Atomic multi-statement programs (stage then commit, one WAL record) #131

Multi-statement programs apply statement by statement. Validation failures continue while other statements commit (handler.rs:2668-2704), and a storage error aborts after earlier statements persisted. A gateway turn can apply a retraction and lose the replacing assert behind a success response. Gateway retries then duplicate data, and client cancellation can release the conversation lock mid-write.
Plan: parse and validate the whole program first, then apply all writes at one logical time under the KG lock as one WAL record, all or nothing. Builds on wp-write-effective-delta and the segmented WAL. Gateway follow-up: idempotency key per turn, and run the critical section in a spawned task.

Roadmap checkpoint — 2026-10-03

R2 delivers the engine transaction boundary; R3 adds durable gateway retry/cancellation semantics. This umbrella is assigned to R3 for whole-issue completion and must remain open until all four slices pass.

• Atomic programs: transaction WAL envelope and all-or-nothing replay #168 — R2: transaction WAL envelope/replay
• Atomic programs: staged fact mutations and one-revision publication #169 — R2: staged fact programs, one revision
• Atomic programs: transactional rules/schema and explicit command boundaries #170 — R2: atomic rules/schema and explicit unsupported commands
• Gateway: durable turn idempotency and message-index reservation #178 — R3: durable gateway turns and index reservation