diff --git a/App/backend/src/adapters/outbound/agent-source/codex/session-discovery.ts b/App/backend/src/adapters/outbound/agent-source/codex/session-discovery.ts
index 57d2b41df..5c2cb1a47 100644
--- a/App/backend/src/adapters/outbound/agent-source/codex/session-discovery.ts
+++ b/App/backend/src/adapters/outbound/agent-source/codex/session-discovery.ts
@@ -5,6 +5,8 @@ import { dirname, join } from "node:path";
 import { readJsonlObjects } from "../jsonl-lines.js";
 import { readDirectoryIfExists } from "../read-directory.js";
 
+const ROLLOUT_FILE_SUFFIX = ".jsonl";
+
 export interface CodexSessionFile {
   /** Session file path. */
   sessionFilePath: string;
@@ -56,7 +58,7 @@ async function listRolloutFiles(
         continue;
       }
 
-      if (entry.isFile() && entry.name.startsWith("rollout-") && entry.name.endsWith(".jsonl")) {
+      if (entry.isFile() && isPrimaryRolloutFile(entry.name)) {
         const fileStat = await stat(path);
         files.push({ path, mtimeMs: fileStat.mtimeMs });
       }
@@ -71,6 +73,12 @@ async function listRolloutFiles(
     .map((file) => file.path);
 }
 
+function isPrimaryRolloutFile(name: string): boolean {
+  return name.startsWith("rollout-") &&
+    name.endsWith(ROLLOUT_FILE_SUFFIX) &&
+    name.indexOf(ROLLOUT_FILE_SUFFIX) === name.length - ROLLOUT_FILE_SUFFIX.length;
+}
+
 async function readFirstCwd(filePath: string): Promise<string | null> {
   try {
     for await (const record of readJsonlObjects(filePath)) {
diff --git a/App/backend/src/adapters/outbound/agent-source/codex/tests/adapter.test.ts b/App/backend/src/adapters/outbound/agent-source/codex/tests/adapter.test.ts
index 0a358c51c..ce2464055 100644
--- a/App/backend/src/adapters/outbound/agent-source/codex/tests/adapter.test.ts
+++ b/App/backend/src/adapters/outbound/agent-source/codex/tests/adapter.test.ts
@@ -69,6 +69,24 @@ describe("codex source adapter", () => {
     ]);
   });
 
+  it("ignores backup copies of rollout files", async () => {
+    const fixture = createFixture();
+    const backupPath = `${fixture.rolloutPath}.bak-strip-input-image.jsonl`;
+    writeFileSync(
+      backupPath,
+      JSON.stringify({
+        timestamp: "2026-05-29T11:00:00.000Z",
+        type: "session_meta",
+        payload: { cwd: join(fixture.workspacePath, "backup-copy") }
+      }),
+      "utf8"
+    );
+
+    await expect(discoverCodexSessions({ root: fixture.sessionsRoot })).resolves.toEqual([
+      expect.objectContaining({ sessionFilePath: fixture.rolloutPath })
+    ]);
+  });
+
   it("redacts large image tool outputs without failing the scan", async () => {
     const fixture = createLargeImageFixture();
     const adapter = createCodexSourceAdapter({ sessionsRoot: fixture.sessionsRoot });
diff --git a/App/backend/src/services/agent-source-service.ts b/App/backend/src/services/agent-source-service.ts
index dc3d6a7f1..c0168a12d 100644
--- a/App/backend/src/services/agent-source-service.ts
+++ b/App/backend/src/services/agent-source-service.ts
@@ -557,6 +557,7 @@ async function collectSourceMessages(
     messages: [],
     errors: []
   };
+  const conversationIds = new Set<string>();
 
   emitProgress(scanOptions, {
     sourceId,
@@ -585,7 +586,8 @@ async function collectSourceMessages(
     })) {
       scanOptions.signal?.throwIfAborted();
       collected.messages.push(message);
-      if (!collected.conversationIds.includes(message.conversationId)) {
+      if (!conversationIds.has(message.conversationId)) {
+        conversationIds.add(message.conversationId);
         collected.conversationIds.push(message.conversationId);
       }
       if (collected.messages.length % SCAN_MESSAGE_YIELD_INTERVAL === 0) {