[Firestore Emulator] firestore: Did not find a Cloud Firestore rules file specified in a firebase.json config file.

### [REQUIRED] Environment info

**firebase-tools:**15.3.0

**Platform:**macOS

### [REQUIRED] Test case

Security rules for the two Firestore databases do not take effect when starting the emulator.

### [REQUIRED] Steps to reproduce

1. Add the following content to firebase.json
"firestore": [
{
"database": "(default)",
"rules": "firestore.rules"
},
{
"database": "data",
"rules": "firestore.data.rules"
}
],
2. Run command: firebase emulators:start --only firestore --debug
3. Console log:
⚠ firestore: Cloud Firestore Emulator does not support multiple databases yet.
⚠ firestore: Did not find a Cloud Firestore rules file specified in a firebase.json config file.

### [REQUIRED] Expected behavior

Security rules in effect

### [REQUIRED] Actual behavior

Security rules not in effect
console log:
⚠ firestore: Cloud Firestore Emulator does not support multiple databases yet. {"metadata":{"emulator":{"name":"firestore"},"message":"Cloud Firestore Emulator does not support multiple databases yet."}}
⚠ firestore: Did not find a Cloud Firestore rules file specified in a firebase.json config file. {"metadata":{"emulator":{"name":"firestore"},"message":"Did not find a Cloud Firestore rules file specified in a firebase.json config file."}}
⚠ firestore: The emulator will default to allowing all reads and writes. Learn more about this option: https://firebase.google.com/docs/emulator-suite/install_and_configure#security_rules_configuration. {"metadata":{"emulator":{"name":"firestore"},"message":"The emulator will default to allowing all reads and writes. Learn more about this option: https://firebase.google.com/docs/emulator-suite/install_and_configure#security_rules_configuration."}}
[2026-01-15T07:49:30.021Z] Ignoring unsupported arg: auto_download {"metadata":{"emulator":{"name":"firestore"},"message":"Ignoring unsupported arg: auto_download"}}
[2026-01-15T07:49:30.021Z] Ignoring unsupported arg: single_project_mode_error {"metadata":{"emulator":{"name":"firestore"},"message":"Ignoring unsupported arg: single_project_mode_error"}}
[2026-01-15T07:49:30.021Z] Starting Firestore Emulator with command {"binary":"java","args":["-Dgoogle.cloud_firestore.debug_log_level=FINE","-Duser.language=en","-jar","/Users/xxxx/.cache/firebase/emulators/cloud-firestore-emulator-v1.20.2.jar","--host","0.0.0.0","--port",8080,"--websocket_port",9150,"--project_id","project","--single_project_mode",true],"optionalArgs":["port","webchannel_port","host","rules","websocket_port","functions_emulator","seed_from_export","project_id","single_project_mode"],"joinArgs":false,"shell":false,"port":8080} {"metadata":{"emulator":{"name":"firestore"},"message":"Starting Firestore Emulator with command {\"binary\":\"java\",\"args\":[\"-Dgoogle.cloud_firestore.debug_log_level=FINE\",\"-Duser.language=en\",\"-jar\",\"/Users/xxx/.cache/firebase/emulators/cloud-firestore-emulator-v1.20.2.jar\",\"--host\",\"0.0.0.0\",\"--port\",8080,\"--websocket_port\",9150,\"--project_id\",\"project\",\"--single_project_mode\",true],\"optionalArgs\":[\"port\",\"webchannel_port\",\"host\",\"rules\",\"websocket_port\",\"functions_emulator\",\"seed_from_export\",\"project_id\",\"single_project_mode\"],\"joinArgs\":false,\"shell\":false,\"port\":8080}"}}
i firestore: Firestore Emulator logging to firestore-debug.log {"metadata":{"emulator":{"name":"firestore"},"message":"Firestore Emulator logging to \u001b[1mfirestore-debug.log\u001b[22m"}}
[2026-01-15T07:49:30.444Z] Jan 15, 2026 3:49:30 PM com.google.cloud.datastore.emulator.firestore.websocket.WebSocketServer start
INFO: Started WebSocket server on ws://0.0.0.0:9150
{"metadata":{"emulator":{"name":"firestore"},"message":"Jan 15, 2026 3:49:30 PM com.google.cloud.datastore.emulator.firestore.websocket.WebSocketServer start\nINFO: Started WebSocket server on ws://0.0.0.0:9150\n"}}