Name the type that actually owns the member a build break rejected

build-failed is the largest attempt kind in the pipeline at 234 of 1311
attempts, and in 34 of 65 build-failed runs the identical file+error recurs
across attempts - the agent re-submits the same mistake.

Restricting the corpus to lines that really say ": error " (rather than
counting occurrences of a code, which puts MAUI's own MSB4011 and NETSDK1206
build warnings on top) leaves 449 real errors, led by CS1061, CS0103 and
CS0117. The recurring ones are all the same mistake: a real API reached for
under a wrong name - SafeAreaEdges.Container, SafeAreaEdges.SoftInput,
Size.Request, Shell.TitleColor.

Get-ReplicationMissingIdentifierEvidence extracted only the member from
"'SafeAreaEdges' does not contain a definition for 'Container'" and searched
for it. 'Container' is a whole word in 151 C# files under src/, so reporting
two of them spends the agent's attention to say nothing. The diagnostic names
the type too, and that was the half being discarded.

For CS0117 and CS1061 it now asks which type actually exposes the member,
ranks by frequency and excludes the type that just rejected it - answering
"use SafeAreaEdges.SoftInput" to "SafeAreaEdges does not contain SoftInput"
is the one reply guaranteed to be wrong, and that string does occur in source.

Verified against the four real corpus failures: Container and SoftInput both
resolve to SafeAreaRegions, Request to SizeRequest, all as the top hit; an
invented member yields no owner line and falls through to the existing "appears
in no C# source file" answer.

Suite 1892/0.

Author: Copilot CI

.github/scripts/Replicate-Issue.Tests.ps1

@@ -11622,6 +11622,53 @@ Describe 'An invented API is named as invented' {
         $evidence | Should -Match 'do not use it again'
     }
 
+    It 'names the type that really owns the member' {
+        # Measured: the bare member behind "'SafeAreaEdges' does not contain a
+        # definition for 'Container'" matches 151 C# files, so reporting two of
+        # them is noise. SafeAreaRegions.Container is the answer, and it is the
+        # top hit by a wide margin. Run 15092216-class build breaks repeated the
+        # identical diagnostic across attempts; 34 of 65 build-failed runs did.
+        $evidence = Get-ReplicationMissingIdentifierEvidence `
+            -Diagnostics ("error CS0117: 'SafeAreaEdges' does not contain a " +
+                "definition for 'Container'") `
+            -RepositoryRoot $script:apiRepoRoot
+        $evidence | Should -Match "'Container' is not a member of 'SafeAreaEdges'"
+        $evidence | Should -Match 'SafeAreaRegions'
+    }
+
+    It 'ranks the owner that is actually used most first' {
+        $evidence = Get-ReplicationMissingIdentifierEvidence `
+            -Diagnostics "error CS1061: 'Size' does not contain a definition for 'Request'" `
+            -RepositoryRoot $script:apiRepoRoot
+        $owners = [regex]::Match($evidence, "'Request' is used on (?<list>[^.]+)\.")
+        $owners.Success | Should -BeTrue
+        $owners.Groups['list'].Value | Should -Match '^SizeRequest'
+    }
+
+    It 'never suggests the type that just rejected the member' {
+        # Answering "use SafeAreaEdges.SoftInput" to "SafeAreaEdges does not
+        # contain SoftInput" is the one reply guaranteed to be wrong, and the
+        # name does occur on that type in source.
+        $evidence = Get-ReplicationMissingIdentifierEvidence `
+            -Diagnostics ("error CS1061: 'SafeAreaEdges' does not contain a " +
+                "definition for 'SoftInput'") `
+            -RepositoryRoot $script:apiRepoRoot
+        $owners = [regex]::Match($evidence, "'SoftInput' is used on (?<list>[^.]+)\.")
+        $owners.Success | Should -BeTrue
+        $owners.Groups['list'].Value | Should -Not -Match 'SafeAreaEdges'
+    }
+
+    It 'claims no owner for a member that exists nowhere' {
+        # Silence is the honest answer here, and the generic search still says
+        # the name is absent.
+        $evidence = Get-ReplicationMissingIdentifierEvidence `
+            -Diagnostics ("error CS1061: 'Picker' does not contain a definition " +
+                "for 'TotallyMadeUpZZZ'") `
+            -RepositoryRoot $script:apiRepoRoot
+        $evidence | Should -Not -Match 'is used on'
+        $evidence | Should -Match 'appears in no C# source file under src/'
+    }
+
     It 'points at the file when the identifier is real' {
         # ItemsSource is a real MAUI member, so the honest answer is where to
         # read it, not that it is absent.

