fix: resolve ultrabrain review findings

- Remove runtime-fallback gate from session.status retry handler — runtime-fallback
  has no session.status handler, so gating it causes retry signals to be silently dropped
- Fix background_output full_session arg description: default is true, not false

src/tools/background-task/create-background-output.ts

@@ -45,7 +45,7 @@ export function createBackgroundOutput(manager: BackgroundOutputManager, client:
           "Wait for completion (default: false). System notifies when done, so blocking is rarely needed."
         ),
       timeout: tool.schema.number().optional().describe("Max wait time in ms (default: 60000, max: 600000)"),
-      full_session: tool.schema.boolean().optional().describe("Return full session messages with filters (default: false)"),
+      full_session: tool.schema.boolean().optional().describe("Return full session messages with filters (default: true)"),
       include_thinking: tool.schema.boolean().optional().describe("Include thinking/reasoning parts in full_session output (default: false)"),
       message_limit: tool.schema.number().optional().describe("Max messages to return (capped at 100)"),
       since_message_id: tool.schema.string().optional().describe("Return messages after this message ID (exclusive)"),