ci(ios): gate hosted build on iOS changes

.github/workflows/ci.yml

@@ -10,8 +10,6 @@ name: ci
 # The T3 content tier asserts Pokemon Red facts; scripts/test.sh detects
 # data/generated/ is absent and skips it rather than failing.
 #
-# Runs alongside release.yml, which is untouched by this file.
-
 on:
   push:
     # Integration branch + release branch. PRs already run via pull_request
@@ -25,6 +23,42 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  ios-changes:
+    name: detect iOS changes
+    runs-on: ubuntu-latest
+    outputs:
+      changed: ${{ steps.paths.outputs.changed }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - id: paths
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha || github.event.before }}
+          HEAD_SHA: ${{ github.sha }}
+        run: |
+          if [ -z "$BASE_SHA" ] || [ "$BASE_SHA" = "0000000000000000000000000000000000000000" ]; then
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+          if git diff --name-only "$BASE_SHA" "$HEAD_SHA" | grep -Eq '^(mobile/ios/|scripts/build_ios\.sh$|\.github/workflows/(ci|release)\.yml$)'; then
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=false" >> "$GITHUB_OUTPUT"
+          fi
+
+  ios-build:
+    name: iOS build
+    needs: ios-changes
+    if: needs.ios-changes.outputs.changed == 'true'
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: install xcbeautify
+        run: brew list xcbeautify >/dev/null 2>&1 || brew install xcbeautify
+      - name: build iOS simulator app
+        run: scripts/build_ios.sh --fetch --release
+
   headless:
     name: headless suites (no ROM)
     runs-on: ubuntu-latest