diff --git a/Realism/app/api/jobs/webhook/route.ts b/Realism/app/api/jobs/webhook/route.ts
index e72ad0c..134fef8 100644
--- a/Realism/app/api/jobs/webhook/route.ts
+++ b/Realism/app/api/jobs/webhook/route.ts
@@ -1,29 +1,65 @@
-import { NextRequest, NextResponse } from 'next/server'
-import { inngest } from '@/lib/inngest'
-
-export async function POST(req: NextRequest) {
-  let jobId: string | undefined
-
-  try {
-    const body = await req.json()
-    jobId = body.jobId
-  } catch {
-    return NextResponse.json({ error: 'Invalid body' }, { status: 400 })
-  }
-
-  if (!jobId) {
-    return NextResponse.json({ error: 'jobId required' }, { status: 400 })
-  }
-
-  try {
-    await inngest.send({
-      name: 'job/webhook',
-      data: { jobId },
-    })
-  } catch (err) {
-    console.error('[webhook] Failed to send Inngest event:', err)
-  }
-
-  // Always 200 to prevent QStash retries
-  return NextResponse.json({ ok: true })
-}
+import { NextRequest, NextResponse } from 'next/server'
+import { inngest } from '@/lib/inngest'
+import { Receiver } from '@upstash/qstash'
+import { checkAndLockMessage, unlockMessage } from '@/lib/jobs'
+
+// SECURITY FIX: Initialize QStash receiver for signature verification
+const receiver = new Receiver({
+  currentSigningKey: process.env.QSTASH_CURRENT_SIGNING_KEY || '',
+  nextSigningKey: process.env.QSTASH_NEXT_SIGNING_KEY || '',
+})
+
+export async function POST(req: NextRequest) {
+  // SECURITY FIX: Verify provider signatures to reject unsigned/unauthenticated requests.
+  const signature = req.headers.get('Upstash-Signature')
+  const messageId = req.headers.get('Upstash-Message-Id')
+
+  if (!signature || !messageId) {
+    return NextResponse.json({ error: 'Missing QStash signature or message ID' }, { status: 401 })
+  }
+
+  const bodyText = await req.text()
+
+  try {
+    const isValid = await receiver.verify({ signature, body: bodyText })
+    if (!isValid) throw new Error("Invalid signature")
+  } catch (err) {
+    return NextResponse.json({ error: 'Unauthorized: Invalid signature' }, { status: 401 })
+  }
+
+  let jobId: string | undefined
+
+  try {
+    const body = JSON.parse(bodyText)
+    jobId = body.jobId
+  } catch {
+    return NextResponse.json({ error: 'Invalid JSON body' }, { status: 400 })
+  }
+
+  if (!jobId) {
+    return NextResponse.json({ error: 'jobId required' }, { status: 400 })
+  }
+
+  // SECURITY FIX: Persist a one-time delivery ID (Idempotency Key) with SETNX.
+  // This prevents the same webhook request from being processed multiple times.
+  const isDuplicate = await checkAndLockMessage(messageId)
+  if (isDuplicate) {
+    return NextResponse.json({ ok: true, note: 'Message already processed' })
+  }
+
+  try {
+    await inngest.send({
+      name: 'job/webhook',
+      data: { jobId },
+    })
+  } catch (err) {
+    console.error('[webhook] Failed to send Inngest event:', err)
+    
+    // SECURITY FIX: Do NOT swallow errors. If delivery fails, we release the idempotency lock 
+    // and return a 500 status code so the upstream scheduler can properly retry the failed delivery.
+    await unlockMessage(messageId)
+    return NextResponse.json({ error: 'Event delivery failed' }, { status: 500 })
+  }
+
+  return NextResponse.json({ ok: true })
+}
\ No newline at end of file
diff --git a/Realism/lib/jobs.ts b/Realism/lib/jobs.ts
index 9f6c18c..925c437 100644
--- a/Realism/lib/jobs.ts
+++ b/Realism/lib/jobs.ts
@@ -1,85 +1,123 @@
-import { randomUUID } from 'crypto'
-import { setJob, getJob, updateJob } from '@/lib/redis'
-import type { Job, JobType, JobCadence, Artifact } from '@/types'
-
-export async function createJob(params: {
-  id?: string
-  userId: string
-  goal: string
-  budget: number
-  type: JobType
-  cadence?: JobCadence
-  spendRuleId?: string
-  qstashScheduleId?: string
-}): Promise<Job> {
-  const job: Job = {
-    id: params.id ?? randomUUID(),
-    userId: params.userId,
-    goal: params.goal,
-    budget: params.budget,
-    type: params.type,
-    status: 'pending',
-    spendRuleId: params.spendRuleId,
-    spendTotal: 0,
-    cadence: params.cadence,
-    qstashScheduleId: params.qstashScheduleId,
-    createdAt: new Date().toISOString(),
-  }
-
-  await setJob(job)
-  return job
-}
-
-export async function startJob(id: string): Promise<Job | null> {
-  return updateJob(id, { status: 'running' })
-}
-
-export async function completeJob(id: string, artifact: Artifact): Promise<Job | null> {
-  return updateJob(id, {
-    status: 'complete',
-    artifact,
-    completedAt: new Date().toISOString(),
-  })
-}
-
-export async function failJob(id: string, reason: string): Promise<Job | null> {
-  return updateJob(id, {
-    status: 'failed',
-    failureReason: reason,
