diff --git a/open-sse/services/combo.ts b/open-sse/services/combo.ts
index 4ce9712934..a86bf5d90f 100644
--- a/open-sse/services/combo.ts
+++ b/open-sse/services/combo.ts
@@ -169,6 +169,7 @@ import {
   isTaskRoutingStrategy,
   reorderByTaskWeight,
 } from "./taskAwareRouting.ts";
+import { expandTargetsByFingerprints } from "./combo/fingerprintExpansion.ts";
 
 export { RESET_WINDOW_NAMES };
 export { QUOTA_SOFT_DEPRIORITIZE_FACTOR, setCandidateQuotaSoftPenalty };
@@ -368,8 +369,19 @@ export async function buildAutoCandidates(
     }
   }
 
+  // #5521: Expand fingerprint-based providers (mimocode, mcode, opencode) so each
+  // fingerprint gets its own combo slot instead of being bundled into one connection.
+  const fingerprintExpandedTargets = expandTargetsByFingerprints(
+    expandedTargets,
+    connectionById,
+    (t) => {
+      const parsed = parseModel(t.modelStr);
+      return t.provider || parsed.provider || parsed.providerAlias || "unknown";
+    }
+  );
+
   const candidates = await Promise.all(
-    expandedTargets.map(async (target) => {
+    fingerprintExpandedTargets.map(async (target) => {
       const modelStr = target.modelStr;
       const parsed = parseModel(modelStr);
       const provider = target.provider || parsed.provider || parsed.providerAlias || "unknown";
diff --git a/open-sse/services/combo/fingerprintExpansion.ts b/open-sse/services/combo/fingerprintExpansion.ts
new file mode 100644
index 0000000000..c96bb3ad05
--- /dev/null
+++ b/open-sse/services/combo/fingerprintExpansion.ts
@@ -0,0 +1,105 @@
+/**
+ * Fingerprint-based target expansion for combo routing.
+ *
+ * Some providers (MiMoCode, MiCode, OpenCode) store multiple device
+ * fingerprints inside a single connection's `providerSpecificData.fingerprints`.
+ * Without expansion the combo system treats the connection as one account,
+ * so only one fingerprint is used per request.  This module splits such
+ * connections into one target per fingerprint so the combo round-robin
+ * distributes requests across all of them.
+ *
+ * Expansion runs AFTER connection-based expansion and BEFORE the
+ * `candidates` scoring pass in `combo.ts`.
+ */
+
+import type { ResolvedComboTarget } from "./types.ts";
+
+/** Providers whose `providerSpecificData.fingerprints` array should be expanded. */
+const FINGERPRINT_PROVIDERS: ReadonlySet<string> = new Set(["mimocode", "mcode", "opencode"]);
+
+/** Check whether a provider uses fingerprint-based multi-account. */
+export function isFingerprintProvider(provider: string): boolean {
+  return FINGERPRINT_PROVIDERS.has(provider);
+}
+
+/** Safely extract the fingerprints array from a connection record. */
+export function getConnectionFingerprints(
+  connection: Record<string, unknown> | undefined | null
+): string[] {
+  if (!connection || typeof connection !== "object") return [];
+  const psd = connection["providerSpecificData"];
+  if (!psd || typeof psd !== "object") return [];
+  const fps = (psd as Record<string, unknown>)["fingerprints"];
+  if (!Array.isArray(fps)) return [];
+  return fps.filter((fp): fp is string => typeof fp === "string" && fp.trim().length > 0);
+}
+
+/** True when a connection carries more than one fingerprint. */
+export function hasMultipleFingerprints(
+  connection: Record<string, unknown> | undefined | null
+): boolean {
+  return getConnectionFingerprints(connection).length > 1;
+}
+
+/**
+ * Build an execution key that encodes a specific fingerprint.
+ * The first fingerprint keeps the original key so backward-compatible
+ * metrics / affinity lookups still work.
+ */
+export function buildFingerprintExecutionKey(
+  originalKey: string,
+  fingerprint: string,
+  isFirst: boolean
+): string {
+  if (isFirst) return originalKey;
+  return `${originalKey}@fp:${fingerprint}`;
+}
+
+/**
+ * Expand `expandedTargets` by splitting targets whose connection carries
+ * multiple fingerprints into one target per fingerprint.
