2026.08.11Pi's Durable AgentHarness: An Agent Loop That Survives kill -918 min read Three stores, one invariant Three stacked bands, one per durable store in a Pi AgentHarness session. First, entries — the conversation itself: messages, compaction summaries and branch summaries, written once, never edited or deleted, belonging to no lane. Second, registers — current mutable state: the lane leaf, the lane configuration, operation metadata and the total operation state, plus facts; a register is overwritten or deleted and keeps no write history, and the operation-state register is the program counter recovery reads. Third, the usage ledger — one append-only row per settled attempt, never edited or deleted, never in the tree. All three share one monotonic sequence number. A transaction is the only write primitive. Recovery reads the operation-state register; it does not replay a journal or infer state from what is missing. Three stores, one invariant every durable payload is an entry, a register, or a ledger row entries — the conversation messages, compaction summaries, branch summarieswrite-once · never edited · never deleted · belongs to no lane registers — current mutable state lane.leaf · lane.config · op.meta · op.state · factsoverwrite or delete · no write history · this is the program counter usage ledger — cost history one row per settled attempt · token and cost eventsappend-only · never edited · never deleted · not in the tree all three share one monotonic seq — a transaction is the only write primitive recovery reads op.state; it does not replay a journal or infer from what is missing
