Restore scoped live history retention

apps/web/app/terminal.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from "bun:test";
 import {
   NAV_ITEMS,
+  appendHistoryTail,
   buildDefaultFlowFilters,
   classifierToneForFamily,
   deriveAlertDirection,
@@ -9,6 +10,7 @@ import {
   formatOptionContractLabel,
   flushPausableTapeData,
   getAlertWindowAnchorTs,
+  getLiveHistoryRetentionCap,
   getOptionTableSnapshot,
   getLiveFeedStatus,
   getLiveManifest,
@@ -240,6 +242,53 @@ describe("live tape pausable helpers", () => {
   });
 });
 
+describe("live tape history helpers", () => {
+  it("appends older scoped rows behind the hot live head", () => {
+    const liveHead = Array.from({ length: 100 }, (_, idx) =>
+      makeItem(`hot-${idx}`, 200 - idx, 2_000 - idx)
+    );
+    const older = [makeItem("older-1", 99, 999), makeItem("older-2", 98, 998)];
+
+    const next = appendHistoryTail([], older, liveHead, 5000);
+
+    expect(next.map((item) => item.trace_id)).toEqual(["older-1", "older-2"]);
+  });
+
+  it("skips duplicates already present in the live head", () => {
+    const liveHead = [makeItem("latest", 3, 300), makeItem("duplicate", 2, 200)];
+    const older = [makeItem("duplicate", 2, 200), makeItem("older", 1, 100)];
+
+    const next = appendHistoryTail([], older, liveHead, 5000);
+
+    expect(next.map((item) => item.trace_id)).toEqual(["older"]);
+  });
+
+  it("trims the history tail to the soft cap", () => {
+    const current = [makeItem("existing", 4, 400)];
+    const older = [makeItem("older-1", 3, 300), makeItem("older-2", 2, 200)];
+
+    const next = appendHistoryTail(current, older, [], 2);
+
+    expect(next.map((item) => item.trace_id)).toEqual(["existing", "older-1"]);
+  });
+
+  it("keeps scoped option and equity history on the normal retention cap", () => {
+    expect(
+      getLiveHistoryRetentionCap({
+        channel: "options",
+        underlying_ids: ["AAPL"],
+        option_contract_id: "AAPL-2025-01-17-200-C"
+      } as any)
+    ).toBeGreaterThan(0);
+    expect(
+      getLiveHistoryRetentionCap({
+        channel: "equities",
+        underlying_ids: ["AAPL"]
+      } as any)
+    ).toBeGreaterThan(0);
+  });
+});
+
 describe("options display formatters", () => {
   it("formats dashed option contracts as ticker strike expiry", () => {
     expect(formatOptionContractLabel("SPY-2025-01-17-450-C")).toEqual({

apps/web/app/terminal.tsx

@@ -510,7 +510,7 @@ const EMPTY_PAUSABLE_TAPE = {
   dropped: 0
 };
 
-const appendHistoryTail = <T extends SortableItem>(
+export const appendHistoryTail = <T extends SortableItem>(
   current: T[],
   incoming: T[],
   liveHead: T[],
@@ -541,6 +541,16 @@ const appendHistoryTail = <T extends SortableItem>(
   return cap > 0 ? appended.slice(0, cap) : appended;
 };
 
+export const getLiveHistoryRetentionCap = (subscription: LiveSubscription): number => {
+  switch (subscription.channel) {
+    case "options":
+    case "equities":
+      return LIVE_HISTORY_SOFT_CAP;
+    default:
+      return LIVE_HISTORY_SOFT_CAP;
+  }
+};
+
 export const getLiveFeedStatus = (
   sourceStatus: WsStatus,
   freshestTs: number | null,
@@ -2924,21 +2934,13 @@ const useLiveSession = (
 
         switch (subscription.channel) {
           case "options":
-            mergeOlder(
-              setOptionsHistory,
-              options,
-              subscription.underlying_ids?.length || subscription.option_contract_id ? 0 : LIVE_HISTORY_SOFT_CAP
-            );
+            mergeOlder(setOptionsHistory, options, getLiveHistoryRetentionCap(subscription));
             break;
           case "nbbo":
             mergeOlder(setNbboHistory, nbbo);
             break;
           case "equities":
-            mergeOlder(
-              setEquitiesHistory,
-              equities,
-              subscription.underlying_ids?.length ? 0 : LIVE_HISTORY_SOFT_CAP
-            );
+            mergeOlder(setEquitiesHistory, equities, getLiveHistoryRetentionCap(subscription));
             break;
           case "equity-quotes":
             break;