A5 — delta sync activation (flagged off)

[Jurij89]

Summary

• Wires the already-plumbed sinceBatchId delta sync into production callers behind a flag (DKG_SYNC_DELTA, default OFF), with full-scan anti-entropy guard rails (every 8th round per peer/CG and after any round with rejected KCs).
• Conservative by design: the watermark is emitted only after a per-CG batchId-monotonicity check, which is itself an open question (verify against the registry contract before defaulting on).

Related

• Part of Sync responder's unbound GRAPH ?g page queries (O(store) per page) + retry/scheduler loops cause the ~9-core oxigraph peg (#1127) and the write-path failures (#1136) — analysis, staged fix plan, and an independent unauthenticated cross-CG read bypass in the same responder #1138 (Track A, PR A5). Flagged off; refines (does not gate) the checkpoint.
• Merge order: Wave 1.5 — after the checkpoint. Keep the flag default OFF until the monotonicity question is resolved.

Files changed

File	What
agent/src/dkg-agent-lifecycle.ts	sinceBatchIdFor wiring + anti-entropy guard rails (flagged)
agent/src/dkg-agent-base.ts	Delta watermark state

Plus 1 test file.

Test plan

• pnpm -F dkg-agent test
• Flag OFF (default): behavior identical to today (full scan)
• Flag ON: delta narrows correctly; anti-entropy forces periodic full scans and after rejected KCs
• pnpm build + lint

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Wave 2 — opened as draft. Gated behind the Wave-1 live-node checkpoint (#1138, Verification): A1-A4 + B0-B2 must merge into integration/issue-1138 and pass the field repro (sustained CPU < 1 core, VM publish < 1 s) before this is un-drafted/merged. Targets integration/issue-1138.

[Jurij89]

Closing without merging — A5 (delta/incremental sync) is not needed and can't be safely activated in V10:

1. Not needed — the sync-responder CPU peg (Online node sustains ~9 CPU cores from per-message/per-CG _meta policy queries scaling with peers × discovered CGs (separate from the fixed R6 idle scan) #1127 / VM publish fails validating contextGraphId when /api/context-graph/list stalls #1136) is already fixed by the un-peg gate (A1–A4 + B0–B2, merged via Issue #1138 — un-peg sync-responder CPU: A1–A4 + B0–B2 (§7 checkpoint PASS) #1164). The §7 field-repro checkpoint confirmed ~10–15 cores → ≤0.38 cores. Delta sync was only an incremental optimization on top of an already-cheap path, not part of the cure.
2. Can't safely activate — incremental sync needs a reliable per-CG cursor; in V10 dkg:batchId is a KA id, not a safe per-CG delta cursor (no sound 'give me everything since X' marker). This branch's own guard already refuses to activate (DKG_SYNC_DELTA=1 warns and stays full-scan).

Deferred to #1174 (revive when V10 has a per-CG ordinal/version cursor; the plumbing + guard here can be revived from this branch). Part of #1138.