Prove runtime signer rotation end-to-end without restarting rollup-node

[dghelm]

Summary

Track downstream acceptance evidence for the runtime authorized-signer refresh implemented by #7 after #6 closes.

The focused tests in #7 prove watcher refresh delivery, forward-head rotation, same-height reorgs, retry semantics, and in-process SystemContractConsensus decisions. The existing node signer-rotation e2e supplements those tests by manually injecting a consensus notification. A real live RotateSequencerSigner transition through the synthetic L1 and watcher bridge remains to be proven.

Cross-repository harness owner: DogeOS69/dogeos-core#722

Related snapshot hardening: #8, blocked by DogeOS69/dogeos-core#721

Acceptance contract

Close this issue when the cross-repository harness demonstrates all of the following using a rollup-node image that contains #7:

• the synthetic L1 executes a real RotateSequencerSigner action while continuing to advance;
• the relevant sequencer and a follower are already running before the transition;
• both use production SystemContractConsensus, not NoopConsensus;
• neither node relies on a static --network.valid_signer override to mask dynamic behavior;
• l1_interface, the standby/new sequencer, and the follower keep the same process/container identities throughout the transition;
• the already-running nodes log Authorized signer updated to: <new signer>;
• the same standby/new-sequencer process begins producing blocks signed by the new signer without restart;
• the follower that started before the switch accepts those blocks and continues advancing; and
• the old signer no longer passes the relevant sequencing/validation checks after the update.

Evidence to attach

• Exact rollup-node image tag, source SHA, and image digest.
• Exact dogeos-core revision and harness command.
• Old and new signer addresses used by the test.
• Pre/post process or container identities.
• Signer-update log excerpts from the pre-existing nodes.
• Block production and follower-advancement assertions.
• Confirmation that no genesis/config patch, replay reseed, or l1_interface restart was used to perform the transition.

Boundaries

This is an acceptance/evidence tracker, not a request to weaken the focused test suite or add a NoopConsensus workaround.

EIP-1898 block-hash pinning is tracked separately in #8. The live harness should first prove #7's supported unpinned runtime behavior; it can later be extended to exercise canonical pinned reads when DogeOS69/dogeos-core#721 and #8 land.