diff --git a/app/api/research/measurement-jobs/route.ts b/app/api/research/measurement-jobs/route.ts
new file mode 100644
index 00000000..51866da6
--- /dev/null
+++ b/app/api/research/measurement-jobs/route.ts
@@ -0,0 +1,26 @@
+import { NextRequest, NextResponse } from "next/server";
+import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
+import { createMeasurementJobHandler } from "@/lib/research/measurement_jobs/createMeasurementJobHandler";
+
+export const maxDuration = 60;
+
+/**
+ * OPTIONS /api/research/measurement-jobs — CORS preflight.
+ *
+ * @returns CORS-enabled 200 response
+ */
+export async function OPTIONS() {
+  return new NextResponse(null, { status: 200, headers: getCorsHeaders() });
+}
+
+/**
+ * POST /api/research/measurement-jobs — create an async ingest job.
+ * `source:"current"` captures present counts; `source:"historical"` enqueues
+ * Songstats deep backfill. Body: `{ scope, source, platforms? }`.
+ *
+ * @param request - body: scope (one of catalog_id/album_ids/isrcs) + source
+ * @returns 202 JSON job payload or error
+ */
+export async function POST(request: NextRequest) {
+  return createMeasurementJobHandler(request);
+}
diff --git a/app/workflows/__tests__/backfillTrackStep.test.ts b/app/workflows/__tests__/backfillTrackStep.test.ts
index 90fc701e..ebe77370 100644
--- a/app/workflows/__tests__/backfillTrackStep.test.ts
+++ b/app/workflows/__tests__/backfillTrackStep.test.ts
@@ -77,11 +77,12 @@ describe("backfillTrackStep", () => {
     expect(result).toEqual({ ok: true, hitsSpent: 1 });
   });
 
-  it("marks the row failed on upstream error and still records the spend attempt", async () => {
+  it("marks a transient upstream error (429) as failed (reclaimable) and records the spend", async () => {
     vi.mocked(fetchSongstats).mockResolvedValue({ status: 429, data: {} });
 
     const result = await backfillTrackStep(ROW);
 
+    // transient -> 'failed' so the daily reclaim sweep returns it to 'pending'
     expect(updateSongstatsBackfillQueue).toHaveBeenCalledWith("q1", { status: "failed" });
     expect(insertSongstatsQuotaLedger).toHaveBeenCalledWith({
       hits: 1,
@@ -90,4 +91,42 @@ describe("backfillTrackStep", () => {
     expect(upsertSongMeasurements).not.toHaveBeenCalled();
     expect(result).toEqual({ ok: false, hitsSpent: 1 });
   });
+
+  it("marks a transient 5xx as failed (reclaimable)", async () => {
+    vi.mocked(fetchSongstats).mockResolvedValue({ status: 504, data: {} });
+
+    const result = await backfillTrackStep(ROW);
+
+    expect(updateSongstatsBackfillQueue).toHaveBeenCalledWith("q1", { status: "failed" });
+    expect(result).toEqual({ ok: false, hitsSpent: 1 });
+  });
+
+  it("marks a permanent client error (403) as done so reclaim never recycles it", async () => {
+    vi.mocked(fetchSongstats).mockResolvedValue({ status: 403, data: {} });
+
+    const result = await backfillTrackStep(ROW);
+
+    // non-retryable 4xx (not 408/429) is terminal -> 'done', not 'failed'
+    expect(updateSongstatsBackfillQueue).toHaveBeenCalledWith("q1", { status: "done" });
+    expect(insertSongstatsQuotaLedger).toHaveBeenCalledWith({
+      hits: 1,
+      purpose: "backfill USA2P2015959 (terminal 403)",
+    });
+    expect(result).toEqual({ ok: false, hitsSpent: 1 });
+  });
+
+  it("marks a definitive 404 (no history exists) as done so it is never retried", async () => {
+    vi.mocked(fetchSongstats).mockResolvedValue({ status: 404, data: {} });
+
+    const result = await backfillTrackStep(ROW);
+
+    // terminal no-data -> 'done', not 'failed' — the reclaim sweep must not resurrect it
+    expect(updateSongstatsBackfillQueue).toHaveBeenCalledWith("q1", { status: "done" });
+    expect(insertSongstatsQuotaLedger).toHaveBeenCalledWith({
+      hits: 1,
+      purpose: "backfill USA2P2015959 (no data 404)",
+    });
+    expect(upsertSongMeasurements).not.toHaveBeenCalled();
+    expect(result).toEqual({ ok: false, hitsSpent: 1 });
+  });
 });
diff --git a/app/workflows/backfillTrackStep.ts b/app/workflows/backfillTrackStep.ts
index bc250d9c..3247ff4c 100644
--- a/app/workflows/backfillTrackStep.ts
+++ b/app/workflows/backfillTrackStep.ts
@@ -26,11 +26,22 @@ export async function backfillTrackStep(
   });
 
   if (result.status !== 200) {
-    await insertSongstatsQuotaLedger({
-      hits: 1,
-      purpose: `backfill ${row.song} (failed ${result.status})`,
-    });
-    await updateSongstatsBackfillQueue(row.id, { status: "failed" });
+    const status = result.status;
+    const isNoData = status === 404;
+    // Only transient errors are retryable: 408 (timeout), 429 (quota), any 5xx.
+    const isRetryable = status === 408 || status === 429 || status >= 500;
+
+    // `failed` is reclaimable (the daily sweep returns it to `pending`, bounded
+    // by the rolling-window budget). 404 no-data and other permanent 4xx are
+    // terminal → `done`, so reclaim never recycles a track that can't succeed.
