diff --git a/apps/server/src/provider/EventNdjsonLogger.test.ts b/apps/server/src/provider/EventNdjsonLogger.test.ts
index eed20381b46cb..0bb55b9bcb39b 100644
--- a/apps/server/src/provider/EventNdjsonLogger.test.ts
+++ b/apps/server/src/provider/EventNdjsonLogger.test.ts
@@ -255,6 +255,65 @@ it.layer(NodeServices.layer)("EventNdjsonLogger", (it) => {
     }),
   );
 
+  it.effect("drops Cursor streaming deltas while keeping its lifecycle updates", () =>
+    Effect.gen(function* () {
+      const tempDir = NodeFS.mkdtempSync(NodePath.join(NodeOS.tmpdir(), "t3-provider-log-"));
+      const basePath = NodePath.join(tempDir, "events.log");
+      const threadId = ThreadId.make("cursor-deltas");
+      const cursorUpdate = (update: object) => ({
+        provider: "cursor",
+        kind: "protocol",
+        event: {
+          direction: "incoming",
+          stage: "decoded",
+          payload: { type: "interaction.update", runId: "run-1", update },
+        },
+      });
+      const toolCall = { type: "shell", args: { command: "ls" } };
+      const transient = [
+        { type: "text-delta", text: "Hel" },
+        { type: "thinking-delta", text: "Hmm" },
+        { type: "token-delta", tokens: 3 },
+        { type: "shell-output-delta", event: { stdout: "a.ts\n" } },
+        { type: "partial-tool-call", callId: "call-1", modelCallId: "m-1", toolCall },
+        {
+          type: "tool-call-delta",
+          callId: "call-1",
+          modelCallId: "m-1",
+          taskUpdate: { type: "text-delta", text: "Sub" },
+        },
+      ].map(cursorUpdate);
+      const retained = [
+        { type: "tool-call-started", callId: "call-1", modelCallId: "m-1", toolCall },
+        {
+          type: "tool-call-delta",
+          callId: "call-1",
+          modelCallId: "m-1",
+          taskUpdate: { type: "tool-call-completed", callId: "call-2", toolCall },
+        },
+        { type: "tool-call-completed", callId: "call-1", modelCallId: "m-1", toolCall },
+        { type: "turn-ended" },
+      ].map(cursorUpdate);
+
+      try {
+        const store = yield* makeEventNdjsonLogStore(basePath, { batchWindowMs: 0 });
+        const native = store.logger("native");
+        for (const event of [...transient, ...retained]) {
+          yield* native.write(event, threadId);
+        }
+        yield* store.close();
+
+        const records = NodeFS.readFileSync(ownedLogPath(basePath, "cursor-deltas"), "utf8")
+          .trim()
+          .split("\n")
+          .map((line) => decodeUnknownJson(parseLogLine(line).payload));
+        assert.deepEqual(records, retained);
+      } finally {
+        NodeFS.rmSync(tempDir, { recursive: true, force: true });
+      }
+    }),
+  );
+
   it.effect("bounds oversized records while retaining failure details", () =>
     Effect.gen(function* () {
       const tempDir = NodeFS.mkdtempSync(NodePath.join(NodeOS.tmpdir(), "t3-provider-log-"));
diff --git a/apps/server/src/provider/EventNdjsonLogger.ts b/apps/server/src/provider/EventNdjsonLogger.ts
index 6a1d3844b2373..5a7b3578578f1 100644
--- a/apps/server/src/provider/EventNdjsonLogger.ts
+++ b/apps/server/src/provider/EventNdjsonLogger.ts
@@ -63,6 +63,13 @@ const transientNativeMethods = new Set([
   "turn/diff/updated",
 ]);
 const transientAcpUpdates = new Set(["agent_message_chunk", "agent_thought_chunk"]);
+const transientCursorUpdates = new Set([
+  "text-delta",
+  "thinking-delta",
+  "token-delta",
+  "shell-output-delta",
+  "partial-tool-call",
+]);
 
 export type EventNdjsonStream = "native" | "canonical" | "orchestration";
 
@@ -219,6 +226,18 @@ export function shouldPersistProviderEvent(stream: EventNdjsonStream, event: unk
       }
     }
 
+    if (nativeType === "interaction.update") {
+      let update = Reflect.get(nativeEvent, "update");
+      if (typeof update !== "object" || update === null) return true;
+      // Subagent updates arrive wrapped; keep the wrapper when it carries a lifecycle record.
+      if (Reflect.get(update, "type") === "tool-call-delta") {
+        update = Reflect.get(update, "taskUpdate");
+        if (typeof update !== "object" || update === null) return true;
+      }
+      const updateType = Reflect.get(update, "type");
+      return typeof updateType !== "string" || !transientCursorUpdates.has(updateType);
+    }
+
     const payload = Reflect.get(nativeEvent, "payload");
     if (typeof payload !== "object" || payload === null) return true;