.github/scripts/Replicate-Issue.ps1

@@ -1115,6 +1115,56 @@ function Get-ReplicationMissingIdentifierEvidence {
         return ''
     }
 
+    # CS0117 and CS1061 name *both* the type and the member, and the member
+    # alone is the less useful half. Measured on the cached corpus, searching
+    # for the bare member behind "'SafeAreaEdges' does not contain a definition
+    # for 'Container'" matches 151 C# files and reports two of them, which is
+    # noise. Asking instead which type actually exposes that member answers it
+    # outright: SafeAreaRegions.Container, 21 uses, top hit. The same lookup
+    # resolves SoftInput to SafeAreaRegions and Request to SizeRequest - in
+    # each case the author had reached for a property name or a Xamarin.Forms
+    # type as though it were the enum.
+    $ownerLines = [Collections.Generic.List[string]]::new()
+    $ownerPattern = "'(?<type>[A-Za-z_][A-Za-z0-9_]*)' does not contain a definition for " +
+        "'(?<name>[A-Za-z_][A-Za-z0-9_]*)'"
+    $seenMembers = [Collections.Generic.HashSet[string]]::new()
+    foreach ($match in [regex]::Matches($Diagnostics, $ownerPattern)) {
+        if ($ownerLines.Count -ge $MaximumIdentifiers) { break }
+        $wrongType = $match.Groups['type'].Value
+        $member = $match.Groups['name'].Value
+        if (-not $seenMembers.Add($member)) { continue }
+
+        $owners = @()
+        try {
+            # -I skips binary files: the aotprofile blobs otherwise contribute a
+            # "Binary file ... matches" line that would be reported as a type.
+            $uses = & git -C $RepositoryRoot grep -hoPI `
+                "(?<![A-Za-z0-9_])[A-Z][A-Za-z0-9_]*\.$member(?![A-Za-z0-9_])" `
+                -- 'src/Controls/src' 'src/Core/src' 2>$null
+            $owners = @($uses |
+                ForEach-Object { ($_ -split '\.')[0] } |
+                Where-Object { $_ -and $_ -ne $wrongType } |
+                Group-Object |
+                Sort-Object -Property @{ Expression = { $_.Count } ; Descending = $true }, Name |
+                Select-Object -First 2)
+        } catch {
+            # A search that could not run says nothing, and inventing an owner
+            # here would be the confident wrong answer this phase exists to stop.
+            continue
+        }
+
+        if ($owners.Count -gt 0) {
+            $described = @($owners | ForEach-Object {
+                $unit = if ($_.Count -eq 1) { 'use' } else { 'uses' }
+                "$($_.Name) ($($_.Count) $unit)"
+            }) -join ', '
+            $ownerLines.Add(
+                "'$member' is not a member of '$wrongType'. In this repository " +
+                "'$member' is used on $described. Read that declaration and use " +
+                "the type that really owns the member instead of renaming it.") | Out-Null
+        }
+    }
+
     $names = [Collections.Generic.List[string]]::new()
     foreach ($pattern in @(
             "does not contain a definition for '(?<name>[A-Za-z_][A-Za-z0-9_]*)'",
@@ -1127,7 +1177,7 @@ function Get-ReplicationMissingIdentifierEvidence {
             }
         }
     }
-    if ($names.Count -eq 0) {
+    if ($names.Count -eq 0 -and $ownerLines.Count -eq 0) {
         return ''
     }
 
@@ -1161,11 +1211,13 @@ function Get-ReplicationMissingIdentifierEvidence {
         }
     }
 
-    if ($lines.Count -eq 0) {
+    if ($lines.Count -eq 0 -and $ownerLines.Count -eq 0) {
         return ''
     }
 
-    return ($lines -join ' ')
+    # The owner evidence goes first: it names the type to use, where the
+    # generic search only says whether a name exists somewhere.
+    return ((@($ownerLines) + @($lines)) -join ' ')
 }
 
 function Get-ReplicationCompilerDiagnostics {