+    const nextStatus = isRetryable ? "failed" : "done";
+
+    let outcome = `terminal ${status}`;
+    if (isNoData) outcome = "no data 404";
+    else if (isRetryable) outcome = `failed ${status}`;
+
+    await insertSongstatsQuotaLedger({ hits: 1, purpose: `backfill ${row.song} (${outcome})` });
+    await updateSongstatsBackfillQueue(row.id, { status: nextStatus });
     return { ok: false, hitsSpent: 1 };
   }
 
diff --git a/lib/research/measurement_jobs/__tests__/createMeasurementJob.test.ts b/lib/research/measurement_jobs/__tests__/createMeasurementJob.test.ts
new file mode 100644
index 00000000..88fd7bd8
--- /dev/null
+++ b/lib/research/measurement_jobs/__tests__/createMeasurementJob.test.ts
@@ -0,0 +1,61 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { createMeasurementJob } from "../createMeasurementJob";
+import { createSnapshot } from "@/lib/research/playcounts/createSnapshot";
+import { enqueueHistoricalBackfill } from "../enqueueHistoricalBackfill";
+
+vi.mock("@/lib/research/playcounts/createSnapshot", () => ({ createSnapshot: vi.fn() }));
+vi.mock("../enqueueHistoricalBackfill", () => ({ enqueueHistoricalBackfill: vi.fn() }));
+
+const req = (source: "current" | "historical") => ({
+  accountId: "acc_1",
+  body: { scope: { album_ids: ["AL1"] }, source, platforms: ["spotify"] as ["spotify"] },
+});
+
+describe("createMeasurementJob", () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it("historical → delegates to enqueueHistoricalBackfill with the scope", async () => {
+    vi.mocked(enqueueHistoricalBackfill).mockResolvedValue({
+      data: { status: "success", source: "historical", id: null, enqueued: 5, skipped: 1 },
+    });
+    const r = await createMeasurementJob(req("historical"));
+    expect(enqueueHistoricalBackfill).toHaveBeenCalledWith({ album_ids: ["AL1"] });
+    expect(createSnapshot).not.toHaveBeenCalled();
+    expect(r).toEqual({
+      data: { status: "success", source: "historical", id: null, enqueued: 5, skipped: 1 },
+    });
+  });
+
+  it("current → reuses the snapshot pipeline and maps snapshot_id to the job id", async () => {
+    vi.mocked(createSnapshot).mockResolvedValue({
+      data: {
+        status: "success",
+        snapshot_id: "snap_9",
+        state: "queued",
+        album_count: 3,
+        estimated_cost_usd: 0.009,
+      },
+    });
+    const r = await createMeasurementJob(req("current"));
+    expect(createSnapshot).toHaveBeenCalledWith({
+      accountId: "acc_1",
+      body: { album_ids: ["AL1"], platforms: ["spotify"], schedule: "once" },
+    });
+    expect(r).toEqual({
+      data: {
+        status: "success",
+        source: "current",
+        id: "snap_9",
+        state: "queued",
+        album_count: 3,
+        estimated_cost_usd: 0.009,
+      },
+    });
+  });
+
+  it("current → propagates a snapshot error (e.g. 429 cap)", async () => {
+    vi.mocked(createSnapshot).mockResolvedValue({ error: "cap reached", status: 429 });
+    const r = await createMeasurementJob(req("current"));
+    expect(r).toEqual({ error: "cap reached", status: 429 });
+  });
+});
diff --git a/lib/research/measurement_jobs/__tests__/createMeasurementJobHandler.test.ts b/lib/research/measurement_jobs/__tests__/createMeasurementJobHandler.test.ts
new file mode 100644
index 00000000..18225479
--- /dev/null
+++ b/lib/research/measurement_jobs/__tests__/createMeasurementJobHandler.test.ts
@@ -0,0 +1,55 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest, NextResponse } from "next/server";
+import { createMeasurementJobHandler } from "../createMeasurementJobHandler";
+import { validateCreateMeasurementJobRequest } from "../validateCreateMeasurementJobRequest";
+import { createMeasurementJob } from "../createMeasurementJob";
+
+vi.mock("@/lib/networking/getCorsHeaders", () => ({ getCorsHeaders: vi.fn(() => ({})) }));
+vi.mock("../validateCreateMeasurementJobRequest", () => ({
+  validateCreateMeasurementJobRequest: vi.fn(),
+}));
+vi.mock("../createMeasurementJob", () => ({ createMeasurementJob: vi.fn() }));
+
+const req = () => new NextRequest("http://x/api/research/measurement-jobs", { method: "POST" });
+const validated = {
+  accountId: "acc_1",
+  body: { scope: { isrcs: ["X"] }, source: "historical", platforms: ["spotify"] },
+} as never;
+
+describe("createMeasurementJobHandler", () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it("returns the job payload with 202 on success", async () => {
+    vi.mocked(validateCreateMeasurementJobRequest).mockResolvedValue(validated);
+    vi.mocked(createMeasurementJob).mockResolvedValue({
+      data: { status: "success", source: "historical", id: null, enqueued: 5, skipped: 0 },
+    });
+    const res = await createMeasurementJobHandler(req());
+    expect(res.status).toBe(202);
+    expect(await res.json()).toMatchObject({ enqueued: 5, source: "historical" });
+  });
+
+  it("short-circuits with the validation response", async () => {
+    vi.mocked(validateCreateMeasurementJobRequest).mockResolvedValue(
+      NextResponse.json({ status: "error" }, { status: 400 }) as never,
+    );
+    const res = await createMeasurementJobHandler(req());
+    expect(res.status).toBe(400);
+    expect(createMeasurementJob).not.toHaveBeenCalled();
+  });
+
+  it("maps error results to error responses", async () => {
+    vi.mocked(validateCreateMeasurementJobRequest).mockResolvedValue(validated);
+    vi.mocked(createMeasurementJob).mockResolvedValue({ error: "cap reached", status: 429 });
+    const res = await createMeasurementJobHandler(req());
+    expect(res.status).toBe(429);
+  });
+
+  it("returns 500 on unexpected errors", async () => {
