diff --git a/__tests__/api/agents/tasks-drain.test.ts b/__tests__/api/agents/tasks-drain.test.ts
index 522d6fea..0197adf8 100644
--- a/__tests__/api/agents/tasks-drain.test.ts
+++ b/__tests__/api/agents/tasks-drain.test.ts
@@ -1,6 +1,6 @@
 import { describe, it, expect, beforeEach } from "vitest"
-import { POST as drainPost } from "@/app/api/agents/[id]/tasks/drain/route"
-import { POST as createPost, DELETE as purgeDel } from "@/app/api/agents/[id]/tasks/route"
+import { POST as drainPost } from "@/app/api/agents/\[id\]/tasks/drain/route"
+import { POST as createPost, DELETE as purgeDel } from "@/app/api/agents/\[id\]/tasks/route"
 import { resetTaskQueue } from "@/lib/agents/task-queue"
 
 async function mockContext(params: Record<string, string>) {
@@ -110,7 +110,7 @@ describe("POST /api/agents/:id/tasks/drain", () => {
     const data = await response.json()
 
     expect(response.status).toBe(200)
-    expect(data.processed).toBe(50) // Default is 50
+    expect(data.processed).toBe(50)
   })
 
   it("returns 409 on concurrent drain attempts", async () => {
@@ -118,14 +118,12 @@ describe("POST /api/agents/:id/tasks/drain", () => {
       await createTask("agent-1", `task-${i}`)
     }
 
-    // Start first drain
     const req1 = new Request("http://localhost/api/agents/agent-1/tasks/drain", {
       method: "POST",
     })
     const context1 = await mockContext({ id: "agent-1" })
     const promise1 = drainPost(req1, context1)
 
-    // Immediately try second drain
     const req2 = new Request("http://localhost/api/agents/agent-1/tasks/drain", {
       method: "POST",
     })
@@ -137,7 +135,6 @@ describe("POST /api/agents/:id/tasks/drain", () => {
     expect(data2.ok).toBe(false)
     expect(data2.error).toContain("already in progress")
 
-    // Wait for first drain to complete
     await promise1
   })
 
@@ -213,7 +210,6 @@ describe("DELETE /api/agents/:id/tasks", () => {
 
     expect(data.purged).toBe(2)
 
-    // Verify agent-2 tasks remain
     const req2 = new Request("http://localhost/api/agents/agent-2/tasks/drain", {
       method: "POST",
     })
@@ -235,7 +231,6 @@ describe("drain + purge integration", () => {
       await createTask("agent-1", `task-${i}`)
     }
 
-    // Drain 10
     const drainReq = new Request("http://localhost/api/agents/agent-1/tasks/drain", {
       method: "POST",
       headers: { "Content-Type": "application/json" },
@@ -246,7 +241,6 @@ describe("drain + purge integration", () => {
     const drainData = await drainRes.json()
     expect(drainData.processed).toBe(10)
 
-    // Purge remaining
     const purgeReq = new Request("http://localhost/api/agents/agent-1/tasks", {
       method: "DELETE",
     })
@@ -260,14 +254,12 @@ describe("drain + purge integration", () => {
     await createTask("agent-1", "task-a")
     await createTask("agent-1", "task-b")
 
-    // Purge all
     const purgeReq = new Request("http://localhost/api/agents/agent-1/tasks", {
       method: "DELETE",
     })
     const purgeContext = await mockContext({ id: "agent-1" })
     await purgeDel(purgeReq, purgeContext)
 
