diff --git a/packages/loopover-engine/src/index.ts b/packages/loopover-engine/src/index.ts
index 128cab2ec3..1e7ebe0d83 100644
--- a/packages/loopover-engine/src/index.ts
+++ b/packages/loopover-engine/src/index.ts
@@ -584,6 +584,15 @@ export {
   type TaskGraphIssueScore,
   type TaskGraphScore,
 } from "./idea-intake.js";
+export {
+  buildResultsPayload,
+  MAX_DIFF_PREVIEW_FILES,
+  type DiffPreviewFile,
+  type IterationResult,
+  type LoopResultStatus,
+  type ResultChangedFile,
+  type ResultsPayload,
+} from "./results-payload.js";
 export {
   buildMetadataRankInput,
   computeMetadataDupRisk,
diff --git a/packages/loopover-engine/src/results-payload.ts b/packages/loopover-engine/src/results-payload.ts
new file mode 100644
index 0000000000..5456152649
--- /dev/null
+++ b/packages/loopover-engine/src/results-payload.ts
@@ -0,0 +1,64 @@
+// Loop results-delivery composer (pure) — packages a completed loop iteration into the customer-facing
+// result: a PR link, a plain-language summary, and a bounded diff preview (#4801, part of the Rent-a-Loop
+// path #4778). Deterministic and side-effect-free: a plain in/out transform over already-computed iteration
+// metadata (no IO, no GitHub calls), mirroring the intake bridge (#4798) at the other end of the loop.
+
+// Cap the preview so a large change never floods the customer surface; the totals below still count every file.
+export const MAX_DIFF_PREVIEW_FILES = 10;
+
+export type LoopResultStatus = "open" | "merged" | "closed";
+
+export type ResultChangedFile = {
+  path: string;
+  additions?: number | undefined;
+  deletions?: number | undefined;
+};
+
+/** The already-computed outcome of one completed loop iteration. */
+export type IterationResult = {
+  repoFullName: string;
+  /** The opened pull request's number, or null/absent when the iteration produced no PR. */
+  prNumber?: number | null | undefined;
+  title: string;
+  changedFiles?: ResultChangedFile[] | undefined;
+  status?: LoopResultStatus | undefined;
+};
+
+export type DiffPreviewFile = { path: string; additions: number; deletions: number };
+
+export type ResultsPayload = {
+  /** Canonical PR URL, or null when no PR was opened. */
+  prLink: string | null;
+  /** One readable, public-safe sentence a customer can act on without assembling anything. */
+  summary: string;
+  /** Up to {@link MAX_DIFF_PREVIEW_FILES} changed files; `totals` still reflects the full change. */
+  diffPreview: DiffPreviewFile[];
+  totals: { files: number; additions: number; deletions: number };
+};
+
+/** Package a completed iteration into the customer-facing results payload (#4801). Pure: it formats
+ *  already-fetched iteration metadata, it does not fetch, open, or deliver anything. */
+export function buildResultsPayload(result: IterationResult): ResultsPayload {
+  const normalized: DiffPreviewFile[] = (result.changedFiles ?? []).map((f) => ({
+    path: f.path,
+    additions: f.additions ?? 0,
+    deletions: f.deletions ?? 0,
+  }));
+  const totals = normalized.reduce(
+    (acc, f) => ({ files: acc.files + 1, additions: acc.additions + f.additions, deletions: acc.deletions + f.deletions }),
+    { files: 0, additions: 0, deletions: 0 },
+  );
+
+  const hasPr = result.prNumber !== null && result.prNumber !== undefined;
+  const prLink = hasPr ? `https://github.com/${result.repoFullName}/pull/${result.prNumber}` : null;
+  const status: LoopResultStatus = result.status ?? "open";
+
+  const prPart = hasPr ? `Opened PR #${result.prNumber} in ${result.repoFullName}` : `No pull request was opened for ${result.repoFullName}`;
+  const changePart =
+    totals.files === 0
+      ? "no file changes"
+      : `${totals.files} file${totals.files === 1 ? "" : "s"} changed (+${totals.additions} / -${totals.deletions})`;
+  const summary = `${prPart}: ${result.title}. ${changePart}. Status: ${status}.`;
+
+  return { prLink, summary, diffPreview: normalized.slice(0, MAX_DIFF_PREVIEW_FILES), totals };
+}
diff --git a/src/mcp/server.ts b/src/mcp/server.ts
index 5521061d7b..6b0c69514b 100644
--- a/src/mcp/server.ts
+++ b/src/mcp/server.ts
@@ -156,6 +156,7 @@ import { buildPredictedGateVerdict, type PredictedGateVerdict } from "../rules/p
 import { buildIssueSlopAssessment } from "../signals/issue-slop";
 import { buildSlopAssessment } from "../signals/slop";
 import { validateIdeaSubmission, buildTaskGraph, buildClaimPlan } from "../idea-intake";
+import { buildResultsPayload } from "../results-payload";
 import { buildStructuralImprovementAssessment } from "../signals/improvement";
 import { buildBoundaryTestGenerationFinding, buildBoundaryTestGenerationSpec } from "../signals/boundary-test-generation";
 import { buildRepoDataQuality } from "../signals/data-quality";
@@ -956,6 +957,25 @@ const planIdeaClaimsOutputSchema = {
   errors: z.array(z.string()).optional(),
 };
 
+// Loop results-delivery input (#4801): a completed iteration's already-computed metadata.