+    const consoleError = vi.spyOn(console, "error").mockImplementation(() => {});
+    vi.mocked(validateCreateMeasurementJobRequest).mockRejectedValue(new Error("boom"));
+    const res = await createMeasurementJobHandler(req());
+    expect(res.status).toBe(500);
+    consoleError.mockRestore();
+  });
+});
diff --git a/lib/research/measurement_jobs/__tests__/enqueueHistoricalBackfill.test.ts b/lib/research/measurement_jobs/__tests__/enqueueHistoricalBackfill.test.ts
new file mode 100644
index 00000000..20cde74a
--- /dev/null
+++ b/lib/research/measurement_jobs/__tests__/enqueueHistoricalBackfill.test.ts
@@ -0,0 +1,60 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { enqueueHistoricalBackfill } from "../enqueueHistoricalBackfill";
+import { resolveScopeSongs } from "../resolveScopeSongs";
+import { selectSongMeasurements } from "@/lib/supabase/song_measurements/selectSongMeasurements";
+import { upsertSongstatsBackfillQueue } from "@/lib/supabase/songstats_backfill_queue/upsertSongstatsBackfillQueue";
+
+vi.mock("../resolveScopeSongs", () => ({ resolveScopeSongs: vi.fn() }));
+vi.mock("@/lib/supabase/song_measurements/selectSongMeasurements", () => ({
+  selectSongMeasurements: vi.fn(),
+}));
+vi.mock("@/lib/supabase/songstats_backfill_queue/upsertSongstatsBackfillQueue", () => ({
+  upsertSongstatsBackfillQueue: vi.fn(),
+}));
+
+describe("enqueueHistoricalBackfill", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.mocked(upsertSongstatsBackfillQueue).mockResolvedValue(undefined);
+  });
+
+  it("400s when the scope resolves to no recordings", async () => {
+    vi.mocked(resolveScopeSongs).mockResolvedValue([]);
+    const r = await enqueueHistoricalBackfill({ isrcs: ["X"] });
+    expect(r).toEqual({
+      error: "No recordings resolvable from the given scope — no identifier mappings exist yet",
+      status: 400,
+    });
+  });
+
+  it("enqueues un-backfilled songs ranked by latest count, skips already-backfilled ones", async () => {
+    vi.mocked(resolveScopeSongs).mockResolvedValue(["I1", "I2", "I3"]);
+    // newest-first rows; I2 already has a songstats row (already backfilled)
+    vi.mocked(selectSongMeasurements).mockResolvedValue([
+      { song: "I1", value: 500, data_source: "apify_spotify_playcount" },
+      { song: "I2", value: 300, data_source: "songstats" },
+      { song: "I3", value: 100, data_source: "apify_spotify_playcount" },
+    ] as never);
+
+    const r = await enqueueHistoricalBackfill({ isrcs: ["I1", "I2", "I3"] });
+
+    expect(upsertSongstatsBackfillQueue).toHaveBeenCalledTimes(2);
+    expect(upsertSongstatsBackfillQueue).toHaveBeenCalledWith({ song: "I1", rank_score: 500 });
+    expect(upsertSongstatsBackfillQueue).toHaveBeenCalledWith({ song: "I3", rank_score: 100 });
+    expect(upsertSongstatsBackfillQueue).not.toHaveBeenCalledWith(
+      expect.objectContaining({ song: "I2" }),
+    );
+    expect(r).toEqual({
+      data: { status: "success", source: "historical", id: null, enqueued: 2, skipped: 1 },
+    });
+  });
+
+  it("ranks a song with no prior measurement at 0", async () => {
+    vi.mocked(resolveScopeSongs).mockResolvedValue(["I9"]);
+    vi.mocked(selectSongMeasurements).mockResolvedValue([] as never);
+
+    await enqueueHistoricalBackfill({ isrcs: ["I9"] });
+
+    expect(upsertSongstatsBackfillQueue).toHaveBeenCalledWith({ song: "I9", rank_score: 0 });
+  });
+});
diff --git a/lib/research/measurement_jobs/__tests__/ensureSongstatsPaymentMethod.test.ts b/lib/research/measurement_jobs/__tests__/ensureSongstatsPaymentMethod.test.ts
new file mode 100644
index 00000000..1e2c1f07
--- /dev/null
+++ b/lib/research/measurement_jobs/__tests__/ensureSongstatsPaymentMethod.test.ts
@@ -0,0 +1,54 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { ensureSongstatsPaymentMethod } from "../ensureSongstatsPaymentMethod";
+import { findStripeCustomerForAccount } from "@/lib/stripe/findStripeCustomerForAccount";
+import { findDefaultPaymentMethodForCustomer } from "@/lib/stripe/findDefaultPaymentMethodForCustomer";
+import { createStripeSession } from "@/lib/stripe/createStripeSession";
+
+vi.mock("@/lib/networking/getCorsHeaders", () => ({ getCorsHeaders: vi.fn(() => ({})) }));
+vi.mock("@/lib/stripe/findStripeCustomerForAccount", () => ({
+  findStripeCustomerForAccount: vi.fn(),
+}));
+vi.mock("@/lib/stripe/findDefaultPaymentMethodForCustomer", () => ({
+  findDefaultPaymentMethodForCustomer: vi.fn(),
+}));
+vi.mock("@/lib/stripe/createStripeSession", () => ({ createStripeSession: vi.fn() }));
+
+describe("ensureSongstatsPaymentMethod", () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it("returns null (proceed) when the account has a card on file", async () => {
+    vi.mocked(findStripeCustomerForAccount).mockResolvedValue("cus_1");
+    vi.mocked(findDefaultPaymentMethodForCustomer).mockResolvedValue("pm_1");
+
+    const r = await ensureSongstatsPaymentMethod("acc_1");
+
+    expect(r).toBeNull();
+    expect(createStripeSession).not.toHaveBeenCalled();
+  });
+
+  it("402s with a free-tier checkout link when there is no Stripe customer", async () => {
+    vi.mocked(findStripeCustomerForAccount).mockResolvedValue(null);
+    vi.mocked(createStripeSession).mockResolvedValue({ url: "https://checkout/free" } as never);
+
+    const r = await ensureSongstatsPaymentMethod("acc_1");
+
+    expect(findDefaultPaymentMethodForCustomer).not.toHaveBeenCalled();
+    expect(createStripeSession).toHaveBeenCalledWith("acc_1", expect.any(String));
+    expect((r as Response).status).toBe(402);
+    expect(await (r as Response).json()).toMatchObject({
+      status: "error",
+      checkoutUrl: "https://checkout/free",
+    });
+  });
+
