diff --git a/Darling/Darling.Tests/DarlingMcpAgToolsTests.cs b/Darling/Darling.Tests/DarlingMcpAgToolsTests.cs
index 683ad61692..71629b769a 100644
--- a/Darling/Darling.Tests/DarlingMcpAgToolsTests.cs
+++ b/Darling/Darling.Tests/DarlingMcpAgToolsTests.cs
@@ -113,6 +113,56 @@ public void Instructions_DocumentTheAgTool()
         Assert.Contains("get_ag_health", DarlingMcpInstructions.Text, StringComparison.Ordinal);
         Assert.Contains("Availability Group", DarlingMcpInstructions.Text, StringComparison.Ordinal);
     }
+
+    /// <summary>
+    /// #3653 A15/A16: the description says the two things the reader's own doc comment warns about, because a
+    /// caller reads the description and never the reader. <see cref="DarlingAgReader"/>'s summary carries two
+    /// bolded traps — <b>Latest collection per server</b> (the collectors write NO row for a server with no AGs,
+    /// so a dropped AG lingers as its last non-empty snapshot and the group's <c>collection_time</c> is the only
+    /// tell) and <b>What the badge deliberately does NOT band</b> (every severity restates a DMV state or health
+    /// string; lag and queue depth are raw magnitudes, so a badly lagging asynchronous secondary carries a healthy
+    /// severity) — and the description used to say neither. #3696 put both sentences on it, plus the trap inside
+    /// the second (the DMV reports 0 lag while data movement is suspended, so lag is read with
+    /// <c>is_suspended</c>). Nothing pinned them, and a description that loses a sentence fails nothing: the
+    /// reader's comment goes on being right in a file no agent opens.
+    ///
+    /// <para>Anchored on the reader's own paragraph headers first, so the pin fails with "re-anchor" if the
+    /// reader stops documenting a trap rather than passing against prose that no longer exists; then on the
+    /// description and the instructions paragraph — the two texts an agent reads before calling — for each
+    /// trap's mechanism, consequence and the field that tells it apart. Phrase matching rather than a
+    /// paraphrase test, because these are the exact words a reader would search for.</para>
+    /// </summary>
+    [Fact]
+    public void Description_SurfacesTheReadersTwoDocumentedTraps()
+    {
+        var reader = RepoFile.ReadRepoFile("Darling", "PerformanceMonitor.Darling.Service", "Mcp", "DarlingAgReader.cs");
+        Assert.Contains("<b>Latest collection per server.</b>", reader, StringComparison.Ordinal);
+        Assert.Contains("<b>What the badge deliberately does NOT band: lag and queue depth.</b>", reader, StringComparison.Ordinal);
+
+        var description = ToolMethods()
+            .Single(m => m.GetCustomAttribute<McpServerToolAttribute>()!.Name == "get_ag_health")
+            .GetCustomAttribute<DescriptionAttribute>()!.Description;
+
+        /* Trap one, the stale snapshot: mechanism, consequence, tell. */
+        Assert.Contains("NO row for a server with no AGs", description, StringComparison.Ordinal);
+        Assert.Contains("last non-empty snapshot", description, StringComparison.Ordinal);
+        Assert.Contains("collection_time", description, StringComparison.Ordinal);
+
+        /* Trap two, the un-banded magnitudes: the negative on the word a caller would look for, the fields to
+           read instead, and the DMV's 0-while-suspended inside it. */
+        Assert.Contains("lag and queue depth are NOT banded", description, StringComparison.Ordinal);
+        Assert.Contains("secondary_lag_seconds", description, StringComparison.Ordinal);
+        Assert.Contains("is_suspended", description, StringComparison.Ordinal);
+        Assert.Contains("0 lag while data movement is suspended", description, StringComparison.Ordinal);
+
+        /* The instructions' AG paragraph is the other text an agent reads first; it carries the same two traps
+           in its own words, and the perspective trap (LOCAL-replica-only columns) it always had. */
+        var instructions = DarlingMcpInstructions.Text;