+ *
+ * Targets that don't have a connectionId, don't belong to a fingerprint
+ * provider, or whose connection has ≤1 fingerprint are passed through
+ * unchanged.
+ *
+ * @param targets       Targets already expanded by connection ID
+ * @param connectionById  Map from connection ID → connection record
+ * @param getProvider   Function to resolve a target's provider string
+ * @returns New array with fingerprint targets expanded
+ */
+export function expandTargetsByFingerprints(
+  targets: ResolvedComboTarget[],
+  connectionById: Map<string, Record<string, unknown>>,
+  getProvider: (target: ResolvedComboTarget) => string
+): ResolvedComboTarget[] {
+  const result: ResolvedComboTarget[] = [];
+
+  for (const target of targets) {
+    const provider = getProvider(target);
+    const { connectionId } = target;
+
+    if (!connectionId || !isFingerprintProvider(provider)) {
+      result.push(target);
+      continue;
+    }
+
+    const connection = connectionById.get(connectionId);
+    const fingerprints = getConnectionFingerprints(connection);
+
+    if (fingerprints.length <= 1) {
+      result.push(target);
+      continue;
+    }
+
+    for (let i = 0; i < fingerprints.length; i++) {
+      const isFirst = i === 0;
+      result.push({
+        ...target,
+        executionKey: buildFingerprintExecutionKey(target.executionKey, fingerprints[i], isFirst),
+      });
+    }
+  }
+
+  return result;
+}
diff --git a/tests/e2e/fingerprint-expansion.test.ts b/tests/e2e/fingerprint-expansion.test.ts
new file mode 100644
index 0000000000..8b46ad7487
--- /dev/null
+++ b/tests/e2e/fingerprint-expansion.test.ts
@@ -0,0 +1,335 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import fsp from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import net from "node:net";
+import { spawn } from "node:child_process";
+import { fileURLToPath } from "node:url";
+import { MockUpstreamServer, buildCompletion } from "./helpers/mockUpstreamServer.ts";
+
+// #5521 — E2E test for fingerprint-based combo expansion.
+// Seeds a mimocode connection with 3 fingerprints, creates a round-robin combo,
+// and verifies that requests route through the combo successfully.
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-fingerprint-e2e-"));
+const DASHBOARD_PORT = await getFreePort();
+const REPO_ROOT = fileURLToPath(new URL("../..", import.meta.url));
+
+process.env.DATA_DIR = TEST_DATA_DIR;
+process.env.DISABLE_SQLITE_AUTO_BACKUP = "true";
+process.env.API_KEY_SECRET = process.env.API_KEY_SECRET || "fingerprint-e2e-secret";
+process.env.REQUIRE_API_KEY = "false";
+
+const core = await import("../../src/lib/db/core.ts");
+const providersDb = await import("../../src/lib/db/providers.ts");
+const combosDb = await import("../../src/lib/db/combos.ts");
+const settingsDb = await import("../../src/lib/db/settings.ts");
+
+function getFreePort(): Promise<number> {
+  return new Promise<number>((resolve, reject) => {
+    const server = net.createServer();
+    server.once("error", reject);
+    server.listen(0, "127.0.0.1", () => {
+      const address = server.address();
+      if (!address || typeof address === "string") {
+        server.close();
+        reject(new Error("Failed to allocate a free port"));
+        return;
+      }
+      const { port } = address;
+      server.close((err) => {
+        if (err) reject(err);
+        else resolve(port);
+      });
+    });
+  });
+}
+
+function sleep(ms: number) {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+function createServerProcess(dataDir: string, port: number) {
+  const stdoutLines: string[] = [];
+  const stderrLines: string[] = [];
+  let exitInfo: { code: number | null; signal: NodeJS.Signals | null } | null = null;
+  const child = spawn(process.execPath, ["scripts/dev/run-next-playwright.mjs", "dev"], {
