Track payer proof spec ambiguities from BOLT PR 1295

[vincenzopalazzo]

This issue tracks two BOLT 12 payer-proof spec questions that came up while implementing lightningdevkit/rust-lightning#4297.

1. missing_hashes example appears to omit one hash

For the selective-disclosure example with TLVs:

• 0 omitted
• 10 included
• 20 omitted
• 30 omitted
• 40 included
• 50 omitted
• 60 omitted

The example in BOLT PR 1295 appears to imply 3 entries in missing_hashes, but tree reconstruction in rust-lightning requires 4:

• hash for TLV 0
• hash for the omitted branch covering TLVs 20 and 30
• hash for TLV 50
• hash for TLV 60

Question: is the spec example incomplete, or is the implementation's tree interpretation wrong?

Relevant rust-lightning review thread:

• [RFC] Add BOLT 12 payer proof primitives lightningdevkit/rust-lightning#4297 (comment)

2. omitted_tlvs trailing-marker rule conflicts with the example

The normative text says omitted_tlvs MUST NOT contain more than one number larger than the largest included non-signature TLV.

However, the same example uses markers [11, 12, 41, 42], and both 41 and 42 are larger than the largest included TLV 40.

Question: should a minimized trailing run after the final included TLV be considered valid, with the text updated accordingly? Or should the example be changed?

Relevant rust-lightning review thread:

• [RFC] Add BOLT 12 payer proof primitives lightningdevkit/rust-lightning#4297 (comment)

Desired outcome

• Confirm the intended interpretation for both cases.
• Update the example and/or normative text in BOLT PR 1295 so implementations converge on the same behavior.