diff --git a/apps/api/prisma/migrations/20260820100000_recipe_source_linking/migration.sql b/apps/api/prisma/migrations/20260820100000_recipe_source_linking/migration.sql
new file mode 100644
index 0000000..877c7a4
--- /dev/null
+++ b/apps/api/prisma/migrations/20260820100000_recipe_source_linking/migration.sql
@@ -0,0 +1,24 @@
+-- Adds `Source.key` (`key String @unique`) — the catalog of implemented
+-- recipe sources is now kept in sync with the adapter registry
+-- (recipe-source-registry.ts) by key, same "stable English camelCase uid"
+-- convention as Diet/Unit/TechStep, rather than hand-maintained. `sources`
+-- has never been seeded (no rows exist pre-launch), so a plain NOT NULL
+-- column with no backfill is safe.
+--
+-- Adds `Recipe.external_id` — the item's identifier on `source`, `null`
+-- for a manually-authored recipe. `@@unique([sourceId, externalId])`
+-- prevents importing the same source recipe twice; Postgres treats each
+-- NULL as distinct, so manually-authored recipes (both columns null) never
+-- collide with each other or with one another here.
+
+-- AlterTable
+ALTER TABLE "sources" ADD COLUMN "key" TEXT NOT NULL;
+
+-- CreateIndex
+CREATE UNIQUE INDEX "sources_key_key" ON "sources"("key");
+
+-- AlterTable
+ALTER TABLE "recipe" ADD COLUMN "external_id" TEXT;
+
+-- CreateIndex
+CREATE UNIQUE INDEX "recipe_source_id_external_id_key" ON "recipe"("source_id", "external_id");
diff --git a/apps/api/prisma/schema.prisma b/apps/api/prisma/schema.prisma
index 23bfef3..91b1a52 100644
--- a/apps/api/prisma/schema.prisma
+++ b/apps/api/prisma/schema.prisma
@@ -211,8 +211,20 @@ model PlanningItem {
 // Recipes
 // -----------------------------------------------------------------------------
 
+/// Catalog of implemented recipe sources (specific websites/APIs the
+/// import pipeline knows how to talk to) — one row per adapter registered
+/// in `apps/api/src/lib/recipe-source-registry.ts`, kept in sync by
+/// `syncRecipeSources` (`apps/api/src/db/recipe-source-sync.ts`) rather
+/// than hand-maintained like `DIETS`/`UNITS` (`reference-seed-data.ts`):
+/// the adapter registry is the actual source of truth for "which sources
+/// exist", this table just mirrors it so `Recipe.sourceId` has something
+/// to point at. `key` matches `RecipeSourceAdapter.key` — same stable
+/// English camelCase uid convention as `Diet.key`/`Unit.key`/`TechStep.key`.
+/// Empty until a concrete adapter is registered (none exists yet, see
+/// recipe-source-adapter.ts).
 model Source {
   id   Int     @id @default(autoincrement())
+  key  String  @unique
   name String
   url  String?
 
@@ -239,6 +251,17 @@ model Recipe {
   id            Int              @id @default(autoincrement())
   name          String
   sourceId      Int?             @map("source_id")
+  /// The item's identifier on `source` (`RecipeSourceListItem.externalId`,
+  /// recipe-source-adapter.ts) — `null` for a manually-authored recipe,
+  /// alongside `sourceId` being `null`. Together with `sourceId`, this is
+  /// what `findImportedExternalIds` (recipe-source-sync.ts) checks against
+  /// to tell an already-imported source item apart from a new one when
+  /// browsing (see `markAlreadyImported`, recipe-source-adapter.ts) — the
+  /// `@@unique([sourceId, externalId])` below is what actually prevents
+  /// importing the same source recipe twice (Postgres treats each `NULL`
+  /// as distinct, so manually-authored recipes never collide with each
+  /// other here).
+  externalId    String?          @map("external_id")
   description   String?
   picture       String?
   /// How many portions this recipe yields as written (its ingredient
@@ -267,6 +290,7 @@ model Recipe {
   favoritedBy   RecipeFavorite[]
   diets         RecipeDiet[]
 
+  @@unique([sourceId, externalId])
   @@map("recipe")
 }
 
diff --git a/apps/api/prisma/seed.ts b/apps/api/prisma/seed.ts
index 87534e6..6bc8ea6 100644
--- a/apps/api/prisma/seed.ts
+++ b/apps/api/prisma/seed.ts
@@ -1,4 +1,5 @@
 import { PrismaClient } from "@prisma/client";
+import { syncRecipeSources } from "../src/db/recipe-source-sync.js";
 import { seedReferenceData } from "../src/db/reference-seed-data.js";
 
