Support serde_2026 generators in trusted RPC helpers

[richardkiss]

Why

#1438 made the INTERNED_GENERATOR consensus path emit and require serde_2026-encoded generators. Bugbot flagged on that PR (r3662079661) that trusted helper functions still parse generators with node_from_bytes_backrefs() only, and arvidn confirmed as a non-blocking follow-up: the helper functions the full node uses to respond to RPCs (like get_puzzle_and_solution_for_coin and additions_and_removals) need to support the new generator format as well.

Layering: consensus stays strict, trusted read helpers sniff

• The consensus path (run_block_generator2) is unchanged: with INTERNED_GENERATOR active, serde_2026 is the only legal encoding, and pre-HF2 the classic/backrefs encodings are the only legal ones. No sniffing there.
• Trusted (non-consensus) helpers run on already-validated blocks, so format detection is appropriate. They now dispatch on the serde_2026 magic prefix via the existing chia_consensus::serde_2026::node_from_bytes_auto() (introduced for exactly this purpose). Detection is unambiguous: the 6-byte magic starts with 0xfd, which cannot begin a valid classic CLVM serialization (0xfd declares an atom length >= 2^40, above the 2^34 cap).

Audited surface

Changed (parsed generator blobs with node_from_bytes_backrefs() only):

• additions_and_removals() (chia-consensus) — also fixes the python binding, which wraps it
• get_puzzle_and_solution_for_coin() and get_puzzle_and_solution_for_coin2() (python bindings; the generator-bytes parsing for these lives in the wheel)
• generator_interned_vbytes() (python binding)

Audited and deliberately unchanged:

• run_block_generator() / run_block_generator2() — consensus path, stays strict
• get_coinspends_for_trusted_block() / get_coinspends_with_conditions_for_trusted_block() — already handle serde_2026 (via INTERNED_GENERATOR flag dispatch, from [CHIA-3823] Add INTERNED_GENERATOR consensus path + serde_2026 prefix guard #1438)
• solution_generator*(), InternedBlockBuilder, run_spendbundle(), fast-forward — parse puzzle/solution blobs from spend bundles, not block generators
• wheel run_chia_program() — general-purpose CLVM runner, not a generator-specific helper
• chia-tools (visit_spends::run_generator, test-block-generators --test-serializer) — offline analysis tools; can be updated when post-HF2 blocks exist on chain

Notes

• Program (Streamable) cannot hold a serde_2026 blob yet (serialized_length_from_bytes* rejects 0xfd), so get_puzzle_and_solution_for_coin2() and the get_coinspends_* wrappers — which take the generator as Program — can't receive serde_2026 blobs from python until that lands. The buffer-taking helpers are covered end-to-end from python now.
• Python-visible behavior is otherwise unchanged: same signatures, same results for classic generators.

Tests

Each changed helper has a test exercising it with both a classic and a serde_2026 encoding of the same spends (built with solution_generator() / solution_generator_2026(), the latter producing the same wire format as InternedBlockBuilder::finalize()), asserting identical results:

• Rust: test_serde_2026_generator_equivalence in additions_and_removals.rs (with pre- and post-HF2 flag sets)
• Python: test_additions_and_removals_serde_2026, test_get_puzzle_and_solution_for_coin_serde_2026, test_generator_interned_vbytes_serde_2026

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[coveralls-official]

Coverage Report for CI Build 30841843169

Coverage increased (+0.1%) to 82.041%

Details

• Coverage increased (+0.1%) from the base build.
• Patch coverage: 13 of 13 lines across 3 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	20035
Covered Lines:	16437
Line Coverage:	82.04%
Coverage Strength:	11581254.31 hits per line

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