Compaction & context
Compaction shows what shaped a session and where its context was silently dropped.
A long session doesn't keep everything in view. When context runs out, the harness summarizes what came before — and later turns see that summary rather than what was actually said. Compaction is OAK's record of where that happened and how much was dropped.
What a compaction is
A compaction is the harness summarizing the conversation when context runs out: everything above the boundary reaches later turns as a summary rather than as what was actually said. It's a normal part of a long session — but it means the agent's later decisions rested on a compressed picture, which is worth knowing when you review them.
How OAK reports it
The observatory marks each boundary in the Actions timeline, counts them per prompt and in Stats, and reports each event's own drop — the context before minus the context after.
OAK reports each compaction's own drop, never the harness's running total — which would overstate every compaction after the first. The number beside a boundary is what that boundary dropped.
A resumed compaction also shows up in Observations' Context section, labeled as what shaped the session — so a summary the agent inherited is visible, not invisible.