 // Standalone CLI entry point (not `src/db/prisma.ts` — that module pulls in
@@ -10,6 +11,7 @@ import { seedReferenceData } from "../src/db/reference-seed-data.js";
 const prisma = new PrismaClient();
 
 seedReferenceData(prisma)
+  .then(() => syncRecipeSources(prisma))
   .then(() => prisma.$disconnect())
   .catch(async (err) => {
     console.error(err);
diff --git a/apps/api/src/db/recipe-source-sync.ts b/apps/api/src/db/recipe-source-sync.ts
new file mode 100644
index 0000000..3ff0eb2
--- /dev/null
+++ b/apps/api/src/db/recipe-source-sync.ts
@@ -0,0 +1,61 @@
+import type { PrismaClient } from "@prisma/client";
+import { listRecipeSources } from "../lib/recipe-source-registry.js";
+
+/**
+ * Upserts one `Source` row (schema.prisma) per adapter currently in
+ * `recipe-source-registry.ts`, keyed by `adapter.key` — keeps the
+ * `sources` catalog an exact mirror of "which sources are actually
+ * implemented in code", rather than a hand-maintained list that can drift
+ * out of sync the way `DIETS`/`UNITS` (`reference-seed-data.ts`) would if
+ * copy-pasted here. Call once at startup (`prisma/seed.ts`) and in test
+ * setup (`test-support/reset-db.ts`), the same place `seedReferenceData`
+ * runs — kept as its own function rather than folded into that one, since
+ * it reads from the adapter registry instead of a static array.
+ *
+ * Never deletes a `Source` row whose key fell out of the registry (e.g. an
+ * adapter temporarily removed from code) — a recipe already imported from
+ * it should keep citing it rather than having `sourceId` silently nulled
+ * out from under it (see `onDelete: SetNull` on `Recipe.source` in
+ * schema.prisma, which is what *would* happen on an actual delete).
+ *
+ * Safe to call with an empty registry — currently always the case, since
+ * no concrete adapter exists yet (see recipe-source-adapter.ts) — leaves
+ * the `sources` table untouched.
+ */
+export async function syncRecipeSources(prisma: PrismaClient): Promise<void> {
+  for (const adapter of listRecipeSources()) {
+    await prisma.source.upsert({
+      where: { key: adapter.key },
+      update: { name: adapter.name },
+      create: { key: adapter.key, name: adapter.name },
+    });
+  }
+}
+
+/**
+ * Which of `externalIds` already have a `Recipe` imported from the source
+ * registered under `sourceKey` — the DB-touching counterpart to
+ * `markAlreadyImported` (recipe-source-adapter.ts), which stays pure and
+ * takes this set as a plain argument rather than querying itself. Returns
+ * an empty set (not an error) for a `sourceKey` with no matching `Source`
+ * row — nothing can have been imported from a source we don't even have a
+ * catalog entry for.
+ */
+export async function findImportedExternalIds(
+  prisma: PrismaClient,
+  sourceKey: string,
+  externalIds: string[],
+): Promise<Set<string>> {
+  if (externalIds.length === 0) return new Set();
+
+  const source = await prisma.source.findUnique({ where: { key: sourceKey } });
+  if (!source) return new Set();
+
+  const imported = await prisma.recipe.findMany({
+    where: { sourceId: source.id, externalId: { in: externalIds } },
+    select: { externalId: true },
+  });
+  return new Set(
+    imported.flatMap((recipe) => (recipe.externalId !== null ? [recipe.externalId] : [])),
+  );
+}
diff --git a/apps/api/src/lib/recipe-source-registry.ts b/apps/api/src/lib/recipe-source-registry.ts
index aca3b42..f12e682 100644
--- a/apps/api/src/lib/recipe-source-registry.ts
+++ b/apps/api/src/lib/recipe-source-registry.ts
@@ -4,13 +4,12 @@ import type { RecipeSourceAdapter } from "./recipe-source-adapter.js";
  * In-memory registry of every {@link RecipeSourceAdapter} (recipe-source-adapter.ts)
  * this process knows about, keyed by `adapter.key`. Deliberately not
  * DB-backed — an adapter *is* code (a website's fetch/parse logic can't
- * live in a database row), unlike the `Source` table in schema.prisma,
- * which records *where a saved recipe came from* (a name/url pair) once
- * the import pipeline actually persists one. The two are related but
- * distinct: this registry is "which sources can we import from right now",
- * `Source` rows are "which sources a saved recipe cites" — wiring the two
- * together is future work for whichever module ends up saving imported
- * recipes.
+ * live in a database row) — but the `Source` table (schema.prisma) is kept
+ * in sync with it (see `syncRecipeSources`, recipe-source-sync.ts) so a
+ * saved `Recipe.sourceId` has a row to point at. Actually saving an
+ * imported recipe (setting `Recipe.sourceId`/`externalId`) is still future
+ * work for whichever module ends up driving the import pipeline — this
+ * registry only answers "which sources can we import from right now".
  *
  * No adapter is registered here yet — this file only provides the
  * mechanism; `registerRecipeSource` is meant to be called once per adapter
diff --git a/apps/api/test-support/reset-db.ts b/apps/api/test-support/reset-db.ts
index 3d6c793..52b264b 100644
--- a/apps/api/test-support/reset-db.ts
+++ b/apps/api/test-support/reset-db.ts
@@ -1,4 +1,5 @@
 import { prisma } from "../src/db/prisma.js";
+import { syncRecipeSources } from "../src/db/recipe-source-sync.js";
 import { seedReferenceData } from "../src/db/reference-seed-data.js";
 
