diff --git a/server/src/__tests__/db-errors.test.ts b/server/src/__tests__/db-errors.test.ts
new file mode 100644
index 0000000000..80dbb536cf
--- /dev/null
+++ b/server/src/__tests__/db-errors.test.ts
@@ -0,0 +1,51 @@
+import { describe, expect, it } from "vitest";
+import { isUniqueViolation } from "../db-errors.js";
+
+const CONSTRAINT = "issues_open_routine_execution_uq";
+
+describe("isUniqueViolation", () => {
+  it("matches a bare postgres.js unique violation", () => {
+    expect(isUniqueViolation({ code: "23505", constraint_name: CONSTRAINT }, CONSTRAINT)).toBe(true);
+  });
+
+  it("matches the node-postgres constraint field", () => {
+    expect(isUniqueViolation({ code: "23505", constraint: CONSTRAINT }, CONSTRAINT)).toBe(true);
+  });
+
+  it("matches the error Drizzle wraps around the driver failure", () => {
+    const wrapped = new Error("Failed query: update \"issues\" set \"execution_run_id\" = $1");
+    (wrapped as { cause?: unknown }).cause = { code: "23505", constraint_name: CONSTRAINT };
+    expect(isUniqueViolation(wrapped, CONSTRAINT)).toBe(true);
+  });
+
+  it("falls back to the driver message when the constraint name is not surfaced", () => {
+    expect(isUniqueViolation({
+      cause: {
+        code: "23505",
+        message: `duplicate key value violates unique constraint "${CONSTRAINT}"`,
+      },
+    }, CONSTRAINT)).toBe(true);
+  });
+
+  it("matches any unique violation when no constraint is named", () => {
+    expect(isUniqueViolation({ cause: { code: "23505" } })).toBe(true);
+  });
+
+  it("ignores a unique violation on a different constraint", () => {
+    expect(isUniqueViolation({ cause: { code: "23505", constraint_name: "issues_identifier_idx" } }, CONSTRAINT))
+      .toBe(false);
+  });
+
+  it("ignores errors that are not unique violations", () => {
+    expect(isUniqueViolation({ cause: { code: "23503", constraint_name: CONSTRAINT } }, CONSTRAINT)).toBe(false);
+    expect(isUniqueViolation(new Error("boom"), CONSTRAINT)).toBe(false);
+    expect(isUniqueViolation(null, CONSTRAINT)).toBe(false);
+    expect(isUniqueViolation(undefined, CONSTRAINT)).toBe(false);
+  });
+
+  it("stops walking a self-referential cause chain", () => {
+    const looped: { cause?: unknown } = {};
+    looped.cause = looped;
+    expect(isUniqueViolation(looped, CONSTRAINT)).toBe(false);
+  });
+});
diff --git a/server/src/db-errors.ts b/server/src/db-errors.ts
new file mode 100644
index 0000000000..667fa65580
--- /dev/null
+++ b/server/src/db-errors.ts
@@ -0,0 +1,33 @@
+const UNIQUE_VIOLATION = "23505";
+const MAX_CAUSE_DEPTH = 4;
+
+/**
+ * Recognizes a Postgres unique-constraint violation (SQLSTATE 23505).
+ *
+ * Drizzle wraps driver failures in its own `Failed query: ...` error, so the
+ * Postgres error that carries the code and the constraint name is reachable
+ * only through `cause` — inspecting the thrown error directly misses it. The
+ * constraint name itself lands on `constraint_name` under postgres.js and on
+ * `constraint` under node-postgres, and is not always surfaced at all, so fall
+ * back to the driver message.
+ */
+export function isUniqueViolation(error: unknown, constraintName?: string): boolean {
+  let current: unknown = error;
+  for (let depth = 0; depth < MAX_CAUSE_DEPTH && current && typeof current === "object"; depth += 1) {
+    const candidate = current as {
+      code?: unknown;
+      constraint?: unknown;
+      constraint_name?: unknown;
+      message?: unknown;
+      cause?: unknown;
+    };
+    if (candidate.code === UNIQUE_VIOLATION) {
+      if (!constraintName) return true;
+      const constraint = candidate.constraint ?? candidate.constraint_name;
+      if (constraint === constraintName) return true;
+      if (typeof candidate.message === "string" && candidate.message.includes(constraintName)) return true;
+    }
+    current = candidate.cause;
+  }
+  return false;
+}
diff --git a/server/src/routes/issues.ts b/server/src/routes/issues.ts
index beb6459dd6..02084fe7cf 100644
--- a/server/src/routes/issues.ts
+++ b/server/src/routes/issues.ts
@@ -103,6 +103,7 @@ import {
 } from "@paperclipai/shared";
 import { trackAgentTaskCompleted } from "@paperclipai/shared/telemetry";
 import { getTelemetryClient } from "../telemetry.js";
+import { isUniqueViolation } from "../db-errors.js";
 import type { StorageService } from "../storage/types.js";
 import { validate } from "../middleware/validate.js";
 import * as serviceIndex from "../services/index.js";
@@ -9983,7 +9984,18 @@ export function issueRoutes(
 
     const checkoutRunId = requireAgentRunId(req, res);
     if (req.actor.type === "agent" && !checkoutRunId) return;
-    const updated = await svc.checkout(id, req.body.agentId, req.body.expectedStatuses, checkoutRunId);
+    let updated;
+    try {
+      updated = await svc.checkout(id, req.body.agentId, req.body.expectedStatuses, checkoutRunId);
+    } catch (error) {
+      if (isUniqueViolation(error, "issues_open_routine_execution_uq")) {
+        res.status(409).json({
+          error: "Another execution for this routine is already in progress",
+        });
+        return;
+      }
+      throw error;
+    }
     const actor = getActorInfo(req);
     if (updated?.harnessKind === "skill_test") {
       await companySkillsSvc.markTestRunRunning(updated.companyId, updated.id);