Implement RFC-026 Phase A MemWAL foundation

[aaltshuler]

Summary

• activate internal manifest schema v7 with identity-keyed MemWAL lifecycle authority
• add a private, main-only Phase-A enrollment adapter for one exact empty unsharded shard
• add recovery-v10 exact N / N+1 classification and roll-forward-or-retire behavior
• put root-shared stream-admission leases outside the existing schema → branch → table gates
• fence ordinary writers, schema changes, maintenance, repair adoption, and recovery against lifecycle-bound tables
• preserve the narrow native-branch exception at SEALED and reject OPEN / DRAINING topology changes
• refuse partial MemWAL format states and enforce the v6 → v7 export/import boundary
• update RFC-026, write-path, versioning, testing, upgrade, and state-of-affairs documentation

Why

RFC-022 made the direct-publish path correct, but streaming cannot safely begin with row admission. We first need durable lifecycle ownership, exact crash classification, and one admission/exclusion order shared by every physical writer. This slice establishes that correctness and format foundation using Lance MemWAL rather than introducing a custom WAL or transaction manager.

Deliberate boundary

This does not expose public stream enrollment, @stream, WAL row put, durable row acknowledgement, fold, drain/resume, or fresh-read behavior. The supported Phase-A topology is canonical main, one empty unsharded shard, and one live writer process.

Validation

• cargo test --workspace --locked
• cargo test -p omnigraph-engine --features failpoints --test failpoints --locked — 140 passed, 1 intentional helper ignored
• MemWAL enrollment gate — 15 passed
• genuine v6 ↔ v7 cross-version refusal/rebuild test
• scripts/check-agents-md.sh
• git diff --check
• independent red-team source review with no remaining blocker

Greptile Summary

This PR adds the RFC-026 Phase A MemWAL foundation. The main changes are:

• Activates manifest schema v7 with identity-keyed stream lifecycle state.
• Adds private enrollment for one empty, unsharded main-table WAL.
• Adds exact recovery and roll-forward behavior for enrollment.
• Fences conflicting writes, schema changes, maintenance, repair, and recovery.
• Enforces v6-to-v7 export and import migration boundaries.
• Updates tests and documentation for the new storage contract.

Confidence Score: 5/5

This looks safe to merge.

• Post-publication sidecar deletion failure no longer turns a completed enrollment into a caller-visible failure.
• Failures before durable publication or audit still propagate.
• A retained sidecar is recovered idempotently without republishing enrollment state.
• No blocking issue remains within the reviewed follow-up scope.

Important Files Changed

Filename	Overview
crates/omnigraph/src/db/manifest/recovery.rs	Adds stream-enrollment recovery and separates required recovery cleanup from best-effort cleanup after durable publication.
crates/omnigraph/src/db/omnigraph/stream_enrollment.rs	Adds the private Phase A enrollment flow and verifies the published OPEN lifecycle.
crates/omnigraph/src/table_store/mem_wal.rs	Adds the bounded MemWAL storage adapter used by Phase A enrollment and recovery.
crates/omnigraph/tests/failpoints.rs	Adds failure-path tests for enrollment publication, cleanup, and later recovery.

_{Reviews (2): Last reviewed commit: "fix: preserve stream enrollment success ..." | Re-trigger Greptile}

Context used:

• Context used - AGENTS.md (source)
• Context used - CLAUDE.md (source)