feat(subnet-splitting): freeze registry version until summary is reached

[pierugo-dfinity]

Because Consensus passes the block’s validation context's registry version to other components (including DSM), it could happen that a subnet split has not yet happened from Consensus' point of view but it would have from the other components' point of view. While it does not necessarily have to lead to misbehavior, this PR proposes to "freeze" the registry version in the validation context from the moment a split is detected in the registry until the next summary block (which will have a Scheduled status).

More precisely, we will not bump the registry version in the validation context of any data block in a DKG interval to any version of the registry which has a flag indicating that the subnet splitting should happen. We only bump it when reaching the summary block (to exactly the registry version the split was scheduled at, not a more recent one).

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to 85b670f.

Security Overview

• 🔎 Scanned files: 9 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f5e9d2bb-29a4-4b64-902a-391d65fd8b2d?scanId=8be8b38b-f2b5-4d1a-b14b-480902417e17&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► rs/consensus/src/consensus/block_maker.rs     Update get_stable_registry_version to consider last summary block and subnet splitting; add last_summary parameter and new logic for freezing/bumping registry version during subnet splitting ► rs/consensus/src/consensus/malicious_consensus.rs     Use updated get_stable_registry_version signature with last_summary_block ► rs/consensus/src/consensus/validator.rs     Integrate subnet_splitting status checks into validation flow and introduce new error variants for subnet splitting scenarios ► rs/consensus/utils/src/subnet_splitting.rs     Add new module implementing subnet splitting status logic (get_status, Status enum, StatusError, tests)
Enhancement	► rs/consensus/utils/src/lib.rs     Expose subnet_splitting module
Enhancement	► rs/consensus/utils/src/subnet_splitting.rs (new file)     Implement get_status and related types for subnet splitting status management
Enhancement	► rs/consensus/utils/BUILD.bazel     Add thiserror and registry/keys dependencies for tests and utilities ► rs/consensus/utils/Cargo.toml     Add thiserror and ic-registry-keys as dependencies; add rstest to dev-dependencies
Enhancement	► rs/consensus/utils/src/lib.rs     Publish subnet_splitting module
Enhancement	► rs/consensus/src/consensus/validator.rs (tests/usage updates)     Update imports and usage to align with new subnet_splitting logic; handle new ValidationFailure variants
Enhancement	► rs/consensus/src/consensus/malicious_consensus.rs (tests/usage updates)     Update call to get_stable_registry_version to pass last_summary_block
Enhancement	► Cargo.lock / dependencies (general) additions     ic-registry-keys, rstest, thiserror included in appropriate sections

[Copilot]

Pull request overview

This PR adjusts consensus’ handling of registry versions during subnet splitting to prevent non-summary (data) blocks from adopting a registry version that already indicates a pending split, and to ensure the summary block adopts exactly the registry version at which the split was scheduled.

Changes:

• Add a subnet_splitting utility to detect whether a subnet split is pending at a given registry version and expose a Status/StatusError API.
• Update block-making to “freeze” the context registry version below the scheduled split version until the next summary block, then bump exactly to the scheduled version.
• Update block validation to reject data blocks that reference a registry version at/above the scheduled split version, and to require summary blocks to reference exactly the scheduled version; add tests.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rs/types/types/src/consensus/catchup.rs	Introduces SubnetSplittingArgs decoding from protobuf for subnet-splitting CUP contents.
rs/consensus/utils/src/subnet_splitting.rs	New helper to determine whether subnet splitting is scheduled vs. already adopted, plus unit tests.
rs/consensus/utils/src/lib.rs	Exposes the new subnet_splitting module.
rs/consensus/utils/Cargo.toml	Adds dependencies for the new module and its tests (thiserror, ic-registry-keys, rstest).
rs/consensus/utils/BUILD.bazel	Mirrors the new Rust deps for Bazel builds/tests.
rs/consensus/src/consensus/validator.rs	Enforces frozen vs. exact registry-version rules during splitting; adds corresponding tests.
rs/consensus/src/consensus/malicious_consensus.rs	Updates call site for get_stable_registry_version signature change.
rs/consensus/src/consensus/block_maker.rs	Implements registry-version freezing/bumping behavior based on subnet-splitting status; adds tests.
Cargo.lock	Records new dependency additions.

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