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/hooks/start-work/index.ts

@@ -10,7 +10,7 @@ import {
   clearBoulderState,
 } from "../../features/boulder-state"
 import { log } from "../../shared/logger"
-import { updateSessionAgent } from "../../features/claude-code-session-state"
+import { getSessionAgent, updateSessionAgent } from "../../features/claude-code-session-state"
 
 export const HOOK_NAME = "start-work"
 
@@ -71,7 +71,10 @@ export function createStartWorkHook(ctx: PluginInput) {
         sessionID: input.sessionID,
       })
 
-      updateSessionAgent(input.sessionID, "atlas")
+      const currentAgent = getSessionAgent(input.sessionID)
+      if (!currentAgent) {
+        updateSessionAgent(input.sessionID, "atlas")
+      }
 
       const existingState = readBoulderState(ctx.directory)
       const sessionId = input.sessionID

src/hooks/todo-continuation-enforcer.ts

@@ -205,7 +205,11 @@ export function createTodoContinuationEnforcer(
       const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
       agentName = agentName ?? prevMessage?.agent
       model = model ?? (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)
       tools = tools ?? prevMessage?.tools
     }