feat(agent-ui): hydrate active session resolve (A6.191)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: efecnc

packages/agent-ui/README.md

@@ -306,6 +306,7 @@ consumption of shared panel shells:
 | A6.188 | Untitled session title check |
 | A6.189 | Desktop New chat uses DEFAULT_SESSION_TITLE |
 | A6.190 | Deleted session id blocklist ops |
+| A6.191 | Hydrate active session resolve |
 
 ### A5 complete enough
 

packages/agent-ui/src/__tests__/resolveActiveSessionOnHydrate.test.ts

@@ -0,0 +1,37 @@
+import { describe, expect, it } from "vitest";
+import { DEFAULT_SESSION_TITLE } from "../lib/backendSessionTitle.js";
+import {
+  createUntitledSessionMeta,
+  resolveActiveSessionOnHydrate,
+} from "../lib/resolveActiveSessionOnHydrate.js";
+
+describe("resolveActiveSessionOnHydrate", () => {
+  it("prefers activeId", () => {
+    const sessions = [
+      { id: "a", title: "A" },
+      { id: "b", title: "B" },
+    ];
+    const r = resolveActiveSessionOnHydrate(sessions, "b", () =>
+      createUntitledSessionMeta("x", 1),
+    );
+    expect(r.active.id).toBe("b");
+    expect(r.created).toBe(false);
+  });
+
+  it("reuses untitled head", () => {
+    const sessions = [{ id: "a", title: DEFAULT_SESSION_TITLE }];
+    const r = resolveActiveSessionOnHydrate(sessions, null, () =>
+      createUntitledSessionMeta("x", 1),
+    );
+    expect(r.active.id).toBe("a");
+    expect(r.created).toBe(false);
+  });
+
+  it("creates when none", () => {
+    const r = resolveActiveSessionOnHydrate([], null, () =>
+      createUntitledSessionMeta("x", 1),
+    );
+    expect(r.created).toBe(true);
+    expect(r.nextSessions).toHaveLength(1);
+  });
+});

packages/agent-ui/src/index.ts

@@ -888,6 +888,11 @@ export {
   filterDeletedSessions,
   appendDeletedSessionId,
 } from "./lib/filterDeletedSessions.js";
+export {
+  resolveActiveSessionOnHydrate,
+  createUntitledSessionMeta,
+} from "./lib/resolveActiveSessionOnHydrate.js";
+export type { SessionIdTitle } from "./lib/resolveActiveSessionOnHydrate.js";
 export type {
   UntitledSessionMeta,
   UntitledSessionMetaSeed,

packages/agent-ui/src/lib/resolveActiveSessionOnHydrate.ts

@@ -0,0 +1,38 @@
+/**
+ * Pure bootstrap session selection for chat hydration (A6.191).
+ */
+
+import { isUntitledSessionTitle } from "./isUntitledSessionTitle.js";
+import { newUntitledSessionMeta } from "./newSessionMeta.js";
+
+export type SessionIdTitle = { id: string; title: string };
+
+/**
+ * Prefer persisted activeId, else first untitled session, else mint a fresh
+ * untitled row. Does not mutate `sessions`.
+ */
+export function resolveActiveSessionOnHydrate<T extends SessionIdTitle>(
+  sessions: readonly T[],
+  activeId: string | null | undefined,
+  createUntitled: () => T,
+): { active: T; nextSessions: T[]; created: boolean } {
+  let active =
+    (activeId ? sessions.find((s) => s.id === activeId) : undefined) ?? null;
+  if (!active && sessions[0] && isUntitledSessionTitle(sessions[0].title)) {
+    active = sessions[0];
+  }
+  if (active) {
+    return { active, nextSessions: [...sessions], created: false };
+  }
+  const created = createUntitled();
+  return {
+    active: created,
+    nextSessions: [created, ...sessions],
+    created: true,
+  };
+}
+
+/** Convenience: mint untitled meta with shared title factory. */
+export function createUntitledSessionMeta(id: string, now?: number) {
+  return newUntitledSessionMeta({ id, now });
+}

src/modules/ai/store/chatStore.ts

@@ -2,6 +2,8 @@ import {
   DEFAULT_SESSION_TITLE,
   isUntitledSessionTitle,
   appendDeletedSessionId,
+  resolveActiveSessionOnHydrate,
+  createUntitledSessionMeta,
 } from "@altai/agent-ui";
 import type { UIMessage } from "ai";
 import { native } from "../lib/native";
@@ -858,22 +860,15 @@ export const useChatStore = create<StoreState>((set, get) => ({
     // most recent conversation instead of an empty "New chat". Else reuse the
     // most recent untitled "New chat" (no point stacking empty placeholders
     // every launch), else create a fresh one.
-    let active =
-      (activeId ? sessions.find((s) => s.id === activeId) : undefined) ?? null;
-    if (!active && isUntitledSessionTitle(sessions[0]?.title)) {
-      active = sessions[0];
-    }
-    let nextSessions: SessionMeta[];
-    if (active) {
-      nextSessions = sessions;
-    } else {
-      active = {
-        id: newSessionId(),
-        title: DEFAULT_SESSION_TITLE,
-        createdAt: Date.now(),
-        updatedAt: Date.now(),
-      };
-      nextSessions = [active, ...sessions];
+    const resolved = resolveActiveSessionOnHydrate(
+      sessions,
+      activeId,
+      () =>
+        createUntitledSessionMeta(newSessionId()) as SessionMeta,
+    );
+    const active = resolved.active;
+    const nextSessions = resolved.nextSessions as SessionMeta[];
+    if (resolved.created) {
       void saveSessionsList(nextSessions);
     }
     const activeSessionId = active.id;