diff --git a/artifacts/api-server/src/lib/lnbits.ts b/artifacts/api-server/src/lib/lnbits.ts
index 07dcc56..9ec576d 100644
--- a/artifacts/api-server/src/lib/lnbits.ts
+++ b/artifacts/api-server/src/lib/lnbits.ts
@@ -26,6 +26,8 @@ export class LNbitsService {
     }
   }
 
+  // ── Inbound invoices ─────────────────────────────────────────────────────
+
   async createInvoice(amountSats: number, memo: string): Promise<LNbitsInvoice> {
     if (this.stubMode) {
       const paymentHash = randomBytes(32).toString("hex");
@@ -34,7 +36,7 @@ export class LNbitsService {
       return { paymentHash, paymentRequest };
     }
 
-    const response = await fetch(`${this.url.replace(/\/$/, "")}/api/v1/payments`, {
+    const response = await fetch(`${this.base()}/api/v1/payments`, {
       method: "POST",
       headers: this.headers(),
       body: JSON.stringify({ out: false, amount: amountSats, memo }),
@@ -58,7 +60,7 @@ export class LNbitsService {
     }
 
     const response = await fetch(
-      `${this.url.replace(/\/$/, "")}/api/v1/payments/${paymentHash}`,
+      `${this.base()}/api/v1/payments/${paymentHash}`,
       { method: "GET", headers: this.headers() },
     );
 
@@ -71,7 +73,68 @@ export class LNbitsService {
     return data.paid;
   }
 
-  /** Stub-only helper: mark an invoice as paid for testing/dev flows. */
+  // ── Outbound payments (refunds) ──────────────────────────────────────────
+
+  /**
+   * Decode a BOLT11 invoice and return its amount in satoshis.
+   * Stub mode: parses the embedded amount from our known stub format (lnbcrtXu1stub_...),
+   * or returns null for externally-generated invoices.
+   */
+  async decodeInvoice(bolt11: string): Promise<{ amountSats: number } | null> {
+    if (this.stubMode) {
+      // Our stub format: lnbcrtNNNu1stub_...  where NNN is the amount in sats
+      const m = bolt11.match(/^lnbcrt(\d+)u1stub_/i);
+      if (m) return { amountSats: parseInt(m[1], 10) };
+      // Unknown format in stub mode — accept blindly (simulated environment)
+      return null;
+    }
+
+    const response = await fetch(`${this.base()}/api/v1/payments/decode`, {
+      method: "POST",
+      headers: this.headers(),
+      body: JSON.stringify({ data: bolt11 }),
+    });
+
+    if (!response.ok) {
+      const body = await response.text();
+      throw new Error(`LNbits decodeInvoice failed (${response.status}): ${body}`);
+    }
+
+    const data = (await response.json()) as { amount_msat?: number };
+    if (!data.amount_msat) return null;
+    return { amountSats: Math.floor(data.amount_msat / 1000) };
+  }
+
+  /**
+   * Pay an outgoing BOLT11 invoice (e.g. to return a refund to a user).
+   * Returns the payment hash.
+   * Stub mode: simulates a successful payment.
+   */
+  async payInvoice(bolt11: string): Promise<string> {
+    if (this.stubMode) {
+      const paymentHash = randomBytes(32).toString("hex");
+      console.log(`[stub] Paid outgoing invoice — fake hash=${paymentHash}`);
+      return paymentHash;
+    }
+
+    const response = await fetch(`${this.base()}/api/v1/payments`, {
+      method: "POST",
+      headers: this.headers(),
+      body: JSON.stringify({ out: true, bolt11 }),
+    });
+
+    if (!response.ok) {
+      const body = await response.text();
+      throw new Error(`LNbits payInvoice failed (${response.status}): ${body}`);
+    }
+
+    const data = (await response.json()) as { payment_hash: string };
+    return data.payment_hash;
+  }
+
+  // ── Stub helpers ─────────────────────────────────────────────────────────
+
+  /** Stub-only: mark an inbound invoice as paid for testing/dev flows. */
   stubMarkPaid(paymentHash: string): void {
     if (!this.stubMode) {
       throw new Error("stubMarkPaid called on a real LNbitsService instance");
@@ -80,6 +143,12 @@ export class LNbitsService {
     console.log(`[stub] Marked invoice paid: hash=${paymentHash}`);
   }
 