+  it("402s with a checkout link when the customer exists but has no card", async () => {
+    vi.mocked(findStripeCustomerForAccount).mockResolvedValue("cus_1");
+    vi.mocked(findDefaultPaymentMethodForCustomer).mockResolvedValue(null);
+    vi.mocked(createStripeSession).mockResolvedValue({ url: "https://checkout/free" } as never);
+
+    const r = await ensureSongstatsPaymentMethod("acc_1");
+
+    expect((r as Response).status).toBe(402);
+    expect(await (r as Response).json()).toMatchObject({ checkoutUrl: "https://checkout/free" });
+  });
+});
diff --git a/lib/research/measurement_jobs/__tests__/resolveScopeSongs.test.ts b/lib/research/measurement_jobs/__tests__/resolveScopeSongs.test.ts
new file mode 100644
index 00000000..7c0bc8d9
--- /dev/null
+++ b/lib/research/measurement_jobs/__tests__/resolveScopeSongs.test.ts
@@ -0,0 +1,42 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { resolveScopeSongs } from "../resolveScopeSongs";
+import { selectSongIdentifiers } from "@/lib/supabase/song_identifiers/selectSongIdentifiers";
+import { selectCatalogSongsWithArtists } from "@/lib/supabase/catalog_songs/selectCatalogSongsWithArtists";
+
+vi.mock("@/lib/supabase/song_identifiers/selectSongIdentifiers", () => ({
+  selectSongIdentifiers: vi.fn(),
+}));
+vi.mock("@/lib/supabase/catalog_songs/selectCatalogSongsWithArtists", () => ({
+  selectCatalogSongsWithArtists: vi.fn(),
+}));
+
+describe("resolveScopeSongs", () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it("returns deduped isrcs directly", async () => {
+    expect(await resolveScopeSongs({ isrcs: ["A", "A", "B"] })).toEqual(["A", "B"]);
+    expect(selectSongIdentifiers).not.toHaveBeenCalled();
+  });
+
+  it("resolves album_ids to their mapped song isrcs", async () => {
+    vi.mocked(selectSongIdentifiers).mockResolvedValue([
+      { song: "I1", platform: "spotify", identifier_type: "album_id", value: "AL1" },
+      { song: "I2", platform: "spotify", identifier_type: "album_id", value: "AL1" },
+    ]);
+    const out = await resolveScopeSongs({ album_ids: ["AL1"] });
+    expect(selectSongIdentifiers).toHaveBeenCalledWith({
+      platform: "spotify",
+      identifierType: "album_id",
+      values: ["AL1"],
+    });
+    expect(out).toEqual(["I1", "I2"]);
+  });
+
+  it("resolves a catalog_id to its song isrcs", async () => {
+    vi.mocked(selectCatalogSongsWithArtists).mockResolvedValue({
+      songs: [{ isrc: "I1" }, { isrc: "I2" }],
+    } as never);
+    const out = await resolveScopeSongs({ catalog_id: "cat-1" });
+    expect(out).toEqual(["I1", "I2"]);
+  });
+});
diff --git a/lib/research/measurement_jobs/__tests__/validateCreateMeasurementJobRequest.test.ts b/lib/research/measurement_jobs/__tests__/validateCreateMeasurementJobRequest.test.ts
new file mode 100644
index 00000000..e36042a7
--- /dev/null
+++ b/lib/research/measurement_jobs/__tests__/validateCreateMeasurementJobRequest.test.ts
@@ -0,0 +1,88 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest, NextResponse } from "next/server";
+import { validateCreateMeasurementJobRequest } from "../validateCreateMeasurementJobRequest";
+import { validateAuthContext } from "@/lib/auth/validateAuthContext";
+import { ensureSongstatsPaymentMethod } from "../ensureSongstatsPaymentMethod";
+
+vi.mock("@/lib/auth/validateAuthContext", () => ({ validateAuthContext: vi.fn() }));
+vi.mock("../ensureSongstatsPaymentMethod", () => ({ ensureSongstatsPaymentMethod: vi.fn() }));
+
+const post = (body: unknown) =>
+  new NextRequest("http://x/api/research/measurement-jobs", {
+    method: "POST",
+    body: JSON.stringify(body),
+    headers: { "content-type": "application/json" },
+  });
+
+describe("validateCreateMeasurementJobRequest", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.mocked(validateAuthContext).mockResolvedValue({ accountId: "acc_1" } as never);
+    vi.mocked(ensureSongstatsPaymentMethod).mockResolvedValue(null); // card on file by default
+  });
+
+  it("returns the auth response (401) when auth fails", async () => {
+    vi.mocked(validateAuthContext).mockResolvedValue(
+      NextResponse.json({ status: "error" }, { status: 401 }) as never,
+    );
+    const r = await validateCreateMeasurementJobRequest(
+      post({ scope: { isrcs: ["X"] }, source: "historical" }),
+    );
+    expect((r as NextResponse).status).toBe(401);
+  });
+
+  it("400 when source is missing", async () => {
+    const r = await validateCreateMeasurementJobRequest(post({ scope: { isrcs: ["X"] } }));
+    expect((r as NextResponse).status).toBe(400);
+  });
+
+  it("400 when source is not current|historical", async () => {
+    const r = await validateCreateMeasurementJobRequest(
+      post({ scope: { isrcs: ["X"] }, source: "future" }),
+    );
+    expect((r as NextResponse).status).toBe(400);
+  });
+
+  it("400 when scope has zero keys", async () => {
+    const r = await validateCreateMeasurementJobRequest(post({ scope: {}, source: "current" }));
+    expect((r as NextResponse).status).toBe(400);
+  });
+
+  it("400 when scope has more than one key", async () => {
+    const r = await validateCreateMeasurementJobRequest(
+      post({ scope: { isrcs: ["X"], album_ids: ["A"] }, source: "current" }),
+    );
+    expect((r as NextResponse).status).toBe(400);
+  });
+
+  it("passes auth + body through on success, defaulting platforms to spotify", async () => {
+    const r = await validateCreateMeasurementJobRequest(
+      post({ scope: { album_ids: ["A1"] }, source: "historical" }),
+    );
+    expect(r).toEqual({
+      accountId: "acc_1",
+      body: { scope: { album_ids: ["A1"] }, source: "historical", platforms: ["spotify"] },
+    });
+  });