 // Single TRUNCATE ... CASCADE covers FK ordering and resets identity
@@ -7,6 +8,9 @@ import { seedReferenceData } from "../src/db/reference-seed-data.js";
 // truncating it, so every test starts from the same realistic reference
 // data the real app seeds (`prisma/seed.ts`) rather than empty tables —
 // tests exercising dietId/allergyIds/unitId need real rows to reference.
+// `syncRecipeSources` runs last, for the same reason: `sources` should
+// reflect whatever adapters this test run happens to have registered
+// (usually none — see recipe-source-registry.ts).
 export async function resetDatabase() {
   await prisma.$executeRawUnsafe(`
     TRUNCATE TABLE
@@ -18,4 +22,5 @@ export async function resetDatabase() {
     RESTART IDENTITY CASCADE;
   `);
   await seedReferenceData(prisma);
+  await syncRecipeSources(prisma);
 }
diff --git a/apps/api/test/recipe-source-sync.test.ts b/apps/api/test/recipe-source-sync.test.ts
new file mode 100644
index 0000000..0eefee3
--- /dev/null
+++ b/apps/api/test/recipe-source-sync.test.ts
@@ -0,0 +1,204 @@
+import type { SignupInput } from "@batch-cooking/shared";
+import { faker } from "@faker-js/faker";
+import { expect } from "chai";
+import request from "supertest";
+import { createApp } from "../src/app.js";
+import { prisma } from "../src/db/prisma.js";
+import { findImportedExternalIds, syncRecipeSources } from "../src/db/recipe-source-sync.js";
+import type { RecipeSourceAdapter } from "../src/lib/recipe-source-adapter.js";
+import { clearRecipeSources, registerRecipeSource } from "../src/lib/recipe-source-registry.js";
+import { resetDatabase } from "../test-support/reset-db.js";
+
+/** See `recipe.test.ts` — generated rather than hardcoded, no test fixture looks like a real person's data. */
+function buildSignupPayload(): SignupInput {
+  const firstName = faker.person.firstName();
+  const lastName = faker.person.lastName();
+  return {
+    firstName,
+    lastName,
+    email: faker.internet.email({ firstName, lastName }).toLowerCase(),
+    password: faker.internet.password({ length: 16 }),
+  };
+}
+
+/** A minimal `RecipeSourceAdapter` whose list/fetchDetail/parse are never actually called here — only `key`/`name` matter for exercising `syncRecipeSources`. */
+function buildFakeAdapter(key: string, name: string): RecipeSourceAdapter {
+  return {
+    key,
+    name,
+    async list() {
+      return { items: [], nextCursor: null };
+    },
+    async fetchDetail() {
+      throw new Error("not implemented");
+    },
+    parse() {
+      throw new Error("not implemented");
+    },
+  };
+}
+
+describe("recipe-source-sync", () => {
+  const app = createApp();
+
+  async function signup(): Promise<{ profileId: number }> {
+    const res = await request.agent(app).post("/auth/signup").send(buildSignupPayload());
+    return { profileId: res.body.id };
+  }
+
+  beforeEach(async () => {
+    await resetDatabase();
+    clearRecipeSources();
+  });
+
+  afterEach(() => {
+    clearRecipeSources();
+  });
+
+  after(async () => {
+    await prisma.$disconnect();
+  });
+
+  describe("syncRecipeSources", () => {
+    it("does nothing when the registry is empty", async () => {
+      await syncRecipeSources(prisma);
+      expect(await prisma.source.count()).to.equal(0);
+    });
+
+    it("creates a Source row per registered adapter", async () => {
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Fake Source"));
+
+      await syncRecipeSources(prisma);
+
+      const source = await prisma.source.findUniqueOrThrow({ where: { key: "fakeSource" } });
+      expect(source.name).to.equal("Fake Source");
+    });
+
+    it("is idempotent — running it twice doesn't duplicate rows", async () => {
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Fake Source"));
+
+      await syncRecipeSources(prisma);
+      await syncRecipeSources(prisma);
+
+      expect(await prisma.source.count()).to.equal(1);
+    });
+
+    it("updates the name when the adapter's own name changes between syncs", async () => {
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Old Name"));
+      await syncRecipeSources(prisma);
+      clearRecipeSources();