+  // ── Private helpers ──────────────────────────────────────────────────────
+
+  private base(): string {
+    return this.url.replace(/\/$/, "");
+  }
+
   private headers(): Record<string, string> {
     return {
       "Content-Type": "application/json",
diff --git a/artifacts/api-server/src/lib/pricing.ts b/artifacts/api-server/src/lib/pricing.ts
index 653452d..193d671 100644
--- a/artifacts/api-server/src/lib/pricing.ts
+++ b/artifacts/api-server/src/lib/pricing.ts
@@ -158,6 +158,35 @@ export class PricingService {
     const amountSats = usdToSats(estimatedCostUsd, btcPriceUsd);
     return { amountSats, estimatedCostUsd, marginPct: this.marginPct, btcPriceUsd };
   }
+
+  // ── Post-work honest accounting ──────────────────────────────────────────
+
+  /**
+   * Full actual charge in USD: raw Anthropic token cost + DO infra amortisation + margin.
+   * Pass in the already-computed actualCostUsd (raw token cost, no extras).
+   */
+  calculateActualChargeUsd(actualCostUsd: number): number {
+    const rawCostUsd = actualCostUsd + DO_INFRA_PER_REQUEST_USD;
+    return rawCostUsd * (1 + this.marginPct / 100);
+  }
+
+  /**
+   * Convert the actual charge to satoshis using the BTC price that was locked
+   * at invoice-creation time. This keeps pre- and post-work accounting in the
+   * same BTC denomination without a second oracle call.
+   */
+  calculateActualChargeSats(actualCostUsd: number, lockedBtcPriceUsd: number): number {
+    const chargeUsd = this.calculateActualChargeUsd(actualCostUsd);
+    return usdToSats(chargeUsd, lockedBtcPriceUsd);
+  }
+
+  /**
+   * Refund amount in sats: what was overpaid by the user.
+   * Always >= 0 (clamped — never ask the user to top up due to BTC price swings).
+   */
+  calculateRefundSats(workAmountSats: number, actualAmountSats: number): number {
+    return Math.max(0, workAmountSats - actualAmountSats);
+  }
 }
 
 export const pricingService = new PricingService();
diff --git a/artifacts/api-server/src/routes/jobs.ts b/artifacts/api-server/src/routes/jobs.ts
index 511c0da..744e504 100644
--- a/artifacts/api-server/src/routes/jobs.ts
+++ b/artifacts/api-server/src/routes/jobs.ts
@@ -50,7 +50,6 @@ async function advanceJob(job: Job): Promise<Job | null> {
       const evalResult = await agentService.evaluateRequest(job.request);
 
       if (evalResult.accepted) {
-        // Cost-based work fee: estimate tokens → fetch BTC price → invoice sats
         const inputEst = pricingService.estimateInputTokens(job.request);
         const outputEst = pricingService.estimateOutputTokens(job.request);
         const breakdown = await pricingService.calculateWorkFeeSats(
@@ -129,12 +128,28 @@ async function advanceJob(job: Job): Promise<Job | null> {
 
     try {
       const workResult = await agentService.executeWork(job.request);
+
+      // ── Honest post-work accounting ───────────────────────────────────────
       const actualCostUsd = pricingService.calculateActualCostUsd(
         workResult.inputTokens,
         workResult.outputTokens,
         agentService.workModel,
       );
 
+      // Re-use the BTC price locked at invoice time so sats arithmetic is
+      // consistent. Fall back to the cached oracle price only if the column
+      // is somehow null (should not happen in normal flow).
+      const lockedBtcPrice = job.btcPriceUsd ?? 100_000;
+      const actualAmountSats = pricingService.calculateActualChargeSats(
+        actualCostUsd,
+        lockedBtcPrice,
+      );
+      const refundAmountSats = pricingService.calculateRefundSats(
+        job.workAmountSats ?? 0,
+        actualAmountSats,
+      );
+      const refundState = refundAmountSats > 0 ? "pending" : "not_applicable";
+
       await db
         .update(jobs)
         .set({
@@ -143,6 +158,9 @@ async function advanceJob(job: Job): Promise<Job | null> {
           actualInputTokens: workResult.inputTokens,
           actualOutputTokens: workResult.outputTokens,
           actualCostUsd,
+          actualAmountSats,
+          refundAmountSats,
+          refundState,
           updatedAt: new Date(),
         })
         .where(eq(jobs.id, job.id));
@@ -160,6 +178,8 @@ async function advanceJob(job: Job): Promise<Job | null> {
   return job;
 }
 
+// ── POST /jobs ────────────────────────────────────────────────────────────────
+
 router.post("/jobs", async (req: Request, res: Response) => {
   const parseResult = CreateJobBody.safeParse(req.body);
   if (!parseResult.success) {
@@ -177,18 +197,10 @@ router.post("/jobs", async (req: Request, res: Response) => {
     const jobId = randomUUID();
     const invoiceId = randomUUID();
 