+    cwd: REPO_ROOT,
+    env: {
+      ...process.env,
+      DATA_DIR: dataDir,
+      PORT: String(port),
+      DASHBOARD_PORT: String(port),
+      API_PORT: String(port),
+      HOST: "127.0.0.1",
+      REQUIRE_API_KEY: "false",
+      API_KEY_SECRET: process.env.API_KEY_SECRET || "fingerprint-e2e-secret",
+      DISABLE_SQLITE_AUTO_BACKUP: "true",
+      INITIAL_PASSWORD: "",
+      NEXT_TELEMETRY_DISABLED: "1",
+      OMNIROUTE_DISABLE_BACKGROUND_SERVICES: "true",
+      OMNIROUTE_DISABLE_TOKEN_HEALTHCHECK: "true",
+      OMNIROUTE_DISABLE_LOCAL_HEALTHCHECK: "true",
+      OMNIROUTE_HIDE_HEALTHCHECK_LOGS: "true",
+      OMNIROUTE_E2E_BOOTSTRAP_MODE: "open",
+    },
+    stdio: ["ignore", "pipe", "pipe"],
+  });
+
+  child.once("exit", (code, signal) => {
+    exitInfo = { code, signal };
+  });
+  child.stdout.on("data", (chunk) => {
+    const lines = String(chunk).split(/\r?\n/).filter(Boolean);
+    stdoutLines.push(...lines);
+    if (stdoutLines.length > 200) stdoutLines.splice(0, stdoutLines.length - 200);
+  });
+  child.stderr.on("data", (chunk) => {
+    const lines = String(chunk).split(/\r?\n/).filter(Boolean);
+    stderrLines.push(...lines);
+    if (stderrLines.length > 200) stderrLines.splice(0, stderrLines.length - 200);
+  });
+
+  return {
+    child,
+    stdoutLines,
+    stderrLines,
+    baseUrl: `http://127.0.0.1:${port}`,
+    get exitInfo() {
+      return exitInfo;
+    },
+  };
+}
+
+async function waitForServer(
+  baseUrl: string,
+  logs: {
+    stdoutLines: string[];
+    stderrLines: string[];
+    exitInfo?: { code: number | null; signal: NodeJS.Signals | null } | null;
+  }
+) {
+  const startedAt = Date.now();
+  let lastError = "";
+  while (Date.now() - startedAt < 120_000) {
+    if (logs.exitInfo) {
+      throw new Error(
+        [
+          `OmniRoute exited before it became ready (code=${logs.exitInfo.code}, signal=${logs.exitInfo.signal})`,
+          "--- stdout ---",
+          ...logs.stdoutLines.slice(-40),
+          "--- stderr ---",
+          ...logs.stderrLines.slice(-40),
+        ].join("\n")
+      );
+    }
+    try {
+      const response = await fetch(`${baseUrl}/api/monitoring/health`, {
+        signal: AbortSignal.timeout(5_000),
+      });
+      if (response.ok) return;
+      lastError = `HTTP ${response.status}`;
+    } catch (error: unknown) {
+      lastError = error instanceof Error ? error.message : String(error);
+    }
+    await sleep(500);
+  }
+  throw new Error(
+    [
+      `Timed out waiting for OmniRoute to start: ${lastError}`,
+      "--- stdout ---",
+      ...logs.stdoutLines.slice(-40),
+      "--- stderr ---",
+      ...logs.stderrLines.slice(-40),
+    ].join("\n")
+  );
+}
+
+async function stopProcess(child: ReturnType<typeof spawn>) {
+  if (child.killed) return;
+  child.kill("SIGTERM");
+  const exited = await Promise.race([
+    new Promise<boolean>((resolve) => child.once("exit", () => resolve(true))),
+    sleep(5_000).then(() => false),
+  ]);
+  if (!exited && !child.killed) {
+    child.kill("SIGKILL");
+    await new Promise<void>((resolve) => child.once("exit", () => resolve()));
+  }
+}
+
+async function postChat(baseUrl: string, model: string, content: string) {
+  const response = await fetch(`${baseUrl}/api/v1/chat/completions`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({
+      model,
+      stream: false,
+      messages: [{ role: "user", content }],
+    }),
+    signal: AbortSignal.timeout(30_000),
+  });
+  const text = await response.text();
+  const json = text ? JSON.parse(text) : {};
+  return { response, json };
+}
+
+// ── Setup ──────────────────────────────────────────────────────────────────
+
+const UPSTREAM_PORT = await getFreePort();
+const upstream = new MockUpstreamServer();
+const TOKEN = "sk-fp-e2e-test";
