Add atomic task deduplication with partial unique index

- Add partial unique index for active resource-scoped tasks
- Implement createTaskRunRecordAtomic for race-free task creation
- Update findOrEnqueueTask to use atomic insert first
- Add tests for concurrent task creation deduplication

drizzle/0013_task_active_resource_unique.sql

@@ -0,0 +1,3 @@
+CREATE UNIQUE INDEX IF NOT EXISTS `task_active_resource_uidx` 
+ON `task_run` (`user_id`, `task_type`, `resource_key`) 
+WHERE `resource_key` IS NOT NULL AND `status` IN ('queued', 'running');

lib/server/db/schema.ts

@@ -668,6 +668,12 @@ export const taskRun = sqliteTable('task_run', {
   taskWorkflowRunUnique: uniqueIndex('task_workflow_run_uidx').on(table.workflow_run_id)
 }));
 
+// Note: Partial unique index for active resource-scoped task deduplication is created via
+// migration 0013_task_active_resource_unique.sql. SQLite does not support partial indexes
+// in drizzle schema DSL, so the index is managed separately:
+// CREATE UNIQUE INDEX task_active_resource_uidx ON task_run (user_id, task_type, resource_key)
+// WHERE resource_key IS NOT NULL AND status IN ('queued', 'running');
+
 export const taskStageEvent = sqliteTable('task_stage_event', {
   id: integer('id').primaryKey({ autoIncrement: true }),
   task_id: text('task_id').notNull().references(() => taskRun.id, { onDelete: 'cascade' }),

lib/server/repos/tasks.test.ts

@@ -68,7 +68,8 @@ describe('task repos', () => {
       '0007_company_financial_bundles.sql',
       '0008_research_workspace.sql',
       '0009_task_notification_context.sql',
-      '0012_company_overview_cache.sql'
+      '0012_company_overview_cache.sql',
+      '0013_task_active_resource_unique.sql'
     ]) {
       applyMigration(sqliteClient, file);
     }
@@ -222,4 +223,106 @@ describe('task repos', () => {
     expect(failed?.error).toContain('Search indexing could not generate embeddings');
     expect(failed?.stage_context?.progress?.current).toBe(2);
   });
+
+  it('atomically deduplicates concurrent task creation for same resource', async () => {
+    if (!tasksRepo) {
+      throw new Error('tasks repo not initialized');
+    }
+
+    const resourceKey = 'sync_filings:AAPL';
+    const concurrentCount = 10;
+
+    const results = await Promise.all(
+      Array.from({ length: concurrentCount }, (_, i) =>
+        tasksRepo!.createTaskRunRecordAtomic({
+          id: `task-race-${i}`,
+          user_id: TEST_USER_ID,
+          task_type: 'sync_filings',
+          payload: { ticker: 'AAPL' },
+          priority: 50,
+          max_attempts: 3,
+          resource_key: resourceKey
+        })
+      )
+    );
+
+    const createdResults = results.filter((r) => r.created);
+    const conflictResults = results.filter((r) => !r.created);
+
+    expect(createdResults.length).toBe(1);
+    expect(conflictResults.length).toBe(concurrentCount - 1);
+    expect(createdResults[0]?.task.resource_key).toBe(resourceKey);
+    expect(createdResults[0]?.task.status).toBe('queued');
+  });
+
+  it('allows creating new task for same resource after previous task completes', async () => {
+    if (!tasksRepo) {
+      throw new Error('tasks repo not initialized');
+    }
+
+    const resourceKey = 'sync_filings:MSFT';
+
+    const first = await tasksRepo.createTaskRunRecordAtomic({
+      id: 'task-first-msft',
+      user_id: TEST_USER_ID,
+      task_type: 'sync_filings',
+      payload: { ticker: 'MSFT' },
+      priority: 50,
+      max_attempts: 3,
+      resource_key: resourceKey
+    });
+
+    expect(first.created).toBe(true);
+    if (!first.created) throw new Error('Expected task to be created');
+
+    await tasksRepo.completeTask(first.task.id, { ticker: 'MSFT' });
+
+    const second = await tasksRepo.createTaskRunRecordAtomic({
+      id: 'task-second-msft',
+      user_id: TEST_USER_ID,
+      task_type: 'sync_filings',
+      payload: { ticker: 'MSFT' },
+      priority: 50,
+      max_attempts: 3,
+      resource_key: resourceKey
+    });
+
+    expect(second.created).toBe(true);
+    if (!second.created) throw new Error('Expected second task to be created');
+    expect(second.task.id).not.toBe(first.task.id);
+  });
+
+  it('allows creating tasks without resource key without deduplication', async () => {
+    if (!tasksRepo) {
+      throw new Error('tasks repo not initialized');
+    }
+
+    const results = await Promise.all([
+      tasksRepo.createTaskRunRecordAtomic({
+        id: 'task-nokey-1',
+        user_id: TEST_USER_ID,
+        task_type: 'sync_filings',
+        payload: { ticker: 'GOOGL' },
+        priority: 50,
+        max_attempts: 3,
+        resource_key: null
+      }),
+      tasksRepo.createTaskRunRecordAtomic({
+        id: 'task-nokey-2',
+        user_id: TEST_USER_ID,
+        task_type: 'sync_filings',
+        payload: { ticker: 'GOOGL' },
+        priority: 50,
+        max_attempts: 3,
+        resource_key: null
+      })
+    ]);
+
+    expect(results[0]?.created).toBe(true);
+    expect(results[1]?.created).toBe(true);
+    if (!results[0]?.created || !results[1]?.created) {
+      throw new Error('Expected both tasks to be created');
+    }
+    expect(results[0].task.id).not.toBe(results[1].task.id);
+  });
 });

lib/server/repos/tasks.ts

@@ -153,6 +153,83 @@ export async function createTaskRunRecord(input: CreateTaskInput) {
   });
 }
 
