Share configured LLM secret extraction across diagnostics paths

internal/framework/proposal_generation/generate.go

@@ -108,7 +108,7 @@ func GenerateCandidates(ctx context.Context, req Request) (Result, error) {
 		writer = diagnosticsWriterAdapter{
 			writer: llm.NewDiagnosticsWriter(
 				filepath.Join(req.DiagnosticsDir, req.ModuleInstance),
-				proposalGenerationSecrets(req.Config),
+				llm.ConfiguredSecrets(req.Config),
 			),
 		}
 	}
@@ -213,17 +213,6 @@ func resolveModel(cfg *config.Config, override string) string {
 	return llm.ResolvePrimaryConfig(*cfg).Model
 }
 
-func proposalGenerationSecrets(cfg *config.Config) []string {
-	if cfg == nil {
-		return nil
-	}
-	return []string{
-		cfg.PrimaryLLM.APIKey,
-		cfg.ValidationLLM.APIKey,
-		cfg.EffectiveValidationLLMConfig().APIKey,
-	}
-}
-
 func errPayload(err error) any {
 	if err == nil {
 		return nil