diff --git a/.changeset/concurrent-data-migration-stamps.md b/.changeset/concurrent-data-migration-stamps.md
new file mode 100644
index 000000000..f040a62a7
--- /dev/null
+++ b/.changeset/concurrent-data-migration-stamps.md
@@ -0,0 +1,5 @@
+---
+"executor": patch
+---
+
+Prevent concurrent SQLite data-migration runners from failing when another runner commits the same ledger stamp first.
diff --git a/packages/core/sdk/src/sqlite-data-migrations.test.ts b/packages/core/sdk/src/sqlite-data-migrations.test.ts
index ab40ffecd..b0d42c3b0 100644
--- a/packages/core/sdk/src/sqlite-data-migrations.test.ts
+++ b/packages/core/sdk/src/sqlite-data-migrations.test.ts
@@ -1,4 +1,5 @@
 import { describe, expect, it } from "@effect/vitest";
+import { createClient } from "@libsql/client";
 import { Effect, Predicate } from "effect";
 
 import {
@@ -76,6 +77,66 @@ describe("runSqliteDataMigrations", () => {
     }),
   );
 
+  it.effect("converges when concurrent runners stamp the same migration", () =>
+    Effect.gen(function* () {
+      const client = createClient({ url: ":memory:" });
+      let bodiesStarted = 0;
+      let releaseBodies: (() => void) | undefined;
+      // Hold both bodies until both runners have read the ledger as empty.
+      const bothBodiesStarted = new Promise<void>((resolve) => {
+        releaseBodies = resolve;
+      });
+      const migration: SqliteDataMigration = {
+        name: "2026-06-05-concurrent",
+        run: () =>
+          Effect.promise(() => {
+            bodiesStarted++;
+            if (bodiesStarted === 2) releaseBodies?.();
+            return bothBodiesStarted;
+          }),
+      };
+
+      const results = yield* Effect.all(
+        [
+          runSqliteDataMigrations(client, [migration]),
+          runSqliteDataMigrations(client, [migration]),
+        ],
+        { concurrency: "unbounded" },
+      );
+
+      expect(results).toEqual([["2026-06-05-concurrent"], ["2026-06-05-concurrent"]]);
+      expect(bodiesStarted).toBe(2);
+      const stamps = yield* Effect.promise(() =>
+        client.execute("SELECT name FROM data_migration ORDER BY name"),
+      );
+      expect(stamps.rows.map((row) => row.name)).toEqual(["2026-06-05-concurrent"]);
+      client.close();
+    }),
+  );
+
+  it.effect("surfaces non-conflict stamp failures", () =>
+    Effect.gen(function* () {
+      const client: SqliteDataMigrationClient = {
+        execute: (stmt) => {
+          const sql = typeof stmt === "string" ? stmt : stmt.sql;
+          if (typeof stmt === "object" && sql.startsWith("INSERT INTO data_migration")) {
+            // oxlint-disable-next-line executor/no-promise-reject -- simulates a storage-driver rejection at the adapter boundary under test
+            return Promise.reject("disk full");
+          }
+          return Promise.resolve({ rows: [] });
+        },
+      };
+      const migration = migrationSpy("2026-06-05-unstamped");
+
+      const failure = yield* runSqliteDataMigrations(client, [migration.migration]).pipe(
+        Effect.flip,
+      );
+
+      expect(Predicate.isTagged(failure, "DataMigrationError")).toBe(true);
+      expect((failure as DataMigrationError).cause).toBe("disk full");
+    }),
+  );
+
   it.effect("a failing migration leaves no stamp and surfaces the failure", () =>
     Effect.gen(function* () {
       const { client, stamps } = makeFakeClient([]);
diff --git a/packages/core/sdk/src/sqlite-data-migrations.ts b/packages/core/sdk/src/sqlite-data-migrations.ts
index 4ebdcd178..60954d3cf 100644
--- a/packages/core/sdk/src/sqlite-data-migrations.ts
+++ b/packages/core/sdk/src/sqlite-data-migrations.ts
@@ -1,9 +1,9 @@
 // ---------------------------------------------------------------------------
-// Stamped data-migration ledger for the libSQL-backed apps (local boot,
-// selfhost boot). Cloud runs schema + data migrations through its drizzle
-// chain out-of-band; the local apps have no operator, so their migrations
-// run at boot — and before this ledger existed, each one re-scanned its
-// tables on every startup to decide "did I already run?" by data shape.
+// Stamped data-migration ledger for the SQLite-backed hosts (local,
+// selfhost, Cloudflare D1). PostgreSQL cloud runs schema + data migrations
+// through its drizzle chain out-of-band; the SQLite hosts run them at boot —
+// and before this ledger existed, each one re-scanned its tables on every
+// startup to decide "did I already run?" by data shape.
 // That accumulates (N migrations = N full-table scans per boot, forever)
 // and makes idempotence a per-migration proof obligation.
 //
@@ -112,10 +112,16 @@ export const runSqliteDataMigrations = (
     for (const migration of migrations) {
       if (completed.has(migration.name)) continue;
       yield* migration.run(client);
+      // Multiple hosts can boot against the same database and observe the same
+      // migration as pending. Their idempotent bodies may both finish, but only
+      // one ledger insert can win. Ignore only a conflict on this exact stamp;
+      // every other ledger failure still fails the boot.
       yield* execute(
         client,
         {
-          sql: `INSERT INTO ${LEDGER_TABLE} (name, time_completed) VALUES (?, ?)`,
+          sql: `INSERT INTO ${LEDGER_TABLE} (name, time_completed)
+            VALUES (?, ?)
+            ON CONFLICT(name) DO NOTHING`,
           args: [migration.name, Date.now()],
         },
         migration.name,