more testing

otel-ui/src/contexts/ObservabilityContextProvider.tsx

@@ -2,7 +2,7 @@
 
 import { useState, useEffect, useRef, useMemo, useCallback, type ReactNode } from "react"
 import { useLocation } from "wouter"
-import { tabForPath, pathForTab } from "../lib/routes"
+import { tabForPath, pathForTab, splitPath, joinPath } from "../lib/routes"
 import type {
   MetricData,
   OtelHistoryMessage,
@@ -150,11 +150,31 @@ export function ObservabilityProvider({
   const setActiveTabWithRoute = useCallback(
     (tab: string) => {
       setActiveTab(tab)
+      // Already inside this tab (possibly on a deep link): keep the sub-route.
+      if (tabForPath(window.location.pathname) === tab) return
       const path = pathForTab(tab)
-      if (path && path !== window.location.pathname) navigate(path)
+      if (path) navigate(path)
     },
     [navigate],
   )
+
+  // Trace selection <-> /traces/<traceId>[/<spanId>]. The URL is adopted when
+  // it names a trace; a bare /traces never clears the selection, because other
+  // views set the trace first and switch tabs second.
+  useEffect(() => {
+    const { base, rest } = splitPath(location)
+    if (base !== "/traces" || !rest[0]) return
+    setActiveTraceId((prev) => (prev === rest[0] ? prev : rest[0]))
+    setActiveSpanId((prev) => (prev === (rest[1] ?? null) ? prev : (rest[1] ?? null)))
+    // eslint-disable-next-line react-hooks/exhaustive-deps -- only follow URL changes
+  }, [location])
+
+  useEffect(() => {
+    if (activeTab !== "tab1" || !activeTraceId) return
+    const target = joinPath("/traces", activeSpanId ? [activeTraceId, activeSpanId] : [activeTraceId])
+    if (target !== window.location.pathname) navigate(target)
+    // eslint-disable-next-line react-hooks/exhaustive-deps -- location is read imperatively
+  }, [activeTab, activeTraceId, activeSpanId, navigate])
   const [filtersExpanded, setFiltersExpanded] = useState<boolean>(false)
   // Trace ids we already have spans for, so selecting a trace that fell
   // outside the initial history window (or arrived before this session