+
+let app:
+  | {
+      child: ReturnType<typeof spawn>;
+      stdoutLines: string[];
+      stderrLines: string[];
+      baseUrl: string;
+    }
+  | undefined;
+
+test.before(async () => {
+  // Start mock upstream
+  const upstreamBaseUrl = await upstream.start();
+  upstream.configureToken(TOKEN, {
+    defaultResponse: buildCompletion("fingerprint ok", { model: "fp-mimocode/mimo-auto" }),
+  });
+
+  // Seed mimocode provider node
+  const providerId = "openai-compatible-fp-mimocode";
+  await providersDb.createProviderNode({
+    id: providerId,
+    type: "openai-compatible",
+    name: "MiMoCode FP Test",
+    prefix: "fp-mimocode",
+    apiType: "chat",
+    baseUrl: upstreamBaseUrl,
+  });
+
+  // Seed connection with 3 fingerprints
+  await providersDb.createProviderConnection({
+    provider: providerId,
+    authType: "apikey",
+    name: "fp-mimocode-multi-device",
+    apiKey: TOKEN,
+    isActive: true,
+    testStatus: "active",
+    providerSpecificData: {
+      baseUrl: upstreamBaseUrl,
+      apiType: "chat",
+      fingerprints: ["fp-device-aaa", "fp-device-bbb", "fp-device-ccc"],
+      accountProxies: [
+        { fingerprint: "fp-device-aaa", proxy: null },
+        { fingerprint: "fp-device-bbb", proxy: null },
+        { fingerprint: "fp-device-ccc", proxy: null },
+      ],
+    },
+  });
+
+  // Create round-robin combo
+  await combosDb.createCombo({
+    name: "fp-round-robin",
+    strategy: "round-robin",
+    config: { maxRetries: 0, retryDelayMs: 0 },
+    models: ["fp-mimocode/mimo-auto"],
+  });
+
+  // Create priority combo (single target, for comparison)
+  await combosDb.createCombo({
+    name: "fp-priority-single",
+    strategy: "priority",
+    config: { maxRetries: 0, retryDelayMs: 0 },
+    models: ["fp-mimocode/mimo-auto"],
+  });
+
+  await settingsDb.updateSettings({
+    resilienceSettings: {
+      requestQueue: {
+        autoEnableApiKeyProviders: true,
+        requestsPerMinute: 120,
+        minTimeBetweenRequestsMs: 0,
+        concurrentRequests: 4,
+        maxWaitMs: 2_000,
+      },
+      connectionCooldown: {
+        oauth: { baseCooldownMs: 500, useUpstreamRetryHints: true, maxBackoffSteps: 3 },
+        apikey: { baseCooldownMs: 200, useUpstreamRetryHints: false, maxBackoffSteps: 0 },
+      },
+      providerBreaker: {
+        oauth: { failureThreshold: 3, resetTimeoutMs: 2_000 },
+        apikey: { failureThreshold: 2, resetTimeoutMs: 1_500 },
+      },
+      waitForCooldown: { enabled: false, maxRetries: 0, maxRetryWaitSec: 0 },
+    },
+    requestRetry: 0,
+    maxRetryIntervalSec: 0,
+    requireLogin: false,
+    setupComplete: true,
+  });
+
+  core.closeDbInstance();
+
+  app = createServerProcess(TEST_DATA_DIR, DASHBOARD_PORT);
+  await waitForServer(app.baseUrl, app);
+});
+
+test.after(async () => {
+  if (app) await stopProcess(app.child);
+  await upstream.stop();
+  core.closeDbInstance();
+  await fsp.rm(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+// ── Tests ──────────────────────────────────────────────────────────────────
+
+test("round-robin combo with 3 fingerprints: all requests succeed", async () => {
+  assert.ok(app);
+
+  // Send 3 requests — round-robin should distribute across expanded targets
+  for (let i = 0; i < 3; i++) {
+    const result = await postChat(app.baseUrl, "fp-round-robin", `request ${i + 1}`);
+    assert.equal(
+      result.response.status,
+      200,
+      `request ${i + 1} failed: ${JSON.stringify(result.json)}`
+    );
+    assert.equal(result.json.choices[0].message.content, "fingerprint ok");
+    assert.equal(result.json.model, "fp-mimocode/mimo-auto");
+  }
+
+  // Mock server should have received all 3 hits
+  const state = upstream.getState(TOKEN);
+  assert.equal(state.hits, 3, `expected 3 hits on mock, got ${state.hits}`);