-    // Try drain
     const drainReq = new Request("http://localhost/api/agents/agent-1/tasks/drain", {
       method: "POST",
     })
diff --git a/app/api/marketplace/skills/[skillId]/invoke/route.ts b/app/api/marketplace/skills/[skillId]/invoke/route.ts
new file mode 100644
index 00000000..06e3ec48
--- /dev/null
+++ b/app/api/marketplace/skills/[skillId]/invoke/route.ts
@@ -0,0 +1,83 @@
+import { NextResponse } from "next/server"
+import { invokeSkillWithPayment } from "@/lib/marketplace/x402-middleware"
+import { recordInvocation } from "@/lib/marketplace/invocation-ledger"
+
+interface RouteContext {
+  params: Promise<{ skillId: string }>
+}
+
+// Mock skill registry for demo — in production this queries the skills store
+const MOCK_SKILLS: Record<string, { callUrl: string; priceXLM: number; ownerWallet: string }> = {
+  "skill-payment": {
+    callUrl: "https://api.example.com/skills/payment",
+    priceXLM: 1.0,
+    ownerWallet: "GAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAWHF",
+  },
+}
+
+function getSkill(skillId: string) {
+  // TODO: Replace with actual skills-store lookup when PR#304 merges
+  return MOCK_SKILLS[skillId] ?? null
+}
+
+export async function POST(req: Request, context: RouteContext) {
+  try {
+    const { skillId } = await context.params
+    const body = await req.json().catch(() => ({}))
+
+    if (!body.agentId || typeof body.agentId !== "string") {
+      return NextResponse.json(
+        { ok: false, error: "agentId is required" },
+        { status: 400, headers: { "Cache-Control": "no-store" } },
+      )
+    }
+
+    const skill = getSkill(skillId)
+    if (!skill) {
+      return NextResponse.json(
+        { ok: false, error: "Skill not found" },
+        { status: 404, headers: { "Cache-Control": "no-store" } },
+      )
+    }
+
+    const result = await invokeSkillWithPayment(
+      skill.callUrl,
+      skill.ownerWallet,
+      skill.priceXLM,
+      { agentId: body.agentId, payload: body.payload },
+    )
+
+    // Record in ledger regardless of outcome
+    const record = recordInvocation(
+      body.agentId,
+      skillId,
+      skill.priceXLM,
+      result.receipt?.txHash ?? "",
+      result.ok ? "success" : result.error === "insufficient_balance" ? "insufficient_balance" : "failed",
+      result.error,
+    )
+
+    if (!result.ok) {
+      const statusCode = result.error === "insufficient_balance" ? 402 : 500
+      return NextResponse.json(
+        { ok: false, error: result.error || "Skill invocation failed", ledgerId: record.id },
+        { status: statusCode, headers: { "Cache-Control": "no-store" } },
+      )
+    }
+
+    return NextResponse.json(
+      {
+        ok: true,
+        response: result.response,
+        receipt: result.receipt,
+        ledgerId: record.id,
+      },
+      { headers: { "Cache-Control": "no-store" } },
+    )
+  } catch (error) {
+    return NextResponse.json(
+      { ok: false, error: error instanceof Error ? error.message : "Failed to invoke skill" },
+      { status: 500, headers: { "Cache-Control": "no-store" } },
+    )
+  }
+}
\ No newline at end of file
diff --git a/lib/marketplace/invocation-ledger.ts b/lib/marketplace/invocation-ledger.ts
new file mode 100644
index 00000000..e94c5a9b
--- /dev/null
+++ b/lib/marketplace/invocation-ledger.ts
@@ -0,0 +1,86 @@
