test(core): Swift oracle — the filius-ipad core built on Linux as the reference

tools/swift-oracle builds the unchanged Swift runtime (pinned 3b5ded0)
in Docker and replays JSON scenarios; the TypeScript engine must produce
the same trace events, results and end state. Five scenarios, 884
events, identical.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/swift-oracle/fetch-upstream.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+# Copies the UI-free Swift sources of filius-ipad, at the commit the port
+# follows, into Sources/FiliusCore and applies the Linux patches.
+set -eu
+here="$(cd "$(dirname "$0")" && pwd)"
+commit=3b5ded0
+upstream="$here/.upstream"
+if [ ! -d "$upstream/.git" ]; then
+    git clone -q https://github.com/filius-project/filius-ipad "$upstream"
+fi
+git -C "$upstream" fetch -q origin
+git -C "$upstream" checkout -q "$commit"
+
+core="$here/Sources/FiliusCore"
+rm -rf "$core"
+mkdir -p "$core"
+editor="$upstream/ios/FiliusPad/TopologyEditor"
+cp "$editor"/State/*.swift "$editor"/State/Reports/*.swift "$editor"/Model/*.swift \
+   "$editor"/Persistence/*.swift "$upstream/ios/FiliusPad/Localization/FiliusLocalization.swift" "$core/"
+# Apple's Network framework has no Linux counterpart; the LAN transport of the
+# remote link is not needed to replay a simulation.
+rm "$core/TopologyRemoteLinkLANController.swift"
+for patch in "$here"/patches/*.patch; do
+    (cd "$core" && patch -p1 --forward --quiet < "$patch")
+done
+echo "filius-ipad $commit → $core ($(ls "$core" | wc -l) files)"