Manual context compaction skips a single long turn #3542

What happened

Manual Context Compaction does nothing when the completed Session history contains only one user Turn, even if that Turn contains a long Agent Loop with many completed assistant and tool steps.

The result is unchanged with reason insufficient_turns. The summarizer is never called.

A Turn can legitimately contain many Agent Loop steps, so Turn count should not decide whether its completed history can be compacted.

How to reproduce

1. Start a Session with one user Turn.
2. Let the Agent Loop produce a substantial number of completed assistant and tool steps.
3. Wait for the Turn to finish.
4. Run manual Context Compaction.
5. Observe insufficient_turns and no new checkpoint.

With the same RuntimeEvents, minRecentTurns: 1 reproduces the skip. Setting it to 0 selects a replaceable prefix and produces a checkpoint draft.

Environment

• Maka commit: f19eede03a829c226be39f001b2684860a3aa1d5
• OS: macOS
• Surface: Desktop / Runtime Host

Logs, screenshots, or additional context

The guard is in packages/runtime/src/history-compact.ts: histories with at most one Turn are rejected unless minRecentTurns === 0.

Manual compaction defaults this value to 1. Oversized-turn recovery already overrides it to 0.

The fix should also remove the duplicated manual policy construction. Manual, pre-turn, mid-turn, and overflow compaction should use the same checkpoint path, with trigger-specific retention expressed as explicit input. The change should cut over atomically and remove the superseded production path in the same PR.

The separate, default-off semanticCompact experiment is out of scope and is being discussed separately in #3541.

Drafted with Codex. I reproduced the behavior and reviewed the report.