feat: disappearing chat history — chunk-limited frontend window with backend pagination

Frontend keeps only a bounded window of chunks in memory (configurable via
settings slider, default 100). Older messages are evicted when at the bottom
and re-fetched from the backend on scroll-up.

- Backend: paginated GET /tabs/:id/messages with ?limit=N&before=seq
- Store: evictMessages trims oldest messages until total chunks ≤ limit
- Store: loadMoreMessages fetches next page and prepends with dedup
- ChatPanel: smart scroll hooks trigger eviction on return-to-bottom
- ChatPanel: onNearTop loads older history with scroll-position maintenance
- Settings: chunk limit slider in Memory section
- Fix: oldestLoadedSeq recalculated after eviction (pagination cursor stays valid)
- Fix: seq preserved on ChatMessage for cursor tracking
- Fix: scrolledUpTabs cleaned up on tab switch (no memory leak)
- Fix: evictMessages reads appSettings.chunkLimit directly (live updates)

1 files changed, 15 insertions, 2 deletions

diff --git a/packages/api/src/routes/tabs.ts b/packages/api/src/routes/tabs.ts
index 6e6734d..afa5735 100644
--- a/packages/api/src/routes/tabs.ts
+++ b/packages/api/src/routes/tabs.ts
@@ -5,6 +5,7 @@ import {
 	getMessagesForTab,
 	getSetting,
 	getTab,
+	getTotalMessageCount,
 	listOpenTabs,
 	setSetting,
 	updateTabModel,
@@ -66,8 +67,20 @@ tabsRoutes.get("/:id", (c) => {
 
 tabsRoutes.get("/:id/messages", (c) => {
 	const id = c.req.param("id");
-	const messages = getMessagesForTab(id);
-	return c.json({ messages });
+	const limitRaw = c.req.query("limit");
+	const beforeRaw = c.req.query("before");
+	const limit = limitRaw !== undefined ? Number(limitRaw) : undefined;
+	const before = beforeRaw !== undefined ? Number(beforeRaw) : undefined;
+	const options =
+		limit !== undefined || before !== undefined
+			? {
+					...(limit !== undefined && Number.isFinite(limit) ? { limit } : {}),
+					...(before !== undefined && Number.isFinite(before) ? { before } : {}),
+				}
+			: undefined;
+	const messages = getMessagesForTab(id, options);
+	const total = getTotalMessageCount(id);
+	return c.json({ messages, total });
 });
 
 tabsRoutes.patch("/:id", async (c) => {