feat(profile): wire usernames through profile and resolver

FlipcashAPI/Sources/FlipcashAPI/Core/proto/common/v1/common.proto

@@ -61,6 +61,13 @@ message UserId {
     }];
 }
 
+// Username is a user's unique handle on Flipcash. It uses the same character
+// set as X — letters, digits and underscores — with the exception that it must
+// be lowercase.
+message Username {
+    string value = 1 [(validate.rules).string.pattern = "^[a-z0-9_]{2,15}$"];
+}
+
 message ChatId {
     // value has the following structure:
     //  - 32 byte hash for DMs

FlipcashAPI/Sources/FlipcashAPI/Core/proto/profile/v1/model.proto

@@ -12,12 +12,20 @@ import "google/protobuf/timestamp.proto";
 import "validate/validate.proto";
 
 message UserProfile {
+	// The ID of the user this profile belongs to. Always set, so a caller that
+	// looked the profile up by username learns the user's ID from the response.
+	common.v1.UserId user_id = 9 [(validate.rules).message.required = true];
+
 	// Display name is the display name of the user (if found).
 	string display_name = 1 [(validate.rules).string = {
 		min_len: 0
 		max_len: 64
 	}];
 
+	// The user's username on Flipcash. Public, so it is returned for any user,
+	// not just the caller. Unset when the user hasn't claimed one yet.
+	common.v1.Username username = 8;
+
 	// Social profiles are links to external social accounts
 	repeated SocialProfile social_profiles = 2 [(validate.rules).repeated = {
         min_items: 0

FlipcashAPI/Sources/FlipcashAPI/Core/proto/profile/v1/profile_service.proto

@@ -38,7 +38,14 @@ service Profile {
 }
 
 message GetProfileRequest {
-	common.v1.UserId user_id = 1 [(validate.rules).message.required = true];
+	// The user whose profile is being fetched, identified either by their user
+	// ID or by their username. Exactly one must be set.
+	oneof identifier {
+		option (validate.required) = true;
+
+		common.v1.UserId   user_id  = 1;
+		common.v1.Username username = 3;
+	}
 
 	// Optional auth to retrieve private profile information for self
 	common.v1.Auth auth = 2;

FlipcashAPI/Sources/FlipcashAPI/Core/proto/resolver/v1/model.proto

@@ -15,8 +15,9 @@ message Identifier {
     oneof kind {
         option (validate.required) = true;
 
-        common.v1.PhoneNumber phone   = 1;
-        common.v1.UserId      user_id = 2;
+        common.v1.PhoneNumber phone    = 1;
+        common.v1.UserId      user_id  = 2;
+        common.v1.Username    username = 3;
     }
 }
 

FlipcashCore/Sources/FlipcashCore/Clients/Flip API/FlipClient+Profile.swift

@@ -10,8 +10,18 @@ import Foundation
 extension FlipClient {
 
     public func fetchProfile(userID: UserID, owner: KeyPair) async throws -> Profile {
+        try await fetchProfile(.userID(userID), owner: owner)
+    }
+
+    /// Fetches the profile behind a claimed handle. The response carries the
+    /// user's id, so a caller holding only a handle learns it from the result.
+    public func fetchProfile(username: Username, owner: KeyPair) async throws -> Profile {
+        try await fetchProfile(.username(username), owner: owner)
+    }
+
+    private func fetchProfile(_ identifier: ProfileIdentifier, owner: KeyPair) async throws -> Profile {
         try await withCheckedThrowingContinuation { c in
-            profileService.fetchProfile(userID: userID, owner: owner) { c.resume(with: $0) }
+            profileService.fetchProfile(identifier, owner: owner) { c.resume(with: $0) }
         }
     }