diff --git a/src/agent-runtime.ts b/src/agent-runtime.ts
index 5fdacdc..d2edbd0 100644
--- a/src/agent-runtime.ts
+++ b/src/agent-runtime.ts
@@ -355,7 +355,8 @@ export class AgentRuntime {
   /** Current step identifier */
   stepId: string | null = null;
   /** Current step index (0-based) */
-  stepIndex: number = 0;
+  // 0-based step indexing (first auto-generated stepId is "step-0")
+  stepIndex: number = -1;
   /** Most recent snapshot (for assertion context) */
   lastSnapshot: Snapshot | null = null;
   private stepPreSnapshot: Snapshot | null = null;
diff --git a/src/debugger.ts b/src/debugger.ts
index 7a58b18..bea3bec 100644
--- a/src/debugger.ts
+++ b/src/debugger.ts
@@ -1,13 +1,53 @@
 import { Page } from 'playwright';
 
-import { AgentRuntime, AttachOptions } from './agent-runtime';
+import { AgentRuntime, AssertionHandle, AttachOptions } from './agent-runtime';
 import { Predicate } from './verification';
 import { Tracer } from './tracing/tracer';
 
+class DebuggerAssertionHandle extends AssertionHandle {
+  private dbg: SentienceDebugger;
+  private autoClose: boolean;
+  private openedStepId: string | null;
+
+  constructor(
+    dbg: SentienceDebugger,
+    predicate: Predicate,
+    label: string,
+    required: boolean,
+    autoClose: boolean,
+    openedStepId: string | null
+  ) {
+    super(dbg.runtime, predicate, label, required);
+    this.dbg = dbg;
+    this.autoClose = autoClose;
+    this.openedStepId = openedStepId;
+  }
+
+  override once(): boolean {
+    const ok = super.once();
+    if (this.autoClose && this.dbg.isAutoStepOpenFor(this.openedStepId)) {
+      void this.dbg.endStep();
+    }
+    return ok;
+  }
+
+  override async eventually(
+    options: Parameters<AssertionHandle['eventually']>[0] = {}
+  ): Promise<boolean> {
+    const ok = await super.eventually(options);
+    if (this.autoClose && this.dbg.isAutoStepOpenFor(this.openedStepId)) {
+      await this.dbg.endStep();
+    }
+    return ok;
+  }
+}
+
 export class SentienceDebugger {
   readonly runtime: AgentRuntime;
   private stepOpen: boolean = false;
   private autoStep: boolean = true;
+  private autoOpenedStep: boolean = false;
+  private autoOpenedStepId: string | null = null;
 
   constructor(runtime: AgentRuntime, options?: { autoStep?: boolean }) {
     this.runtime = runtime;
@@ -19,13 +59,31 @@ export class SentienceDebugger {
     return new SentienceDebugger(runtime);
   }
 
+  isAutoStepOpenFor(stepId: string | null): boolean {
+    return Boolean(
+      this.stepOpen &&
+      this.autoOpenedStep &&
+      this.autoOpenedStepId &&
+      stepId &&
+      this.autoOpenedStepId === stepId
+    );
+  }
+
   beginStep(goal: string, stepIndex?: number): string {
+    // If we previously auto-opened a verification step, close it before starting a real step.
+    if (this.stepOpen && this.autoOpenedStep) {
+      void this.endStep();
+      this.autoOpenedStep = false;
+      this.autoOpenedStepId = null;
+    }
     this.stepOpen = true;
     return this.runtime.beginStep(goal, stepIndex);
   }
 
   async endStep(opts: Parameters<AgentRuntime['emitStepEnd']>[0] = {}): Promise<any> {
     this.stepOpen = false;
+    this.autoOpenedStep = false;
+    this.autoOpenedStepId = null;
     // emitStepEnd is synchronous; wrap to satisfy async/await lint rules.
     return await Promise.resolve(this.runtime.emitStepEnd(opts));
   }
@@ -43,7 +101,13 @@ export class SentienceDebugger {
     return this.runtime.snapshot(options);
   }
 
+  async recordAction(action: string, url?: string): Promise<void> {
+    return await this.runtime.recordAction(action, url);
+  }
+
   check(predicate: Predicate, label: string, required: boolean = false) {
+    let didAutoOpen = false;
+    let openedStepId: string | null = null;
     if (!this.stepOpen) {
       if (!this.autoStep) {
         throw new Error(
@@ -53,7 +117,17 @@ export class SentienceDebugger {
         );
       }
       this.beginStep(`verify:${label}`);
+      didAutoOpen = true;
+      openedStepId = this.runtime.stepId;
+      this.autoOpenedStep = true;
+      this.autoOpenedStepId = openedStepId;
+    }
+    const base = this.runtime.check(predicate, label, required);
+    if (!didAutoOpen) {
+      return base;
     }
-    return this.runtime.check(predicate, label, required);
+    // Return an auto-closing handle for the common "casual" sidecar usage pattern.
+    // We still call runtime.check(...) above to keep behavior consistent.
+    return new DebuggerAssertionHandle(this, predicate, label, required, true, openedStepId);
   }
 }
diff --git a/tests/agent-runtime-assertions.test.ts b/tests/agent-runtime-assertions.test.ts
index 0948d43..4069b09 100644
--- a/tests/agent-runtime-assertions.test.ts
+++ b/tests/agent-runtime-assertions.test.ts
@@ -57,12 +57,12 @@ describe('AgentRuntime.beginStep() stepId format', () => {
     const runtime = new AgentRuntime(browserLike as any, page as any, tracer);
 
     const stepId1 = runtime.beginStep('Step 1');
-    expect(stepId1).toBe('step-1');
-    expect(runtime.stepIndex).toBe(1);
+    expect(stepId1).toBe('step-0');
+    expect(runtime.stepIndex).toBe(0);
 
     const stepId2 = runtime.beginStep('Step 2');
-    expect(stepId2).toBe('step-2');
-    expect(runtime.stepIndex).toBe(2);
+    expect(stepId2).toBe('step-1');
+    expect(runtime.stepIndex).toBe(1);
   });
 
   it('generates stepId matching explicit stepIndex', () => {
diff --git a/tests/debugger.test.ts b/tests/debugger.test.ts
index 3c2f189..11bc4bf 100644
--- a/tests/debugger.test.ts
+++ b/tests/debugger.test.ts
@@ -64,7 +64,7 @@ describe('SentienceDebugger', () => {
 
     expect(runtime.beginStep).toHaveBeenCalledWith('verify:has_cart', undefined);
     expect(runtime.check).toHaveBeenCalled();
-    expect(handle).toBe('handle');
+    expect(typeof (handle as any).once).toBe('function');
   });
 
   it('can disable auto-step (strict mode)', () => {