+const buildResultsPayloadShape = {
+  repoFullName: z.string().min(1),
+  prNumber: z.number().int().nullable().optional(),
+  title: z.string(),
+  changedFiles: z
+    .array(z.object({ path: z.string(), additions: z.number().int().optional(), deletions: z.number().int().optional() }))
+    .max(5000)
+    .optional(),
+  status: z.enum(["open", "merged", "closed"]).optional(),
+};
+
+const buildResultsPayloadOutputSchema = {
+  prLink: z.string().nullable().optional(),
+  summary: z.string().optional(),
+  diffPreview: z.unknown().optional(),
+  totals: z.unknown().optional(),
+};
+
 // Deterministic structural-improvement counterpart to checkSlopRiskShape (#4746, sub-issue I of epic #4737):
 // the positive-axis mirror of checkSlopRisk, same pure local-metadata contract. changedFiles/tests/testFiles
 // are reused verbatim (same shape as checkSlopRiskShape) so the two signals never disagree about what counts
@@ -1728,6 +1748,17 @@ export class LoopoverMcp {
       async (input) => this.toolResult(await this.planIdeaClaims(input)),
     );
 
+    server.registerTool(
+      "loopover_build_results_payload",
+      {
+        description:
+          "Package a completed loop iteration into the customer-facing result (#4801): a PR link, a plain-language summary, and a bounded diff preview, from already-computed iteration metadata. Deterministic and source-free — it formats the result, it does not fetch, open, or deliver anything.",
+        inputSchema: buildResultsPayloadShape,
+        outputSchema: buildResultsPayloadOutputSchema,
+      },
+      async (input) => this.toolResult(await this.buildLoopResults(input)),
+    );
+
     server.registerTool(
       "loopover_check_slop_risk",
       {
@@ -3032,6 +3063,15 @@ export class LoopoverMcp {
     };
   }
 
+  private async buildLoopResults(input: z.infer<z.ZodObject<typeof buildResultsPayloadShape>>): Promise<ToolPayload> {
+    await this.enforceToolRateLimit("loopover_build_results_payload");
+    const payload = buildResultsPayload(input);
+    return {
+      summary: payload.summary,
+      data: payload as unknown as Record<string, unknown>,
+    };
+  }
+
   private async checkSlopRisk(input: z.infer<z.ZodObject<typeof checkSlopRiskShape>>): Promise<ToolPayload> {
     await this.enforceToolRateLimit("loopover_check_slop_risk");
     const assessment = buildSlopAssessment(input);
diff --git a/src/results-payload.ts b/src/results-payload.ts
new file mode 100644
index 0000000000..e0ad84665a
--- /dev/null
+++ b/src/results-payload.ts
@@ -0,0 +1,5 @@
+// Loop results-delivery composer (#4801) — thin re-export shim. The canonical implementation lives in
+// `@loopover/engine` (packages/loopover-engine/src/results-payload.ts), imported via the relative source
+// path (matching src/idea-intake.ts / src/signals/slop.ts) so the published loopover-mcp / loopover-miner
+// CLIs share one composer, and so this never depends on the engine's built dist/ during typecheck/test.
