feat(#15): session audit log domain, store, and instrumentation

src/GmRelay.Web/Services/AuthorizedSessionService.cs

@@ -66,6 +66,15 @@ public sealed class AuthorizedSessionService(ISessionStore sessionStore)
         }
 
         await sessionStore.UpdateSessionAsync(sessionId, session.GroupId, title, scheduledAt, joinLink, maxPlayers);
+
+        if (session.Title != title)
+            await sessionStore.LogSessionChangeAsync(sessionId, gmId, "ГМ", "Title", session.Title, title);
+        if (session.ScheduledAt != scheduledAt)
+            await sessionStore.LogSessionChangeAsync(sessionId, gmId, "ГМ", "Time", session.ScheduledAt.ToString("O"), scheduledAt.ToString("O"));
+        if (session.JoinLink != joinLink)
+            await sessionStore.LogSessionChangeAsync(sessionId, gmId, "ГМ", "Link", session.JoinLink, joinLink);
+        if (session.MaxPlayers != maxPlayers)
+            await sessionStore.LogSessionChangeAsync(sessionId, gmId, "ГМ", "MaxPlayers", session.MaxPlayers?.ToString(), maxPlayers?.ToString());
     }
 
     public async Task PromoteWaitlistedPlayerForGmAsync(Guid sessionId, long gmId)
@@ -77,6 +86,7 @@ public sealed class AuthorizedSessionService(ISessionStore sessionStore)
         }
 
         await sessionStore.PromoteWaitlistedPlayerAsync(sessionId, session.GroupId);
+        await sessionStore.LogSessionChangeAsync(sessionId, gmId, "ГМ", "WaitlistPromote", null, null);
     }
 
     public async Task UpdateBatchDetailsForGmAsync(Guid batchId, long gmId, string title, string joinLink)
@@ -115,6 +125,7 @@ public sealed class AuthorizedSessionService(ISessionStore sessionStore)
         }
 
         await sessionStore.RescheduleBatchAsync(batchId, batch.GroupId, firstScheduledAt, intervalDays);
+        await sessionStore.LogSessionChangeAsync(batchId, gmId, "ГМ", "BatchRescheduled", batch.FirstScheduledAt.ToString("O"), firstScheduledAt.ToString("O"));
     }
 
     public async Task<WebSessionBatch> CloneBatchForGmAsync(Guid batchId, long gmId, BatchCloneInterval interval)
@@ -239,6 +250,7 @@ public sealed class AuthorizedSessionService(ISessionStore sessionStore)
         }
 
         await sessionStore.RemovePlayerFromSessionAsync(sessionId, session.GroupId, participantId);
+        await sessionStore.LogSessionChangeAsync(sessionId, gmId, "ГМ", "PlayerRemoved", participantId.ToString(), null);
     }
 
     private async Task<bool> GroupBelongsToGmAsync(Guid groupId, long gmId)

src/GmRelay.Web/Services/ISessionStore.cs

@@ -15,6 +15,17 @@ public sealed record PlayerAttendanceStats(
     decimal AttendanceRate
 );
 
+public sealed record SessionAuditLogEntry(
+    Guid Id,
+    Guid SessionId,
+    long ActorTelegramId,
+    string ActorName,
+    string ChangeType,
+    string? OldValue,
+    string? NewValue,
+    DateTime ChangedAt
+);
+
 public interface ISessionStore
 {
     Task<List<WebGameGroup>> GetGroupsForGmAsync(long gmId);
@@ -41,4 +52,6 @@ public interface ISessionStore
     Task<List<WebParticipant>> GetSessionParticipantsAsync(Guid sessionId);
     Task RemovePlayerFromSessionAsync(Guid sessionId, Guid groupId, Guid participantId);
     Task<List<PlayerAttendanceStats>> GetGroupAttendanceStatsAsync(Guid groupId);
+    Task LogSessionChangeAsync(Guid sessionId, long actorTelegramId, string actorName, string changeType, string? oldValue, string? newValue);
+    Task<List<SessionAuditLogEntry>> GetSessionHistoryAsync(Guid sessionId);
 }

src/GmRelay.Web/Services/SessionService.cs

@@ -202,6 +202,32 @@ public sealed class SessionService(
             new { GroupId = groupId })).ToList();
     }
 
+    public async Task LogSessionChangeAsync(Guid sessionId, long actorTelegramId, string actorName, string changeType, string? oldValue, string? newValue)
+    {
+        await using var conn = await dataSource.OpenConnectionAsync();
+        await conn.ExecuteAsync(
+            """
+            INSERT INTO session_audit_log (session_id, actor_telegram_id, actor_name, change_type, old_value, new_value)
+            VALUES (@SessionId, @ActorTelegramId, @ActorName, @ChangeType, @OldValue, @NewValue)
+            """,
+            new { SessionId = sessionId, ActorTelegramId = actorTelegramId, ActorName = actorName, ChangeType = changeType, OldValue = oldValue, NewValue = newValue });
+    }
+
+    public async Task<List<SessionAuditLogEntry>> GetSessionHistoryAsync(Guid sessionId)
+    {
+        await using var conn = await dataSource.OpenConnectionAsync();
+        var entries = await conn.QueryAsync<SessionAuditLogEntry>(
+            """
+            SELECT id, session_id AS SessionId, actor_telegram_id AS ActorTelegramId, actor_name AS ActorName,
+                   change_type AS ChangeType, old_value AS OldValue, new_value AS NewValue, changed_at AS ChangedAt
+            FROM session_audit_log
+            WHERE session_id = @SessionId
+            ORDER BY changed_at DESC
+            """,
+            new { SessionId = sessionId });
+        return entries.ToList();
+    }
+
     public async Task AddGroupCoGmAsync(
         Guid groupId,
         long ownerTelegramId,