feat(core): compact v2 session context (#30986)

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Kit Langton 2026-06-05 13:17:23 -04:00 committed by GitHub
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@ -98,12 +98,22 @@ Current Context Epoch follow-ups:
- Add configured, remote, and nested instruction sources with explicit precedence and removal semantics.
- Add durable post-crash activity recovery for promoted or provider-dispatched work.
- Integrate actual automatic/context-pressure compaction with epoch replacement.
- Add provider-overflow recovery and explicit manual compaction on top of automatic request-budget compaction.
- Add operational metrics for observation latency, unavailable sources, contention, baseline size, and chronological-update growth.
- Consider watcher-backed per-file caching only if measurements show direct safe-boundary observation is too expensive.
- Expose plugin-defined Context Sources only after plugin reload and scoped cleanup semantics are designed.
- Add clustered Session execution ownership and stale-runtime fencing.
## Automatic Compaction
Before each provider turn, the runner estimates the complete model-visible request and compares it with the selected model's context window minus absolute reserved headroom. The reserve is the greater of the requested/model output allowance and configured `compaction.buffer`. When the request exceeds that budget and older complete turns are available, the runner compacts before executing the pending turn.
Compaction keeps the full transcript durable while replacing its active model representation with one hidden checkpoint containing a structured rolling summary and token-bounded serialized recent context. Provider-native assistant, reasoning, and tool messages never survive across the boundary, avoiding signature and encrypted-reasoning failures when the earlier prefix changes.
`session.next.compaction.started.1` durably identifies the attempt. Compaction deltas are live-only progress. `session.next.compaction.ended.2` durably stores the final summary and serialized recent context; only this completed event projects a model-visible compaction message and requests Context Epoch replacement. A failed or interrupted attempt therefore leaves the previous history boundary active.
Repeated compactions update the previous structured summary with newly compacted messages. The runner then reloads projected history and executes the original pending turn. Provider overflow recovery and deterministic old tool-result pruning remain separate follow-ups.
## V1 Runtime Context Parity
This is the canonical checklist for model-visible runtime context still needed before the V2 runner replaces V1. Keep each behavior in its owning boundary rather than treating all model-visible text as a durable Context Source. Update this table in the PR that changes a status.