diff --git a/apps/server/src/provider/Layers/CodexAdapter.test.ts b/apps/server/src/provider/Layers/CodexAdapter.test.ts
index 31d394c3ec..721aff2a54 100644
--- a/apps/server/src/provider/Layers/CodexAdapter.test.ts
+++ b/apps/server/src/provider/Layers/CodexAdapter.test.ts
@@ -400,6 +400,41 @@ lifecycleLayer("CodexAdapterLive lifecycle", (it) => {
     }),
   );
 
+  it.effect("maps raw codex/event/plan_delta to canonical turn.proposed.delta", () =>
+    Effect.gen(function* () {
+      const adapter = yield* CodexAdapter;
+      const firstEventFiber = yield* Stream.runHead(adapter.streamEvents).pipe(Effect.forkChild);
+
+      lifecycleManager.emit("event", {
+        id: asEventId("evt-raw-plan-delta"),
+        kind: "notification",
+        provider: "codex",
+        createdAt: new Date().toISOString(),
+        method: "codex/event/plan_delta",
+        threadId: asThreadId("thread-1"),
+        turnId: asTurnId("turn-1"),
+        payload: {
+          msg: {
+            turn_id: "turn-1",
+            delta: "- Step 1: read the file",
+          },
+        },
+      } satisfies ProviderEvent);
+
+      const firstEvent = yield* Fiber.join(firstEventFiber);
+
+      assert.equal(firstEvent._tag, "Some");
+      if (firstEvent._tag !== "Some") {
+        return;
+      }
+      assert.equal(firstEvent.value.type, "turn.proposed.delta");
+      if (firstEvent.value.type !== "turn.proposed.delta") {
+        return;
+      }
+      assert.equal(firstEvent.value.payload.delta, "- Step 1: read the file");
+    }),
+  );
+
   it.effect("maps session/closed lifecycle events to canonical session.exited runtime events", () =>
     Effect.gen(function* () {
       const adapter = yield* CodexAdapter;
diff --git a/apps/server/src/provider/Layers/codexEventMapping.test.ts b/apps/server/src/provider/Layers/codexEventMapping.test.ts
new file mode 100644
index 0000000000..1334b1e2cc
--- /dev/null
+++ b/apps/server/src/provider/Layers/codexEventMapping.test.ts
@@ -0,0 +1,116 @@
+/**
+ * Unit tests for codexEventMapping — calls mapToRuntimeEvents directly
+ * without the full adapter/stream infrastructure.
+ */
+import { describe, it, expect } from "bun:test";
+import { mapToRuntimeEvents } from "./codexEventMapping.ts";
+import {
+  EventId,
+  type ProviderEvent,
+  ProviderItemId,
+  ThreadId,
+  TurnId,
+} from "@t3tools/contracts";
+
+const threadId = ThreadId.makeUnsafe("thread-1");
+
+function makeEvent(overrides: Partial<ProviderEvent>): ProviderEvent {
+  return {
+    id: EventId.makeUnsafe("evt-1"),
+    kind: "notification",
+    provider: "codex",
+    createdAt: new Date().toISOString(),
+    threadId,
+    ...overrides,
+  } as ProviderEvent;
+}
+
+describe("codexEventMapping — codex/event/plan_delta", () => {
+  it("maps plan_delta with msg.delta to turn.proposed.delta", () => {
+    const events = mapToRuntimeEvents(
+      makeEvent({
+        method: "codex/event/plan_delta",
+        turnId: TurnId.makeUnsafe("turn-1"),
+        payload: {
+          msg: {
+            turn_id: "turn-1",
+            delta: "- Step 1: read the file",
+          },
+        },
+      }),
+      threadId,
+    );
+
+    expect(events).toHaveLength(1);
+    expect(events[0]!.type).toBe("turn.proposed.delta");
+    if (events[0]!.type === "turn.proposed.delta") {
+      expect(events[0]!.payload.delta).toBe("- Step 1: read the file");
+    }
+  });
+
+  it("maps plan_delta with msg.text fallback", () => {
+    const events = mapToRuntimeEvents(
+      makeEvent({
+        method: "codex/event/plan_delta",
+        payload: {
+          msg: {
+            text: "plan text via text field",
+          },
+        },
+      }),
+      threadId,
+    );
+
+    expect(events).toHaveLength(1);
+    if (events[0]!.type === "turn.proposed.delta") {
+      expect(events[0]!.payload.delta).toBe("plan text via text field");
+    }
+  });
+
+  it("maps plan_delta with msg.content.text fallback", () => {
+    const events = mapToRuntimeEvents(
+      makeEvent({
+        method: "codex/event/plan_delta",
+        payload: {
+          msg: {
+            content: { text: "nested content text" },
+          },
+        },
+      }),
+      threadId,
+    );
+
+    expect(events).toHaveLength(1);
+    if (events[0]!.type === "turn.proposed.delta") {
+      expect(events[0]!.payload.delta).toBe("nested content text");
+    }
+  });
+
+  it("returns empty for plan_delta with no extractable delta", () => {
+    const events = mapToRuntimeEvents(
+      makeEvent({
+        method: "codex/event/plan_delta",
+        payload: {
+          msg: {},
+        },
+      }),
+      threadId,
+    );
+
+    expect(events).toHaveLength(0);
+  });
+
+  it("returns empty for plan_delta with empty delta string", () => {
+    const events = mapToRuntimeEvents(
+      makeEvent({
+        method: "codex/event/plan_delta",
+        payload: {
+          msg: { delta: "" },
+        },
+      }),
+      threadId,
+    );
+
+    expect(events).toHaveLength(0);
+  });
+});
diff --git a/apps/server/src/provider/Layers/codexEventMapping.ts b/apps/server/src/provider/Layers/codexEventMapping.ts
index 213b33d4fd..fd2d5e1ad4 100644
--- a/apps/server/src/provider/Layers/codexEventMapping.ts
+++ b/apps/server/src/provider/Layers/codexEventMapping.ts
@@ -1362,6 +1362,22 @@ export function mapToRuntimeEvents(
     ];
   }
 
+  if (event.method === "codex/event/plan_delta") {
+    const msg = codexEventMessage(payload);
+    const delta =
+      asString(msg?.delta) ?? asString(msg?.text) ?? asString(asObject(msg?.content)?.text);
+    if (!delta || delta.length === 0) {
+      return [];
+    }
+    return [
+      {
+        ...codexEventBase(event, canonicalThreadId),
+        type: "turn.proposed.delta" as const,
+        payload: { delta },
+      },
+    ];
+  }
+
   // Log unmapped events to aid debugging — skip known-noisy non-critical ones.
   if (event.method && !QUIET_UNMAPPED_EVENTS.has(event.method)) {
     console.debug(`[codexEventMapping] unmapped event: ${event.method}`, event.payload ?? "");