get_pg_extensions/get_pg_write_stats/get_pg_server_config(_changes) move reading guidance off tools/list (#3898)

Darling/Darling.Tests/McpToolGuideHeads.PgB.cs

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2026 Erik Darling, Darling Data LLC
+ *
+ * This file is part of the SQL Server Performance Monitor.
+ *
+ * Licensed under the MIT License. See LICENSE file in the project root for full license information.
+ */
+
+using System;
+using PerformanceMonitor.Common;
+using Xunit;
+
+namespace Darling.Tests;
+
+/// <summary>
+/// #3898 D3 head pins for the "pgB" family: <c>get_pg_extensions</c>, <c>get_pg_write_stats</c>,
+/// <c>get_pg_server_config</c> and <c>get_pg_server_config_changes</c>, all declared on
+/// <c>DarlingMcpPgServerStateTools</c> (Darling only - none of the four has a Lite twin). Follows the pattern in
+/// <see cref="McpToolGuideHeadsPgATests"/>.
+/// </summary>
+public sealed class McpToolGuideHeadsPgBTests
+{
+    private static readonly string[] ConvertedTools =
+    [
+        "get_pg_extensions",
+        "get_pg_write_stats",
+        "get_pg_server_config",
+        "get_pg_server_config_changes",
+    ];
+
+    /// <summary>The per-tool guardrail phrase each head must state.</summary>
+    private static readonly (string Tool, string Fact)[] HeadFacts =
+    [
+        ("get_pg_extensions", "Per-DATABASE, not per-cluster"),
+        ("get_pg_extensions", "truncated withholds state totals"),
+        ("get_pg_extensions", "installed rows like plpgsql are cut first"),
+        ("get_pg_extensions", "Read install_census for the complete picture"),
+        ("get_pg_write_stats", "as ONE row, not a series"),
+        ("get_pg_write_stats", "checkpoints_requested is the signal"),
+        ("get_pg_write_stats", "buffers_backend/buffers_backend_fsync are NULL on PostgreSQL 17+"),
+        ("get_pg_write_stats", "wal_* columns are NULL on Aurora"),
+        ("get_pg_write_stats", "A restart inside the window nulls checkpoints_requested"),
+        ("get_pg_server_config", "LATEST IS A TIME"),
+        ("get_pg_server_config", "captured_at is when it was taken"),
+        ("get_pg_server_config", "pending_restart=true means the file and server disagree"),
+        ("get_pg_server_config", "non_default_count is the snapshot's, not the page's"),
+        ("get_pg_server_config", "database_overrides (present only if any exist)"),
+        ("get_pg_server_config_changes", "NOT reported as a change"),
+        ("get_pg_server_config_changes", "Session-scoped rows are excluded"),
+        ("get_pg_server_config_changes", "change_kind: changed, set (old_value null) or reset (new_value null)"),
+    ];
+
+    [Fact]
+    public void EveryConvertedHead_CarriesItsGuardrailFact_AndThePointer()
+    {
+        foreach (var tool in ConvertedTools)
+        {
+            var served = McpToolGuideTests.Served(tool);
+            Assert.NotNull(served.Tail);
+            Assert.EndsWith(McpToolGuide.GuidePointer, served.Served, StringComparison.Ordinal);
+            Assert.True(served.Served.Length <= 620, $"{tool}: served head {served.Served.Length} is over the 620 target");
+            Assert.All(served.ParameterDescriptionLengths, p => Assert.True(p.Length <= 200, $"{tool}.{p.Parameter}: {p.Length} > 200"));
+        }
+
+        foreach (var (tool, fact) in HeadFacts)
+        {
+            Assert.Contains(fact, McpToolGuideTests.Served(tool).Served, StringComparison.Ordinal);
+        }
+    }
+
+    /// <summary>Nothing dropped: the parameter-overflow sentences D2 moved off <c>get_pg_server_config</c>'s
+    /// <c>include_defaults</c> and <c>get_pg_extensions</c>' <c>database_name</c> land verbatim in their tool's
+    /// tail rather than disappearing when the parameter itself was trimmed to a guardrail sentence.</summary>
+    [Fact]
+    public void D2ParameterOverflow_LandsInTheTail_NotJustTheGuardrailSentence()
+    {
+        var serverConfig = McpToolGuideTests.Served("get_pg_server_config");
+        Assert.Contains("kept in the non-default view whatever its source", serverConfig.Tail!, StringComparison.Ordinal);
+
+        var extensions = McpToolGuideTests.Served("get_pg_extensions");
+        Assert.Contains("1,632 rows against the 1,000-row maximum", extensions.Tail!, StringComparison.Ordinal);
+    }
+
+    /// <summary>D8: no renames, no consolidation - all four still resolve as the same tool names with the same
+    /// parameters, just a shorter served head and the two over-cap parameters (D2) trimmed to a pointer.</summary>
+    [Fact]
+    public void OverCapParameters_StayAtOrUnder200_AndKeepThePointer()
+    {
+        foreach (var (tool, param) in new[] { ("get_pg_server_config", "include_defaults"), ("get_pg_extensions", "database_name") })
+        {
+            var served = McpToolGuideTests.Served(tool);
+            var p = Assert.Single(served.ParameterDescriptionLengths, x => x.Parameter == param);
+            Assert.True(p.Length <= 200, $"{tool}.{param}: {p.Length} > 200");
+        }
+    }
+}

Darling/Darling.Tests/McpToolsListBudget/DarlingMcpPgServerStateTools.txt

@@ -5,9 +5,9 @@ param get_pg_buffer_usage.hours_back 40
 param get_pg_buffer_usage.limit 35
 param get_pg_buffer_usage.server_name 28
 
-tool get_pg_extensions 1727
+tool get_pg_extensions 498
 param get_pg_extensions.as_of 167
-param get_pg_extensions.database_name 803
+param get_pg_extensions.database_name 196
 param get_pg_extensions.hours_back 78
 param get_pg_extensions.limit 35
 param get_pg_extensions.server_name 28
@@ -18,18 +18,18 @@ param get_pg_lock_stats.hours_back 40
 param get_pg_lock_stats.limit 35
 param get_pg_lock_stats.server_name 28
 
-tool get_pg_server_config 2252
-param get_pg_server_config.include_defaults 249
+tool get_pg_server_config 612
+param get_pg_server_config.include_defaults 164
 param get_pg_server_config.limit 198
 param get_pg_server_config.server_name 28
 
-tool get_pg_server_config_changes 1146
+tool get_pg_server_config_changes 568
 param get_pg_server_config_changes.as_of 167
 param get_pg_server_config_changes.hours_back 52
 param get_pg_server_config_changes.limit 39
 param get_pg_server_config_changes.server_name 28
 
-tool get_pg_write_stats 1509
+tool get_pg_write_stats 598
 param get_pg_write_stats.as_of 167
 param get_pg_write_stats.hours_back 40
 param get_pg_write_stats.server_name 28