-    const lnbitsInvoice = await lnbitsService.createInvoice(
-      evalFee,
-      `Eval fee for job ${jobId}`,
-    );
+    const lnbitsInvoice = await lnbitsService.createInvoice(evalFee, `Eval fee for job ${jobId}`);
 
     await db.transaction(async (tx) => {
-      await tx.insert(jobs).values({
-        id: jobId,
-        request,
-        state: "awaiting_eval_payment",
-        evalAmountSats: evalFee,
-      });
+      await tx.insert(jobs).values({ id: jobId, request, state: "awaiting_eval_payment", evalAmountSats: evalFee });
       await tx.insert(invoices).values({
         id: invoiceId,
         jobId,
@@ -198,18 +210,12 @@ router.post("/jobs", async (req: Request, res: Response) => {
         type: "eval",
         paid: false,
       });
-      await tx
-        .update(jobs)
-        .set({ evalInvoiceId: invoiceId, updatedAt: new Date() })
-        .where(eq(jobs.id, jobId));
+      await tx.update(jobs).set({ evalInvoiceId: invoiceId, updatedAt: new Date() }).where(eq(jobs.id, jobId));
     });
 
     res.status(201).json({
       jobId,
-      evalInvoice: {
-        paymentRequest: lnbitsInvoice.paymentRequest,
-        amountSats: evalFee,
-      },
+      evalInvoice: { paymentRequest: lnbitsInvoice.paymentRequest, amountSats: evalFee },
     });
   } catch (err) {
     const message = err instanceof Error ? err.message : "Failed to create job";
@@ -217,20 +223,16 @@ router.post("/jobs", async (req: Request, res: Response) => {
   }
 });
 
+// ── GET /jobs/:id ─────────────────────────────────────────────────────────────
+
 router.get("/jobs/:id", async (req: Request, res: Response) => {
   const paramResult = GetJobParams.safeParse(req.params);
-  if (!paramResult.success) {
-    res.status(400).json({ error: "Invalid job id" });
-    return;
-  }
+  if (!paramResult.success) { res.status(400).json({ error: "Invalid job id" }); return; }
   const { id } = paramResult.data;
 
   try {
     let job = await getJobById(id);
-    if (!job) {
-      res.status(404).json({ error: "Job not found" });
-      return;
-    }
+    if (!job) { res.status(404).json({ error: "Job not found" }); return; }
 
     const advanced = await advanceJob(job);
     if (advanced) job = advanced;
@@ -264,7 +266,6 @@ router.get("/jobs/:id", async (req: Request, res: Response) => {
               ...(lnbitsService.stubMode ? { paymentHash: inv.paymentHash } : {}),
             },
           } : {}),
-          // Cost breakdown so callers understand the invoice amount
           ...(job.estimatedCostUsd != null ? {
             pricingBreakdown: {
               estimatedCostUsd: job.estimatedCostUsd,
@@ -284,14 +285,25 @@ router.get("/jobs/:id", async (req: Request, res: Response) => {
         res.json({
           ...base,
           result: job.result ?? undefined,
-          // Actual token usage + cost ledger
           ...(job.actualCostUsd != null ? {
             costLedger: {
+              // Token usage
               actualInputTokens: job.actualInputTokens,
               actualOutputTokens: job.actualOutputTokens,
               totalTokens: (job.actualInputTokens ?? 0) + (job.actualOutputTokens ?? 0),
+              // USD costs
               actualCostUsd: job.actualCostUsd,
+              actualChargeUsd: job.actualAmountSats != null && job.btcPriceUsd
+                ? (job.actualAmountSats / 1e8) * job.btcPriceUsd
+                : undefined,
               estimatedCostUsd: job.estimatedCostUsd,
+              // Sat amounts
+              actualAmountSats: job.actualAmountSats,
+              workAmountSats: job.workAmountSats,
+              // Refund
+              refundAmountSats: job.refundAmountSats,
+              refundState: job.refundState,
+              // Rate context
               marginPct: job.marginPct,
               btcPriceUsd: job.btcPriceUsd,
             },
@@ -312,4 +324,72 @@ router.get("/jobs/:id", async (req: Request, res: Response) => {
   }
 });
 
