diff --git a/packages/core/src/agents/team/tasks.test.ts b/packages/core/src/agents/team/tasks.test.ts
index 5fa71f4fb3c..ecafad60f5c 100644
--- a/packages/core/src/agents/team/tasks.test.ts
+++ b/packages/core/src/agents/team/tasks.test.ts
@@ -24,6 +24,7 @@ import {
   notifyTasksUpdated,
   TaskOwnershipError,
   RECIPROCAL_CALLER,
+  normalizeTaskId,
 } from './tasks.js';
 import { mockCompromisedLock } from '../../test-utils/mock-compromised-lock.js';
 
@@ -53,6 +54,23 @@ function setMockDir(dir: string): void {
   ).__setMockGlobalDir(dir);
 }
 
+describe('normalizeTaskId', () => {
+  it('trims whitespace and strips one leading #', () => {
+    expect(normalizeTaskId(' 1 ')).toBe('1');
+    expect(normalizeTaskId('#1')).toBe('1');
+    expect(normalizeTaskId(' #42 ')).toBe('42');
+    // Only one leading # is stripped.
+    expect(normalizeTaskId('##1')).toBe('#1');
+  });
+
+  it('returns undefined when nothing remains', () => {
+    expect(normalizeTaskId('')).toBeUndefined();
+    expect(normalizeTaskId('   ')).toBeUndefined();
+    expect(normalizeTaskId('#')).toBeUndefined();
+    expect(normalizeTaskId(' # ')).toBeUndefined();
+  });
+});
+
 describe('tasks', () => {
   let tmpDir: string;
 
diff --git a/packages/core/src/agents/team/tasks.ts b/packages/core/src/agents/team/tasks.ts
index 93f27fec91d..3f0dbf50f76 100644
--- a/packages/core/src/agents/team/tasks.ts
+++ b/packages/core/src/agents/team/tasks.ts
@@ -187,6 +187,19 @@ export function assertValidTaskId(taskId: string): void {
   }
 }
 
+/**
+ * Normalize a model-supplied task-ID reference: trim surrounding
+ * whitespace and strip one leading `#` (the rendered display form,
+ * e.g. `#1`). Returns `undefined` when nothing remains, so callers
+ * can treat blank references as absent instead of forwarding `''`
+ * to filters that activate on `!== undefined`. The result must
+ * still pass `assertValidTaskId` before use.
+ */
+export function normalizeTaskId(raw: string): string | undefined {
+  const id = raw.trim().replace(/^#/, '');
+  return id === '' ? undefined : id;
+}
+
 /** Path to a single task file. */
 export function getTaskPath(teamName: string, taskId: string): string {
   assertValidTaskId(taskId);
diff --git a/packages/core/src/tools/task-list.test.ts b/packages/core/src/tools/task-list.test.ts
index 49ffd01f07e..222f8cd1604 100644
--- a/packages/core/src/tools/task-list.test.ts
+++ b/packages/core/src/tools/task-list.test.ts
@@ -137,6 +137,120 @@ describe('TaskListTool', () => {
     expect(String(result.llmContent)).toContain('owner must include');
   });
 
