Add macOS concurrency test workflow

.gitea/workflows/macos-concurrency.yaml

@@ -0,0 +1,67 @@
+name: Mac Runner Concurrency Test
+on: [workflow_dispatch, push]
+
+jobs:
+  long-job-a:
+    name: Long job A
+    runs-on: macos-arm64
+    steps:
+      - name: Print info
+        run: |
+          echo "Job A on $(uname -a)"
+          sw_vers || true
+          whoami
+          pwd
+
+      - name: Create artifact
+        run: |
+          mkdir -p _work/concurrentA
+          echo "concurrent A" > _work/concurrentA/marker.txt
+          ls -lah _work/concurrentA
+
+      - name: Simulate long work
+        run: |
+          echo "Sleeping to simulate long task..."
+          sleep 60
+
+  long-job-b:
+    name: Long job B
+    runs-on: macos-arm64
+    steps:
+      - name: Print info
+        run: |
+          echo "Job B on $(uname -a)"
+          sw_vers || true
+          whoami
+          pwd
+
+      - name: Create artifact
+        run: |
+          mkdir -p _work/concurrentB
+          echo "concurrent B" > _work/concurrentB/marker.txt
+          ls -lah _work/concurrentB
+
+      - name: Simulate long work
+        run: |
+          echo "Sleeping to simulate long task..."
+          sleep 60
+
+  inspect-after:
+    name: Inspect after concurrency
+    runs-on: macos-arm64
+    needs: [long-job-a, long-job-b]
+    steps:
+      - name: List act_runner directory
+        run: |
+          echo "Listing /var/lib/act_runner contents"
+          sudo ls -lah /var/lib/act_runner || true
+
+      - name: Find _work directories and sizes
+        run: |
+          sudo find /var/lib/act_runner -type d -name '_work' -print -exec sudo du -sh {} + || true
+
+      - name: Fail if artifacts left
+        run: |
+          echo "Checking for marker files"
+          sudo find /var/lib/act_runner -type f -name 'marker.txt' -print
+          # Do not fail intentionally; user can inspect results and choose cleanup