feat: add fusion for multi-run sessions

Adds Run fusion for multi-run-like sessions
Combines sibling outputs into a new fusion session
Adds configurable Fusion prompts in Magic Prompts settings

packages/ui/src/lib/i18n/messages/en.settings.ts

@@ -164,6 +164,7 @@ export const settingsDict = {
   'settings.magicPrompts.sidebar.item.planImplement': 'Implement Plan',
   'settings.magicPrompts.sidebar.item.sessionSummary': 'Session Summary',
   'settings.magicPrompts.sidebar.item.sessionWorkspaceReview': 'Workspace Review',
+  'settings.magicPrompts.sidebar.item.sessionFusion': 'Fusion',
   'settings.remoteInstances.sidebar.title': 'Remote Instances',
   'settings.remoteInstances.sidebar.total': 'Total {count}',
   'settings.remoteInstances.sidebar.newSshInstanceName': 'New SSH Instance',
@@ -1541,6 +1542,8 @@ export const settingsDict = {
   'settings.magicPrompts.page.group.sessionSummary.description': 'Prompts used by the /summary slash command: visible user message + hidden instructions. Non-destructive - does not compact session history.',
   'settings.magicPrompts.page.group.sessionWorkspaceReview.title': 'Workspace Review',
   'settings.magicPrompts.page.group.sessionWorkspaceReview.description': 'Prompts used by the /workspace-review slash command: visible user message + hidden instructions. Reviews current workspace changes for high-signal issues only.',
+  'settings.magicPrompts.page.group.sessionFusion.title': 'Fusion',
+  'settings.magicPrompts.page.group.sessionFusion.description': 'Prompts used when combining multi-run outputs into one final answer: visible user message + hidden instructions before source results.',
   'settings.magicPrompts.page.actions.resetting': 'Resetting...',
   'settings.magicPrompts.page.actions.resetAllOverrides': 'Reset All Overrides',
   'settings.magicPrompts.page.actions.resetToDefault': 'Reset to Default',