fix(sync): enforce end-of-input on header receive (match the reload path and sibling sinks)

[cafebedouin]

This change was prepared with AI assistance (Claude, model Claude Opus 4.8); every claim below was verified against the source and the fix is covered by the included regression test.

pre_validate_header (ergo-sync/src/header_proc.rs) parses an inbound header with read_header but does not check that the parse consumed all of the payload bytes. Two consequences:

1. A header delivered as canonical_bytes ++ trailing_junk is accepted — read_header stops at the end of the header and ignores the trailing bytes.
2. The header id is blake2b256(header_bytes) over the raw received bytes, so the same block content entering with different trailing bytes is stored under different, non-canonical ids.

This is looser than the node's own reload path (ergo-validation/src/header/mod.rs), which already rejects consumed != header_bytes.len() (with a comment noting the same gap), and looser than the sibling receive sinks — the transaction deserializer (ergo-validation/src/tx/mod.rs, !r.is_empty()), block-section verify (ergo-sync/src/coordinator/section_verify.rs, r.remaining() != 0), and deserialize_nipopow_proof (ergo-ser/src/popow_proof.rs, r.remaining() != 0) all reject trailing bytes. The Ergo reference node also rejects a trailing-byte header at parse.

Fix: enforce end-of-input in pre_validate_header immediately after read_header, matching the reload path. Because trailing bytes are then rejected, header_bytes is canonical and its blake2b256 id is the canonical id — closing both the trailing-byte acceptance and the raw-vs-canonical-id divergence in one check. read_header already consumes a header's own unparsed_bytes field, so a canonical header (including v5+ headers carrying real unparsed_bytes) lands exactly at end-of-input and is not affected.

Test: ergo-sync/tests/header_receive_eof.rs — a canonical mainnet header is accepted; the same header with trailing bytes appended is rejected. Existing header_proc unit tests (7) and the header_sync_integration suite (23) pass unchanged.

🤖 Generated with Claude Code

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