Finish incomplete dyad write (#475)

Fixes #452 
Fixes #456 
Fixes #195

e2e-tests/partial_response.spec.ts

@@ -0,0 +1,12 @@
+import { test } from "./helpers/test_helper";
+
+test("partial message is resumed", async ({ po }) => {
+  await po.setUp({ autoApprove: true });
+  await po.importApp("minimal");
+  await po.sendPrompt("tc=partial-write");
+
+  // This is a special test case which triggers a dump.
+  await po.snapshotServerDump("all-messages");
+  await po.snapshotMessages({ replaceDumpPath: true });
+  await po.snapshotAppFiles();
+});