+        Assert.Contains("lag and queue depth are NOT banded", instructions, StringComparison.Ordinal);
+        Assert.Contains("the DMV reports lag as 0 (not null) while data movement is suspended", instructions, StringComparison.Ordinal);
+        Assert.Contains("keeps returning its last non-empty snapshot", instructions, StringComparison.Ordinal);
+        Assert.Contains("populated only for the LOCAL replica", instructions, StringComparison.Ordinal);
+    }
 }
 
 /// <summary>
diff --git a/Darling/Darling.Tests/DarlingMcpTrendToolsTests.cs b/Darling/Darling.Tests/DarlingMcpTrendToolsTests.cs
index 3ea6fec2f2..4758c3e5aa 100644
--- a/Darling/Darling.Tests/DarlingMcpTrendToolsTests.cs
+++ b/Darling/Darling.Tests/DarlingMcpTrendToolsTests.cs
@@ -18,6 +18,7 @@
 using Npgsql;
 using PerformanceMonitor.Collectors;
 using PerformanceMonitor.Common;
+using PerformanceMonitor.Darling.Service;
 using PerformanceMonitor.Darling.Service.Mcp;
 using PerformanceMonitor.Darling.Storage;
 using PerformanceMonitor.Darling.Viewer;
@@ -117,6 +118,47 @@ public void MemoryTrend_Description_PromisesTheJoinedGrantSeries_AndNamesTheNull
         Assert.Contains("get_memory_grants", description, StringComparison.Ordinal);
     }
 
+    /// <summary>
+    /// #3653 A15/A16: the web catalogue's line for get_query_duration_trend said "percentiles". The payload has
+    /// never carried one — <c>SerializeTrend</c>, the helper the duration trio shares, publishes
+    /// <c>elapsed_ms_per_second</c> and <c>executions_per_second</c> per point, a rate over the collection's
+    /// stored interval on the raw route and over the bucket width on the hourly one — and the tool's own
+    /// description has said so since #3541 A12. The catalogue (<see cref="DarlingWebEndpoints.CatalogDescriptors"/>)
+    /// is what the web client's view composer and the reads listing show a human choosing a read, so it was
+    /// the one place a wrong word about this read was still standing. #3696 corrected the line; this pins the
+    /// correction against BOTH ends so they cannot drift apart again: the line names the two rates the
+    /// serializer publishes, the serializer still publishes exactly those, and across the whole catalogue the
+    /// word "percentile" appears only negated — no read here computes one. A read that genuinely returns a
+    /// percentile (none does today) would add itself beside this sentence rather than fall through it.
+    /// </summary>
+    [Fact]
+    public void QueryDurationTrend_CatalogueLine_NamesTheRatesThePayloadCarries_NotPercentiles()
+    {
+        var line = DarlingWebEndpoints.CatalogDescriptors["get_query_duration_trend"].Description;
+        Assert.Contains("ms/sec", line, StringComparison.Ordinal);
+        Assert.Contains("executions/sec", line, StringComparison.Ordinal);
+        Assert.Contains("not percentiles", line, StringComparison.Ordinal);
+
+        /* The payload side: the shared serializer's point projection, and no percentile of anything in it. */
+        var source = Lf(RepoFile.ReadRepoFile("Darling", "PerformanceMonitor.Darling.Service", "Mcp", "DarlingMcpTrendTools.cs"));
+        var at = source.IndexOf("private static string SerializeTrend(", StringComparison.Ordinal);
+        Assert.True(at > 0, "SerializeTrend moved — re-anchor this pin");
+        var end = source.IndexOf("\n    }\n", at, StringComparison.Ordinal);
+        var body = source[at..end];
+        Assert.Contains("elapsed_ms_per_second = p.Value", body, StringComparison.Ordinal);
+        Assert.Contains("executions_per_second = p.ExecutionsPerSecond", body, StringComparison.Ordinal);
+        Assert.DoesNotContain("percentile", body, StringComparison.OrdinalIgnoreCase);
+
+        /* And the whole catalogue: "percentile" only ever as a negation. */
+        var claims = DarlingWebEndpoints.CatalogDescriptors
+            .Where(kv => System.Text.RegularExpressions.Regex.IsMatch(kv.Value.Description, @"(?<!not )percentiles?", System.Text.RegularExpressions.RegexOptions.IgnoreCase))
+            .Select(kv => kv.Key)
