fix(spec-0030): resolve solution-wide CS8604/CS8601/CS8618 from string?-widened operators

D8 widened nine core value-type implicit operators from `operator string(T)`
to the null-safe `operator string?(T) => t?.Value` (commit cb3e4ef, matching
the ChannelName precedent). Because src/Directory.Build.props sets
TreatWarningsAsErrors, every call site feeding one of these conversions into a
non-nullable string broke at compile time. The earlier fixes (6262cc1,
7f451cd) only covered Paramore.Brighter and ServiceActivator; a full-solution
build across all TFMs surfaced 326 more sites across ~28 src assemblies plus the
dependent test projects.

Fix (mechanical, behaviour-preserving): use `.Value` at each call site where the
value type is non-nullable, and `?.Value ?? <existing fallback>` where the source
is itself nullable (e.g. MessageHeader.ReplyTo, Publication.Topic). A few sites
that were already guarded non-null by an upstream IsNullOrEmpty-throw use
`Topic!.Value`, matching the established repo convention.

Tenant (Transformers.JustSaying) is reverted to the non-nullable
`operator string`: it is a readonly record struct, so its receiver can never be
null and `tenant?.Value` was both unnecessary and invalid (CS0023).

Test-only fixes (fallout from the Phase 2 contract retyping, surfaced once src
compiled): `Assert.Equal(n, x.Version)` -> `.Version.Value` across the
BoxProvisioning migration tests, and the MySQL fake VersionCapturingMigrationRunner
MigrateAsync override retyped to the value-type IAmABoxMigrationRunner signature.

Full solution now builds clean across netstandard2.0;net8.0;net9.0;net10.0 (and
net462/net472 where applicable).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: iancooper

src/Paramore.Brighter.BoxProvisioning.MsSql/MsSqlBoxMigrationRunner.cs

@@ -430,7 +430,7 @@ await InsertHistoryRowAsync(
             await ExecuteUpScriptAsync(connection, transaction!, migration, cancellationToken);
             await InsertHistoryRowAsync(
                 connection, transaction!, effectiveSchema, tableName,
-                migration.Version, migration.Description, cancellationToken);
+                migration.Version, migration.Description.Value, cancellationToken);
         }
     }
 
@@ -450,14 +450,14 @@ protected override async Task RunNormalPathAsync(
             await ExecuteUpScriptAsync(connection, transaction!, migration, cancellationToken);
             await InsertHistoryRowAsync(
                 connection, transaction!, effectiveSchema, tableName,
-                migration.Version, migration.Description, cancellationToken);
+                migration.Version, migration.Description.Value, cancellationToken);
         }
     }
 
     private static Task ExecuteUpScriptAsync(
         SqlConnection connection, SqlTransaction transaction,
         IAmABoxMigration migration, CancellationToken cancellationToken)
-        => ExecuteDdlAsync(connection, transaction, migration.UpScript, cancellationToken);
+        => ExecuteDdlAsync(connection, transaction, migration.UpScript.Value, cancellationToken);
 
     private static async Task ExecuteDdlAsync(
         SqlConnection connection, SqlTransaction transaction,

src/Paramore.Brighter.BoxProvisioning.MySql/MySqlBoxMigrationRunner.cs

@@ -210,7 +210,7 @@ await InsertHistoryRowAsync(
             await ExecuteUpScriptAsync(connection, migration, cancellationToken);
             await InsertHistoryRowAsync(
                 connection, effectiveSchema, tableName,
-                migration.Version, migration.Description, cancellationToken);
+                migration.Version, migration.Description.Value, cancellationToken);
         }
     }
 
@@ -229,14 +229,14 @@ protected override async Task RunNormalPathAsync(
             await ExecuteUpScriptAsync(connection, migration, cancellationToken);
             await InsertHistoryRowAsync(
                 connection, effectiveSchema, tableName,
-                migration.Version, migration.Description, cancellationToken);
+                migration.Version, migration.Description.Value, cancellationToken);
         }
     }
 
     private static Task ExecuteUpScriptAsync(
         MySqlConnection connection, IAmABoxMigration migration,
         CancellationToken cancellationToken)
-        => ExecuteDdlAsync(connection, migration.UpScript, cancellationToken);
+        => ExecuteDdlAsync(connection, migration.UpScript.Value, cancellationToken);
 
     private static async Task ExecuteDdlAsync(
         MySqlConnection connection, string ddl,

src/Paramore.Brighter.BoxProvisioning.PostgreSql/PostgreSqlBoxMigrationRunner.cs

@@ -462,7 +462,7 @@ await InsertHistoryRowAsync(
             await ExecuteUpScriptAsync(connection, transaction!, migration, cancellationToken);
             await InsertHistoryRowAsync(
                 connection, transaction!, effectiveSchema, tableName,
-                migration.Version, migration.Description, cancellationToken);
+                migration.Version, migration.Description.Value, cancellationToken);
         }
     }
 
