Compaction has three entrances, one main pipeline

User-initiated compaction, reaching the automatic threshold, and the Provider rejecting an overly long context are triggered in different ways, but summary generation and boundary commit all share the same CompactionService.

Diagram source

flowchart TD
    MAN["/compact or rind/session/compact"] --> PIPE["CompactionService"]
    AUTO["ContextManager decides the threshold is reached"] --> PIPE
    ERR["Provider context-length error"] --> PIPE
    PIPE --> CORPUS["Prepare corpus and retained suffix"]
    CORPUS --> SUM["Generate handoff"]
    SUM --> COMMIT[("Commit the compaction boundary")]
    COMMIT --> REBUILD["Rebuild context"]

Manual compaction occupies the session's execution slot, emitting turn_started with operation=compact, context_compacted, and a terminal state; without new input it starts no extra conversation sampling. Automatic compaction happens before sampling in the current turn, and the original turn_id is unchanged. A first context-length error attempts compaction; later recovery tightens the hard limit and enables explicit context rescue.

The compaction service only generates and commits the handoff; whether to continue sampling is decided by the caller. If the pre-summary input budget precheck fails, the old context is kept and the error is raised directly, the model is not called, and that error is not disguised as a deterministic fallback after a summary failure.

Each entrance determines the follow-up action

Entrance	Turn identity and follow-up action
Manual compact	Occupies the execution slot exclusively and reports a maintenance-operation terminal state; holds no extra conversation without input
Automatic threshold trigger	Tidies up context before the next sampling in the current turn and continues the original task
context-length error	The first attempt compacts; later attempts tighten the hard limit and attempt rescue, under bounded recovery

The automatic threshold follows ContextManager's budget decision; it does not trigger on "more than N messages". A provider can still reject input sooner than the local estimate predicts, so error recovery is a necessary complement, and tightening the hard limit by 0.8 for later attempts does not mean retrying without bound until something happens to succeed.

Code entry points: TurnRunner, CompactionService, manual entrance. Verification: compaction mainline, input and compaction.

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