+export interface InvocationRecord {
+  id: string
+  agentId: string
+  skillId: string
+  amountXLM: number
+  txHash: string
+  invokedAt: string
+  status: "success" | "failed" | "insufficient_balance"
+  error?: string
+}
+
+type LedgerDb = InvocationRecord[]
+
+const globalState = globalThis as typeof globalThis & {
+  __openStellarInvocationLedger__?: LedgerDb
+}
+
+function getDb(): LedgerDb {
+  if (!globalState.__openStellarInvocationLedger__) {
+    globalState.__openStellarInvocationLedger__ = []
+  }
+  return globalState.__openStellarInvocationLedger__
+}
+
+export function recordInvocation(
+  agentId: string,
+  skillId: string,
+  amountXLM: number,
+  txHash: string,
+  status: InvocationRecord["status"] = "success",
+  error?: string,
+): InvocationRecord {
+  const record: InvocationRecord = {
+    id: `inv_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 8)}`,
+    agentId: agentId.trim(),
+    skillId: skillId.trim(),
+    amountXLM: Math.max(0, Number(amountXLM) || 0),
+    txHash: txHash.trim(),
+    invokedAt: new Date().toISOString(),
+    status,
+    error,
+  }
+
+  const db = getDb()
+  db.push(record)
+
+  // Cap at 50k entries
+  if (db.length > 50_000) {
+    db.splice(0, db.length - 50_000)
+  }
+
+  return record
+}
+
+export function listInvocations(
+  filters: { agentId?: string; skillId?: string; limit?: number } = {},
+): InvocationRecord[] {
+  const db = getDb()
+  let results = [...db].reverse()
+
+  if (filters.agentId) {
+    results = results.filter((r) => r.agentId === filters.agentId)
+  }
+  if (filters.skillId) {
+    results = results.filter((r) => r.skillId === filters.skillId)
+  }
+  if (filters.limit && filters.limit > 0) {
+    results = results.slice(0, filters.limit)
+  }
+
+  return results
+}
+
+export function getInvocationById(id: string): InvocationRecord | null {
+  return getDb().find((r) => r.id === id) ?? null
+}
+
+export function getTotalSpentByAgent(agentId: string): number {
+  return getDb()
+    .filter((r) => r.agentId === agentId && r.status === "success")
+    .reduce((sum, r) => sum + r.amountXLM, 0)
+}
+
+export function resetInvocationLedger(): void {
+  getDb().splice(0, getDb().length)
+}
\ No newline at end of file
diff --git a/lib/marketplace/x402-middleware.ts b/lib/marketplace/x402-middleware.ts
new file mode 100644
index 00000000..ed882b3e
--- /dev/null
+++ b/lib/marketplace/x402-middleware.ts
@@ -0,0 +1,135 @@
+import { createX402Quote, settleX402, type X402Quote, type X402SettlementResult } from "@/lib/protocols/x402"
+import { isMockMode } from "@/lib/mock/mock-mode"
+import { settleMockX402 } from "@/lib/mock/x402-mock"
+
+export interface SkillInvocationRequest {
+  agentId: string
+  payload: unknown
+}
+
+export interface PaymentRequirement {
+  quote: X402Quote
+  paymentRef: string
+}
+
+export interface InvocationResult {
+  ok: boolean
+  response?: unknown
+  receipt?: { txHash: string; chain: string; amountUsd: number }
+  error?: string
+}
+
+/**
+ * Attempt an HTTP request to a skill's callUrl.
+ * If the response is 402, extract payment requirements and return them.
+ */
+export async function attemptSkillInvocation(
+  callUrl: string,
+  request: SkillInvocationRequest,
+): Promise<{ status: number; body: unknown; headers: Record<string, string> }> {
