ci: A" fix-shape validation target (canonical-root respell) in the Windows repro

Run 28776276301 verified: cross-package typealias-sugar variant fires the
identical assertion + frame on Swift 6.3.3 AND 6.4-dev a42409e978ff428
(single-file CLEAN on both) — Option B's 6.4-fixes-it premise is refuted
for this shape. RespellModule is CrashModule with ONLY the two downcasts
spelled through the canonical root (any ISO_32000.…): CLEAN on 6.3.3
validates a one-token-per-site production fix at
PDF.HTML.Context+Rendering.swift:267/:283.

Author: coenttb

.github/repro/cross-package/crash/Package.swift

@@ -23,7 +23,18 @@ let package = Package(
                 .enableUpcomingFeature("InternalImportsByDefault"),
                 .enableUpcomingFeature("MemberImportVisibility"),
             ]
-        )
+        ),
+        .target(
+            name: "RespellModule",
+            dependencies: [
+                .product(name: "BasePDF", package: "base")
+            ],
+            swiftSettings: [
+                .enableUpcomingFeature("ExistentialAny"),
+                .enableUpcomingFeature("InternalImportsByDefault"),
+                .enableUpcomingFeature("MemberImportVisibility"),
+            ]
+        ),
     ],
     swiftLanguageModes: [.v6]
 )

.github/repro/cross-package/crash/Sources/RespellModule/RespellModule.swift

@@ -0,0 +1,95 @@
+// A″ fix-shape validation: IDENTICAL to CrashModule except the two
+// existential downcasts (and only those) are respelled through the
+// CANONICAL namespace root `ISO_32000` instead of the `PDF` typealias.
+// Declarations still extend via the `PDF` alias (declaration parity with
+// production). If this target is CLEAN on Windows 6.3.3 while CrashModule
+// fires, the typealias sugar in the WRITTEN type at the downcast site is
+// the trigger, and the production fix is a one-token respell at
+// PDF.HTML.Context+Rendering.swift:267/:283.
+
+public import BasePDF
+
+extension PDF {
+    public enum HTML {}
+}
+
+extension PDF.HTML {
+    public enum Style {}
+
+    public struct Configuration {
+        public init() {}
+    }
+}
+
+extension PDF.HTML.Style {
+    public enum Context {}
+
+    public protocol Modifier {
+        func apply(to context: inout PDF.Context, configuration: PDF.HTML.Configuration)
+    }
+}
+
+extension PDF.HTML.Style.Context {
+    public protocol Modifier {
+        func apply(to context: inout PDF.HTML.Context)
+    }
+}
+
+extension PDF.HTML {
+    public struct Context {
+        public var pdf: PDF.Context
+        public var configuration: PDF.HTML.Configuration
+
+        public init() {
+            self.pdf = PDF.Context()
+            self.configuration = PDF.HTML.Configuration()
+        }
+
+        public mutating func apply(inlineStyle property: Any) -> Bool {
+            let unwrapped: Any
+            let mirror = Mirror(reflecting: property)
+            if mirror.displayStyle == .optional {
+                guard let first = mirror.children.first else { return false }
+                unwrapped = first.value
+            } else {
+                unwrapped = property
+            }
+
+            var handled = false
+
+            // Canonical-root spelling — the only difference from CrashModule.
+            if let modifier = unwrapped as? any ISO_32000.HTML.Style.Modifier {
+                modifier.apply(to: &pdf, configuration: configuration)
+                handled = true
+            }
+
+            if let htmlModifier = unwrapped as? any ISO_32000.HTML.Style.Context.Modifier {
+                htmlModifier.apply(to: &self)
+                handled = true
+            }
+
+            return handled
+        }
+    }
+}
+
+public struct Bold: PDF.HTML.Style.Modifier {
+    public init() {}
+    public func apply(to context: inout PDF.Context, configuration: PDF.HTML.Configuration) {
+        context.value += 1
+    }
+}
+
+public struct PageBreak: PDF.HTML.Style.Context.Modifier {
+    public init() {}
+    public func apply(to context: inout PDF.HTML.Context) {
+        context.pdf.value += 1
+    }
+}
+
+public func exercise() -> Int {
+    var context = PDF.HTML.Context()
+    _ = context.apply(inlineStyle: Bold())
+    _ = context.apply(inlineStyle: Optional.some(PageBreak()) as Any)
+    return context.pdf.value
+}