+            .OrderBy(k => k, StringComparer.Ordinal)
+            .ToArray();
+        Assert.True(claims.Length == 0,
+            "catalogue line(s) claim a percentile no read computes: " + string.Join(", ", claims));
+    }
+
     [Fact]
     public void MemoryTrendSql_WindowedBothSides_CastsNumericToDouble()
     {
diff --git a/Darling/Darling.Tests/ServerPageTabsTests.cs b/Darling/Darling.Tests/ServerPageTabsTests.cs
index cab1466fa7..2c2f8395fd 100644
--- a/Darling/Darling.Tests/ServerPageTabsTests.cs
+++ b/Darling/Darling.Tests/ServerPageTabsTests.cs
@@ -440,6 +440,73 @@ public void TheQueryTrendDrillDown_ReadsTheWindowFloorOffItsOwnKey()
         Assert.DoesNotContain("trend.data.truncated", body, StringComparison.Ordinal);
     }
 
+    /// <summary>
+    /// The latest-snapshot reads are read by their stamp's one spelling. #3637 made <c>captured_at</c> the
+    /// census's word for "when this snapshot was taken" and <see cref="McpLatestSnapshotStampTests"/> holds
+    /// every latest read to it; four of them (<c>get_database_sizes</c>, <c>get_running_jobs</c>,
+    /// <c>get_server_properties</c>, <c>get_session_stats</c>) had stamped themselves as <c>collection_time</c>
+    /// before that vocabulary existed, and this page's Sessions tile read the old key — the one consumer outside
+    /// that census's boundary, and the reason the four sat in a named allowance instead of the roster (#3653
+    /// A15/A16). #3697 renamed the payloads on both SKUs and moved the tile. Nothing pinned the tile, and a key
+    /// drifting back fails silently: an absent key renders as the empty dash, the tile still draws, and the
+    /// snapshot's age — the one number that says whether a Stamped read is stale — quietly stops appearing.
+    ///
+    /// <para>Derived, not listed. Every read the stamp census rosters as Stamped or SearchBound publishes its
+    /// stamp ONCE at the top as <c>captured_at</c> and nothing under <c>collection_time</c> anywhere in its
+    /// payload (the census's negative sweep refuses the top-level key, and none of those tools projects the word
+    /// into a row either), so ANY descriptor this page binds to one of those reads that names
+    /// <c>collection_time</c> is a dead read — whether a stat tile over the top-level object or a table column
+    /// over its rows. Windowed reads are excluded on purpose: their <c>grants[]</c> rows carry a per-row
+    /// <c>collection_time</c> that IS a series column. The positive half is the one tile the item named: it must
+    /// show the stamp under the new word, so the pin cannot pass by the tile being deleted.</para>
+    /// </summary>
+    [Fact]
+    public void TheStampedReads_AreReadByTheirStamp_NeverTheRetiredKey()
+    {
+        var js = ServerTabsJs;
+
+        var stamped = McpLatestSnapshotStampTests.LatestTools
+            .Where(t => t.Shape is McpLatestSnapshotStampTests.Shape.Stamped or McpLatestSnapshotStampTests.Shape.SearchBound)
+            .Select(t => t.ToolName)
+            .ToHashSet(StringComparer.Ordinal);
+        Assert.True(stamped.IsSupersetOf(["get_database_sizes", "get_running_jobs", "get_server_properties", "get_session_stats"]),
+            "the four reads this pin was written for have left the stamp roster — re-anchor before editing");
+
+        var arrays = DescriptorArraysIn(js);
+        var problems = new List<string>();
+        var examined = new List<string>();
+
+        foreach (var (read, arrayNames) in DescriptorArraysBoundIn(js))
+        {
+            if (!stamped.Contains(read)) continue;
+
+            foreach (var name in arrayNames)
+            {
+                Assert.True(arrays.TryGetValue(name, out var descriptors),
+                    $"{name}, bound to {read}, is not a top-level const array in server-tabs.js — the parser below needs re-anchoring");
+                examined.Add($"{read}/{name}");
+
+                if (Regex.IsMatch(descriptors, @"key:\s*""collection_time"""))
+                {
