fix(start-work): prevent overwriting session agent if already set; inherit parent model for subagent types (#1201)

* fix(start-work): prevent overwriting session agent if already set; inherit parent model for subagent types

* fix(model): include variant in StoredMessage model structure for better context propagation

* fix(injector): include variant in model structure for hook message injection

src/tools/delegate-task/tools.ts

@@ -287,7 +287,11 @@ Prompts MUST be in English.`
         resolvedParentAgent: parentAgent,
       })
       const parentModel = prevMessage?.model?.providerID && prevMessage?.model?.modelID
-        ? { providerID: prevMessage.model.providerID, modelID: prevMessage.model.modelID }
+        ? { 
+            providerID: prevMessage.model.providerID, 
+            modelID: prevMessage.model.modelID,
+            ...(prevMessage.model.variant ? { variant: prevMessage.model.variant } : {})
+          }
         : undefined
 
       if (args.session_id) {
@@ -806,6 +810,13 @@ Create the work plan directly - that's your job as the planning agent.`
         } catch {
           // If we can't fetch agents, proceed anyway - the session.prompt will fail with a clearer error
         }
+
+        // When using subagent_type directly, inherit parent model so agents don't default
+        // to their hardcoded models (like grok-code) which may not be available
+        if (parentModel) {
+          categoryModel = parentModel
+          modelInfo = { model: `${parentModel.providerID}/${parentModel.modelID}`, type: "inherited" }
+        }
       }
 
       const systemContent = buildSystemContent({ skillContent, categoryPromptAppend, agentName: agentToUse })