feat(webapp): incremental live tail for the run trace view

Live runs in the run trace view now update incrementally. Instead of
reloading the whole trace on every update, the page fetches only the
rows written since its last read and merges them into the tree it
already has, so large live traces keep updating without re-downloading
everything. Progressive trace loading now always uses this live tail.

Mono-RevId: 8cc2387d2af102abc3a17d23b3ad1e0a2846aca5

Author: Mariefay

.env.schema

@@ -41,6 +41,8 @@ RUN_REPLICATION_CLICKHOUSE_URL=${CLICKHOUSE_URL}
 RUN_REPLICATION_ENABLED=1
 # LOGS_SEARCH_PROJECTOR_ENABLED=1
 # LOGS_SEARCH_PROJECTOR_PREVIEW_ENABLED=1
+# Live tail for progressive trace loading; "1" turns it on, anything else turns it off.
+# INCREMENTAL_LIVE_TAIL_ENABLED=0
 # Store task run spans/traces in ClickHouse so the dashboard trace view is
 # populated in local dev. The local stack is ClickHouse-backed (see above), so
 # leaving this unset falls back to the "postgres" store and dev run traces show

apps/webapp/app/env.server.ts

@@ -1116,6 +1116,8 @@ const EnvironmentSchema = z
     EVENT_LOOP_UTILIZATION_MONITOR_ENABLED: z.string().default("1"),
     MAXIMUM_LIVE_RELOADING_EVENTS: z.coerce.number().int().default(1000),
     MAXIMUM_TRACE_SUMMARY_VIEW_COUNT: z.coerce.number().int().default(25_000),
+    // Live tail for progressive trace loading; "1" on, anything else off.
+    INCREMENTAL_LIVE_TAIL_ENABLED: z.string().default("0"),
     MAXIMUM_TRACE_DETAILED_SUMMARY_VIEW_COUNT: z.coerce.number().int().default(10_000),
     // Emergency circuit breaker: when set, clamps the trace summary and detailed
     // summary span limits on both event store paths to this value. Unset = disabled.

apps/webapp/app/hooks/liveTail.ts

@@ -0,0 +1,27 @@
+// React-free live tail helpers.
+
+// How far back each tail re-reads for late-visible rows; a full sweep runs periodically.
+export const LIVE_TAIL_OVERLAP_MS = 5_000;
+export const LIVE_TAIL_SWEEP_OVERLAP_MS = 30_000;
+export const LIVE_TAIL_SWEEP_INTERVAL_MS = 20_000;
+
+export function tailOverlapMs(nowMs: number, lastSweepAtMs: number): number {
+  return nowMs - lastSweepAtMs >= LIVE_TAIL_SWEEP_INTERVAL_MS
+    ? LIVE_TAIL_SWEEP_OVERLAP_MS
+    : LIVE_TAIL_OVERLAP_MS;
+}
+
+// Min spacing between tail reads, growing with trace size.
+export function tailMinIntervalMs(loadedSpans: number): number {
+  if (loadedSpans >= 100_000) return 15_000;
+  if (loadedSpans >= 50_000) return 5_000;
+  if (loadedSpans >= 5_000) return 2_000;
+  return 0;
+}
+
+// Tail only when the server enabled it for a progressive payload.
+export function resolveLiveTailEnabled(
+  progressive: { liveTailEnabled?: boolean } | null | undefined
+): boolean {
+  return progressive != null && progressive.liveTailEnabled === true;
+}