From 6b63e9a5f3efbfc5bd1bf9e0bf6cc90e7df84c66 Mon Sep 17 00:00:00 2001
From: Paul Trowbridge <paul@hptrow.me>
Date: Fri, 18 Sep 2026 08:38:04 -0400
Subject: [PATCH] Say how many rows the load is waiting on
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X-Row-Count arrives with the headers, long before the body has been read, so
the overlay can name the wait instead of saying "Loading…" over a grey
screen for fifteen seconds. On this data the row count *is* the wait -- the
bytes are quick and the rows are not -- so it is the number worth showing
beside the transfer bar, which only ever measured the fast part.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 ui/src/views/Forecast.jsx | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/ui/src/views/Forecast.jsx b/ui/src/views/Forecast.jsx
index 3f4fb3e..c5fc360 100644
--- a/ui/src/views/Forecast.jsx
+++ b/ui/src/views/Forecast.jsx
@@ -57,6 +57,11 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   const [loading,      setLoading]      = useState(false)
   const [largeDataset, setLargeDataset] = useState(false)
   const [loadProgress, setLoadProgress] = useState(null)  // { received, total }
+  // Rows the server says it is sending, from X-Row-Count. Known as soon as the
+  // headers land, well before the body has been read, so the wait can say what
+  // it is waiting for -- on this data the row count is the wait (see CLAUDE.md,
+  // "Load time is dominated by row count").
+  const [loadRows,     setLoadRows]     = useState(null)
   const [msg,          setMsg]          = useState(null)
 
   // layouts
@@ -619,6 +624,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
     if (!r.ok) { const { error } = await r.json(); throw new Error(error || 'Failed to load data') }
     const rowCount = parseInt(r.headers.get('X-Row-Count') || '0')
     const total    = parseInt(r.headers.get('Content-Length') || '0') || null
+    setLoadRows(rowCount || null)
     const reader   = r.body.getReader()
     const chunks   = []
     let received   = 0
@@ -655,6 +661,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
     setLoading(true)
     setLargeDataset(false)
     setLoadProgress(null)
+    setLoadRows(null)
     setSlices([])
     setExpandDepth(null)
     adoptSplit([], 0)
@@ -1820,7 +1827,9 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
         <div className="relative flex-1 min-w-0 min-h-0">
           {loading && (
             <div className="absolute inset-0 flex flex-col items-center justify-center bg-gray-50 z-10 gap-2">
-              <span className="text-sm text-gray-400">Loading…</span>
+              <span className="text-sm text-gray-400">
+                {loadRows ? `Loading ${loadRows.toLocaleString()} rows…` : 'Loading…'}
+              </span>
               {loadProgress && (
                 <>
                   <span className="text-xs text-gray-400 font-mono">