Server: FCM HTTP v1 target in fid instead of deprecated token (D-083 follow-up)

The stored fcm_token is the Firebase Installation ID; HTTP v1 deprecates
message.token (accepted only during the transition) in favour of message.fid.
Push examples and push_fcm tests follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

contracts/examples/push/expense_created.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/expense_deleted.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/expense_updated.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/recurring_expense_created.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/settlement_created.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/settlement_deleted.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/settlement_updated.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

contracts/examples/push/sync_batch.json

@@ -1,6 +1,6 @@
 {
   "message": {
-    "token": "dGhpcyBpcyBhbiBleGFtcGxlIGZjbSB0b2tlbg",
+    "fid": "dExampleFid0Kvitt12345",
     "android": {
       "priority": "high",
       "ttl": "86400s"

server/crates/kvitt-server/src/push/fcm.rs

@@ -113,10 +113,12 @@ pub fn entity_type_of(push_type: PushType) -> &'static str {
 }
 
 /// The HTTP v1 request body for one device (SPEC §14.6): data only, every value a string, ids only (AC-13.8).
+/// The target is `fid`: the stored `fcm_token` is the Firebase Installation ID the phone registered (D-083), and
+/// HTTP v1 deprecates `token` in favour of `fid` (D-096).
 pub fn message_body(fcm_token: &str, message: &PushMessage) -> Value {
     json!({
         "message": {
-            "token": fcm_token,
+            "fid": fcm_token,
             "android": { "priority": "high", "ttl": MESSAGE_TTL },
             "data": {
                 "v": PAYLOAD_VERSION,

server/crates/kvitt-server/tests/push_fcm/fcm.rs

@@ -117,7 +117,7 @@ fn payload_of_every_type_equals_the_contract_example() {
             actor_user_id: data["actor_user_id"].as_str().unwrap().parse().unwrap(),
             count: data["count"].as_str().unwrap().parse().unwrap(),
         };
-        let body = message_body(expected["message"]["token"].as_str().unwrap(), &msg);
+        let body = message_body(expected["message"]["fid"].as_str().unwrap(), &msg);
         assert_eq!(body, expected, "{}", push_type.as_str());
         // Data only, every value a string (SPEC §14.6), ids only (AC-13.8).
         assert!(body["message"].get("notification").is_none());
@@ -178,7 +178,7 @@ async fn oauth_jwt_and_send_request_follow_the_http_v1_flow() {
         sends[0].authorization.as_deref(),
         Some("Bearer ya29.stub-1")
     );
-    let expected = json!({"message": {"token": "tok-member", "android": {"priority": "high", "ttl": "86400s"},
+    let expected = json!({"message": {"fid": "tok-member", "android": {"priority": "high", "ttl": "86400s"},
         "data": {"v": "1", "type": "expense_created", "entity_type": "expense", "entity_id": EXPENSE,
                  "actor_user_id": ADMIN_ID, "count": "1"}}});
     assert_eq!(sends[0].json(), expected);
@@ -460,7 +460,8 @@ async fn sync_push_reaches_fcm_through_the_queue_and_the_sender_task() {
     let sends = s.stub.sends();
     assert_eq!(sends.len(), 1);
     let body = sends[0].json();
-    assert_eq!(body["message"]["token"], "tok-admin");
+    assert_eq!(body["message"]["fid"], "tok-admin");
+    assert!(body["message"].get("token").is_none());
     assert_eq!(body["message"]["data"]["entity_id"], id);
     assert_eq!(body["message"]["data"]["actor_user_id"], MEMBER_ID);
 }