+export * from "../packages/loopover-engine/src/results-payload";
diff --git a/test/unit/mcp-results-payload.test.ts b/test/unit/mcp-results-payload.test.ts
new file mode 100644
index 0000000000..8d08f7b1d8
--- /dev/null
+++ b/test/unit/mcp-results-payload.test.ts
@@ -0,0 +1,47 @@
+import { Client } from "@modelcontextprotocol/sdk/client/index.js";
+import { InMemoryTransport } from "@modelcontextprotocol/sdk/inMemory.js";
+import { describe, expect, it } from "vitest";
+import { LoopoverMcp } from "../../src/mcp/server";
+import { createTestEnv } from "../helpers/d1";
+
+async function connect() {
+  const server = new LoopoverMcp(createTestEnv()).createServer();
+  const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+  await server.connect(serverTransport);
+  const client = new Client({ name: "gittensory-results-test", version: "0.1.0" }, { capabilities: {} });
+  await client.connect(clientTransport);
+  return client;
+}
+
+describe("MCP loopover_build_results_payload", () => {
+  it("packages a completed iteration into a PR link, summary, and diff preview", async () => {
+    const client = await connect();
+    const result = await client.callTool({
+      name: "loopover_build_results_payload",
+      arguments: {
+        repoFullName: "acme/widgets",
+        prNumber: 42,
+        title: "Add retry to uploads",
+        changedFiles: [{ path: "src/upload.ts", additions: 12, deletions: 2 }],
+        status: "open",
+      },
+    });
+    expect(result.isError).toBeFalsy();
+    const data = result.structuredContent as { prLink: string; summary: string; diffPreview: unknown[]; totals: { files: number } };
+    expect(data.prLink).toBe("https://github.com/acme/widgets/pull/42");
+    expect(data.summary).toContain("Opened PR #42 in acme/widgets");
+    expect(data.diffPreview).toHaveLength(1);
+    expect(data.totals.files).toBe(1);
+  });
+
+  it("reports no PR when prNumber is null", async () => {
+    const client = await connect();
+    const result = await client.callTool({
+      name: "loopover_build_results_payload",
+      arguments: { repoFullName: "acme/widgets", prNumber: null, title: "No PR produced" },
+    });
+    const data = result.structuredContent as { prLink: string | null; summary: string };
+    expect(data.prLink).toBeNull();
+    expect(data.summary).toContain("No pull request was opened");
+  });
+});
diff --git a/test/unit/results-payload.test.ts b/test/unit/results-payload.test.ts
new file mode 100644
index 0000000000..cbc323e83a
--- /dev/null
+++ b/test/unit/results-payload.test.ts
@@ -0,0 +1,58 @@
+import { describe, expect, it } from "vitest";
+import { buildResultsPayload, MAX_DIFF_PREVIEW_FILES, type IterationResult } from "../../packages/loopover-engine/src/results-payload";
+
+describe("buildResultsPayload — packages a completed loop iteration (#4801)", () => {
+  it("builds a PR link, plain-language summary, and diff preview for a completed PR", () => {
+    const r: IterationResult = {
+      repoFullName: "acme/widgets",
+      prNumber: 12,
+      title: "Uploads should retry on 5xx",
+      changedFiles: [
+        { path: "src/upload.ts", additions: 30, deletions: 4 },
+        { path: "test/upload.test.ts", additions: 10, deletions: 1 },
+      ],
+      status: "merged",
+    };
+    const p = buildResultsPayload(r);
+    expect(p.prLink).toBe("https://github.com/acme/widgets/pull/12");
+    expect(p.summary).toBe("Opened PR #12 in acme/widgets: Uploads should retry on 5xx. 2 files changed (+40 / -5). Status: merged.");
+    expect(p.diffPreview).toEqual([
+      { path: "src/upload.ts", additions: 30, deletions: 4 },
+      { path: "test/upload.test.ts", additions: 10, deletions: 1 },
+    ]);
+    expect(p.totals).toEqual({ files: 2, additions: 40, deletions: 5 });
+  });
+
+  it("reports no PR (and defaults status to open) when prNumber is null", () => {
+    const p = buildResultsPayload({ repoFullName: "acme/widgets", prNumber: null, title: "Attempted change", changedFiles: [{ path: "a.ts" }] });
+    expect(p.prLink).toBeNull();
+    expect(p.summary).toBe("No pull request was opened for acme/widgets: Attempted change. 1 file changed (+0 / -0). Status: open.");
+  });
+
+  it("treats an omitted prNumber the same as null", () => {
+    const p = buildResultsPayload({ repoFullName: "acme/widgets", title: "No PR", changedFiles: [] });
+    expect(p.prLink).toBeNull();
+    // omitted changedFiles + empty array both yield "no file changes"
+    expect(p.summary).toBe("No pull request was opened for acme/widgets: No PR. no file changes. Status: open.");
+  });
+
+  it("says 'no file changes' when changedFiles is omitted entirely", () => {
+    const p = buildResultsPayload({ repoFullName: "o/r", prNumber: 3, title: "Docs" });
+    expect(p.totals).toEqual({ files: 0, additions: 0, deletions: 0 });
+    expect(p.diffPreview).toEqual([]);
+    expect(p.summary).toContain("no file changes");
+  });
+
+  it("defaults missing per-file additions/deletions to zero", () => {
+    const p = buildResultsPayload({ repoFullName: "o/r", prNumber: 1, title: "t", changedFiles: [{ path: "x.ts" }] });
+    expect(p.diffPreview).toEqual([{ path: "x.ts", additions: 0, deletions: 0 }]);
+  });
+
+  it("caps the diff preview at MAX_DIFF_PREVIEW_FILES while totals still count every file", () => {
+    const files = Array.from({ length: MAX_DIFF_PREVIEW_FILES + 3 }, (_, i) => ({ path: `f${i}.ts`, additions: 1, deletions: 1 }));
+    const p = buildResultsPayload({ repoFullName: "o/r", prNumber: 9, title: "Big change", changedFiles: files });
+    expect(p.diffPreview).toHaveLength(MAX_DIFF_PREVIEW_FILES);
+    expect(p.totals.files).toBe(MAX_DIFF_PREVIEW_FILES + 3);
+    expect(p.summary).toContain(`${MAX_DIFF_PREVIEW_FILES + 3} files changed`); // plural
+  });
+});