fix(tui): restore compaction model marker

packages/schema/test/session-message.test.ts

@@ -0,0 +1,21 @@
+import { describe, expect, test } from "bun:test"
+import { Schema } from "effect"
+import { SessionMessage } from "../src/session-message.js"
+
+describe("session message", () => {
+  test("decodes completed compactions recorded before model attribution", () => {
+    const encoded = {
+      type: "compaction" as const,
+      id: "msg_compaction",
+      time: { created: 0 },
+      status: "completed" as const,
+      reason: "manual" as const,
+      summary: "summary",
+      recent: "",
+    }
+    const message = Schema.decodeUnknownSync(SessionMessage.CompactionCompleted)(encoded)
+
+    expect(message.model).toBeUndefined()
+    expect(Schema.encodeSync(SessionMessage.CompactionCompleted)(message)).toEqual(encoded)
+  })
+})