Gate live feed staleness and isolate Next dev artifacts

- delay stale status for paused live feeds before surfacing disconnects
- keep `next dev` output separate from production build artifacts
- add coverage for the new live-feed stale threshold

apps/web/app/terminal.test.ts

@@ -185,6 +185,11 @@ describe("live tape pausable helpers", () => {
     expect(getLiveFeedStatus("disconnected", 1000, 500, 1601)).toBe("disconnected");
   });
 
+  it("waits for an additional behind-delay before surfacing stale", () => {
+    expect(getLiveFeedStatus("connected", 1000, 500, 2000, 15_000)).toBe("connected");
+    expect(getLiveFeedStatus("connected", 1000, 500, 16_501, 15_000)).toBe("stale");
+  });
+
   it("keeps visible history even when live status is stale", () => {
     const projected = projectPausableTapeState([makeItem("stale", 7, 1000)], "stale", 2000);
     expect(projected.items.map((item) => item.trace_id)).toEqual(["stale"]);

apps/web/app/terminal.tsx

@@ -72,6 +72,7 @@ const LIVE_HOT_WINDOW_OPTIONS = parseBoundedInt(
 const LIVE_OPTIONS_STALE_MS = 15_000;
 const LIVE_NBBO_STALE_MS = 15_000;
 const LIVE_EQUITIES_STALE_MS = 15_000;
+const LIVE_FEED_BEHIND_DELAY_MS = 15_000;
 const LIVE_EQUITIES_SILENT_WARNING_MS = parseBoundedInt(
   process.env.NEXT_PUBLIC_LIVE_EQUITIES_SILENT_WARNING_MS,
   25_000,
@@ -491,7 +492,8 @@ export const getLiveFeedStatus = (
   sourceStatus: WsStatus,
   freshestTs: number | null,
   thresholdMs: number,
-  now = Date.now()
+  now = Date.now(),
+  behindDelayMs = 0
 ): WsStatus => {
   if (sourceStatus !== "connected") {
     return sourceStatus;
@@ -499,7 +501,14 @@ export const getLiveFeedStatus = (
   if (freshestTs === null) {
     return "connected";
   }
-  return isFreshLiveItem(freshestTs, thresholdMs, now) ? "connected" : "stale";
+
+  const ageMs = now - freshestTs;
+  if (ageMs <= thresholdMs) {
+    return "connected";
+  }
+
+  const behindMs = ageMs - thresholdMs;
+  return behindMs > behindDelayMs ? "stale" : "connected";
 };
 
 type TapeState<T> = {
@@ -945,8 +954,6 @@ export const countActiveFlowFilterGroups = (filters: OptionFlowFilters): number
   return count;
 };
 
-const isFreshLiveItem = (ts: number, thresholdMs: number, now = Date.now()): boolean => now - ts <= thresholdMs;
-
 export const toggleFilterValue = <T extends string>(
   values: T[] | undefined,
   value: T,
@@ -1995,7 +2002,13 @@ const usePausableTapeView = <T extends SortableItem & { seq: number }>(
   }, [config.sourceItems, getItemTs]);
 
   const status = config.enabled
-    ? getLiveFeedStatus(config.sourceStatus, freshestTs, config.freshnessMs, clock)
+    ? getLiveFeedStatus(
+        config.sourceStatus,
+        freshestTs,
+        config.freshnessMs,
+        clock,
+        LIVE_FEED_BEHIND_DELAY_MS
+      )
     : "disconnected";
   const projected = projectPausableTapeState(data.visible, status, config.lastUpdate);
 

apps/web/next.config.mjs

@@ -0,0 +1,16 @@
+import { PHASE_DEVELOPMENT_SERVER } from "next/constants.js";
+
+/**
+ * Keep dev and production build artifacts separate to avoid chunk/runtime
+ * mismatches when `next dev` and `next build` are run in overlapping sessions.
+ *
+ * @param {string} phase
+ * @returns {import("next").NextConfig}
+ */
+export default function nextConfig(phase) {
+  const isDev = phase === PHASE_DEVELOPMENT_SERVER;
+
+  return {
+    distDir: isDev ? ".next-dev" : ".next"
+  };
+}

apps/web/scripts/dev.ts

@@ -1,9 +1,17 @@
+import { rm } from "node:fs/promises";
+
 const run = async () => {
   const port = 3000;
+  const distDir = ".next-dev";
   console.log(`[web] starting Next.js dev server on port ${port}`);
 
   const path = Bun.env.PATH ?? "";
   const cwd = `${import.meta.dir}/..`;
+  const distPath = `${cwd}/${distDir}`;
+
+  // Clear potentially stale dev artifacts from interrupted prior runs.
+  await rm(distPath, { recursive: true, force: true });
+  console.log(`[web] cleared stale Next.js dev artifacts at ${distDir}`);
 
   const child = Bun.spawn(["next", "dev", "-p", String(port)], {
     cwd,

apps/web/tsconfig.json

@@ -21,7 +21,8 @@
     "next-env.d.ts",
     "**/*.ts",
     "**/*.tsx",
-    ".next/types/**/*.ts"
+    ".next/types/**/*.ts",
+    ".next-dev/types/**/*.ts"
   ],
   "exclude": [
     "node_modules",