Fix new sessions to inherit last used variant from previous session (Vibe Kanban) (#1870)

* The implementation is complete. Here's a summary of the changes:

## Summary

Fixed the issue where new sessions were inheriting the last used executor but not the last used variant.

### Changes Made to `vibe-kanban/frontend/src/components/ui-new/containers/SessionChatBoxContainer.tsx`:

1. **Added import** for `useExecutionProcesses` hook

2. **Added `lastSessionId`** - gets the most recent session's ID only when in new session mode:
   ```tsx
   const lastSessionId = isNewSessionMode ? sessions?.[0]?.id : undefined;
   ```

3. **Added `useExecutionProcesses` call** - fetches processes from the last session to get the full executor profile:
   ```tsx
   const { executionProcesses: lastSessionProcesses } =
     useExecutionProcesses(lastSessionId);
   ```

4. **Added `lastSessionProfile` memo** - extracts the full profile (executor + variant) from the last session's processes:
   ```tsx
   const lastSessionProfile = useMemo(() => {
     if (!lastSessionProcesses?.length) return null;
     return getLatestProfileFromProcesses(lastSessionProcesses);
   }, [lastSessionProcesses]);
   ```

5. **Updated `latestProfileId` computation** - now uses `lastSessionProfile` (which includes the variant) before falling back to just the executor with `variant: null`

The type check passes successfully. When a user creates a new session, it will now correctly inherit both the executor AND variant from the most recently used session in that workspace.

* Done! The refactoring is complete. Here's a summary of the changes:

## Summary

Refactored the `latestProfileId` logic in `SessionChatBoxContainer.tsx` to be cleaner:

**Before:** 4 separate declarations
- `lastSessionExecutor` memo
- `lastSessionId`
- `lastSessionProcesses` hook
- `lastSessionProfile` memo
- `latestProfileId` memo (referencing all the above)

**After:** 3 declarations, consolidated
- `lastSessionId`
- `lastSessionProcesses` hook
- `latestProfileId` memo (all logic inlined)

**Changes:**
- Removed 2 intermediate `useMemo` hooks
- Inlined `lastSessionExecutor` and `lastSessionProfile` directly into `latestProfileId`
- Same 3-tier fallback behavior preserved: current processes → last session processes → session metadata
- Type check passes

frontend/src/components/ui-new/containers/SessionChatBoxContainer.tsx

@@ -6,6 +6,7 @@ import {
   type BaseCodingAgent,
 } from 'shared/types';
 import { useAttemptExecution } from '@/hooks/useAttemptExecution';
+import { useExecutionProcesses } from '@/hooks/useExecutionProcesses';
 import { useUserSystem } from '@/components/ConfigProvider';
 import { useApprovalFeedbackOptional } from '@/contexts/ApprovalFeedbackContext';
 import { useMessageEditContext } from '@/contexts/MessageEditContext';
@@ -176,21 +177,23 @@ export function SessionChatBoxContainer({
   // User profiles, config preference, and latest executor from processes
   const { profiles, config } = useUserSystem();
 
-  // Get last used executor from the most recently used session in this workspace
-  const lastSessionExecutor = useMemo(() => {
-    if (!sessions?.length) return null;
-    // Sessions are sorted by most recently used (first is most recent)
-    const mostRecentSession = sessions[0];
-    return mostRecentSession?.executor ?? null;
-  }, [sessions]);
+  // Fetch processes from last session to get full profile (only in new session mode)
+  const lastSessionId = isNewSessionMode ? sessions?.[0]?.id : undefined;
+  const { executionProcesses: lastSessionProcesses } =
+    useExecutionProcesses(lastSessionId);
 
-  // Compute latestProfileId: from processes, or fall back to last session's executor
+  // Compute latestProfileId: current processes > last session processes > session metadata
   const latestProfileId = useMemo(() => {
-    // If we have processes (existing session), use them
+    // Current session's processes take priority
     const fromProcesses = getLatestProfileFromProcesses(processes);
     if (fromProcesses) return fromProcesses;
 
-    // Fall back to last session's executor (useful for new session mode)
+    // Try full profile from last session's processes (includes variant)
+    const fromLastSession = getLatestProfileFromProcesses(lastSessionProcesses);
+    if (fromLastSession) return fromLastSession;
+
+    // Fallback: just executor from session metadata, no variant
+    const lastSessionExecutor = sessions?.[0]?.executor;
     if (lastSessionExecutor) {
       return {
         executor: lastSessionExecutor as BaseCodingAgent,
@@ -199,7 +202,7 @@ export function SessionChatBoxContainer({
     }
 
     return null;
-  }, [processes, lastSessionExecutor]);
+  }, [processes, lastSessionProcesses, sessions]);
 
   // Message editor state
   const {