@@ -482,14 +482,14 @@ protected override async Task RunNormalPathAsync(
             await ExecuteUpScriptAsync(connection, transaction!, migration, cancellationToken);
             await InsertHistoryRowAsync(
                 connection, transaction!, effectiveSchema, tableName,
-                migration.Version, migration.Description, cancellationToken);
+                migration.Version, migration.Description.Value, cancellationToken);
         }
     }
 
     private static Task ExecuteUpScriptAsync(
         NpgsqlConnection connection, NpgsqlTransaction transaction,
         IAmABoxMigration migration, CancellationToken cancellationToken)
-        => ExecuteDdlAsync(connection, transaction, migration.UpScript, cancellationToken);
+        => ExecuteDdlAsync(connection, transaction, migration.UpScript.Value, cancellationToken);
 
     private static async Task ExecuteDdlAsync(
         NpgsqlConnection connection, NpgsqlTransaction transaction,

src/Paramore.Brighter.BoxProvisioning.Sqlite/SqliteBoxMigrationRunner.cs

@@ -282,23 +282,23 @@ private static async Task ApplyOrSkipAsync(
         // Per ADR §6: if IdempotencyCheckSql is non-null, evaluate it under the lock-bearing
         // transaction. A non-zero scalar means the migration's effect is already present —
         // skip UpScript but still record history so MAX(V) advances.
-        if (!string.IsNullOrEmpty(migration.IdempotencyCheckSql))
+        if (!string.IsNullOrEmpty(migration.IdempotencyCheckSql?.Value))
         {
             var alreadyApplied = await ScalarIsPositiveAsync(
                 connection, transaction, migration.IdempotencyCheckSql!, cancellationToken);
             if (!alreadyApplied)
             {
-                await ExecuteUpScriptAsync(connection, transaction, migration.UpScript, cancellationToken);
+                await ExecuteUpScriptAsync(connection, transaction, migration.UpScript.Value, cancellationToken);
             }
         }
         else
         {
-            await ExecuteUpScriptAsync(connection, transaction, migration.UpScript, cancellationToken);
+            await ExecuteUpScriptAsync(connection, transaction, migration.UpScript.Value, cancellationToken);
         }
 
         await InsertHistoryRowAsync(
             connection, transaction, tableName,
-            migration.Version, migration.Description, cancellationToken);
+            migration.Version, migration.Description.Value, cancellationToken);
     }
 
     private static async Task<bool> ScalarIsPositiveAsync(

src/Paramore.Brighter.Inbox.DynamoDB.V4/CommandItem.cs

@@ -36,7 +36,7 @@ public CommandItem(T command, string contextKey)
         var type = typeof(T).Name;
 
         Time = $"{TimeStamp.Ticks}";
-        CommandId = command.Id;
+        CommandId = command.Id.Value;
         CommandType = typeof(T).Name;
         CommandBody = JsonSerializer.Serialize(command, JsonSerialisationOptions.Options);
         ContextKey = contextKey;

src/Paramore.Brighter.Inbox.DynamoDB.V4/DynamoDbInbox.cs

@@ -143,7 +143,7 @@ public async Task AddAsync<T>(T command, string contextKey, RequestContext? requ
     {
         var dbAttributes = new Dictionary<string, string>()
         {
-            {"db.operation.parameter.command.id", command.Id}
+            {"db.operation.parameter.command.id", command.Id.Value}
         };
         var span = Tracer?.CreateDbSpan(
             new BoxSpanInfo(DbSystem.Dynamodb, DYNAMO_DB_NAME, BoxDbOperation.Add, _configuration.TableName, dbAttributes: dbAttributes),

src/Paramore.Brighter.Inbox.DynamoDB/DynamoDbInbox.cs

@@ -135,7 +135,7 @@ public async Task AddAsync<T>(T command, string contextKey, RequestContext? requ
         {
             var dbAttributes = new Dictionary<string, string>()
             {
-                {"db.operation.parameter.command.id", command.Id}
+                {"db.operation.parameter.command.id", command.Id.Value}
             };
             var span = Tracer?.CreateDbSpan(
                 new BoxSpanInfo(DbSystem.Dynamodb, DYNAMO_DB_NAME, BoxDbOperation.Add, _configuration.TableName, dbAttributes: dbAttributes),

src/Paramore.Brighter.Inbox.Firestore/FirestoreInbox.cs

@@ -76,7 +76,7 @@ public void Add<T>(T command, string contextKey, RequestContext? requestContext,
     {
         var dbAttributes = new Dictionary<string, string>
         {
-            ["db.operation.parameter.command.id"] = command.Id,
+            ["db.operation.parameter.command.id"] = command.Id.Value,
             ["db.operation.parameter.command.context_key"] = contextKey,
         };
 