+
+  it("historical: short-circuits with the 402 when no card is on file", async () => {
+    vi.mocked(ensureSongstatsPaymentMethod).mockResolvedValue(
+      NextResponse.json(
+        { status: "error", checkoutUrl: "https://checkout" },
+        { status: 402 },
+      ) as never,
+    );
+    const r = await validateCreateMeasurementJobRequest(
+      post({ scope: { isrcs: ["X"] }, source: "historical" }),
+    );
+    expect((r as NextResponse).status).toBe(402);
+  });
+
+  it("current: does NOT require a card (Apify-only, exempt from the Songstats gate)", async () => {
+    const r = await validateCreateMeasurementJobRequest(
+      post({ scope: { album_ids: ["A1"] }, source: "current" }),
+    );
+    expect(ensureSongstatsPaymentMethod).not.toHaveBeenCalled();
+    expect(r).toMatchObject({ accountId: "acc_1", body: { source: "current" } });
+  });
+});
diff --git a/lib/research/measurement_jobs/createMeasurementJob.ts b/lib/research/measurement_jobs/createMeasurementJob.ts
new file mode 100644
index 00000000..adb383e0
--- /dev/null
+++ b/lib/research/measurement_jobs/createMeasurementJob.ts
@@ -0,0 +1,47 @@
+import { createSnapshot } from "@/lib/research/playcounts/createSnapshot";
+import { enqueueHistoricalBackfill } from "./enqueueHistoricalBackfill";
+import type { ValidatedCreateMeasurementJobRequest } from "./validateCreateMeasurementJobRequest";
+
+export type CreateMeasurementJobResult = { data: unknown } | { error: string; status: number };
+
+type SnapshotData = {
+  snapshot_id: string;
+  state: string;
+  album_count: number;
+  estimated_cost_usd: number;
+};
+
+/**
+ * Dispatch a measurement job by `source`. `historical` enqueues Songstats deep
+ * backfill; `current` reuses the snapshot capture pipeline (replacing
+ * `POST /api/research/snapshots`) and maps `snapshot_id` to the resource's `id`.
+ *
+ * @param req - The validated create request (accountId + body)
+ */
+export async function createMeasurementJob(
+  req: ValidatedCreateMeasurementJobRequest,
+): Promise<CreateMeasurementJobResult> {
+  const { accountId, body } = req;
+
+  if (body.source === "historical") {
+    return enqueueHistoricalBackfill(body.scope);
+  }
+
+  const result = await createSnapshot({
+    accountId,
+    body: { ...body.scope, platforms: body.platforms, schedule: "once" },
+  });
+  if ("error" in result) return result;
+
+  const d = result.data as SnapshotData;
+  return {
+    data: {
+      status: "success",
+      source: "current",
+      id: d.snapshot_id,
+      state: d.state,
+      album_count: d.album_count,
+      estimated_cost_usd: d.estimated_cost_usd,
+    },
+  };
+}
diff --git a/lib/research/measurement_jobs/createMeasurementJobHandler.ts b/lib/research/measurement_jobs/createMeasurementJobHandler.ts
new file mode 100644
index 00000000..663e02dd
--- /dev/null
+++ b/lib/research/measurement_jobs/createMeasurementJobHandler.ts
@@ -0,0 +1,31 @@
+import { type NextRequest, NextResponse } from "next/server";
+import { errorResponse } from "@/lib/networking/errorResponse";
+import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
+import { createMeasurementJob } from "@/lib/research/measurement_jobs/createMeasurementJob";
+import { validateCreateMeasurementJobRequest } from "@/lib/research/measurement_jobs/validateCreateMeasurementJobRequest";
+
+/**
+ * POST /api/research/measurement-jobs
+ *
+ * One async ingest resource. `source:"current"` captures present counts via the
+ * snapshot pipeline (replaces `POST /api/research/snapshots`); `source:"historical"`
+ * enqueues Songstats deep backfill ranked by all-time streams (idempotent —
+ * already-backfilled songs are skipped). Returns 202.
+ *
+ * @param request - The incoming HTTP request.
+ * @returns The JSON response.
+ */
+export async function createMeasurementJobHandler(request: NextRequest): Promise<NextResponse> {
+  try {
+    const validated = await validateCreateMeasurementJobRequest(request);
+    if (validated instanceof NextResponse) return validated;
+
+    const result = await createMeasurementJob(validated);
+    if ("error" in result) return errorResponse(result.error, result.status);
+
+    return NextResponse.json(result.data, { status: 202, headers: getCorsHeaders() });
+  } catch (error) {
+    console.error("[ERROR] createMeasurementJobHandler:", error);
+    return errorResponse("Internal error", 500);
+  }
+}
diff --git a/lib/research/measurement_jobs/enqueueHistoricalBackfill.ts b/lib/research/measurement_jobs/enqueueHistoricalBackfill.ts
new file mode 100644
index 00000000..3c0cc7af
--- /dev/null
+++ b/lib/research/measurement_jobs/enqueueHistoricalBackfill.ts
@@ -0,0 +1,65 @@
+import { resolveScopeSongs } from "./resolveScopeSongs";
+import { selectSongMeasurements } from "@/lib/supabase/song_measurements/selectSongMeasurements";
+import { upsertSongstatsBackfillQueue } from "@/lib/supabase/songstats_backfill_queue/upsertSongstatsBackfillQueue";
+import type { CreateMeasurementJobBody } from "./validateCreateMeasurementJobRequest";
+
+const METRIC = "platform_displayed_play_count";
+/** Max concurrent queue upserts per batch (bounds round trips on large catalogs). */
+const ENQUEUE_CONCURRENCY = 25;
+
+export type EnqueueHistoricalBackfillResult = { data: unknown } | { error: string; status: number };
+
+/**
+ * `source: "historical"` path of a measurement job. Resolves the scope to song
+ * ISRCs, enqueues each for Songstats deep backfill ranked by its latest known
+ * count, and skips songs that already carry `songstats` history (so no track is
+ * fetched from Songstats twice). Free — no credit deduction. The queue drains
+ * via the daily maintenance worker.
