fix(ci): save previous HEAD for reliable change detection

- build-and-unit saves git rev-parse HEAD before reset
- backward-compat uses saved PREV to compute exact diff
- Falls back to HEAD~3 diff if prev-head is missing

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

.gitea/workflows/deploy.yml

@@ -25,9 +25,13 @@ jobs:
       - name: Checkout
         run: |
           if [ -d $WORKDIR ]; then
-            cd $WORKDIR && git fetch origin && git reset --hard origin/main
+            cd $WORKDIR
+            # Save previous HEAD before reset — used by backward-compat for change detection
+            git rev-parse HEAD > /tmp/prev-head 2>/dev/null || true
+            git fetch origin && git reset --hard origin/main
           else
             git clone http://10.2.0.7:3000/wangdl/api-server.git $WORKDIR
+            git rev-parse HEAD > /tmp/prev-head 2>/dev/null || true
           fi
 
       - name: Install dependencies
@@ -126,9 +130,19 @@ jobs:
             echo "run_compat=true" > /tmp/compat-decision
             exit 0
           fi
-          # Diff against origin/main to catch all changes in this push
-          git fetch origin main 2>/dev/null || true
-          CHANGED=$(git diff --name-only origin/main...HEAD 2>/dev/null || git diff --name-only HEAD~1..HEAD 2>/dev/null || echo "")
+          # Diff HEAD against previous HEAD saved by build-and-unit checkout step.
+          # This catches exactly what changed in this push.
+          PREV=$(cat /tmp/prev-head 2>/dev/null || echo "")
+          if [ -n "$PREV" ] && [ "$PREV" != "$(git rev-parse HEAD)" ]; then
+            CHANGED=$(git diff --name-only $PREV..HEAD 2>/dev/null || echo "")
+          else
+            # Fallback: check last 3 commits
+            CHANGED=""
+            for n in 1 2 3; do
+              CHANGED="$CHANGED $(git diff --name-only HEAD~$n..HEAD 2>/dev/null || echo "")"
+            done
+          fi
+          echo "Previous HEAD: ${PREV:-none}"
           echo "Changed files: $CHANGED"
           if echo "$CHANGED" | grep -qE "prisma/schema.prisma|prisma/migrations/|src/modules/ai-analysis/|src/workers/ai-analysis.worker.ts|src/infrastructure/queue/|src/infrastructure/outbox/|src/modules/ai-runtime/ai-job"; then
             echo "DB-related changes detected — running backward compatibility"