+export type AtomicCreateResult = 
+  | { task: Task; created: true }
+  | { task: null; created: false };
+
+const SQLITE_CONSTRAINT_UNIQUE = 2067;
+
+async function attemptAtomicInsert(
+  tx: Parameters<Parameters<typeof db.transaction>[0]>[0],
+  input: CreateTaskInput,
+  now: string
+): Promise<{ task: Task; created: true } | null> {
+  try {
+    const [row] = await tx
+      .insert(taskRun)
+      .values({
+        id: input.id,
+        user_id: input.user_id,
+        task_type: input.task_type,
+        status: 'queued',
+        stage: 'queued',
+        stage_detail: null,
+        stage_context: null,
+        resource_key: input.resource_key ?? null,
+        notification_read_at: null,
+        notification_silenced_at: null,
+        priority: input.priority,
+        payload: input.payload,
+        result: null,
+        error: null,
+        attempts: 0,
+        max_attempts: input.max_attempts,
+        workflow_run_id: null,
+        created_at: now,
+        updated_at: now,
+        finished_at: null
+      })
+      .returning();
+
+    if (!row) {
+      return null;
+    }
+
+    await insertTaskStageEvent(tx, {
+      task_id: row.id,
+      user_id: row.user_id,
+      stage: row.stage as TaskStage,
+      stage_detail: row.stage_detail,
+      stage_context: row.stage_context ?? null,
+      status: row.status,
+      created_at: now
+    });
+
+    return { task: toTask(row), created: true };
+  } catch (error) {
+    const sqliteError = error as { code?: number; message?: string };
+    if (
+      sqliteError.code === SQLITE_CONSTRAINT_UNIQUE ||
+      sqliteError.message?.includes('UNIQUE constraint failed')
+    ) {
+      return null;
+    }
+    throw error;
+  }
+}
+
+export async function createTaskRunRecordAtomic(input: CreateTaskInput): Promise<AtomicCreateResult> {
+  const now = new Date().toISOString();
+
+  return await db.transaction(async (tx) => {
+    const result = await attemptAtomicInsert(tx, input, now);
+    if (result) {
+      return result;
+    }
+    return { task: null, created: false };
+  });
+}
+
 export async function setTaskWorkflowRunId(taskId: string, workflowRunId: string) {
   await db
     .update(taskRun)

lib/server/tasks.ts

@@ -7,6 +7,7 @@ import { describeTaskFailure } from '@/lib/server/task-errors';
 import {
   countTasksByStatus,
   createTaskRunRecord,
+  createTaskRunRecordAtomic,
   findInFlightTaskByResourceKey,
   getTaskByIdForUser,
   listTaskStageEventsForTask,
@@ -134,6 +135,38 @@ export async function findOrEnqueueTask(input: EnqueueTaskInput) {
     return await enqueueTask(input);
   }
 
+  const taskId = randomUUID();
+  const result = await createTaskRunRecordAtomic({
+    id: taskId,
+    user_id: input.userId,
+    task_type: input.taskType,
+    payload: input.payload ?? {},
+    priority: input.priority ?? 50,
+    max_attempts: input.maxAttempts ?? 3,
+    resource_key: input.resourceKey
+  });
+
+  if (result.created) {
+    try {
+      const run = await start(runTaskWorkflow, [result.task.id]);
+      await setTaskWorkflowRunId(result.task.id, run.runId);
+
+      return {
+        ...result.task,
+        workflow_run_id: run.runId
+      } satisfies Task;
+    } catch (error) {
+      const failure = describeTaskFailure(result.task, 'Failed to start workflow');
+      await markTaskFailure(result.task.id, failure.detail, 'failed', {
+        detail: failure.summary
+      });
+
+      const wrapped = new Error(failure.detail);
+      (wrapped as Error & { cause?: unknown }).cause = error;
+      throw wrapped;
+    }
+  }
+
   const existingTask = await findInFlightTaskByResourceKey(
     input.userId,
     input.taskType,
@@ -141,13 +174,10 @@ export async function findOrEnqueueTask(input: EnqueueTaskInput) {
   );
 
   if (existingTask) {
-    const reconciledTask = await reconcileTaskWithWorkflow(existingTask);
-    if (reconciledTask.status === 'queued' || reconciledTask.status === 'running') {
-      return reconciledTask;
-    }
+    return await reconcileTaskWithWorkflow(existingTask);
   }
 
-  return await enqueueTask(input);
+  throw new Error('Task deduplication conflict detected but no in-flight task found');
 }
 
 export async function findInFlightTask(userId: string, taskType: TaskType, resourceKey: string) {