.github/workflows/windows-existential-repro.yml

@@ -13,9 +13,15 @@ name: Windows existential repro
 #      Per swiftlang/swift#86202 (the `any HTML.View` sibling), cross-package
 #      + namespace-typealias sugar are load-bearing ingredients; the written
 #      existential carries TypeAliasType sugar at its root, which is the
-#      non-canonical type the mangler chokes on. 6.4 carries typealias-
-#      existential debug-info fixes (45547be3f8f, 6f60adf009c, 2934386efde)
-#      absent from 6.3.
+#      non-canonical type the mangler chokes on. VERIFIED 2026-07-06 (run
+#      28776276301): STILL FIRING on 6.3.3 AND on 6.4-dev a42409e978ff428 —
+#      the 6.4 typealias-existential debug-info fixes (45547be3f8f,
+#      6f60adf009c, 2934386efde) do NOT cover this shape; single-file CLEAN
+#      on both (cross-package + alias sugar are load-bearing);
+#   3. respell-canonical — identical to (2) except the two downcasts are
+#      spelled through the canonical root (`any ISO_32000.…`). CLEAN here
+#      while (2) fires validates the surgical production fix: respell the
+#      written existential type at the two crash-site downcasts.
 #
 # Reading the legs together (per variant):
 #   6.3.3 FIRING  + 6.4 CLEAN  → the 6.4 fix is empirically confirmed for that
@@ -89,12 +95,17 @@ jobs:
           Write-Host $out1
           Write-Host "::notice title=single-file::$disp1 on Swift ${{ matrix.swift-version }}"
 
-          $out2 = & swift build -c debug --package-path '.github/repro/cross-package/crash' 2>&1 | Out-String
+          $out2 = & swift build -c debug --package-path '.github/repro/cross-package/crash' --target CrashModule 2>&1 | Out-String
           $disp2 = Get-Disposition -Output $out2 -Code $LASTEXITCODE
           Write-Host $out2
           Write-Host "::notice title=cross-package::$disp2 on Swift ${{ matrix.swift-version }}"
 
-          Write-Host "DISPOSITION MATRIX (Swift ${{ matrix.swift-version }}): single-file=$disp1 cross-package=$disp2"
-          if (($disp1 -eq 'CLEAN') -and ($disp2 -eq 'CLEAN')) { exit 0 }
-          if (($disp1 -eq 'INCONCLUSIVE') -or ($disp2 -eq 'INCONCLUSIVE')) { exit 1 }
+          $out3 = & swift build -c debug --package-path '.github/repro/cross-package/crash' --target RespellModule 2>&1 | Out-String
+          $disp3 = Get-Disposition -Output $out3 -Code $LASTEXITCODE
+          Write-Host $out3
+          Write-Host "::notice title=respell-canonical::$disp3 on Swift ${{ matrix.swift-version }}"
+
+          Write-Host "DISPOSITION MATRIX (Swift ${{ matrix.swift-version }}): single-file=$disp1 cross-package=$disp2 respell-canonical=$disp3"
+          if (($disp1 -eq 'CLEAN') -and ($disp2 -eq 'CLEAN') -and ($disp3 -eq 'CLEAN')) { exit 0 }
+          if (($disp1 -eq 'INCONCLUSIVE') -or ($disp2 -eq 'INCONCLUSIVE') -or ($disp3 -eq 'INCONCLUSIVE')) { exit 1 }
           exit 2