perf(chat): fast open of long in-flight turns

- Batch live chat events: fold a burst in one pass per animation frame
  (rAF + timeout fallback for hidden tabs) instead of one reactive cycle per
  WS frame. Flushed before send/resync to keep ordering.
- De-dup the late-join replay against committed history: provisional chunks
  of the in-flight turn already persisted (CR-6 per-step persistence) are
  hidden by aligned-prefix matching (fail-safe: mismatch shows, never hides).
- Memoize chunks/turnMetrics getters by state identity.
- LazyCollapse: tool/thinking card bodies mount only on first open.
- content-visibility:auto on transcript rows.
- scripts/probe-replay.ts + bench-pure.ts for measuring the replay path.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/app/store.test.ts b/src/app/store.test.ts
index 206eaa4..89e418e 100644
--- a/src/app/store.test.ts
+++ b/src/app/store.test.ts
@@ -509,6 +509,7 @@ describe("createAppStore", () => {
       socketFactory: () => ws,
       fetchImpl: fakeFetchImpl(),
       localStorage: createFakeStorage(),
+      chatFlushScheduler: null,
     });
     ws.resolveOpen();
 
@@ -887,6 +888,7 @@ describe("createAppStore", () => {
       socketFactory: () => ws,
       fetchImpl: fakeFetchImpl(),
       localStorage: createFakeStorage(),
+      chatFlushScheduler: null,
     });
     ws.resolveOpen();