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/features/builtin-commands/commands.ts

@@ -55,7 +55,6 @@ ${REFACTOR_TEMPLATE}
   },
   "start-work": {
     description: "(builtin) Start Sisyphus work session from Prometheus plan",
-    agent: "atlas",
     template: `<command-instruction>
 ${START_WORK_TEMPLATE}
 </command-instruction>

src/features/hook-message-injector/injector.ts

@@ -5,7 +5,7 @@ import type { MessageMeta, OriginalMessageContext, TextPart, ToolPermission } fr
 
 export interface StoredMessage {
   agent?: string
-  model?: { providerID?: string; modelID?: string }
+  model?: { providerID?: string; modelID?: string; variant?: string }
   tools?: Record<string, ToolPermission>
 }
 
@@ -141,9 +141,17 @@ export function injectHookMessage(
   const resolvedAgent = originalMessage.agent ?? fallback?.agent ?? "general"
   const resolvedModel =
     originalMessage.model?.providerID && originalMessage.model?.modelID
-      ? { providerID: originalMessage.model.providerID, modelID: originalMessage.model.modelID }
+      ? { 
+          providerID: originalMessage.model.providerID, 
+          modelID: originalMessage.model.modelID,
+          ...(originalMessage.model.variant ? { variant: originalMessage.model.variant } : {})
+        }
       : fallback?.model?.providerID && fallback?.model?.modelID
-        ? { providerID: fallback.model.providerID, modelID: fallback.model.modelID }
+        ? { 
+            providerID: fallback.model.providerID, 
+            modelID: fallback.model.modelID,
+            ...(fallback.model.variant ? { variant: fallback.model.variant } : {})
+          }
         : undefined
   const resolvedTools = originalMessage.tools ?? fallback?.tools
 

src/features/hook-message-injector/types.ts

@@ -12,6 +12,7 @@ export interface MessageMeta {
   model?: {
     providerID: string
     modelID: string
+    variant?: string
   }
   path?: {
     cwd: string
@@ -25,6 +26,7 @@ export interface OriginalMessageContext {
   model?: {
     providerID?: string
     modelID?: string
+    variant?: string
   }
   path?: {
     cwd?: string