+ *
+ * @param scope - The job scope (catalog_id / album_ids / isrcs)
+ * @returns 202 payload with `enqueued`/`skipped`, or a 400 when nothing resolves
+ */
+export async function enqueueHistoricalBackfill(
+  scope: CreateMeasurementJobBody["scope"],
+): Promise<EnqueueHistoricalBackfillResult> {
+  const isrcs = await resolveScopeSongs(scope);
+  if (isrcs.length === 0) {
+    return {
+      error: "No recordings resolvable from the given scope — no identifier mappings exist yet",
+      status: 400,
+    };
+  }
+
+  const measurements = await selectSongMeasurements({
+    songs: isrcs,
+    platform: "spotify",
+    metric: METRIC,
+  });
+
+  // rows are newest-first: the first row per song is its latest count (the rank);
+  // a song is already backfilled if any of its rows is `songstats`-sourced.
+  const latestValue = new Map<string, number>();
+  const alreadyBackfilled = new Set<string>();
+  for (const row of measurements) {
+    if (!latestValue.has(row.song)) latestValue.set(row.song, Number(row.value) || 0);
+    if (row.data_source === "songstats") alreadyBackfilled.add(row.song);
+  }
+
+  const candidates = isrcs.filter(isrc => !alreadyBackfilled.has(isrc));
+  const skipped = isrcs.length - candidates.length;
+
+  // Enqueue in bounded-concurrency batches so a large catalog doesn't fan out
+  // into N serial round trips (which would blow the route's duration budget).
+  let enqueued = 0;
+  for (let i = 0; i < candidates.length; i += ENQUEUE_CONCURRENCY) {
+    const batch = candidates.slice(i, i + ENQUEUE_CONCURRENCY);
+    await Promise.all(
+      batch.map(isrc =>
+        upsertSongstatsBackfillQueue({ song: isrc, rank_score: latestValue.get(isrc) ?? 0 }),
+      ),
+    );
+    enqueued += batch.length;
+  }
+
+  return { data: { status: "success", source: "historical", id: null, enqueued, skipped } };
+}
diff --git a/lib/research/measurement_jobs/ensureSongstatsPaymentMethod.ts b/lib/research/measurement_jobs/ensureSongstatsPaymentMethod.ts
new file mode 100644
index 00000000..71e3dd37
--- /dev/null
+++ b/lib/research/measurement_jobs/ensureSongstatsPaymentMethod.ts
@@ -0,0 +1,35 @@
+import { NextResponse } from "next/server";
+import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
+import { findStripeCustomerForAccount } from "@/lib/stripe/findStripeCustomerForAccount";
+import { findDefaultPaymentMethodForCustomer } from "@/lib/stripe/findDefaultPaymentMethodForCustomer";
+import { createStripeSession } from "@/lib/stripe/createStripeSession";
+import { CREDIT_AUTO_RECHARGE_FALLBACK_SUCCESS_URL } from "@/lib/credits/const";
+
+/**
+ * Payment-method gate for Songstats-backed work (the heavily quota-capped
+ * provider). The authenticated account must have a card on file before it can
+ * spend Songstats quota. Returns `null` to proceed; otherwise a **402** carrying
+ * a Stripe Checkout URL for the free tier (subscription + trial) so the caller
+ * can add a card. Mirrors the credit gate's short-circuit shape.
+ *
+ * @param accountId - The authenticated account.
+ * @returns `null` when a card exists, else a 402 NextResponse with `checkoutUrl`.
+ */
+export async function ensureSongstatsPaymentMethod(
+  accountId: string,
+): Promise<NextResponse | null> {
+  const customerId = await findStripeCustomerForAccount(accountId);
+  const paymentMethod = customerId ? await findDefaultPaymentMethodForCustomer(customerId) : null;
+  if (paymentMethod) return null;
+
+  const session = await createStripeSession(accountId, CREDIT_AUTO_RECHARGE_FALLBACK_SUCCESS_URL);
+  return NextResponse.json(
+    {
+      status: "error",
+      error:
+        "A payment method is required to use Songstats-backed endpoints. Add a card to continue.",
+      checkoutUrl: session.url,
+    },
+    { status: 402, headers: getCorsHeaders() },
+  );
+}
diff --git a/lib/research/measurement_jobs/resolveScopeSongs.ts b/lib/research/measurement_jobs/resolveScopeSongs.ts
new file mode 100644
index 00000000..9da9e5ab
--- /dev/null
+++ b/lib/research/measurement_jobs/resolveScopeSongs.ts
@@ -0,0 +1,35 @@
+import { selectSongIdentifiers } from "@/lib/supabase/song_identifiers/selectSongIdentifiers";
+import { selectCatalogSongsWithArtists } from "@/lib/supabase/catalog_songs/selectCatalogSongsWithArtists";
+import type { CreateMeasurementJobBody } from "./validateCreateMeasurementJobRequest";
+
+/**
+ * Resolve a measurement-job `scope` to a deduped list of song ISRCs.
+ * `isrcs` pass through; `album_ids` resolve through the album_id identifier
+ * mappings; `catalog_id` resolves through its songs. Mirrors
+ * {@link resolveSnapshotAlbums} but returns songs (the backfill queue is keyed
+ * by ISRC).