+});
+
+test("priority combo with fingerprint connection: request succeeds", async () => {
+  assert.ok(app);
+  upstream.resetState(TOKEN);
+
+  const result = await postChat(app.baseUrl, "fp-priority-single", "priority test");
+  assert.equal(result.response.status, 200, JSON.stringify(result.json));
+  assert.equal(result.json.choices[0].message.content, "fingerprint ok");
+
+  const state = upstream.getState(TOKEN);
+  assert.equal(state.hits, 1);
+});
+
+test("round-robin combo handles 5 sequential requests", async () => {
+  assert.ok(app);
+  upstream.resetState(TOKEN);
+
+  for (let i = 0; i < 5; i++) {
+    const result = await postChat(app.baseUrl, "fp-round-robin", `sequential ${i + 1}`);
+    assert.equal(
+      result.response.status,
+      200,
+      `request ${i + 1} failed: ${JSON.stringify(result.json)}`
+    );
+  }
+
+  const state = upstream.getState(TOKEN);
+  assert.equal(state.hits, 5, `expected 5 hits, got ${state.hits}`);
+});
diff --git a/tests/unit/combo-fingerprint-expansion.test.ts b/tests/unit/combo-fingerprint-expansion.test.ts
new file mode 100644
index 0000000000..dda557f948
--- /dev/null
+++ b/tests/unit/combo-fingerprint-expansion.test.ts
@@ -0,0 +1,277 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+// #5521 — A mimocode connection with multiple fingerprints in
+// provider_specific_data.fingerprints was treated as a single combo target,
+// so only one fingerprint (one IP) was used per request.  The combo system
+// must now expand each fingerprint into its own target so all of them
+// participate in the round-robin.
+
+const {
+  isFingerprintProvider,
+  getConnectionFingerprints,
+  hasMultipleFingerprints,
+  buildFingerprintExecutionKey,
+  expandTargetsByFingerprints,
+} = await import("../../open-sse/services/combo/fingerprintExpansion.ts");
+
+// ── isFingerprintProvider ────────────────────────────────────────────────────
+
+test("isFingerprintProvider: mimocode returns true", () => {
+  assert.equal(isFingerprintProvider("mimocode"), true);
+});
+
+test("isFingerprintProvider: mcode returns true", () => {
+  assert.equal(isFingerprintProvider("mcode"), true);
+});
+
+test("isFingerprintProvider: opencode returns true", () => {
+  assert.equal(isFingerprintProvider("opencode"), true);
+});
+
+test("isFingerprintProvider: openai returns false", () => {
+  assert.equal(isFingerprintProvider("openai"), false);
+});
+
+test("isFingerprintProvider: anthropic returns false", () => {
+  assert.equal(isFingerprintProvider("anthropic"), false);
+});
+
+test("isFingerprintProvider: empty string returns false", () => {
+  assert.equal(isFingerprintProvider(""), false);
+});
+
+// ── getConnectionFingerprints ────────────────────────────────────────────────
+
+test("getConnectionFingerprints: extracts valid fingerprint strings", () => {
+  const conn = {
+    providerSpecificData: {
+      fingerprints: ["fp-aaa", "fp-bbb", "fp-ccc"],
+    },
+  };
+  assert.deepEqual(getConnectionFingerprints(conn), ["fp-aaa", "fp-bbb", "fp-ccc"]);
+});
+
+test("getConnectionFingerprints: filters out non-string entries", () => {
+  const conn = {
+    providerSpecificData: {
+      fingerprints: ["fp-aaa", null, 123, "fp-bbb", undefined],
+    },
+  };
+  assert.deepEqual(getConnectionFingerprints(conn), ["fp-aaa", "fp-bbb"]);
+});
+
+test("getConnectionFingerprints: filters out empty strings", () => {
+  const conn = {
+    providerSpecificData: {
+      fingerprints: ["fp-aaa", "", "  ", "fp-bbb"],
+    },
+  };
+  assert.deepEqual(getConnectionFingerprints(conn), ["fp-aaa", "fp-bbb"]);
+});
+
+test("getConnectionFingerprints: returns empty array for null connection", () => {
+  assert.deepEqual(getConnectionFingerprints(null), []);
+});
+
+test("getConnectionFingerprints: returns empty array for undefined", () => {
