fix(multiplayer): reject typed claim coercion

Game/scripts/match_net.gd

@@ -335,7 +335,13 @@ func _valid_join_authorisation(token: String) -> bool:
 	var claims = envelope["Authorisation"]
 	if not claims is Dictionary:
 		return false
-	if str(claims.get("PlayerID", "")).is_empty():
+	for string_claim in ["MatchID", "ServerID", "PlayerID", "SteamID", "Protocol", "ExpiresAt"]:
+		if not claims.has(string_claim) or not claims[string_claim] is String or String(claims[string_claim]).is_empty():
+			return false
+	for integer_claim in ["Slot", "Team", "Generation"]:
+		if not claims.has(integer_claim) or not _valid_integer_claim(claims[integer_claim]):
+			return false
+	if not envelope["Signature"] is String or String(envelope["Signature"]).is_empty():
 		return false
 	var claimed_team := int(claims.get("Team", -1))
 	var claimed_slot := int(claims.get("Slot", -1))
@@ -374,6 +380,14 @@ func _valid_join_authorisation(token: String) -> bool:
 		and expiry > Time.get_unix_time_from_system()
 
 
+static func _valid_integer_claim(value: Variant) -> bool:
+	if value is int:
+		return int(value) >= 0
+	if value is float:
+		return is_finite(float(value)) and float(value) >= 0.0 and float(value) == floor(float(value))
+	return false
+
+
 func _join_identity(token: String) -> String:
 	if token.is_empty():
 		return ""

Game/tests/cases/test_match_net.gd

@@ -78,6 +78,10 @@ func test_allocated_join_authorisation_is_allowlisted_and_bound_to_server() -> v
 	malformed_claims["ExpiresAt"] = "tomorrow"
 	var malformed_token := Marshalls.raw_to_base64(JSON.stringify({"Authorisation": malformed_claims, "Signature": "trusted-signature"}).to_utf8_buffer())
 	assert_true(not match_net._valid_join_authorisation(malformed_token), "malformed expiry claim is rejected before admission")
+	var string_slot_claims := claims.duplicate()
+	string_slot_claims["Slot"] = "5"
+	var string_slot_token := Marshalls.raw_to_base64(JSON.stringify({"Authorisation": string_slot_claims, "Signature": "trusted-signature"}).to_utf8_buffer())
+	assert_true(not match_net._valid_join_authorisation(string_slot_token), "string slot claim is rejected instead of coerced")
 	assert_true(not match_net._valid_join_authorisation(token + "tampered"), "token mutation is rejected")
 	var wrong_claims := claims.duplicate()
 	wrong_claims["ServerID"] = "other-server"

multiplayer-next.md

@@ -1577,4 +1577,6 @@ Assignment expiry validation now fails closed on malformed non-empty timestamps
 
 MatchNet join-authorisation admission now applies the same expiry format guard before parsing signed roster claims, closing the malformed-expiry gap at the transport handshake boundary.
 
+Signed MatchNet claims now also require exact JSON string/integer types for every identity, protocol, expiry, slot, team, and generation field; string-number coercion is rejected before canonical signature verification.
+
 Presentation progress: a shared `Game/themes/cosmic_clash_theme.tres` now gives the menu, lobby, matchmaking, and settings surfaces consistent button, input, option, and label styling. The custom-font portion of `TODO.md` remains open until a distributable font asset is selected.