+  const response = await fetch(callUrl, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(request),
+  })
+
+  const body = await response.json().catch(() => ({}))
+  const headers: Record<string, string> = {}
+  response.headers.forEach((value, key) => {
+    headers[key.toLowerCase()] = value
+  })
+
+  return { status: response.status, body, headers }
+}
+
+/**
+ * Generate a Stellar payment transaction and settle it via x402.
+ * In mock mode, simulates the settlement without real on-chain calls.
+ */
+export async function settleSkillPayment(
+  paymentRef: string,
+  txHash: string,
+  chain: "stellar" | "bnb" | "base" = "stellar",
+): Promise<X402SettlementResult> {
+  if (isMockMode()) {
+    const receipt = settleMockX402({ paymentRef, chain, txHash })
+    return { ok: true, receipt }
+  }
+
+  return settleX402({ paymentRef, chain, txHash })
+}
+
+/**
+ * Full x402 payment flow for skill invocation:
+ * 1. Attempt the HTTP call
+ * 2. If 402, generate quote and settle payment
+ * 3. Retry the HTTP call with payment proof
+ * 4. Return the final response
+ */
+export async function invokeSkillWithPayment(
+  callUrl: string,
+  skillOwnerWallet: string,
+  priceXLM: number,
+  request: SkillInvocationRequest,
+): Promise<InvocationResult> {
+  // Step 1: Attempt initial call
+  const initial = await attemptSkillInvocation(callUrl, request)
+
+  // If not 402, return the response directly
+  if (initial.status !== 402) {
+    return {
+      ok: initial.status >= 200 && initial.status < 300,
+      response: initial.body,
+    }
+  }
+
+  // Step 2: Generate x402 quote for the skill payment
+  const quote = createX402Quote({
+    serviceId: callUrl,
+    chain: "stellar",
+    payer: request.agentId,
+    units: 1,
+    unitPriceUsd: priceXLM * 0.1, // approximate USD price
+    ttlSeconds: 300,
+  })
+
+  // Step 3: Generate a mock/real payment txHash
+  // In production, the caller would sign and submit a Stellar tx
+  const txHash = `mock_tx_${Date.now()}_${Math.random().toString(36).slice(2, 10)}`
+
+  // Step 4: Settle the payment
+  const settlement = await settleSkillPayment(quote.paymentRef, txHash, "stellar")
+
+  if (!settlement.ok || !settlement.receipt) {
+    return {
+      ok: false,
+      error: settlement.error || "Payment settlement failed",
+    }
+  }
+
+  // Step 5: Retry the HTTP call with payment proof header
+  const retry = await fetch(callUrl, {
+    method: "POST",
+    headers: {
+      "Content-Type": "application/json",
+      "X-Payment": JSON.stringify({
+        paymentRef: quote.paymentRef,
+        txHash: settlement.receipt.txHash,
+        chain: settlement.receipt.chain,
+      }),
+    },
+    body: JSON.stringify(request),
+  })
+
+  const retryBody = await retry.json().catch(() => ({}))
+
+  return {
+    ok: retry.ok,
+    response: retryBody,
+    receipt: {
+      txHash: settlement.receipt.txHash,
+      chain: settlement.receipt.chain,
+      amountUsd: settlement.receipt.amountUsd ?? 0,
+    },
+  }
+}
\ No newline at end of file
diff --git a/tests/lib/agents/task-drain.test.ts b/tests/lib/agents/task-drain.test.ts
index 62513263..392d9154 100644
--- a/tests/lib/agents/task-drain.test.ts
+++ b/tests/lib/agents/task-drain.test.ts
@@ -72,7 +72,7 @@ describe("task-queue drain and purge", () => {
         createTask("agent-1", { type: `task-${i}`, payload: {} })
       }
 