+  assert.deepEqual(getConnectionFingerprints(undefined), []);
+});
+
+test("getConnectionFingerprints: returns empty array when no providerSpecificData", () => {
+  assert.deepEqual(getConnectionFingerprints({}), []);
+});
+
+test("getConnectionFingerprints: returns empty array when no fingerprints field", () => {
+  assert.deepEqual(getConnectionFingerprints({ providerSpecificData: {} }), []);
+});
+
+test("getConnectionFingerprints: returns empty array when fingerprints is not an array", () => {
+  assert.deepEqual(
+    getConnectionFingerprints({ providerSpecificData: { fingerprints: "not-array" } }),
+    []
+  );
+});
+
+// ── hasMultipleFingerprints ──────────────────────────────────────────────────
+
+test("hasMultipleFingerprints: true when 2+ fingerprints", () => {
+  const conn = { providerSpecificData: { fingerprints: ["fp-1", "fp-2"] } };
+  assert.equal(hasMultipleFingerprints(conn), true);
+});
+
+test("hasMultipleFingerprints: false when exactly 1 fingerprint", () => {
+  const conn = { providerSpecificData: { fingerprints: ["fp-1"] } };
+  assert.equal(hasMultipleFingerprints(conn), false);
+});
+
+test("hasMultipleFingerprints: false when 0 fingerprints", () => {
+  const conn = { providerSpecificData: { fingerprints: [] } };
+  assert.equal(hasMultipleFingerprints(conn), false);
+});
+
+test("hasMultipleFingerprints: false for null connection", () => {
+  assert.equal(hasMultipleFingerprints(null), false);
+});
+
+// ── buildFingerprintExecutionKey ─────────────────────────────────────────────
+
+test("buildFingerprintExecutionKey: first fingerprint keeps original key", () => {
+  assert.equal(buildFingerprintExecutionKey("step-0", "fp-aaa", true), "step-0");
+});
+
+test("buildFingerprintExecutionKey: non-first fingerprint appends fp: suffix", () => {
+  assert.equal(buildFingerprintExecutionKey("step-0", "fp-bbb", false), "step-0@fp:fp-bbb");
+});
+
+test("buildFingerprintExecutionKey: long fingerprint is preserved verbatim", () => {
+  const longFp = "a".repeat(64);
+  assert.equal(buildFingerprintExecutionKey("key", longFp, false), `key@fp:${longFp}`);
+});
+
+// ── expandTargetsByFingerprints ──────────────────────────────────────────────
+
+function makeTarget(overrides: Record<string, unknown> = {}) {
+  return {
+    kind: "model" as const,
+    stepId: "step-0",
+    executionKey: "step-0",
+    modelStr: "mimocode/mimo-auto",
+    provider: "mimocode",
+    providerId: null,
+    connectionId: "conn-1",
+    weight: 0,
+    label: null,
+    ...overrides,
+  };
+}
+
+function makeConnection(fps: string[]) {
+  return {
+    id: "conn-1",
+    provider: "mimocode",
+    providerSpecificData: { fingerprints: fps },
+  };
+}
+
+test("expandTargetsByFingerprints: non-fingerprint provider passes through", () => {
+  const targets = [makeTarget({ provider: "openai", modelStr: "openai/gpt-4o" })];
+  const connById = new Map<string, Record<string, unknown>>();
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 1);
+  assert.equal(result[0].executionKey, "step-0");
+});
+
+test("expandTargetsByFingerprints: target with no connectionId passes through", () => {
+  const targets = [makeTarget({ connectionId: null })];
+  const connById = new Map<string, Record<string, unknown>>();
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 1);
+  assert.equal(result[0].connectionId, null);
+});
+
+test("expandTargetsByFingerprints: single fingerprint passes through", () => {
+  const conn = makeConnection(["fp-aaa"]);
+  const targets = [makeTarget()];
+  const connById = new Map([["conn-1", conn]]);
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 1);
+  assert.equal(result[0].executionKey, "step-0");
+});
+
+test("expandTargetsByFingerprints: 10 fingerprints expands to 10 targets", () => {