+// ── POST /jobs/:id/refund ─────────────────────────────────────────────────────
+
+router.post("/jobs/:id/refund", async (req: Request, res: Response) => {
+  const paramResult = GetJobParams.safeParse(req.params);
+  if (!paramResult.success) { res.status(400).json({ error: "Invalid job id" }); return; }
+  const { id } = paramResult.data;
+
+  const { invoice } = req.body as { invoice?: string };
+  if (!invoice || typeof invoice !== "string" || invoice.trim().length === 0) {
+    res.status(400).json({ error: "Body must include 'invoice' (BOLT11 string)" });
+    return;
+  }
+  const bolt11 = invoice.trim();
+
+  try {
+    const job = await getJobById(id);
+    if (!job) { res.status(404).json({ error: "Job not found" }); return; }
+    if (job.state !== "complete") {
+      res.status(409).json({ error: `Job is in state '${job.state}', not 'complete'` });
+      return;
+    }
+    if (job.refundState !== "pending") {
+      if (job.refundState === "not_applicable") {
+        res.status(409).json({ error: "No refund is owed for this job (actual cost matched or exceeded the invoice amount)" });
+      } else if (job.refundState === "paid") {
+        res.status(409).json({ error: "Refund has already been sent", refundPaymentHash: job.refundPaymentHash });
+      } else {
+        res.status(409).json({ error: "Refund is not available for this job" });
+      }
+      return;
+    }
+
+    const refundSats = job.refundAmountSats ?? 0;
+    if (refundSats <= 0) {
+      res.status(409).json({ error: "Refund amount is zero — nothing to return" });
+      return;
+    }
+
+    // ── Validate invoice amount ───────────────────────────────────────────
+    const decoded = await lnbitsService.decodeInvoice(bolt11);
+    if (decoded !== null && decoded.amountSats !== refundSats) {
+      res.status(400).json({
+        error: `Invoice amount (${decoded.amountSats} sats) does not match refund owed (${refundSats} sats)`,
+        refundAmountSats: refundSats,
+      });
+      return;
+    }
+
+    // ── Send refund ───────────────────────────────────────────────────────
+    const paymentHash = await lnbitsService.payInvoice(bolt11);
+
+    await db
+      .update(jobs)
+      .set({ refundState: "paid", refundPaymentHash: paymentHash, updatedAt: new Date() })
+      .where(and(eq(jobs.id, id), eq(jobs.refundState, "pending")));
+
+    res.json({
+      ok: true,
+      refundAmountSats: refundSats,
+      paymentHash,
+      message: `Refund of ${refundSats} sats sent successfully`,
+    });
+  } catch (err) {
+    const message = err instanceof Error ? err.message : "Failed to process refund";
+    res.status(500).json({ error: message });
+  }
+});
+
 export default router;
diff --git a/lib/api-client-react/src/generated/api.schemas.ts b/lib/api-client-react/src/generated/api.schemas.ts
index 7771eb9..3a2f8e7 100644
--- a/lib/api-client-react/src/generated/api.schemas.ts
+++ b/lib/api-client-react/src/generated/api.schemas.ts
@@ -53,7 +53,19 @@ export interface PricingBreakdown {
 }
 
 /**
- * Actual cost record stored after the job completes
+ * Lifecycle of the refund for this job
+ */
+export type CostLedgerRefundState =
+  (typeof CostLedgerRefundState)[keyof typeof CostLedgerRefundState];
+
+export const CostLedgerRefundState = {
+  not_applicable: "not_applicable",
+  pending: "pending",
+  paid: "paid",
+} as const;
+
+/**
+ * Honest post-work accounting stored after the job completes
  */
 export interface CostLedger {
   actualInputTokens?: number;
@@ -62,8 +74,20 @@ export interface CostLedger {
   totalTokens?: number;
   /** Raw Anthropic token cost (no infra, no margin) */
   actualCostUsd?: number;
+  /** What we honestly charged in USD (actual token cost + DO infra + margin) */
+  actualChargeUsd?: number;
+  /** Original estimate used to create the work invoice */
   estimatedCostUsd?: number;
+  /** Honest sats charge (actual cost converted at the locked BTC price) */
+  actualAmountSats?: number;
+  /** Amount the user originally paid in sats */
+  workAmountSats?: number;
+  /** Sats owed back to the user (workAmountSats - actualAmountSats, >= 0) */
+  refundAmountSats?: number;
+  /** Lifecycle of the refund for this job */
+  refundState?: CostLedgerRefundState;
   marginPct?: number;
+  /** BTC/USD price locked at invoice creation time */
   btcPriceUsd?: number;
 }
 
@@ -79,6 +103,18 @@ export interface JobStatusResponse {
   errorMessage?: string;
 }
 
