fix(git): select USC Gitea login for PR merges (#516)

packages/mosaic/framework/tools/git/pr-merge.sh

@@ -69,6 +69,11 @@ if [[ -z "$PR_NUMBER" ]]; then
     usage
 fi
 
+if [[ ! "$PR_NUMBER" =~ ^[0-9]+$ ]]; then
+    echo "Error: PR number must be numeric." >&2
+    exit 1
+fi
+
 if [[ "$MERGE_METHOD" != "squash" ]]; then
     echo "Error: Mosaic policy enforces squash merge only. Received '$MERGE_METHOD'." >&2
     exit 1
@@ -94,19 +99,31 @@ REPO=$(get_repo_name)
 
 case "$PLATFORM" in
     github)
-        CMD="gh pr merge $PR_NUMBER --squash"
-        [[ "$DELETE_BRANCH" == true ]] && CMD="$CMD --delete-branch"
-        eval "$CMD"
+        CMD=(gh pr merge "$PR_NUMBER" --squash)
+        [[ "$DELETE_BRANCH" == true ]] && CMD+=(--delete-branch)
+        "${CMD[@]}"
         ;;
     gitea)
-        CMD="tea pr merge $PR_NUMBER --style squash --repo $OWNER/$REPO --login ${GITEA_LOGIN:-mosaicstack}"
+        HOST=$(get_remote_host) || {
+            echo "Error: Could not determine remote host." >&2
+            exit 1
+        }
+        CMD=(tea pr merge "$PR_NUMBER" --style squash --repo "$OWNER/$REPO")
+        GITEA_TEA_LOGIN=$(get_gitea_login "$HOST" || true)
+        if [[ -n "$GITEA_TEA_LOGIN" ]]; then
+            if [[ ! "$GITEA_TEA_LOGIN" =~ ^[A-Za-z0-9._-]+$ ]]; then
+                echo "Error: Gitea tea login contains unsupported characters." >&2
+                exit 1
+            fi
+            CMD+=(--login "$GITEA_TEA_LOGIN")
+        fi
 
         # Delete branch after merge if requested
         if [[ "$DELETE_BRANCH" == true ]]; then
             echo "Note: Branch deletion after merge may need to be done separately with tea" >&2
         fi
 
-        eval "$CMD"
+        "${CMD[@]}"
         ;;
     *)
         echo "Error: Could not detect git platform" >&2