Fix steering held until run end after automatic compaction

[tmustier]

Summary

Fix steering staying queued until the run ends after automatic compaction. Compaction completion now releases delivery at the next safe turn boundary, while native input and command ordering remain intact.

Simplification review

• Replace two native-input booleans with none, pending and running states.
• Share one completion path for manual and automatic compaction.
• Inline the single-use batch-selection and delivery helpers into boundary dispatch.
• Remove the unreachable synchronous compaction-start recovery and its fabricated failure test. Keep real asynchronous failures and resource/send boundary recovery.
• Replace the new mocked lifecycle regressions with real AgentSession, bash-tool and compaction success/failure/cancellation tests.
• Shorten the validation record and prepare release 0.2.1, including npm installation instructions and release notes.

This removes about 75 production lines from the first PR version. No Pi core or production settings changes.

Verification

• All 3 public-session regressions fail against the original 91e3a5f implementation.
• npm run ci: 84 tests pass on Pi 0.87.0 and 0.99.2.
• The full TUI harness passes on both releases at afd4db0, with a clean tree.
• Live openai/gpt-6.1-sol, medium thinking, Pi 0.99.2: actual model-issued tools and normal Pi summarization. Steering after compaction causes the model to record STEERED before the original run ends.
• Independent result-file, transcript and event-log checks confirm one steering message and one agent run.
• Final head adds only the verification document, and its suite passes.

docs/validation.md records the prompt, model, settings, tested revision, observations and coverage limits. Attached images are rendered text captures from the actual scratch TUI, not desktop screenshots.