+export interface ClaimRefundRequest {
+  /** BOLT11 invoice for exactly refundAmountSats */
+  invoice: string;
+}
+
+export interface ClaimRefundResponse {
+  ok: boolean;
+  refundAmountSats: number;
+  paymentHash: string;
+  message: string;
+}
+
 export interface DemoResponse {
   result: string;
 }
diff --git a/lib/api-client-react/src/generated/api.ts b/lib/api-client-react/src/generated/api.ts
index 63374e3..64f851d 100644
--- a/lib/api-client-react/src/generated/api.ts
+++ b/lib/api-client-react/src/generated/api.ts
@@ -17,6 +17,8 @@ import type {
 } from "@tanstack/react-query";
 
 import type {
+  ClaimRefundRequest,
+  ClaimRefundResponse,
   CreateJobRequest,
   CreateJobResponse,
   DemoResponse,
@@ -274,6 +276,98 @@ export function useGetJob<
   return { ...query, queryKey: queryOptions.queryKey };
 }
 
+/**
+ * After a job completes, if the actual cost (tokens used + infra + margin) was
+less than the work invoice amount, the difference is owed back to the user.
+Submit a BOLT11 invoice for exactly `refundAmountSats` to receive the payment.
+Idempotent: returns 409 if already paid or if no refund is owed.
+
+ * @summary Claim a refund for overpayment
+ */
+export const getClaimRefundUrl = (id: string) => {
+  return `/api/jobs/${id}/refund`;
+};
+
+export const claimRefund = async (
+  id: string,
+  claimRefundRequest: ClaimRefundRequest,
+  options?: RequestInit,
+): Promise<ClaimRefundResponse> => {
+  return customFetch<ClaimRefundResponse>(getClaimRefundUrl(id), {
+    ...options,
+    method: "POST",
+    headers: { "Content-Type": "application/json", ...options?.headers },
+    body: JSON.stringify(claimRefundRequest),
+  });
+};
+
+export const getClaimRefundMutationOptions = <
+  TError = ErrorType<ErrorResponse>,
+  TContext = unknown,
+>(options?: {
+  mutation?: UseMutationOptions<
+    Awaited<ReturnType<typeof claimRefund>>,
+    TError,
+    { id: string; data: BodyType<ClaimRefundRequest> },
+    TContext
+  >;
+  request?: SecondParameter<typeof customFetch>;
+}): UseMutationOptions<
+  Awaited<ReturnType<typeof claimRefund>>,
+  TError,
+  { id: string; data: BodyType<ClaimRefundRequest> },
+  TContext
+> => {
+  const mutationKey = ["claimRefund"];
+  const { mutation: mutationOptions, request: requestOptions } = options
+    ? options.mutation &&
+      "mutationKey" in options.mutation &&
+      options.mutation.mutationKey
+      ? options
+      : { ...options, mutation: { ...options.mutation, mutationKey } }
+    : { mutation: { mutationKey }, request: undefined };
+
+  const mutationFn: MutationFunction<
+    Awaited<ReturnType<typeof claimRefund>>,
+    { id: string; data: BodyType<ClaimRefundRequest> }
+  > = (props) => {
+    const { id, data } = props ?? {};
+
+    return claimRefund(id, data, requestOptions);
+  };
+
+  return { mutationFn, ...mutationOptions };
+};
+
+export type ClaimRefundMutationResult = NonNullable<
+  Awaited<ReturnType<typeof claimRefund>>
+>;
+export type ClaimRefundMutationBody = BodyType<ClaimRefundRequest>;
+export type ClaimRefundMutationError = ErrorType<ErrorResponse>;
+
+/**
+ * @summary Claim a refund for overpayment
+ */
+export const useClaimRefund = <
+  TError = ErrorType<ErrorResponse>,
+  TContext = unknown,
+>(options?: {
+  mutation?: UseMutationOptions<
+    Awaited<ReturnType<typeof claimRefund>>,
+    TError,
+    { id: string; data: BodyType<ClaimRefundRequest> },
+    TContext
+  >;
+  request?: SecondParameter<typeof customFetch>;
+}): UseMutationResult<
+  Awaited<ReturnType<typeof claimRefund>>,
+  TError,
+  { id: string; data: BodyType<ClaimRefundRequest> },
+  TContext
+> => {
+  return useMutation(getClaimRefundMutationOptions(options));
+};
+
 /**
  * Runs the agent without payment. Limited to 5 requests per IP per hour.
  * @summary Free demo (rate-limited)
diff --git a/lib/api-spec/openapi.yaml b/lib/api-spec/openapi.yaml
index 390eee7..45e2d48 100644
--- a/lib/api-spec/openapi.yaml
+++ b/lib/api-spec/openapi.yaml
@@ -90,6 +90,59 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorResponse"
+  /jobs/{id}/refund:
+    post:
+      operationId: claimRefund
+      tags: [jobs]
+      summary: Claim a refund for overpayment
+      description: |
+        After a job completes, if the actual cost (tokens used + infra + margin) was
+        less than the work invoice amount, the difference is owed back to the user.
+        Submit a BOLT11 invoice for exactly `refundAmountSats` to receive the payment.
+        Idempotent: returns 409 if already paid or if no refund is owed.
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/ClaimRefundRequest"
+      responses:
+        "200":
+          description: Refund sent
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/ClaimRefundResponse"
+        "400":
