diff --git a/docs/plans/state.json b/docs/plans/state.json
index b47a7f3..6551803 100644
--- a/docs/plans/state.json
+++ b/docs/plans/state.json
@@ -368,6 +368,20 @@
       ],
       "test_status": "pnpm test:run src/companion/heartbeatLoop.test.ts src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
     },
+    "companion-runtime-and-loop-option-validation": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added constructor option validation guards for companion runtime utilities (`requestTimeoutMs > 0`, `intervalMs > 0`, and valid `maxConsecutiveFailures` bounds) with regression tests.",
+      "files_modified": [
+        "src/companion/runtimeClient.ts",
+        "src/companion/runtimeClient.test.ts",
+        "src/companion/heartbeatLoop.ts",
+        "src/companion/heartbeatLoop.test.ts",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.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/heartbeatLoop.test.ts b/src/companion/heartbeatLoop.test.ts
index 3532cde..3f4928d 100644
--- a/src/companion/heartbeatLoop.test.ts
+++ b/src/companion/heartbeatLoop.test.ts
@@ -37,6 +37,16 @@ describe('CompanionHeartbeatLoop', () => {
     loop.stop();
   });
 
+  it('validates constructor options', () => {
+    const publisher = { publishHeartbeat: vi.fn(async () => buildStatusResult()) };
+    expect(() => new CompanionHeartbeatLoop(publisher, { intervalMs: 0 })).toThrow(
+      'intervalMs must be a positive number',
+    );
+    expect(() => new CompanionHeartbeatLoop(publisher, { maxConsecutiveFailures: 0 })).toThrow(
+      'maxConsecutiveFailures must be >= 1 when specified',
+    );
+  });
+
   it('supports delayed first run when runImmediately=false', async () => {
     const publishHeartbeat = vi.fn(async () => buildStatusResult());
     const loop = new CompanionHeartbeatLoop({ publishHeartbeat }, { intervalMs: 500 });
diff --git a/src/companion/heartbeatLoop.ts b/src/companion/heartbeatLoop.ts
index 2e2c889..04c1469 100644
--- a/src/companion/heartbeatLoop.ts
+++ b/src/companion/heartbeatLoop.ts
@@ -31,11 +31,23 @@ export class CompanionHeartbeatLoop {
   private consecutiveFailures = 0;
 
   constructor(publisher: HeartbeatPublisher, options: CompanionHeartbeatLoopOptions = {}) {
+    const intervalMs = options.intervalMs ?? 30_000;
+    if (!Number.isFinite(intervalMs) || intervalMs <= 0) {
+      throw new Error('intervalMs must be a positive number');
+    }
+    const maxConsecutiveFailures = options.maxConsecutiveFailures ?? Number.POSITIVE_INFINITY;
+    if (!Number.isFinite(maxConsecutiveFailures) && maxConsecutiveFailures !== Number.POSITIVE_INFINITY) {
+      throw new Error('maxConsecutiveFailures must be a positive number or Infinity');
+    }
+    if (Number.isFinite(maxConsecutiveFailures) && maxConsecutiveFailures < 1) {
+      throw new Error('maxConsecutiveFailures must be >= 1 when specified');
+    }
+
     this.publisher = publisher;
-    this.intervalMs = options.intervalMs ?? 30_000;
+    this.intervalMs = intervalMs;
     this.buildHeartbeat = options.buildHeartbeat;
     this.onError = options.onError;
-    this.maxConsecutiveFailures = options.maxConsecutiveFailures ?? Number.POSITIVE_INFINITY;
+    this.maxConsecutiveFailures = maxConsecutiveFailures;
     this.onFailureLimitReached = options.onFailureLimitReached;
   }
 
diff --git a/src/companion/runtimeClient.test.ts b/src/companion/runtimeClient.test.ts
index f8a44b2..2fad71c 100644
--- a/src/companion/runtimeClient.test.ts
+++ b/src/companion/runtimeClient.test.ts
@@ -96,6 +96,15 @@ afterAll(async () => {
 });
 
 describe('CompanionRuntimeClient', () => {
+  it('validates requestTimeoutMs option', () => {
+    expect(() => {
+      new CompanionRuntimeClient({
+        url: 'ws://127.0.0.1:1',
+        requestTimeoutMs: 0,
+      });
+    }).toThrow('requestTimeoutMs must be a positive number');
+  });
+
   it('dispatches gateway events to subscribed handlers and supports unsubscribe', () => {
     const client = new CompanionRuntimeClient({
       url: 'ws://127.0.0.1:1',
diff --git a/src/companion/runtimeClient.ts b/src/companion/runtimeClient.ts
index 321dec7..53c304e 100644
--- a/src/companion/runtimeClient.ts
+++ b/src/companion/runtimeClient.ts
@@ -270,9 +270,13 @@ export class CompanionRuntimeClient {
   private readonly eventHandlers = new Set<CompanionEventHandler>();
 
   constructor(options: CompanionRuntimeClientOptions) {
+    const requestTimeoutMs = options.requestTimeoutMs ?? 15_000;
+    if (!Number.isFinite(requestTimeoutMs) || requestTimeoutMs <= 0) {
+      throw new Error('requestTimeoutMs must be a positive number');
+    }
     this.url = options.url;
     this.token = options.token;
-    this.requestTimeoutMs = options.requestTimeoutMs ?? 15_000;
+    this.requestTimeoutMs = requestTimeoutMs;
     this.autoConnect = options.autoConnect ?? false;
     this.websocketFactory = options.websocketFactory ?? ((url) => new WebSocket(url));
   }