+ *
+ * @param scope - Exactly one of catalog_id / album_ids / isrcs
+ * @returns Unique song ISRCs ([] when nothing is mapped yet)
+ */
+export async function resolveScopeSongs(
+  scope: CreateMeasurementJobBody["scope"],
+): Promise<string[]> {
+  if (scope.isrcs) return [...new Set(scope.isrcs)];
+
+  if (scope.album_ids) {
+    const rows = await selectSongIdentifiers({
+      platform: "spotify",
+      identifierType: "album_id",
+      values: scope.album_ids,
+    });
+    return [...new Set(rows.map(r => r.song))];
+  }
+
+  if (scope.catalog_id) {
+    const { songs } = await selectCatalogSongsWithArtists({ catalogId: scope.catalog_id });
+    return [...new Set(songs.map(s => s.isrc))];
+  }
+
+  return [];
+}
diff --git a/lib/research/measurement_jobs/validateCreateMeasurementJobRequest.ts b/lib/research/measurement_jobs/validateCreateMeasurementJobRequest.ts
new file mode 100644
index 00000000..8218fa5f
--- /dev/null
+++ b/lib/research/measurement_jobs/validateCreateMeasurementJobRequest.ts
@@ -0,0 +1,57 @@
+import { type NextRequest, NextResponse } from "next/server";
+import { z } from "zod";
+import { validateAuthContext } from "@/lib/auth/validateAuthContext";
+import { errorResponse } from "@/lib/networking/errorResponse";
+import { ensureSongstatsPaymentMethod } from "@/lib/research/measurement_jobs/ensureSongstatsPaymentMethod";
+
+const scopeSchema = z
+  .object({
+    catalog_id: z.string().uuid("scope.catalog_id must be a valid UUID").optional(),
+    album_ids: z.array(z.string()).min(1).optional(),
+    isrcs: z.array(z.string()).min(1).optional(),
+  })
+  .refine(s => [s.catalog_id, s.album_ids, s.isrcs].filter(Boolean).length === 1, {
+    message: "Provide exactly one of scope.catalog_id, scope.album_ids, scope.isrcs",
+  });
+
+export const createMeasurementJobBodySchema = z.object({
+  scope: scopeSchema,
+  source: z.enum(["current", "historical"], { message: "source must be current or historical" }),
+  platforms: z.array(z.enum(["spotify"])).default(["spotify"]),
+});
+
+export type CreateMeasurementJobBody = z.infer<typeof createMeasurementJobBodySchema>;
+
+export type ValidatedCreateMeasurementJobRequest = {
+  accountId: string;
+  body: CreateMeasurementJobBody;
+};
+
+/**
+ * Validates `POST /api/research/measurement-jobs` — auth + body: a `scope`
+ * (exactly one of `catalog_id` / `album_ids` / `isrcs`) and a `source`
+ * (`current` = Apify capture, `historical` = Songstats backfill).
+ *
+ * @param request - The incoming HTTP request.
+ */
+export async function validateCreateMeasurementJobRequest(
+  request: NextRequest,
+): Promise<NextResponse | ValidatedCreateMeasurementJobRequest> {
+  const authResult = await validateAuthContext(request);
+  if (authResult instanceof NextResponse) return authResult;
+
+  const raw = await request.json().catch(() => null);
+  const result = createMeasurementJobBodySchema.safeParse(raw);
+  if (!result.success) {
+    return errorResponse(result.error.issues[0].message, 400);
+  }
+
+  // `historical` spends Songstats quota → require a card on file (402 + free-tier
+  // checkout link if absent). `current` is Apify-only, so it's exempt.
+  if (result.data.source === "historical") {
+    const short = await ensureSongstatsPaymentMethod(authResult.accountId);
+    if (short) return short;
+  }
+
+  return { accountId: authResult.accountId, body: result.data };
+}
diff --git a/lib/research/playcounts/__tests__/playcountMaintenanceHandler.test.ts b/lib/research/playcounts/__tests__/playcountMaintenanceHandler.test.ts
new file mode 100644
index 00000000..e0b7ad9a
--- /dev/null
+++ b/lib/research/playcounts/__tests__/playcountMaintenanceHandler.test.ts
@@ -0,0 +1,62 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest, NextResponse } from "next/server";
+import { playcountMaintenanceHandler } from "../playcountMaintenanceHandler";
+import { validateCronRequest } from "@/lib/internal/validateCronRequest";
+import { start } from "workflow/api";
+import { startDueMonthlySnapshots } from "../startDueMonthlySnapshots";
+import { reclaimStaleSongstatsBackfillRows } from "@/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue";
+
+vi.mock("@/lib/networking/getCorsHeaders", () => ({ getCorsHeaders: vi.fn(() => ({})) }));
+vi.mock("@/lib/internal/validateCronRequest", () => ({ validateCronRequest: vi.fn() }));
+vi.mock("workflow/api", () => ({ start: vi.fn() }));
+vi.mock("@/app/workflows/songstatsBackfillWorkflow", () => ({
+  songstatsBackfillWorkflow: vi.fn(),
+}));
+vi.mock("../startDueMonthlySnapshots", () => ({ startDueMonthlySnapshots: vi.fn() }));
+vi.mock("@/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue", () => ({
+  reclaimStaleSongstatsBackfillRows: vi.fn(),
+}));
+
+const req = () => new NextRequest("http://x/api/internal/playcount-maintenance");
+
+describe("playcountMaintenanceHandler", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.mocked(validateCronRequest).mockReturnValue(null as never);
+    vi.mocked(start).mockResolvedValue({ runId: "run_1" } as never);
+    vi.mocked(startDueMonthlySnapshots).mockResolvedValue(2 as never);
+    vi.mocked(reclaimStaleSongstatsBackfillRows).mockResolvedValue(5);
+  });
+
+  it("reclaims stale rows BEFORE starting the drain, and reports the count", async () => {
+    const order: string[] = [];
+    vi.mocked(reclaimStaleSongstatsBackfillRows).mockImplementation(async () => {
+      order.push("reclaim");
+      return 5;
+    });
+    vi.mocked(start).mockImplementation(async () => {
+      order.push("drain");
+      return { runId: "run_1" } as never;
+    });
+
+    const res = await playcountMaintenanceHandler(req());
+
+    expect(order).toEqual(["reclaim", "drain"]);
+    expect(res.status).toBe(202);
+    expect(await res.json()).toMatchObject({
+      status: "success",
+      reclaimed: 5,
+      backfill_run_id: "run_1",
+      monthly_snapshots_started: 2,
+    });
+  });
+
+  it("denies non-cron requests", async () => {
+    vi.mocked(validateCronRequest).mockReturnValue(
+      NextResponse.json({ status: "error" }, { status: 401 }) as never,
+    );
+    const res = await playcountMaintenanceHandler(req());
+    expect(res.status).toBe(401);
+    expect(reclaimStaleSongstatsBackfillRows).not.toHaveBeenCalled();
+  });
+});
diff --git a/lib/research/playcounts/playcountMaintenanceHandler.ts b/lib/research/playcounts/playcountMaintenanceHandler.ts
index facba435..092420ec 100644
--- a/lib/research/playcounts/playcountMaintenanceHandler.ts
+++ b/lib/research/playcounts/playcountMaintenanceHandler.ts
@@ -3,6 +3,7 @@ import { start } from "workflow/api";
 import { validateCronRequest } from "@/lib/internal/validateCronRequest";
 import { songstatsBackfillWorkflow } from "@/app/workflows/songstatsBackfillWorkflow";
 import { startDueMonthlySnapshots } from "@/lib/research/playcounts/startDueMonthlySnapshots";
+import { reclaimStaleSongstatsBackfillRows } from "@/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue";
 import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
 
 /**
@@ -18,11 +19,19 @@ export async function playcountMaintenanceHandler(request: NextRequest): Promise
   if (denied) return denied;
 
   try {
+    // Return transiently-failed / orphaned rows to `pending` before draining, so
+    // tracks that 429'd in a prior run get retried instead of being stranded.
