }
       }
+      // A worker that dies mid-run (an uncaught error, out of memory,
+      // process.exit) never posts 'done' or 'error'. Settle the run instead of
+      // waiting forever, and drop the dead worker so the next run starts a
+      // fresh one rather than posting into it.
+      const onError = (err: Error) => {
+        settle()
+        this.discardWorker(worker)
+        reject(err)
+      }
+      const onExit = (code: number) => {
+        settle()
+        this.discardWorker(worker)
+        reject(new Error(`Process extension worker exited with code ${code}`))
+      }
 
       worker.on('message', handler)
+      worker.on('error', onError)
+      worker.on('exit', onExit)
       worker.postMessage({ action: 'run', input, params })
     })
   }
 
+  private discardWorker(worker: Worker): void {
+    if (this.worker !== worker) return
+    this.worker = null
+    this.ready  = false
+  }
+
   terminate(): void {
     this.worker?.terminate()
     this.worker = null