Bound large exec output while preserving searchable artifacts

Summary

Large shell/unified-exec outputs can currently become very large model-visible and UI-visible payloads. This can bloat the agent context, make transcript rendering expensive, and obscure the useful part of the result.

I would like to propose bounding the inline command output while preserving the full output as a local artifact path that the agent can inspect with normal lexical tools such as rg, sed, or tail.

Proposed behavior

• Keep small command outputs inline as today.
• When command output exceeds a configurable threshold, write the full output to a temp artifact file.
• Return a bounded preview plus metadata that includes the saved file path, byte count, approximate token count, and suggested inspection commands.
• Ensure telemetry/log previews do not create spill artifacts.
• Ensure app-server/TUI command transcript display prefers bounded formatted output when it exists, rather than loading the raw full output.

Why this helps

This keeps model-visible context bounded without losing access to the complete command result. It also protects TUI transcript rendering from very large command cells while keeping the full output available for follow-up searches.

Validation from prototype

A prototype branch adds config, core spill handling, unified exec wiring, app-server display handling, and tests for the spill paths. Targeted spill tests pass locally, and app-server-protocol tests pass locally.

I understand external code contributions are by invitation only; opening this issue first to see whether the approach aligns with the maintainers' intended direction.