Fix app stream/timeline ordering desync and init lifecycle race (#73)

* fix(app): enforce canonical stream sequencing and init resolution

* refactor: extract timeline and stream reducers to pure functions

packages/app/src/hooks/use-agent-initialization.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+import { __private__ } from "./use-agent-initialization";
+
+describe("useAgentInitialization timeline request policy", () => {
+  it("uses canonical tail bootstrap when cursor is missing", () => {
+    expect(__private__.buildInitialTimelineRequest(undefined)).toEqual({
+      direction: "tail",
+      limit: 200,
+      projection: "canonical",
+    });
+  });
+
+  it("uses canonical catch-up after the current cursor when present", () => {
+    expect(
+      __private__.buildInitialTimelineRequest({
+        epoch: "epoch-1",
+        endSeq: 42,
+      })
+    ).toEqual({
+      direction: "after",
+      cursor: { epoch: "epoch-1", seq: 42 },
+      limit: 0,
+      projection: "canonical",
+    });
+  });
+});