-    completedAt: new Date().toISOString(),
-  })
-}
-
-export async function addSpend(id: string, amount: number): Promise<Job | null> {
-  const job = await getJob(id)
-  if (!job) return null
-  return updateJob(id, { spendTotal: job.spendTotal + amount })
-}
-
-export async function pauseJob(id: string): Promise<Job | null> {
-  return updateJob(id, { status: 'paused' })
-}
-
-export async function recordRun(
-  id: string,
-  artifact: Artifact,
-  spentThisRun: number
-): Promise<Job | null> {
-  const job = await getJob(id)
-  if (!job) return null
-
-  const now = new Date()
-  const nextRun = job.cadence === 'daily'
-    ? new Date(now.getTime() + 24 * 60 * 60 * 1000)
-    : new Date(now.getTime() + 7 * 24 * 60 * 60 * 1000)
-
-  return updateJob(id, {
-    artifact,
-    lastRunAt: now.toISOString(),
-    nextRunAt: nextRun.toISOString(),
-    spendTotal: (job.spendTotal ?? 0) + spentThisRun,
-    status: 'running',
-  })
-}
-
-export { getJob }
+import { randomUUID } from 'crypto'
+// Added 'redis' client export to utilize SETNX commands directly
+import { setJob, getJob, updateJob, redis } from '@/lib/redis' 
+import type { Job, JobType, JobCadence, Artifact } from '@/types'
+
+// SECURITY FIX: Webhook Idempotency locking via SETNX
+export async function checkAndLockMessage(messageId: string): Promise<boolean> {
+  try {
+    const key = `webhook:idempotency:${messageId}`
+    // SETNX returns 1 if the key was set successfully, 0 if it already existed
+    const acquired = await redis.setnx(key, '1')
+    if (acquired === 1) {
+      // Set expiration to clean up old locks (e.g., 7 days)
+      await redis.expire(key, 86400 * 7)
+      return false // Not a duplicate
+    }
+    return true // Duplicate execution rejected
+  } catch (err) {
+    console.warn('Idempotency check failed, defaulting to block:', err)
+    return true
+  }
+}
+
+// Releases the lock if the downstream action fails, allowing for a retry
+export async function unlockMessage(messageId: string): Promise<void> {
+  try {
+    await redis.del(`webhook:idempotency:${messageId}`)
+  } catch (err) {
+    console.error('Failed to unlock message:', err)
+  }
+}
+
+export async function createJob(params: {
+  id?: string
+  userId: string
+  goal: string
+  budget: number
+  type: JobType
+  cadence?: JobCadence
+  spendRuleId?: string
+  qstashScheduleId?: string
+}): Promise<Job> {
+  const job: Job = {
+    id: params.id ?? randomUUID(),
+    userId: params.userId,
+    goal: params.goal,
+    budget: params.budget,
+    type: params.type,
+    status: 'pending',
+    spendRuleId: params.spendRuleId,
+    spendTotal: 0,
+    cadence: params.cadence,
+    qstashScheduleId: params.qstashScheduleId,
+    createdAt: new Date().toISOString(),
+  }
+
+  await setJob(job)
+  return job
+}
+
+export async function startJob(id: string): Promise<Job | null> {
+  const job = await getJob(id)
+  if (!job) return null
+
+  // SECURITY FIX: Enforce an atomic state transition check.
+  // Reject duplicate/concurrent executions by ensuring a job can only transition to 
+  // 'running' if it is currently 'pending' or 'paused'.
+  if (job.status !== 'pending' && job.status !== 'paused') {
+    throw new Error(`Cannot start job. Current status is '${job.status}'. Duplicate execution rejected.`)
+  }
+
+  return updateJob(id, { status: 'running' })
+}
+
+export async function completeJob(id: string, artifact: Artifact): Promise<Job | null> {
+  return updateJob(id, {
+    status: 'complete',
+    artifact,
+    completedAt: new Date().toISOString(),
+  })
+}
+
+export async function failJob(id: string, reason: string): Promise<Job | null> {
+  return updateJob(id, {
+    status: 'failed',
+    failureReason: reason,
+    completedAt: new Date().toISOString(),
+  })
+}
+
+export async function addSpend(id: string, amount: number): Promise<Job | null> {
+  const job = await getJob(id)
+  if (!job) return null
+  return updateJob(id, { spendTotal: job.spendTotal + amount })
+}
+
+export async function pauseJob(id: string): Promise<Job | null> {
+  return updateJob(id, { status: 'paused' })
+}
+
+export async function recordRun(
+  id: string,
+  artifact: Artifact,
+  spentThisRun: number
+): Promise<Job | null> {
+  const job = await getJob(id)
+  if (!job) return null
+
+  const now = new Date()
+  const nextRun = job.cadence === 'daily'
+    ? new Date(now.getTime() + 24 * 60 * 60 * 1000)
+    : new Date(now.getTime() + 7 * 24 * 60 * 60 * 1000)
+
+  return updateJob(id, {
+    artifact,
+    lastRunAt: now.toISOString(),
+    nextRunAt: nextRun.toISOString(),
+    spendTotal: (job.spendTotal ?? 0) + spentThisRun,
+    status: 'running',
+  })
+}
+
+export { getJob }
\ No newline at end of file