+      registerRecipeSource(buildFakeAdapter("fakeSource", "New Name"));
+
+      await syncRecipeSources(prisma);
+
+      const source = await prisma.source.findUniqueOrThrow({ where: { key: "fakeSource" } });
+      expect(source.name).to.equal("New Name");
+    });
+
+    it("never deletes a Source row whose key fell out of the registry", async () => {
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Fake Source"));
+      await syncRecipeSources(prisma);
+      clearRecipeSources();
+
+      await syncRecipeSources(prisma);
+
+      expect(await prisma.source.count()).to.equal(1);
+    });
+  });
+
+  describe("findImportedExternalIds", () => {
+    it("returns an empty set for a sourceKey with no matching Source row", async () => {
+      expect(await findImportedExternalIds(prisma, "unknown", ["1", "2"])).to.deep.equal(new Set());
+    });
+
+    it("returns an empty set for an empty externalIds list", async () => {
+      expect(await findImportedExternalIds(prisma, "fakeSource", [])).to.deep.equal(new Set());
+    });
+
+    it("returns exactly the externalIds already imported from that source", async () => {
+      const { profileId } = await signup();
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Fake Source"));
+      await syncRecipeSources(prisma);
+      const source = await prisma.source.findUniqueOrThrow({ where: { key: "fakeSource" } });
+
+      await prisma.recipe.create({
+        data: {
+          name: "Tarte",
+          authorId: profileId,
+          portions: 4,
+          sourceId: source.id,
+          externalId: "1",
+        },
+      });
+      // Manually-authored, not tied to any source — shouldn't ever show up as "imported".
+      await prisma.recipe.create({ data: { name: "Salade", authorId: profileId, portions: 2 } });
+
+      const result = await findImportedExternalIds(prisma, "fakeSource", ["1", "2", "3"]);
+      expect(result).to.deep.equal(new Set(["1"]));
+    });
+
+    it("scopes matches to the given source — the same externalId from a different source doesn't count", async () => {
+      const { profileId } = await signup();
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Fake Source"));
+      registerRecipeSource(buildFakeAdapter("otherSource", "Other Source"));
+      await syncRecipeSources(prisma);
+      const otherSource = await prisma.source.findUniqueOrThrow({ where: { key: "otherSource" } });
+
+      await prisma.recipe.create({
+        data: {
+          name: "Tarte",
+          authorId: profileId,
+          portions: 4,
+          sourceId: otherSource.id,
+          externalId: "1",
+        },
+      });
+
+      expect(await findImportedExternalIds(prisma, "fakeSource", ["1"])).to.deep.equal(new Set());
+    });
+  });
+
+  describe("Recipe(sourceId, externalId) uniqueness", () => {
+    it("rejects importing the same source recipe twice", async () => {
+      const { profileId } = await signup();
+      registerRecipeSource(buildFakeAdapter("fakeSource", "Fake Source"));
+      await syncRecipeSources(prisma);
+      const source = await prisma.source.findUniqueOrThrow({ where: { key: "fakeSource" } });
+
+      await prisma.recipe.create({
+        data: {
+          name: "Tarte",
+          authorId: profileId,
+          portions: 4,
+          sourceId: source.id,
+          externalId: "1",
+        },
+      });
+
+      let rejected = false;
+      try {
+        await prisma.recipe.create({
+          data: {
+            name: "Tarte (again)",
+            authorId: profileId,
+            portions: 4,
+            sourceId: source.id,
+            externalId: "1",
+          },
+        });
+      } catch {
+        rejected = true;
+      }
+      expect(rejected).to.be.true;
+    });
+
+    it("allows any number of manually-authored recipes (both columns null)", async () => {
+      const { profileId } = await signup();
+
+      await prisma.recipe.create({ data: { name: "Une", authorId: profileId, portions: 4 } });
+      await prisma.recipe.create({ data: { name: "Deux", authorId: profileId, portions: 4 } });
+
+      expect(await prisma.recipe.count()).to.equal(2);
+    });
+  });
+});