+    const reclaimed = await reclaimStaleSongstatsBackfillRows();
     const run = await start(songstatsBackfillWorkflow);
     const monthlyStarted = await startDueMonthlySnapshots();
 
     return NextResponse.json(
-      { status: "success", backfill_run_id: run.runId, monthly_snapshots_started: monthlyStarted },
+      {
+        status: "success",
+        reclaimed,
+        backfill_run_id: run.runId,
+        monthly_snapshots_started: monthlyStarted,
+      },
       { status: 202, headers: getCorsHeaders() },
     );
   } catch (error) {
diff --git a/lib/supabase/songstats_backfill_queue/__tests__/updateSongstatsBackfillQueue.test.ts b/lib/supabase/songstats_backfill_queue/__tests__/updateSongstatsBackfillQueue.test.ts
index f9321530..eb8d0230 100644
--- a/lib/supabase/songstats_backfill_queue/__tests__/updateSongstatsBackfillQueue.test.ts
+++ b/lib/supabase/songstats_backfill_queue/__tests__/updateSongstatsBackfillQueue.test.ts
@@ -1,5 +1,8 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
-import { updateSongstatsBackfillQueue } from "../updateSongstatsBackfillQueue";
+import {
+  updateSongstatsBackfillQueue,
+  reclaimStaleSongstatsBackfillRows,
+} from "../updateSongstatsBackfillQueue";
 import supabase from "../../serverClient";
 
 vi.mock("../../serverClient", () => {
@@ -33,3 +36,34 @@ describe("updateSongstatsBackfillQueue", () => {
     );
   });
 });
+
+describe("reclaimStaleSongstatsBackfillRows", () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it("resets failed + AND-grouped stale in_progress rows to pending and returns the count", async () => {
+    const select = vi.fn().mockResolvedValue({ data: [{ id: "a" }, { id: "b" }], error: null });
+    const or = vi.fn().mockReturnValue({ select });
+    const update = vi.fn().mockReturnValue({ or });
+    vi.mocked(supabase.from).mockReturnValue({ update } as never);
+
+    const count = await reclaimStaleSongstatsBackfillRows();
+
+    expect(update).toHaveBeenCalledWith({ status: "pending" });
+    // The and() grouping around in_progress + updated_at is load-bearing — it is
+    // what prevents reclaiming `done`/`pending` rows. Assert the exact structure,
+    // not just substrings.
+    const orArg = or.mock.calls[0][0] as string;
+    expect(orArg).toMatch(/^status\.eq\.failed,and\(status\.eq\.in_progress,updated_at\.lt\..+\)$/);
+    expect(count).toBe(2);
+  });
+
+  it("throws on a reclaim DB error instead of masking it as 0", async () => {
+    const select = vi.fn().mockResolvedValue({ data: null, error: { message: "boom" } });
+    const or = vi.fn().mockReturnValue({ select });
+    vi.mocked(supabase.from).mockReturnValue({ update: vi.fn().mockReturnValue({ or }) } as never);
+
+    await expect(reclaimStaleSongstatsBackfillRows()).rejects.toThrow(
+      "Failed to reclaim stale songstats backfill rows: boom",
+    );
+  });
+});
diff --git a/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue.ts b/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue.ts
index df3c8a16..b462381a 100644
--- a/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue.ts
+++ b/lib/supabase/songstats_backfill_queue/updateSongstatsBackfillQueue.ts
@@ -18,3 +18,33 @@ export async function updateSongstatsBackfillQueue(
     throw new Error(`Failed to update songstats backfill queue: ${error.message}`);
   }
 }
+
+/** In-progress rows older than this are treated as orphaned (crashed mid-claim). */
+const STALE_IN_PROGRESS_MS = 60 * 60 * 1000; // 1 hour
+
+/**
+ * Reset reclaimable rows to `pending` so the next drain retries them: every
+ * `failed` row (transient upstream errors — `backfillTrackStep` reserves
+ * `failed` for retryable 408/429/5xx; terminal no-data / permanent 4xx is
+ * marked `done`) plus any `in_progress` row orphaned by a crashed run.
+ * Idempotent — safe before every drain. Throws on a DB error so the caller can
+ * fail loudly rather than silently skip the reclaim.
+ *
+ * @returns Number of rows returned to `pending`.
+ * @throws Error if the update fails
+ */
+export async function reclaimStaleSongstatsBackfillRows(): Promise<number> {
+  const staleBefore = new Date(Date.now() - STALE_IN_PROGRESS_MS).toISOString();
+
+  const { data, error } = await supabase
+    .from("songstats_backfill_queue")
+    .update({ status: "pending" })
+    .or(`status.eq.failed,and(status.eq.in_progress,updated_at.lt.${staleBefore})`)
+    .select("id");
+
+  if (error) {
+    throw new Error(`Failed to reclaim stale songstats backfill rows: ${error.message}`);
+  }
+
+  return data?.length ?? 0;
+}