+  // #9281: blank optional filters must behave like absent filters,
+  // matching how the tool's description/schema present them.
+  describe('blank filters are treated as absent (#9281)', () => {
+    it('treats an empty owner filter as no filter', async () => {
+      await createTask(TEAM, {
+        subject: 'Owned',
+        description: 'desc',
+        owner: 'alice',
+      });
+      await createTask(TEAM, {
+        subject: 'Unowned',
+        description: 'desc',
+      });
+
+      const invocation = tool.build({ owner: '' });
+      const result = await invocation.execute(new AbortController().signal);
+      expect(result.error).toBeUndefined();
+      expect(result.llmContent).toContain('Owned');
+      expect(result.llmContent).toContain('Unowned');
+    });
+
+    it('treats a whitespace-only owner filter as no filter', async () => {
+      await createTask(TEAM, {
+        subject: 'Owned',
+        description: 'desc',
+        owner: 'alice',
+      });
+
+      const invocation = tool.build({ owner: '   ' });
+      const result = await invocation.execute(new AbortController().signal);
+      expect(result.error).toBeUndefined();
+      expect(result.llmContent).toContain('Owned');
+      expect(invocation.getDescription()).toBe('List all tasks');
+    });
+
+    it('treats an empty blockedBy filter as no filter', async () => {
+      await createTask(TEAM, {
+        subject: 'Task A',
+        description: 'desc',
+      });
+
+      const invocation = tool.build({ blockedBy: '' });
+      const result = await invocation.execute(new AbortController().signal);
+      expect(result.error).toBeUndefined();
+      expect(result.llmContent).toContain('Task A');
+    });
+
+    it('treats a whitespace-only blockedBy filter as no filter', async () => {
+      await createTask(TEAM, {
+        subject: 'Task A',
+        description: 'desc',
+      });
+
+      const invocation = tool.build({ blockedBy: '   ' });
+      const result = await invocation.execute(new AbortController().signal);
+      expect(result.error).toBeUndefined();
+      expect(result.llmContent).toContain('Task A');
+      expect(invocation.getDescription()).toBe('List all tasks');
+    });
+
+    it('still filters precisely by a non-empty blockedBy', async () => {
+      const blocker = await createTask(TEAM, {
+        subject: 'Blocker',
+        description: 'desc',
+      });
+      const blocked = await createTask(TEAM, {
+        subject: 'Blocked',
+        description: 'desc',
+      });
+      await createTask(TEAM, {
+        subject: 'Free',
+        description: 'desc',
+      });
+      await updateTask(TEAM, blocked.id, { addBlockedBy: [blocker.id] });
+
+      const invocation = tool.build({ blockedBy: blocker.id });
+      const result = await invocation.execute(new AbortController().signal);
+      expect(result.error).toBeUndefined();
+      expect(result.llmContent).toContain('Blocked');
+      expect(result.llmContent).not.toContain('Blocker');
+      expect(result.llmContent).not.toContain('Free');
+
+      const formatted = tool.build({ blockedBy: ` #${blocker.id} ` });
+      const formattedResult = await formatted.execute(
+        new AbortController().signal,
+      );
+      expect(formattedResult.error).toBeUndefined();
+      expect(formattedResult.llmContent).toContain('Blocked');
+
+      const invalid = await tool
+        .build({ blockedBy: 'task-1' })
+        .execute(new AbortController().signal);
+      expect(invalid.error).toBeDefined();
+    });
+
+    it('rejects a non-blank blockedBy that normalizes to nothing', async () => {
+      await createTask(TEAM, {
+        subject: 'Task A',
+        description: 'desc',
+      });
+
+      // A bare '#' must fail closed like the owner path, not activate
+      // a never-matching '' filter (silent empty board) nor behave as
+      // absent while getDescription() still advertises the filter.
+      for (const blockedBy of ['#', ' #']) {
+        const result = await tool
+          .build({ blockedBy })
+          .execute(new AbortController().signal);
+        expect(result.error).toBeDefined();
+        expect(result.llmContent).toContain('blockedBy');
+      }
+    });
+  });
+
   it('returns TaskListResultDisplay', async () => {
     await createTask(TEAM, {
       subject: 'Task X',
diff --git a/packages/core/src/tools/task-list.ts b/packages/core/src/tools/task-list.ts
index 2d339772cc0..1c38da4ebf9 100644
--- a/packages/core/src/tools/task-list.ts
+++ b/packages/core/src/tools/task-list.ts
@@ -18,7 +18,11 @@ import { ToolNames, ToolDisplayNames } from './tool-names.js';
 import type { Config } from '../config/config.js';
 import { getTeamName, resolveActiveTeamName } from '../agents/team/identity.js';
 import { sanitizeName } from '../agents/team/teamHelpers.js';
-import { listTasks } from '../agents/team/tasks.js';
+import {
+  assertValidTaskId,
+  listTasks,
+  normalizeTaskId,
+} from '../agents/team/tasks.js';
 
 export interface TaskListParams {
   status?: 'pending' | 'in_progress' | 'completed';
@@ -42,10 +46,10 @@ class TaskListInvocation extends BaseToolInvocation<
     if (this.params.status) {
       filters.push(`status=${this.params.status}`);
     }
-    if (this.params.owner) {
+    if (this.params.owner?.trim()) {
       filters.push(`owner=${this.params.owner}`);
     }
-    if (this.params.blockedBy) {
+    if (this.params.blockedBy?.trim()) {
       filters.push(`blockedBy=${this.params.blockedBy}`);
     }
     return filters.length > 0
@@ -66,8 +70,12 @@ class TaskListInvocation extends BaseToolInvocation<
       };
     }
 
+    // Blank (empty/whitespace-only) optional filters behave as absent:
+    // the schema marks them optional and `getDescription()` only shows
+    // truthy filter values, so a blank value must not activate a
+    // filter (#9281).
     let ownerFilter: string | undefined;
-    if (this.params.owner !== undefined) {
+    if (this.params.owner !== undefined && this.params.owner.trim() !== '') {
       ownerFilter = sanitizeName(this.params.owner);
       if (!ownerFilter) {
         const msg =
@@ -81,10 +89,38 @@ class TaskListInvocation extends BaseToolInvocation<
       }
     }
 
+    let blockedByFilter: string | undefined;
+    if (this.params.blockedBy?.trim()) {
+      blockedByFilter = normalizeTaskId(this.params.blockedBy);
+      if (blockedByFilter === undefined) {
+        // Non-blank input that normalizes to nothing (e.g. a bare
+        // '#'): fail closed like the owner path instead of
+        // activating a filter that can never match.
+        const msg =
+          'Cannot filter by blockedBy: blockedBy must be a task ID, ' +
+          'optionally prefixed with #.';
+        return {
+          llmContent: msg,
+          returnDisplay: msg,
+          error: { message: msg },
+        };
+      }
+      try {
+        assertValidTaskId(blockedByFilter);
+      } catch (err) {
+        const msg = err instanceof Error ? err.message : String(err);
+        return {
+          llmContent: msg,
+          returnDisplay: msg,
+          error: { message: msg },
+        };
+      }
+    }
+
     const tasks = await listTasks(teamName, {
       status: this.params.status,
       owner: ownerFilter,
-      blockedBy: this.params.blockedBy,
+      blockedBy: blockedByFilter,
     });
 
     if (tasks.length === 0) {