[CPerezz]

make migration-offline (args/migration-offline.yaml) runs the full lap plus the offline path of EIP-8347.
A non-validating geth (P6) and erigon (P2) export a PBT snapshot and preimage file at a finalized anchor. Then
Nethermind (P5) and geth (P3) stop, import it, restart and replay to the tip, one at a time, while the network
keeps finalizing.

Added

• cmd/migration-swap: the host-side orchestrator.
  • geth converts a copy of P6's datadir; erigon exports live.
  • Swaps run as a serial queue, gated on: anchor finalized and canonical, fresh finality, the other validators
    healthy, no partition, a chaos gap, the deadline.
  • Writes swaps.json and posts each step to the monitor.
• images/geth, images/nethermind: thin layers over the client images that run the import on start.
• main.star: pbt_migration.offline with plan-time checks. Observers (validator_count: 0) are kept out of
  stake, chaos and the gate.
• Monitor: POST /api/lifecycle, per-node export/import steps, derived replaying/caught_up, a swap panel
  and anchor markers. README clip re-recorded.
• Judge: artifact-produced, import-accepted, swaps-serialized, replay-caught-up and offline-coverage
  (INCONCLUSIVE on online laps).

Pins

scripts/sources.sh fetches each fork at a pinned commit into ../pbt-devnet-src/<name>. PBT_*_REF moves a
pin (a branch name tracks the tip); PBT_*_SRC builds a local checkout as-is.

Fork	Branch	Pin
geth	pbt	fbfd486b
erigon	binary-trie	7b675afb
egg	pbt-offset	b56f205b
besu (matkt)	glamsterdam-devnet-8-pbt	ba419e5f
besu-stateless	feat/partitioned-binary-trie	9a9a9817
Nethermind	pbt-state	323217bc

Fixed

• shadow-samples: after I* only "binary parked" is required, since geth freezes merkle at I*. Erigon stopping
  its hex shadow 96 blocks past activation counts as retirement once the fork block is finalized, not a stall.
• The observer bridged every partition: it sat in no disruptoor group. Observers now join the anchor's group
  (--observer on migration-chaos, migration-gate and pbtchaos).
• partitions-healed: a repeated isolate (the straddle hold) replaced the open chaos window, so a late fork
  crossing looked unscheduled.
• lap.sh gave no verdict when an EL was stopped. The judge now gets an unreachable URL for it, so those
  checks fail with evidence.
• swaps-serialized failed a skipped swap for having no stop time. Skipped swaps are excluded;
  offline-coverage still fails them.
• lap-manifest failed the lap on a pbtchaos "inconclusive", which now gives INCONCLUSIVE.
• caught_up was measured against the node's own head, which right after a restart is as stale as its
  cursor. It is now measured against node 1's head.
• tree-at-genesis: erigon refused to write the bin-only genesis under its new parallel-commitment default.
  Both erigons set COMMITMENT_PARALLEL=false until db/state, cmd: let a bin-only datadir drop an unrequested parallel-commitment default erigontech/erigon#24617 lands.

Verification

• go test -race ./... passes.
• make migration-offline: exit 0, 21/21 PASS. Exports at anchors 161 and 159; Nethermind and geth caught up
  to the tip 59 s and 37 s after stopping.
• make migration: exit 0, 16 PASS, with the 5 offline checks INCONCLUSIVE by design.
• make migration-smoke: exit 0.
• make tree-at-genesis: 8 clients agree over 100 blocks.

Client findings from these laps

• erigon: binary-trie: a genesis with binaryTrieTime 0 cannot be initialised with default settings erigontech/erigon#24612, fix in db/state, cmd: let a bin-only datadir drop an unrequested parallel-commitment default erigontech/erigon#24617.
• besu: Read the trie branch cursor from the world state's own storage matkt/besu#33.
• Nethermind: Restart deletes the whole chain: genesis is replayed on an empty state NethermindEth/nethermind#14323, fix in fix(processing): refuse a branch that reaches genesis without state NethermindEth/nethermind#14324.