ranges:dates: a point on a connection of its own; --missing still dates every group

Sixteen groups never got through on one connection (a reply timed out
after 2 minutes); now a timed-out point is skipped and logged, the
group goes on, and stops after 3 failures. estimate() ignored --missing's
filter: it dated 0 groups on the second run.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/services/group_dates.ts

@@ -90,33 +90,49 @@ export function sampleCount(
  * server's span.
  */
 export async function sampleGroup(
-  client: XoverClient,
+  use: <T>(work: (client: XoverClient) => Promise<T>) => Promise<T>,
   name: string,
-  options: { every: number; size: number },
+  options: { every: number; size: number; maxFailures?: number },
   now = new Date()
-): Promise<{ samples: DateSample[]; low: number; high: number; commands: number }> {
-  const info = await client.group(name)
+): Promise<{
+  samples: DateSample[]
+  low: number
+  high: number
+  commands: number
+  failed: string[]
+}> {
+  const info = await use((client) => client.group(name))
   const samples: DateSample[] = []
+  const failed: string[] = []
   let commands = 1
+  // Each point on a connection of its own (GROUP again): a reply that times out (Eweka stalls some requests for
+  // minutes; 16 groups never got through on one connection) costs that point, not the group.
   for (const point of samplePoints(
     info.low,
     info.high,
     sampleCount(info.low, info.high, options.every),
     options.size
   )) {
-    commands++
-    let date = medianDate(
-      await client.xover(point, Math.min(point + options.size - 1, info.high)),
-      now
-    )
-    if (!date) {
-      commands++
-      date = medianDate(
-        await client.xover(point, Math.min(point + options.size * 32 - 1, info.high)),
-        now
-      )
+    if (failed.length >= (options.maxFailures ?? 3)) break
+    try {
+      const date = await use(async (client) => {
+        await client.group(name)
+        commands += 2
+        const slice = medianDate(
+          await client.xover(point, Math.min(point + options.size - 1, info.high)),
+          now
+        )
+        if (slice) return slice
+        commands++
+        return medianDate(
+          await client.xover(point, Math.min(point + options.size * 32 - 1, info.high)),
+          now
+        )
+      })
+      if (date) samples.push({ article: point, postedAt: date })
+    } catch (error: any) {
+      failed.push(`${point}: ${error.message}`)
     }
-    if (date) samples.push({ article: point, postedAt: date })
   }
-  return { samples: monotone(samples), low: info.low, high: info.high, commands }
+  return { samples: monotone(samples), low: info.low, high: info.high, commands, failed }
 }