feat: add controlled codex thread compaction

tests/fixtures/codex-app-server-runtime.mjs

@@ -592,6 +592,33 @@ rl.on("line", (line) => {
     return;
   }
 
+  if (message.method === "thread/compact/start") {
+    send({
+      id: message.id,
+      result: {},
+    });
+    send({
+      method: "item/completed",
+      params: {
+        threadId: message.params?.threadId,
+        turnId: "compact-turn-secret-should-not-leak",
+        item: {
+          type: "contextCompaction",
+          id: "context-compaction-secret-should-not-leak",
+          summary: "private compaction summary should not leak",
+        },
+      },
+    });
+    send({
+      method: "thread/compacted",
+      params: {
+        threadId: message.params?.threadId,
+        turnId: "compact-turn-secret-should-not-leak",
+      },
+    });
+    return;
+  }
+
   if (message.method === "thread/read") {
     send({
       id: message.id,