+  const fps = Array.from({ length: 10 }, (_, i) => `fp-${String(i).padStart(2, "0")}`);
+  const conn = makeConnection(fps);
+  const targets = [makeTarget()];
+  const connById = new Map([["conn-1", conn]]);
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 10);
+  assert.equal(result[0].executionKey, "step-0");
+  for (let i = 1; i < 10; i++) {
+    assert.equal(result[i].executionKey, `step-0@fp:fp-${String(i).padStart(2, "0")}`);
+  }
+});
+
+test("expandTargetsByFingerprints: preserves all target properties across copies", () => {
+  const fps = ["fp-aaa", "fp-bbb", "fp-ccc"];
+  const conn = makeConnection(fps);
+  const targets = [
+    makeTarget({ connectionId: "conn-1", modelStr: "mimocode/mimo-auto", weight: 5 }),
+  ];
+  const connById = new Map([["conn-1", conn]]);
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 3);
+  for (const r of result) {
+    assert.equal(r.kind, "model");
+    assert.equal(r.connectionId, "conn-1");
+    assert.equal(r.modelStr, "mimocode/mimo-auto");
+    assert.equal(r.provider, "mimocode");
+    assert.equal(r.weight, 5);
+  }
+});
+
+test("expandTargetsByFingerprints: connection not found in map passes through", () => {
+  const targets = [makeTarget({ connectionId: "conn-missing" })];
+  const connById = new Map<string, Record<string, unknown>>();
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 1);
+  assert.equal(result[0].connectionId, "conn-missing");
+});
+
+test("expandTargetsByFingerprints: mixed providers expand only fingerprint ones", () => {
+  const fps = ["fp-1", "fp-2"];
+  const conn = makeConnection(fps);
+  const targets = [
+    makeTarget({ provider: "openai", modelStr: "openai/gpt-4o", connectionId: "conn-oai" }),
+    makeTarget({ connectionId: "conn-1" }),
+  ];
+  const connById = new Map([
+    ["conn-1", conn],
+    ["conn-oai", { id: "conn-oai", provider: "openai", providerSpecificData: {} }],
+  ]);
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 3);
+  assert.equal(result[0].executionKey, "step-0");
+  assert.equal(result[1].executionKey, "step-0");
+  assert.equal(result[2].executionKey, "step-0@fp:fp-2");
+});
+
+test("expandTargetsByFingerprints: empty input returns empty array", () => {
+  const connById = new Map<string, Record<string, unknown>>();
+  const result = expandTargetsByFingerprints([], connById, (t) => t.provider);
+  assert.equal(result.length, 0);
+});
+
+test("expandTargetsByFingerprints: mcode provider expands correctly", () => {
+  const fps = ["mfp-1", "mfp-2", "mfp-3"];
+  const conn = {
+    id: "conn-m",
+    provider: "mcode",
+    providerSpecificData: { fingerprints: fps },
+  };
+  const targets = [
+    makeTarget({ provider: "mcode", modelStr: "mcode/auto", connectionId: "conn-m" }),
+  ];
+  const connById = new Map([["conn-m", conn]]);
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 3);
+  assert.equal(result[0].executionKey, "step-0");
+  assert.equal(result[1].executionKey, "step-0@fp:mfp-2");
+  assert.equal(result[2].executionKey, "step-0@fp:mfp-3");
+});
+
+test("expandTargetsByFingerprints: multiple targets each expand independently", () => {
+  const conn1 = makeConnection(["fp-a1", "fp-a2"]);
+  const conn2 = makeConnection(["fp-b1", "fp-b2", "fp-b3"]);
+  const targets = [
+    makeTarget({ stepId: "step-0", executionKey: "step-0", connectionId: "conn-1" }),
+    makeTarget({ stepId: "step-1", executionKey: "step-1", connectionId: "conn-1" }),
+  ];
+  const connById = new Map([["conn-1", conn1]]);
+  const result = expandTargetsByFingerprints(targets, connById, (t) => t.provider);
+  assert.equal(result.length, 4);
+  assert.equal(result[0].executionKey, "step-0");
+  assert.equal(result[1].executionKey, "step-0@fp:fp-a2");
+  assert.equal(result[2].executionKey, "step-1");
+  assert.equal(result[3].executionKey, "step-1@fp:fp-a2");
+});