@@ -18,6 +18,10 @@
       "types": "./src/snapshot/android-replacement-surface-occlusion.ts",
       "default": "./src/snapshot/android-replacement-surface-occlusion.ts"
     },
+    "./app-log-polling": {
+      "types": "./src/app-log-polling.ts",
+      "default": "./src/app-log-polling.ts"
+    },
     "./audio-probe-admission-ledger": {
       "types": "./src/capture-admission/audio-probe-admission-ledger.ts",
       "default": "./src/capture-admission/audio-probe-admission-ledger.ts"
 
@@ -0,0 +1,87 @@
+import type { AppLogRuntimeHost } from '@agent-device/contracts/app-log-runtime';
+
+export type DeferredSleeps = Readonly<{
+  wait(milliseconds: number): Promise<void>;
+  resolveNext(milliseconds: number): void;
+  resolveAny(): void;
+  hasPending(milliseconds: number): boolean;
+}>;
+
+export function createDeferredSleeps(): DeferredSleeps {
+  const pending: Array<{ milliseconds: number; resolve: () => void }> = [];
+  return {
+    wait: async (milliseconds: number) =>
+      await new Promise<void>((resolve) => pending.push({ milliseconds, resolve })),
+    resolveNext: (milliseconds: number) => {
+      const index = pending.findIndex((entry) => entry.milliseconds === milliseconds);
+      if (index < 0) throw new Error(`No ${milliseconds}ms sleep is pending`);
+      pending.splice(index, 1)[0]?.resolve();
+    },
+    resolveAny: () => pending.shift()?.resolve(),
+    hasPending: (milliseconds: number) =>
+      pending.some((entry) => entry.milliseconds === milliseconds),
+  };
+}
+
+export function createPollerHost(options: {
+  existingTail: string;
+  writes: string[];
+  sleeps: DeferredSleeps;
+  onOutputDispose?: () => void;
+  outputDisposeError?: boolean;
+  failure?: 'readTail' | 'openAppend';
+}): AppLogRuntimeHost {
+  return {
+    appleTools: {
+      isXcrunAvailable: async () => false,
+      run: async () => {
+        throw new Error('unused');
+      },
+    },
+    toolchains: { prepare: async () => undefined },
+    artifacts: {
+      resolveSession: () => ({
+        outputPath: '/sessions/one/app.log',
+        pidPath: '/sessions/one/app-log.pid',
+      }),
+    },
+    commands: {
+      which: async () => undefined,
+      run: async () => ({ stdout: '', stderr: '', exitCode: 0 }),
+    },
+    outputs: {
+      readTail: async () => {
+        if (options.failure === 'readTail') throw new Error('tail failed');
+        return options.existingTail;
+      },
+      openAppend: async () => {
+        if (options.failure === 'openAppend') throw new Error('open failed');
+        return {
+          write: async (chunk) => {
+            options.writes.push(String(chunk));
+          },
+          [Symbol.asyncDispose]: async () => {
+            if (options.outputDisposeError) throw new Error('output cleanup failed');
+            options.onOutputDispose?.();
+          },
+        };
+      },
+    },
+    processTransports: {
+      resolve: async () => ({ mode: 'local' }),
+    },
+    processes: {
+      start: async () => {
+        throw new Error('unused');
+      },
+      readMarker: async () => ({ status: 'missing' }),
+      clearMarker: async () => {},
+      inspect: async () => 'missing',
+      terminate: async () => 'already-missing',
+    },
+    clock: {
+      now: () => 100,
+      sleep: async (milliseconds) => await options.sleeps.wait(milliseconds),
+    },
+  };
+}