test(mobile): exercise native signing in linked iOS Runner

Signed-off-by: Tom Brow <tomb@block.xyz>

scripts/test-mobile-linked-signing.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Run the Dart production signer through symbols exported by the actual Runner.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+. ./bin/activate-hermit
+device=${1:?Pass a booted simulator UDID}
+fixture=$(mktemp -d)
+bundle=xyz.block.buzz.signing-probe
+trap 'xcrun simctl terminate "$device" "$bundle" >/dev/null 2>&1 || true; rm -rf "$fixture"' EXIT
+xcodebuild -workspace mobile/ios/Runner.xcworkspace -scheme Runner \
+  -configuration Debug -sdk iphonesimulator -destination "id=$device" \
+  -derivedDataPath "${BUZZ_SIGNING_DERIVED_DATA:-$fixture/build}" -jobs 2 \
+  BUNDLE_IDENTIFIER="$bundle" CODE_SIGNING_ALLOWED=NO ONLY_ACTIVE_ARCH=YES \
+  FLUTTER_TARGET=tool/native_signing_probe.dart build > "$fixture/build.log" 2>&1 || {
+    cat "$fixture/build.log"
+    exit 1
+  }
+xcrun simctl install "$device" "${BUZZ_SIGNING_DERIVED_DATA:-$fixture/build}/Build/Products/Debug-iphonesimulator/Buzz.app"
+launch=$(xcrun simctl launch --terminate-running-process "$device" "$bundle")
+probe_pid=${launch##*: }
+[[ "$probe_pid" =~ ^[0-9]+$ ]] || { echo "Unexpected launch result: $launch" >&2; exit 1; }
+# Flutter's iOS logger writes to the unified log, not redirected stdout.
+for ((attempt = 0; attempt < 90; attempt++)); do
+  xcrun simctl spawn "$device" log show --last 5m --style compact \
+    --predicate "processIdentifier == $probe_pid AND eventMessage CONTAINS \"SIGNING_PROBE\"" \
+    > "$fixture/probe.log" 2>/dev/null
+  if grep -q 'SIGNING_PROBE COMPLETE' "$fixture/probe.log"; then
+    cat "$fixture/probe.log"
+    exit 0
+  fi
+  sleep 1
+done
+cat "$fixture/probe.log"
+echo 'Linked iOS signing probe did not complete' >&2
+exit 1