+          description: Missing invoice, wrong amount, or invalid BOLT11
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/ErrorResponse"
+        "404":
+          description: Job not found
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/ErrorResponse"
+        "409":
+          description: Job not complete, refund already paid, or no refund owed
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/ErrorResponse"
+        "500":
+          description: Server error (e.g. Lightning payment failure)
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/ErrorResponse"
   /demo:
     get:
       operationId: runDemo
@@ -196,7 +249,7 @@ components:
           description: BTC/USD spot price used to convert the invoice to sats
     CostLedger:
       type: object
-      description: Actual cost record stored after the job completes
+      description: Honest post-work accounting stored after the job completes
       properties:
         actualInputTokens:
           type: integer
@@ -208,12 +261,30 @@ components:
         actualCostUsd:
           type: number
           description: Raw Anthropic token cost (no infra, no margin)
+        actualChargeUsd:
+          type: number
+          description: What we honestly charged in USD (actual token cost + DO infra + margin)
         estimatedCostUsd:
           type: number
+          description: Original estimate used to create the work invoice
+        actualAmountSats:
+          type: integer
+          description: Honest sats charge (actual cost converted at the locked BTC price)
+        workAmountSats:
+          type: integer
+          description: Amount the user originally paid in sats
+        refundAmountSats:
+          type: integer
+          description: Sats owed back to the user (workAmountSats - actualAmountSats, >= 0)
+        refundState:
+          type: string
+          enum: [not_applicable, pending, paid]
+          description: Lifecycle of the refund for this job
         marginPct:
           type: number
         btcPriceUsd:
           type: number
+          description: BTC/USD price locked at invoice creation time
     JobStatusResponse:
       type: object
       required:
@@ -238,6 +309,30 @@ components:
           $ref: "#/components/schemas/CostLedger"
         errorMessage:
           type: string
+    ClaimRefundRequest:
+      type: object
+      required:
+        - invoice
+      properties:
+        invoice:
+          type: string
+          description: BOLT11 invoice for exactly refundAmountSats
+    ClaimRefundResponse:
+      type: object
+      required:
+        - ok
+        - refundAmountSats
+        - paymentHash
+        - message
+      properties:
+        ok:
+          type: boolean
+        refundAmountSats:
+          type: integer
+        paymentHash:
+          type: string
+        message:
+          type: string
     DemoResponse:
       type: object
       required:
diff --git a/lib/api-zod/src/generated/api.ts b/lib/api-zod/src/generated/api.ts
index 8789c90..63f5c74 100644
--- a/lib/api-zod/src/generated/api.ts
+++ b/lib/api-zod/src/generated/api.ts
@@ -90,15 +90,70 @@ export const GetJobResponse = zod.object({
         .number()
         .optional()
         .describe("Raw Anthropic token cost (no infra, no margin)"),
-      estimatedCostUsd: zod.number().optional(),
+      actualChargeUsd: zod
+        .number()
+        .optional()
+        .describe(
+          "What we honestly charged in USD (actual token cost + DO infra + margin)",
+        ),
+      estimatedCostUsd: zod
+        .number()
+        .optional()
+        .describe("Original estimate used to create the work invoice"),
+      actualAmountSats: zod
+        .number()
+        .optional()
+        .describe(
+          "Honest sats charge (actual cost converted at the locked BTC price)",
+        ),
+      workAmountSats: zod
+        .number()
+        .optional()
+        .describe("Amount the user originally paid in sats"),
+      refundAmountSats: zod
+        .number()
+        .optional()
+        .describe(
+          "Sats owed back to the user (workAmountSats - actualAmountSats, >= 0)",
+        ),
+      refundState: zod
+        .enum(["not_applicable", "pending", "paid"])
+        .optional()
+        .describe("Lifecycle of the refund for this job"),
       marginPct: zod.number().optional(),
-      btcPriceUsd: zod.number().optional(),
+      btcPriceUsd: zod
+        .number()
+        .optional()
+        .describe("BTC\/USD price locked at invoice creation time"),
     })
     .optional()
-    .describe("Actual cost record stored after the job completes"),
+    .describe("Honest post-work accounting stored after the job completes"),
   errorMessage: zod.string().optional(),
 });
 
