tapassets: persist asset state for mixed OOR transfers

[darioAnongba]

Summary

• persist SDK-neutral asset reference, uint64 amount, and commitment root while keeping carrier sats separate
• support positional Bitcoin-only checkpoint package slots for mixed asset/BTC OOR graphs
• reconstruct chained proof sources from the exact creating package across restarts
• propagate complete asset metadata through onboarding, signing descriptors, recipients, snapshots, incoming events, and VTXO RPCs

Validation

• full and focused unit suites
• focused race tests
• make build
• make lint-changed-local base=origin/main workers=2
• formatting, diff, and commit-message checks

Stack

• base: multi: reserve asset carrier inputs #1035
• tap-sdk output preview used by the next partial-send builder: customanchor: preview output commitments tap-sdk#166

Prototype boundaries

• Lumos must bind ref/amount to sealed packages before admitting a spend
• asset-aware seed recovery still needs an indexer inventory query
• live cross-repository regtest remains in the final E2E branch

[gemini-code-assist]

Code Review

This pull request implements SDK-neutral Taproot Asset state persistence and mixed out-of-round (OOR) package bindings, allowing virtual transaction outputs (VTXOs) to carry asset references and full-width uint64 amounts without altering their Bitcoin carrier values. It introduces database migration 18, updates protobuf definitions, propagates asset metadata across various wire and persistence boundaries, and adds a proof-source resolver to reconstruct compact proof paths. The review feedback points out an opportunity to optimize payload serialization in encodeIncomingRecipientPayload by conditionally appending the asset reference and amount TLV records only when they are non-empty, preventing unnecessary bloat for ordinary Bitcoin VTXOs.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

In encodeIncomingRecipientPayload, the taprootAssetRef and taprootAssetAmount TLV records are unconditionally included in the records slice. For ordinary Bitcoin VTXOs (which do not carry Taproot Assets), this unnecessarily serializes empty/zero TLV records, bloating the payload size. To optimize efficiency and maintain consistency with encodeRecipientPayload and encodeTransferInputSnapshot, these records should only be appended conditionally when they are non-empty/non-zero.

	}
	if len(taprootAssetRef) > 0 {
		records = append(
			records, tlv.MakePrimitiveRecord(
				recipientTaprootAssetRefType, &taprootAssetRef,
			),
		)
	}
	if taprootAssetAmount != 0 {
		records = append(
			records, tlv.MakePrimitiveRecord(
				recipientTaprootAssetAmountType, &taprootAssetAmount,
			),
		)
	}

[lightninglabs-deploy]

@darioAnongba, remember to re-request review from reviewers when ready

[darioAnongba]

Superseded by #1062, which aggregates the full Taproot Asset OOR prototype stack (all files touched here are covered there).