@@ -282,7 +282,7 @@ public async Task AddAsync<T>(T command, string contextKey, RequestContext? requ
     {
         var dbAttributes = new Dictionary<string, string>
         {
-            ["db.operation.parameter.command.id"] = command.Id,
+            ["db.operation.parameter.command.id"] = command.Id.Value,
             ["db.operation.parameter.command.context_key"] = contextKey,
         };
 

src/Paramore.Brighter.Inbox.MongoDb/MongoDbInbox.cs

@@ -50,7 +50,7 @@ public async Task AddAsync<T>(T command, string contextKey, RequestContext? requ
     {
         var dbAttributes = new Dictionary<string, string>()
         {
-            {"db.operation.parameter.command.id", command.Id}
+            {"db.operation.parameter.command.id", command.Id.Value}
         };
         var span = Tracer?.CreateDbSpan(
             new BoxSpanInfo(DbSystem.Mongodb,
@@ -63,7 +63,7 @@ public async Task AddAsync<T>(T command, string contextKey, RequestContext? requ
 
         try
         {
-            var message = new InboxMessage(command, command.Id, contextKey, Configuration.TimeProvider.GetUtcNow(),
+            var message = new InboxMessage(command, command.Id.Value, contextKey, Configuration.TimeProvider.GetUtcNow(),
                 ExpireAfterSeconds);
             await Collection.InsertOneAsync(message, cancellationToken: cancellationToken)
                 .ConfigureAwait(ContinueOnCapturedContext);
@@ -159,7 +159,7 @@ public void Add<T>(T command, string contextKey, RequestContext? requestContext,
     {
         var dbAttributes = new Dictionary<string, string>()
         {
-            {"db.operation.parameter.command.id", command.Id}
+            {"db.operation.parameter.command.id", command.Id.Value}
         };
         var span = Tracer?.CreateDbSpan(
             new BoxSpanInfo(DbSystem.Mongodb,
@@ -172,7 +172,7 @@ public void Add<T>(T command, string contextKey, RequestContext? requestContext,
 
         try
         {
-            var message = new InboxMessage(command, command.Id, contextKey, Configuration.TimeProvider.GetUtcNow(),
+            var message = new InboxMessage(command, command.Id.Value, contextKey, Configuration.TimeProvider.GetUtcNow(),
                 ExpireAfterSeconds);
             Collection.InsertOne(message);
         }

src/Paramore.Brighter.MessageScheduler.AWS.V4/AwsScheduler.cs

@@ -264,12 +264,12 @@ private async Task<Target> CreateTargetAsync(string id, Message message, bool as
 
     private ValueTask<string?> GetTopicAsync(Message message)
     {
-        if (s_topic.TryGetValue(message.Header.Topic, out var topicArn))
+        if (s_topic.TryGetValue(message.Header.Topic.Value, out var topicArn))
         {
             return new ValueTask<string?>(topicArn);
         }
 
-        return new ValueTask<string?>(GetTopicArnAsync(message.Header.Topic));
+        return new ValueTask<string?>(GetTopicArnAsync(message.Header.Topic.Value));
 
 
         async Task<string?> GetTopicArnAsync(string topicName)
@@ -289,12 +289,12 @@ private async Task<Target> CreateTargetAsync(string id, Message message, bool as
 
     private ValueTask<string?> GetQueueAsync(Message message)
     {
-        if (s_queueUrl.TryGetValue(message.Header.Topic, out var queueUrl))
+        if (s_queueUrl.TryGetValue(message.Header.Topic.Value, out var queueUrl))
         {
             return new ValueTask<string?>(queueUrl);
         }
 
-        return new ValueTask<string?>(GetQueueUrlAsync(message.Header.Topic));
+        return new ValueTask<string?>(GetQueueUrlAsync(message.Header.Topic.Value));
 
         async Task<string?> GetQueueUrlAsync(string queueName)
         {