+/**
+ * After a job completes, if the actual cost (tokens used + infra + margin) was
+less than the work invoice amount, the difference is owed back to the user.
+Submit a BOLT11 invoice for exactly `refundAmountSats` to receive the payment.
+Idempotent: returns 409 if already paid or if no refund is owed.
+
+ * @summary Claim a refund for overpayment
+ */
+export const ClaimRefundParams = zod.object({
+  id: zod.coerce.string(),
+});
+
+export const ClaimRefundBody = zod.object({
+  invoice: zod.string().describe("BOLT11 invoice for exactly refundAmountSats"),
+});
+
+export const ClaimRefundResponse = zod.object({
+  ok: zod.boolean(),
+  refundAmountSats: zod.number(),
+  paymentHash: zod.string(),
+  message: zod.string(),
+});
+
 /**
  * Runs the agent without payment. Limited to 5 requests per IP per hour.
  * @summary Free demo (rate-limited)
diff --git a/lib/api-zod/src/generated/types/claimRefundRequest.ts b/lib/api-zod/src/generated/types/claimRefundRequest.ts
new file mode 100644
index 0000000..cdd7eae
--- /dev/null
+++ b/lib/api-zod/src/generated/types/claimRefundRequest.ts
@@ -0,0 +1,12 @@
+/**
+ * Generated by orval v8.5.3 🍺
+ * Do not edit manually.
+ * Api
+ * API specification
+ * OpenAPI spec version: 0.1.0
+ */
+
+export interface ClaimRefundRequest {
+  /** BOLT11 invoice for exactly refundAmountSats */
+  invoice: string;
+}
diff --git a/lib/api-zod/src/generated/types/claimRefundResponse.ts b/lib/api-zod/src/generated/types/claimRefundResponse.ts
new file mode 100644
index 0000000..8643ece
--- /dev/null
+++ b/lib/api-zod/src/generated/types/claimRefundResponse.ts
@@ -0,0 +1,14 @@
+/**
+ * Generated by orval v8.5.3 🍺
+ * Do not edit manually.
+ * Api
+ * API specification
+ * OpenAPI spec version: 0.1.0
+ */
+
+export interface ClaimRefundResponse {
+  ok: boolean;
+  refundAmountSats: number;
+  paymentHash: string;
+  message: string;
+}
diff --git a/lib/api-zod/src/generated/types/costLedger.ts b/lib/api-zod/src/generated/types/costLedger.ts
index 264683a..6b2e39e 100644
--- a/lib/api-zod/src/generated/types/costLedger.ts
+++ b/lib/api-zod/src/generated/types/costLedger.ts
@@ -5,9 +5,10 @@
  * API specification
  * OpenAPI spec version: 0.1.0
  */
+import type { CostLedgerRefundState } from "./costLedgerRefundState";
 
 /**
- * Actual cost record stored after the job completes
+ * Honest post-work accounting stored after the job completes
  */
 export interface CostLedger {
   actualInputTokens?: number;
@@ -16,7 +17,19 @@ export interface CostLedger {
   totalTokens?: number;
   /** Raw Anthropic token cost (no infra, no margin) */
   actualCostUsd?: number;
+  /** What we honestly charged in USD (actual token cost + DO infra + margin) */
+  actualChargeUsd?: number;
+  /** Original estimate used to create the work invoice */
   estimatedCostUsd?: number;
+  /** Honest sats charge (actual cost converted at the locked BTC price) */
+  actualAmountSats?: number;
+  /** Amount the user originally paid in sats */
+  workAmountSats?: number;
+  /** Sats owed back to the user (workAmountSats - actualAmountSats, >= 0) */
+  refundAmountSats?: number;
+  /** Lifecycle of the refund for this job */
+  refundState?: CostLedgerRefundState;
   marginPct?: number;
+  /** BTC/USD price locked at invoice creation time */
   btcPriceUsd?: number;
 }
diff --git a/lib/api-zod/src/generated/types/costLedgerRefundState.ts b/lib/api-zod/src/generated/types/costLedgerRefundState.ts
new file mode 100644
index 0000000..7f44b92
--- /dev/null
+++ b/lib/api-zod/src/generated/types/costLedgerRefundState.ts
@@ -0,0 +1,19 @@
+/**
+ * Generated by orval v8.5.3 🍺
+ * Do not edit manually.
+ * Api
+ * API specification
+ * OpenAPI spec version: 0.1.0
+ */
+
+/**
+ * Lifecycle of the refund for this job
+ */
+export type CostLedgerRefundState =
+  (typeof CostLedgerRefundState)[keyof typeof CostLedgerRefundState];
+
+export const CostLedgerRefundState = {
+  not_applicable: "not_applicable",
+  pending: "pending",
+  paid: "paid",
+} as const;
diff --git a/lib/api-zod/src/generated/types/index.ts b/lib/api-zod/src/generated/types/index.ts
index 5c7ac17..9547d3e 100644
--- a/lib/api-zod/src/generated/types/index.ts
+++ b/lib/api-zod/src/generated/types/index.ts
@@ -6,7 +6,10 @@
  * OpenAPI spec version: 0.1.0
  */
 
