diff --git a/README.md b/README.md
index a230645..d6706cf 100644
--- a/README.md
+++ b/README.md
@@ -1190,7 +1190,7 @@ Methods:
 - `system.capabilities` returns gateway protocol and node policy snapshot.
 
 Companion runtime helper:
-- `src/companion/runtimeClient.ts` provides a typed Node/WebSocket client for companion runtimes (macOS/iOS/Android workers) with wrappers for `node.register`, `node.capabilities.get`, `node.location.set/get`, `node.status.set`, `node.push_token.set`, `system.capabilities`, `system.nodes`, and canvas artifact RPCs (`canvas.put/get/list/delete/clear`), plus convenience helpers (`bootstrapNode`, optional `autoConnect`, `dispose()`, `waitForIdle()` for pending-work drain synchronization) and event helpers (`subscribeEvents()`, `subscribeEvent()`, `subscribeAgentStream()`, `subscribeAgentTyping()`, `subscribeContextWarning()`, `waitForEvent()` with timeout/predicate/abort support, non-empty event-name validation, and deterministic teardown cancellation (including socket-close rejection), `waitForAnyEvent()` (with non-empty event-name-list validation), `waitForAgentStream()`, `waitForAgentTyping()`, `waitForContextWarning()`, `clearEventSubscriptions()`, `listKnownEventNames()`, `eventSubscriptionCount`) plus in-flight observability via `pendingRequestCount`, `pendingEventWaitCount`, `hasPendingWork`, `idle`, and `getPendingWorkSnapshot()`.
+- `src/companion/runtimeClient.ts` provides a typed Node/WebSocket client for companion runtimes (macOS/iOS/Android workers) with wrappers for `node.register`, `node.capabilities.get`, `node.location.set/get`, `node.status.set`, `node.push_token.set`, `system.capabilities`, `system.nodes`, and canvas artifact RPCs (`canvas.put/get/list/delete/clear`), plus convenience helpers (`bootstrapNode`, optional `autoConnect`, `dispose()`, `waitForIdle()` for pending-work drain synchronization) and event helpers (`subscribeEvents()`, `subscribeEvent()`, `subscribeAgentStream()`, `subscribeAgentTyping()`, `subscribeContextWarning()`, `waitForEvent()` with timeout/predicate/abort support plus event-name/timeout validation and deterministic teardown cancellation including socket-close rejection, `waitForAnyEvent()` with event-list/timeout validation, `waitForAgentStream()`, `waitForAgentTyping()`, `waitForContextWarning()`, `clearEventSubscriptions()`, `listKnownEventNames()`, `eventSubscriptionCount`) plus in-flight observability via `pendingRequestCount`, `pendingEventWaitCount`, `hasPendingWork`, `idle`, and `getPendingWorkSnapshot()`.
 - `src/companion/platformClients.ts` provides platform-focused wrappers:
   - `MacOSCompanionClient` (`platform: "macos"`, APNs push registration)
   - `IOSCompanionClient` (`platform: "ios"`, APNs push registration)
diff --git a/docs/plans/state.json b/docs/plans/state.json
index 64656f8..8f9460c 100644
--- a/docs/plans/state.json
+++ b/docs/plans/state.json
@@ -1027,6 +1027,19 @@
       ],
       "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
     },
+    "companion-runtime-event-timeout-validation": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added explicit `timeoutMs` validation (`> 0`) for `waitForEvent()` and `waitForAnyEvent()` to ensure deterministic option guardrails across runtime event wait helpers.",
+      "files_modified": [
+        "src/companion/runtimeClient.ts",
+        "src/companion/runtimeClient.test.ts",
+        "README.md",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
+    },
     "browser-tools-activation-clarity": {
       "status": "completed",
       "date": "2026-02-17",
diff --git a/src/companion/runtimeClient.test.ts b/src/companion/runtimeClient.test.ts
index 5b70189..0364b24 100644
--- a/src/companion/runtimeClient.test.ts
+++ b/src/companion/runtimeClient.test.ts
@@ -359,6 +359,9 @@ describe('CompanionRuntimeClient', () => {
     expect(() => client.waitForEvent(123 as unknown as string)).toThrow(
       'eventName must be a non-empty string',
     );
+    expect(() => client.waitForEvent('agent.stream', { timeoutMs: 0 })).toThrow(
+      'timeoutMs must be a positive number',
+    );
   });
 
   it('waitForEvent supports AbortSignal cancellation', async () => {
@@ -600,6 +603,9 @@ describe('CompanionRuntimeClient', () => {
     expect(() => client.waitForAnyEvent(['agent.stream', 123 as unknown as string])).toThrow(
       'eventNames must not contain empty values',
     );
+    expect(() => client.waitForAnyEvent(['agent.stream'], { timeoutMs: 0 })).toThrow(
+      'timeoutMs must be a positive number',
+    );
   });
 
   it('tracks pendingRequestCount for in-flight RPCs', async () => {
diff --git a/src/companion/runtimeClient.ts b/src/companion/runtimeClient.ts
index c470feb..ae8adb2 100644
--- a/src/companion/runtimeClient.ts
+++ b/src/companion/runtimeClient.ts
@@ -477,6 +477,9 @@ export class CompanionRuntimeClient {
       throw new Error('eventName must be a non-empty string');
     }
     const timeoutMs = options?.timeoutMs ?? this.requestTimeoutMs;
+    if (!Number.isFinite(timeoutMs) || timeoutMs <= 0) {
+      throw new Error('timeoutMs must be a positive number');
+    }
     const predicate = options?.predicate;
     const signal = options?.signal;
 
@@ -550,6 +553,9 @@ export class CompanionRuntimeClient {
     }
     const eventNameSet = new Set(eventNames);
     const timeoutMs = options?.timeoutMs ?? this.requestTimeoutMs;
+    if (!Number.isFinite(timeoutMs) || timeoutMs <= 0) {
+      throw new Error('timeoutMs must be a positive number');
+    }
     const predicate = options?.predicate;
     const signal = options?.signal;