diff --git a/CHANGELOG.md b/CHANGELOG.md
index e7b44807..09d2224a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- **Plan cancellation is now prompt during parallel wave execution.** When every concurrency slot was full of slow steps, a cancelled plan kept spinning the `maxConcurrent` slot-wait until a step happened to finish — the wave-top abort check couldn't fire while the inner scheduling loop held control. The slot-wait (and the step-scheduling loop) now re-check `signal.aborted` and stop scheduling new steps immediately. Already-scheduled steps are still awaited via `Promise.all` before the abort is surfaced, so no in-flight promise is orphaned (which would otherwise become an unhandled rejection).
+
 ## [0.7.1] - 2026-06-05
 
 ### Fixed
diff --git a/packages/gateway/src/plans/executor.test.ts b/packages/gateway/src/plans/executor.test.ts
index e0387d1e..b98bc62f 100644
--- a/packages/gateway/src/plans/executor.test.ts
+++ b/packages/gateway/src/plans/executor.test.ts
@@ -936,6 +936,69 @@ describe('PlanExecutor', () => {
     });
   });
 
+  describe('wave execution abort', () => {
+    beforeEach(() => {
+      vi.useFakeTimers();
+    });
+    afterEach(() => {
+      vi.useRealTimers();
+    });
+
+    it('stops scheduling further steps and resolves cancelled when aborted during the slot-wait', async () => {
+      // Regression: with all concurrency slots full of slow steps, a cancelled
+      // plan used to spin the maxConcurrent slot-wait until a step finished
+      // (the wave-top abort check can't fire while the inner loop holds
+      // control). The slot-wait now re-checks signal.aborted and breaks; the
+      // scheduled steps are still awaited via Promise.all (no orphaned promise
+      // / unhandled rejection), then the abort is surfaced as 'cancelled'.
+      const waveExecutor = new PlanExecutor({
+        userId: 'user-1',
+        enableWaveExecution: true,
+        maxConcurrent: 1,
+      });
+      const stepA = makeStep({ id: 'step-a', config: { toolName: 'tool_a', toolArgs: {} } });
+      const stepB = makeStep({ id: 'step-b', config: { toolName: 'tool_b', toolArgs: {} } });
+
+      mockPlanService.getPlan.mockResolvedValue(makePlan());
+      mockPlanService.getSteps.mockResolvedValue([stepA, stepB]);
+      mockPlanService.getStepsByStatus.mockResolvedValue([stepA, stepB]);
+      mockPlanService.areDependenciesMet.mockResolvedValue(true);
+      (hasTool as ReturnType<typeof vi.fn>).mockResolvedValue(true);
+
+      // Gate tool_a so stepA holds the only slot while stepB waits.
+      let releaseA!: () => void;
+      const calledTools: string[] = [];
+      (executeTool as ReturnType<typeof vi.fn>).mockImplementation(async (toolName: string) => {
+        calledTools.push(toolName);
+        if (toolName === 'tool_a') {
+          await new Promise<void>((resolve) => (releaseA = resolve));
+        }
+        return { success: true, result: {} };
+      });
+
+      const failedListener = vi.fn();
+      waveExecutor.on('plan:failed', failedListener);
+
+      const promise = waveExecutor.execute('plan-1');
+      // Schedule stepA (occupying the slot) and enter the slot-wait for stepB.
+      await vi.advanceTimersByTimeAsync(20);
+      expect(calledTools).toEqual(['tool_a']); // stepB blocked on the full slot
+
+      // Abort while stepB waits for a slot.
+      expect(await waveExecutor.abort('plan-1')).toBe(true);
+
+      // Release stepA and let the executor unwind.
+      releaseA();
+      await vi.advanceTimersByTimeAsync(50);
+      const result = await promise;
+
+      // stepB was never scheduled; the plan is cancelled, not failed.
+      expect(calledTools).toEqual(['tool_a']);
+      expect(result.status).toBe('cancelled');
+      expect(failedListener).not.toHaveBeenCalled();
+    });
+  });
+
   // ========================================================================
   // Resume after pause
   // ========================================================================
diff --git a/packages/gateway/src/plans/executor.ts b/packages/gateway/src/plans/executor.ts
index e4f8b708..1e5a9feb 100644
--- a/packages/gateway/src/plans/executor.ts
+++ b/packages/gateway/src/plans/executor.ts
@@ -463,10 +463,21 @@ export class PlanExecutor extends EventEmitter {
       const stepPromises: Promise<void>[] = [];
 
       for (const step of readySteps) {
-        // Respect maxConcurrent
+        // Stop scheduling new steps if the plan was aborted mid-wave. We must
+        // NOT throw here — that would orphan the already-pushed stepPromises
+        // (Promise.all below is what attaches their rejection handlers), so a
+        // later-failing in-flight step would surface as an unhandled rejection.
+        // Instead break, let Promise.all await what was scheduled, then throw.
+        if (signal.aborted) break;
+
+        // Respect maxConcurrent. Re-check abort inside the slot-wait so a
+        // cancelled plan with every slot full of slow steps stops promptly
+        // rather than spinning this poll until a step happens to finish.
         while (executingSteps.size >= this.config.maxConcurrent) {
+          if (signal.aborted) break;
           await new Promise((r) => setTimeout(r, 10));
         }
+        if (signal.aborted) break;
 
         executingSteps.add(step.id);
         const promise = this.executeStep(planId, step, results, signal)
@@ -480,9 +491,17 @@ export class PlanExecutor extends EventEmitter {
         stepPromises.push(promise);
       }
 
-      // Wait for all steps in this wave to complete
+      // Wait for all steps in this wave to complete. Always awaited (even on
+      // the abort break above) so no scheduled promise is left unhandled.
       await Promise.all(stepPromises);
 
+      // Honor a mid-wave abort now that the scheduled steps have settled. The
+      // wave-top check would also catch it next iteration, but throwing here
+      // surfaces 'cancelled' immediately instead of looping once more.
+      if (signal.aborted) {
+        throw new Error('Plan execution aborted');
+      }
+
       // Update progress
       await this.planService.recalculateProgress(this.config.userId, planId);