+export * from "./claimRefundRequest";
+export * from "./claimRefundResponse";
 export * from "./costLedger";
+export * from "./costLedgerRefundState";
 export * from "./createJobRequest";
 export * from "./createJobResponse";
 export * from "./demoResponse";
diff --git a/lib/db/migrations/0003_refund_mechanism.sql b/lib/db/migrations/0003_refund_mechanism.sql
new file mode 100644
index 0000000..573fc66
--- /dev/null
+++ b/lib/db/migrations/0003_refund_mechanism.sql
@@ -0,0 +1,13 @@
+-- Migration: Add refund/honest-accounting columns to jobs table
+-- Users are refunded the overpayment (work invoice amount - actual cost) after job completion.
+
+ALTER TABLE jobs
+  ADD COLUMN IF NOT EXISTS actual_amount_sats  INTEGER,
+  ADD COLUMN IF NOT EXISTS refund_amount_sats  INTEGER,
+  ADD COLUMN IF NOT EXISTS refund_state        TEXT,
+  ADD COLUMN IF NOT EXISTS refund_payment_hash TEXT;
+
+COMMENT ON COLUMN jobs.actual_amount_sats   IS 'Actual charge in sats (raw token cost + DO infra + margin), computed post-execution using the locked BTC price';
+COMMENT ON COLUMN jobs.refund_amount_sats   IS 'Overpayment in sats to return to the user (work_amount_sats - actual_amount_sats, clamped >= 0)';
+COMMENT ON COLUMN jobs.refund_state         IS 'Refund lifecycle: not_applicable | pending | paid';
+COMMENT ON COLUMN jobs.refund_payment_hash  IS 'Payment hash of the outgoing Lightning refund payment once sent';
diff --git a/lib/db/src/schema/jobs.ts b/lib/db/src/schema/jobs.ts
index 161bbb9..535c651 100644
--- a/lib/db/src/schema/jobs.ts
+++ b/lib/db/src/schema/jobs.ts
@@ -36,6 +36,12 @@ export const jobs = pgTable("jobs", {
   actualOutputTokens: integer("actual_output_tokens"),
   actualCostUsd: real("actual_cost_usd"),
 
+  // ── Post-work honest accounting & refund ─────────────────────────────────
+  actualAmountSats: integer("actual_amount_sats"),
+  refundAmountSats: integer("refund_amount_sats"),
+  refundState: text("refund_state").$type<"not_applicable" | "pending" | "paid">(),
+  refundPaymentHash: text("refund_payment_hash"),
+
   createdAt: timestamp("created_at", { withTimezone: true }).defaultNow().notNull(),
   updatedAt: timestamp("updated_at", { withTimezone: true }).defaultNow().notNull(),
 });
diff --git a/replit.md b/replit.md
index dca698a..c6e6de0 100644
--- a/replit.md
+++ b/replit.md
@@ -93,6 +93,17 @@ Every package extends `tsconfig.base.json` which sets `composite: true`. The roo
 Work fee flow: estimate tokens → fetch BTC price from CoinGecko (60s cache) → `(token_cost + DO_infra) × (1 + margin%)` → convert USD → sats.
 After work runs, actual token counts and raw Anthropic spend are stored in `jobs` as `actual_input_tokens`, `actual_output_tokens`, `actual_cost_usd`.
 
+### Honest accounting and automatic refunds
+
+After every job completes, Timmy re-prices the job using **actual** token counts, adds DO infra amortisation and margin, converts back to sats using the **same BTC price locked at invoice time**, and computes the overpayment:
+
+```
+actual_amount_sats = ceil((actual_cost_usd + DO_infra) × (1 + margin%) / btc_price_usd × 1e8)
+refund_amount_sats = max(0, work_amount_sats - actual_amount_sats)
+```
+
+The `costLedger` in `GET /api/jobs/:id` shows all figures side-by-side. If `refundState = "pending"` and `refundAmountSats > 0`, the user submits a BOLT11 invoice for that exact amount to `POST /api/jobs/:id/refund` to receive the Lightning payment. The endpoint is idempotent — subsequent calls return 409 with the original `refundPaymentHash`.
+
 ### Node bootstrap secrets (for `POST /api/bootstrap`)
 
 | Secret | Description | Default |