diff --git a/internal/agent/agent.go b/internal/agent/agent.go
index c7c96cd42cfce58eab918e9ae2e267ac3f78ad8d..b2074b066b49038703a05dbe190dbe8e18a835f9 100644
--- a/internal/agent/agent.go
+++ b/internal/agent/agent.go
@@ -249,12 +249,17 @@ func (a *sessionAgent) Run(ctx context.Context, call SessionAgentCall) (*fantasy
 
 	var currentAssistant *message.Message
 	var shouldSummarize bool
+	// Don't send MaxOutputTokens if 0 — some providers (e.g. LM Studio) reject it
+	var maxOutputTokens *int64
+	if call.MaxOutputTokens > 0 {
+		maxOutputTokens = &call.MaxOutputTokens
+	}
 	result, err := agent.Stream(genCtx, fantasy.AgentStreamCall{
 		Prompt:           message.PromptWithTextAttachments(call.Prompt, call.Attachments),
 		Files:            files,
 		Messages:         history,
 		ProviderOptions:  call.ProviderOptions,
-		MaxOutputTokens:  &call.MaxOutputTokens,
+		MaxOutputTokens:  maxOutputTokens,
 		TopP:             call.TopP,
 		Temperature:      call.Temperature,
 		PresencePenalty:  call.PresencePenalty,
@@ -425,6 +430,11 @@ func (a *sessionAgent) Run(ctx context.Context, call SessionAgentCall) (*fantasy
 		StopWhen: []fantasy.StopCondition{
 			func(_ []fantasy.StepResult) bool {
 				cw := int64(largeModel.CatwalkCfg.ContextWindow)
+				// If context window is unknown (0), skip auto-summarize
+				// to avoid immediately truncating custom/local models.
+				if cw == 0 {
+					return false
+				}
 				tokens := currentSession.CompletionTokens + currentSession.PromptTokens
 				remaining := cw - tokens
 				var threshold int64