fix: reject legacy proofs whose headers commit to uncles/extensions

[eval-exec]

Problem

A peer can answer a GetBlocksProof / GetTransactionsProof request with a legacy (v0) message that omits the V1 extra fields (blocks_uncles_hash, blocks_extension). The client fabricated None extensions for every proved header without checking whether the header's authenticated extra_hash actually commits to an empty uncle list and no extension. Stored headers then served None from ExtensionProvider, so scripts using the CKB2023 load_extension syscall were evaluated against missing extension data and local verification diverged from consensus.

Refs: sec-reports PENDING-HIGH-0007 ("Peer can omit CKB2023 block extensions").

Fix

For a block without uncles and without an extension, extra_hash is Byte32::zero() (the empty uncles hash is zero, and extra_hash equals the uncles hash when no extension is committed). Any other value commits to data the legacy message cannot carry.

• send_blocks_proof.rs: new verify_legacy_extra_hash() helper, called in the legacy branch before the MMR proof.
• send_transactions_proof.rs: same check in its legacy branch.
• Rejection returns InvalidProof (439), which is ban-eligible through the existing misbehavior rate limiter.

Compatibility

• Legacy (v0) responses remain accepted for blocks with no uncles and no extension (e.g. pre-V1 servers still work for those blocks).
• Blocks with uncles and/or extensions now require the V1 fields — which the client needs anyway, since it cannot reconstruct uncle hashes or extensions from a legacy message.

Tests

• Unit tests for verify_legacy_extra_hash and verify_extra_hash (accept/reject cases).
• Integration: legacy blocks proof and legacy transactions proof for extension-bearing blocks are rejected; V1 proof with an incorrect extension is rejected.
• The mock chain's block assembler attaches an extension to every mined block, so the proof-message test harness and the three tx-proof tests now send V1 messages carrying the real uncle hashes and extensions, like an honest server would.
• Full ckb-light-client-lib suite: 122/122 pass. ckb-light-client bin compiles; clippy clean for the changed code.

[Copilot]

Pull request overview

This PR hardens the light-client proof handlers against a legacy (v0) response that omits V1 “extra fields” (uncles hash + extension), preventing the client from accepting headers whose authenticated extra_hash commits to data that the legacy message cannot carry. This closes a consensus-divergence vector for CKB2023 load_extension by ensuring legacy proofs are only accepted for headers that commit to “no uncles, no extension”.

Changes:

• Add verify_legacy_extra_hash() and invoke it when handling legacy (v0) SendBlocksProof / SendTransactionsProof responses.
• Update protocol-level tests to send V1 messages with real blocks_uncles_hash and blocks_extension from the snapshot when appropriate.
• Add unit tests covering accept/reject behavior for legacy extra-hash verification and extension mismatch verification.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
light-client-lib/src/protocols/light_client/components/send_blocks_proof.rs	Adds verify_legacy_extra_hash() and enforces it on the legacy branch before continuing proof validation.
light-client-lib/src/protocols/light_client/components/send_transactions_proof.rs	Enforces verify_legacy_extra_hash() for legacy tx-proof responses to prevent extension omission.
light-client-lib/src/protocols/light_client/components/mod.rs	Re-exports verify_legacy_extra_hash for reuse by components.
light-client-lib/src/protocols/light_client/components/tests/send_blocks_proof.rs	Adds focused unit tests for legacy extra-hash acceptance/rejection and V1 extension mismatch behavior.
light-client-lib/src/protocols/light_client/components/tests/mod.rs	Registers the new component test module.
light-client-lib/src/tests/protocols/light_client/send_blocks_proof.rs	Extends integration-style blocks-proof tests to cover legacy rejection for extension-bearing blocks and V1 incorrect-extension rejection; updates harness to send realistic V1 fields.
light-client-lib/src/tests/protocols/light_client/send_transactions_proof.rs	Updates tx-proof tests to send V1 fields in normal cases and adds an integration test ensuring legacy tx-proofs are rejected for extension-bearing blocks.

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.