-      const { result } = await drainAgentTasks("agent-1", { maxItems: 300 })
+      const { result } = await drainAgentTasks("agent-1", { maxItems: 200 })
 
       expect(result).not.toBeNull()
       // MAX_PENDING_PER_AGENT=100 limits queue to 100 tasks
@@ -194,7 +194,7 @@ describe("task-queue drain and purge", () => {
   })
 
   describe("purgeAgentTasks", () => {
-    it("purges all pending tasks", () => {
+    it("purges all pending tasks", async () => {
       createTask("agent-1", { type: "a", payload: {} })
       createTask("agent-1", { type: "b", payload: {} })
       createTask("agent-1", { type: "c", payload: {} })
@@ -254,7 +254,7 @@ describe("task-queue drain and purge", () => {
       expect(stats.totalAgents).toBe(0)
     })
 
-    it("handles partial purge correctly", () => {
+    it("handles partial purge correctly", async () => {
       createTask("agent-1", { type: "a", payload: {} })
       createTask("agent-1", { type: "b", payload: {} })
 
diff --git a/tests/lib/marketplace/invocation-ledger.test.ts b/tests/lib/marketplace/invocation-ledger.test.ts
new file mode 100644
index 00000000..942a3746
--- /dev/null
+++ b/tests/lib/marketplace/invocation-ledger.test.ts
@@ -0,0 +1,93 @@
+import { describe, it, expect, beforeEach } from "vitest"
+import {
+  recordInvocation,
+  listInvocations,
+  getInvocationById,
+  getTotalSpentByAgent,
+  resetInvocationLedger,
+} from "@/lib/marketplace/invocation-ledger"
+
+describe("invocation-ledger", () => {
+  beforeEach(() => {
+    resetInvocationLedger()
+  })
+
+  it("records a successful invocation", () => {
+    const record = recordInvocation("agent-1", "skill-a", 2.5, "tx_abc123")
+
+    expect(record.id).toMatch(/^inv_/)
+    expect(record.agentId).toBe("agent-1")
+    expect(record.skillId).toBe("skill-a")
+    expect(record.amountXLM).toBe(2.5)
+    expect(record.txHash).toBe("tx_abc123")
+    expect(record.status).toBe("success")
+    expect(record.invokedAt).toBeDefined()
+  })
+
+  it("records a failed invocation", () => {
+    const record = recordInvocation("agent-1", "skill-a", 1.0, "", "failed", "Network error")
+
+    expect(record.status).toBe("failed")
+    expect(record.error).toBe("Network error")
+  })
+
+  it("lists invocations newest-first", () => {
+    recordInvocation("agent-1", "skill-a", 1.0, "tx1")
+    recordInvocation("agent-1", "skill-b", 2.0, "tx2")
+    recordInvocation("agent-2", "skill-a", 3.0, "tx3")
+
+    const all = listInvocations()
+    expect(all).toHaveLength(3)
+    // Newest first: tx3 (agent-2/skill-a), tx2 (agent-1/skill-b), tx1 (agent-1/skill-a)
+    expect(all[0].skillId).toBe("skill-a")
+    expect(all[0].agentId).toBe("agent-2")
+    expect(all[1].skillId).toBe("skill-b")
+    expect(all[1].agentId).toBe("agent-1")
+    expect(all[2].skillId).toBe("skill-a")
+    expect(all[2].agentId).toBe("agent-1")
+
+    const filtered = listInvocations({ agentId: "agent-1" })
+    expect(filtered).toHaveLength(2)
+    expect(filtered[0].skillId).toBe("skill-b")
+    expect(filtered[1].skillId).toBe("skill-a")
+  })
+
+  it("filters by skillId and limits results", () => {
+    recordInvocation("agent-1", "skill-a", 1.0, "tx1")
+    recordInvocation("agent-1", "skill-a", 2.0, "tx2")
+    recordInvocation("agent-1", "skill-b", 3.0, "tx3")
+
+    const skillA = listInvocations({ skillId: "skill-a", limit: 1 })
+    expect(skillA).toHaveLength(1)
+    expect(skillA[0].txHash).toBe("tx2")
+  })
+
+  it("retrieves invocation by id", () => {
+    const record = recordInvocation("agent-1", "skill-a", 1.0, "tx1")
+    const found = getInvocationById(record.id)
+
+    expect(found).not.toBeNull()
+    expect(found?.id).toBe(record.id)
+  })
+
+  it("calculates total spent by agent", () => {
+    recordInvocation("agent-1", "skill-a", 1.0, "tx1", "success")
+    recordInvocation("agent-1", "skill-b", 2.5, "tx2", "success")
+    recordInvocation("agent-1", "skill-c", 3.0, "tx3", "failed")
+    recordInvocation("agent-2", "skill-a", 5.0, "tx4", "success")
+
+    expect(getTotalSpentByAgent("agent-1")).toBe(3.5)
+    expect(getTotalSpentByAgent("agent-2")).toBe(5.0)
+  })
+
+  it("caps ledger at 50k entries", () => {
+    for (let i = 0; i < 50_001; i++) {
+      recordInvocation("agent-1", "skill-a", 0.01, `tx${i}`)
+    }
+
+    const all = listInvocations()
+    expect(all).toHaveLength(50_000)
+    expect(all[0].txHash).toBe("tx50000")
+    expect(all[all.length - 1].txHash).toBe("tx1")
+  })
+})