+                    problems.Add($"{read} is read through {name}, which names collection_time — a key no Stamped read publishes; its stamp is captured_at");
+                }
+            }
+        }
+
+        /* The four named reads must all have been reached, or the parser has silently stopped seeing the panels
+           and every assertion above passed on nothing. */
+        foreach (var read in new[] { "get_database_sizes", "get_running_jobs", "get_server_properties", "get_session_stats" })
+        {
+            Assert.Contains(examined, e => e.StartsWith(read + "/", StringComparison.Ordinal));
+        }
+
+        Assert.True(problems.Count == 0, string.Join("; ", problems));
+
+        /* The positive half: the Sessions tile shows the stamp, under the word the census uses, as an age. */
+        Assert.True(arrays.TryGetValue("SESSION_STATS", out var sessionStats), "SESSION_STATS moved — re-anchor this pin");
+        Assert.Matches(@"\{ key: ""captured_at"", label: ""Collected"", format: ""reltime""", sessionStats);
+    }
+
     /// <summary>
     /// Every viz a descriptor names is in the shipped vocabulary. The four kinds are the whole registry; a fifth
     /// would have to be added to panels.js's VIZ, to <c>KnownVizList</c> (or the composer could not offer it), to
@@ -1096,4 +1163,50 @@ private static HashSet<string> ReadNamesIn(string js) =>
             yield return (m.Groups[1].Value, keys);
         }
     }
+
+    /// <summary>Every top-level <c>const NAME = [ ... ];</c> descriptor array in the module, by name. These are
+    /// the column and stat vocabularies the panels bind to (<c>*_COLUMNS</c>, <c>*_STATS</c>, <c>*_SERIES</c>);
+    /// the body is the text between the brackets, comments included.</summary>
+    private static Dictionary<string, string> DescriptorArraysIn(string js) =>
+        Regex.Matches(js, @"^const ([A-Z][A-Z0-9_]+) = \[(.*?)^\];", RegexOptions.Multiline | RegexOptions.Singleline)
+            .ToDictionary(m => m.Groups[1].Value, m => m.Groups[2].Value, StringComparer.Ordinal);
+
+    /// <summary>
+    /// The (read, descriptor-array names) pairs the module's panel helpers bind: <c>stat("T", "read", {...},
+    /// NAME, ...)</c>, <c>table("T", "read", {...}, "rows", NAME, ...)</c> and <c>fanout("read", {...}, [{ stats:
+    /// NAME }, { columns: NAME }])</c>. Each call is sliced by bracket balance rather than by regex because a
+    /// fanout's spec array nests objects inside an array inside the call; the read is the first read-shaped
+    /// literal in the call, and the arrays are every <c>*_COLUMNS</c> / <c>*_STATS</c> token in it. The
+    /// helpers' own definitions (<c>function stat(title, read, ...)</c>) carry no literal and are skipped.
+    /// String literals are NOT skipped: a bracket inside a title or an empty-state sentence is balanced in
+    /// practice, and a lone one would end the slice early — a silent miss on the arrays after it, never a false
+    /// alarm, which the caller's reach check on its named reads bounds.
+    /// </summary>
+    private static IEnumerable<(string Read, string[] Arrays)> DescriptorArraysBoundIn(string js)
+    {
+        foreach (Match open in Regex.Matches(js, @"(?<![A-Za-z0-9_])(?:stat|table|fanout)\("))
+        {
+            var depth = 1;
+            var i = open.Index + open.Length;
+            while (depth > 0 && i < js.Length)
+            {
+                switch (js[i])
+                {
+                    case '(' or '[' or '{': depth++; break;
+                    case ')' or ']' or '}': depth--; break;
+                }
+                i++;
+            }
+
+            var call = js[open.Index..i];
+            var read = Regex.Match(call, "\"(get_[a-z0-9_]+|audit_config)\"");
+            if (!read.Success) continue;
+
+            var arrays = Regex.Matches(call, @"\b([A-Z][A-Z0-9_]*_(?:COLUMNS|STATS))\b")
+                .Select(m => m.Groups[1].Value)
+                .Distinct(StringComparer.Ordinal)
+                .ToArray();
+            yield return (read.Groups[1].Value, arrays);
+        }
+    }
 }