M30: resilient compaction with fallback and persistence #792
Description
Make compaction resilient to failures, add progressive fallback, persist compacted state.
Gap: Zeph has only proactive compaction with no fallback and in-memory-only state. Missing: reactive compaction on ContextLengthExceeded, middle-out tool removal fallback, structured multi-section compaction prompt, and durable compaction via SQLite persistence.
Acceptance Criteria
- Reactive compaction on ContextLengthExceeded
- Middle-out progressive tool response removal fallback
- Structured 9-section compaction prompt
- Persist compacted state to SQLite
Depends on: M28 (#790)
Ref: .local/plan/m27-m31-context-memory-improvements.md