Summary

• Show what_to_summarize as the collapsed basher preview while the agent is still running.
• Switch completed basher previews to a one-line, truncated output preview, using streamed text first and terminal command output as a fallback.
• Add focused tests for running, completed, fallback, and truncation behavior.

Validation

• bun test cli/src/utils/__tests__/agent-display.test.ts
• bun run --cwd cli typecheck
• bunx prettier --check cli/src/utils/agent-display.ts cli/src/components/blocks/agent-branch-wrapper.tsx cli/src/utils/__tests__/agent-display.test.ts