chore(assistant): mark the step store and the model pick as independent writes

lint:tx counted the three step writes of the store and the ChatGPT sign-in
renewal before a model pick as one sequence. Each stands on its own.

server/src/nest/ai-connections/ai-connections.service.ts

@@ -195,6 +195,10 @@ export class AiConnectionsService implements SharedAiConnectionPort {
     return this.ownView(userId);
   }
 
+  /**
+   * Picks the model of the user's own connection, one the provider offers.
+   * @txIndependent reading the credential may renew a ChatGPT sign-in first; that write stands on its own.
+   */
   async setOwnModel(userId: number, model: string): Promise<AiConnectionView> {
     const row = await this.ownRow(userId);
     const models = await this.modelsOf(userId, row);

server/src/nest/assistant/assistant.service.ts

@@ -897,7 +897,10 @@ export class AssistantService {
     return new Map(categories.map((category): [number, string] => [category.id, category.name]));
   }
 
-  /** Where the loop keeps its steps: one row each, the chat turn's first one made already. */
+  /**
+   * Where the loop keeps its steps: one row each, the chat turn's first one made already.
+   * @txIndependent each step is opened and saved on its own, with a provider's answer between them.
+   */
   private stepStore(spec: TurnSpec): AgentStore {
     let first = spec.firstRowId;
     const fields = (step: StepRecord) => ({