diff --git a/src/plugin-sdk/persistent-dedupe.test.ts b/src/plugin-sdk/persistent-dedupe.test.ts
index f072482b33f..31c740ff6e7 100644
--- a/src/plugin-sdk/persistent-dedupe.test.ts
+++ b/src/plugin-sdk/persistent-dedupe.test.ts
@@ -129,6 +129,24 @@ describe("createClaimableDedupe", () => {
     await expect(dedupe.claim("line:evt-1")).resolves.toEqual({ kind: "duplicate" });
   });
 
+  it("serializes concurrent first-claim races onto one in-flight owner", async () => {
+    const dedupe = createClaimableDedupe({
+      ttlMs: 10_000,
+      memoryMaxSize: 100,
+    });
+
+    const claims = await Promise.all([dedupe.claim("line:race-1"), dedupe.claim("line:race-1")]);
+    expect(claims.filter((claim) => claim.kind === "claimed")).toHaveLength(1);
+    expect(claims.filter((claim) => claim.kind === "inflight")).toHaveLength(1);
+
+    const waitingClaim = claims.find((claim) => claim.kind === "inflight");
+    await expect(dedupe.commit("line:race-1")).resolves.toBe(true);
+    if (waitingClaim?.kind === "inflight") {
+      await expect(waitingClaim.pending).resolves.toBe(true);
+    }
+    await expect(dedupe.claim("line:race-1")).resolves.toEqual({ kind: "duplicate" });
+  });
+
   it("rejects waiting duplicates when the active claim releases with an error", async () => {
     const dedupe = createClaimableDedupe({
       ttlMs: 10_000,
diff --git a/src/plugin-sdk/persistent-dedupe.ts b/src/plugin-sdk/persistent-dedupe.ts
index e07d45073dd..79dd33e2779 100644
--- a/src/plugin-sdk/persistent-dedupe.ts
+++ b/src/plugin-sdk/persistent-dedupe.ts
@@ -347,9 +347,6 @@ export function createClaimableDedupe(options: ClaimableDedupeOptions): Claimabl
     if (existing) {
       return { kind: "inflight", pending: existing.promise };
     }
-    if (await hasRecent(trimmed, dedupeOptions)) {
-      return { kind: "duplicate" };
-    }
 
     let resolve!: (result: boolean) => void;
     let reject!: (error: unknown) => void;
@@ -359,7 +356,18 @@ export function createClaimableDedupe(options: ClaimableDedupeOptions): Claimabl
     });
     void promise.catch(() => {});
     inflight.set(scopedKey, { promise, resolve, reject });
-    return { kind: "claimed" };
+    try {
+      if (await hasRecent(trimmed, dedupeOptions)) {
+        resolve(false);
+        inflight.delete(scopedKey);
+        return { kind: "duplicate" };
+      }
+      return { kind: "claimed" };
+    } catch (error) {
+      reject(error);
+      inflight.delete(scopedKey);
+      throw error;
+    }
   }
 
   async function commit(