Prepare Liquid2 merge into dev

[BullishNode]

Summary

Prepare features/liquid2 for merge into dev, including features/elgetaddrinfo.

This branch brings the Liquid/Elements integration forward onto current dev, keeps Bitcoin behavior compatible, hardens the Liquid request/runtime paths, and adds repeatable merge-readiness test coverage.

Merge strategy

The strategy was compatibility-first:

• Bring the Liquid2 feature work onto current dev.
• Include the separate Elements getaddressinfo endpoint because the Liquid watch flow benefits from a first-class way to inspect owned Elements addresses.
• Avoid redesigning the Liquid2 architecture.
• Add only focused merge-readiness changes on top: concrete runtime fixes, defensive request handling at API/RPC boundaries, database migration coverage, and repeatable local/staging validation.

Commit-level rationale

elements_getaddressinfo endpoint

Rationale:

• This intentionally brings in features/elgetaddrinfo.
• It exposes the Elements equivalent of address inspection through the existing proxy/Gatekeeper path.
• It is useful for Liquid watch flows because Elements Core can report wallet ownership and the unconfidential form of a confidential address.

Strategy:

• Keep the endpoint permission at the existing watcher level, matching the address-inspection use case.
• Add it to both sample and generated Gatekeeper API properties.
• Add it to the Gatekeeper authorization test coverage.
• Route the request through the existing Elements RPC helper, with optional wallet support.

Make Liquid integration merge-ready

Rationale:

• This is the main reconciliation commit after bringing Liquid2 onto current dev.
• It addresses concrete merge-readiness gaps found while exercising Elements watches, migrations, Paymentalist build/runtime behavior, and callback handling.
• It keeps the existing Liquid2 model intact while aligning fresh installs and upgraded databases.

Strategy:

• Add a PostgreSQL migration that makes the Elements watch identity include watching_assetid, matching the fresh-install schema and allowing the same address/callback pair to be watched for different assets.
• Make the migration idempotent and transactional so it is safe to run during upgrades.
• Select a deterministic matching Elements transaction detail by watched address and optional asset before persisting callback state.
• Preserve one-shot callback semantics while making the persisted vout, amount, and asset come from the selected watched output.
• Fix Elements wallet/RPC routing and response handling where tests showed mismatches.
• Add Elements regression tests for the merge-sensitive cases rather than relying only on manual smoke testing.

Harden Elements RPC request handling

Rationale:

• The Elements RPC layer accepts API-provided values such as addresses, txids, asset ids, labels, wallet selectors, and callback parameters.
• For merge readiness, these values should be passed to JSON-RPC as data, not by string-splicing request bodies.
• Invalid wallet selectors or malformed request values should fail deterministically before reaching the node.

Strategy:

• Build Elements JSON-RPC payloads with jq --arg and --argjson so request values cannot alter the JSON-RPC method or structure.
• Validate wallet selector values before constructing wallet-specific RPC URLs.
• Validate txid and asset-id shape where those values are used for persistence or lookup.
• Validate JSON-RPC response shape from Elements before treating a response as successful.
• Keep endpoint response shapes compatible while tightening error paths and adding regression coverage.

Harden Liquid watch and Paymentalist runtime

Rationale:

• Liquid watch/unwatch paths store and return API-provided strings in SQL and JSON responses.
• Those paths need consistent quoting and input validation because they are merge-critical: watches must be persisted, removed, and reported reliably.
• Paymentalist should run as a lean service image without shipping test helpers or logging request/response bodies.

Strategy:

• Add shared shell helpers for SQL string literals and JSON string literals, then use them in Elements watch/unwatch paths.
• Validate numeric watch ids, txids, xpub derivation positions, and callback requirements before mutating watch state.
• Support a Liquid-specific xpub derivation-gap override while preserving the existing generic default.
• Ensure watch/unwatch JSON responses remain valid even when labels, callbacks, xpubs, or addresses contain special characters.
• Trim the Paymentalist runtime image to the service binary and reduce HTTP middleware logging to metadata/status/duration.

Add Liquid2 merge-readiness test harness

Rationale:

• The PR needs repeatable evidence that the branch can be reviewed and retested without depending on one-off manual commands.
• Existing regression scripts needed to work reliably in non-interactive Docker Compose environments.
• Upgrade safety needed a direct check from current dev schema to the candidate Liquid2 schema.

Strategy:

• Add contrib/liquid2-merge-readiness/local-static.sh for local static checks, Elements shell regressions, Paymentalist Rust checks, and Docker image builds.
• Add contrib/liquid2-merge-readiness/migration-dev-to-liquid2.sh to create an isolated current-dev database, run candidate migrations twice, and verify Bitcoin data survives while Liquid tables/indexes are present.
• Add contrib/liquid2-merge-readiness/staging-server-live-smoke.sh for live deployed-stack smoke coverage against Bitcoin Core and Elements without broadcasting spends.
• Add contrib/liquid2-merge-readiness/gatekeeper-auth-matrix.sh to test every deployed Gatekeeper action against no token, invalid token, and all configured API ids.
• Make the existing watch/missed-confirmation test helpers non-interactive and Docker Compose-aware so they can be run repeatedly in local automation.
• Keep the readiness scripts outside runtime paths; they are review/test gates, not production dependencies.

Validation

Passed:

• contrib/liquid2-merge-readiness/local-static.sh
• contrib/liquid2-merge-readiness/migration-dev-to-liquid2.sh
• contrib/liquid2-merge-readiness/gatekeeper-auth-matrix.sh
• contrib/liquid2-merge-readiness/staging-server-live-smoke.sh
• proxy_docker/app/tests/test-watches.sh
• proxy_docker/app/tests/test-elements-manage-missed.sh
• proxy_docker/app/tests/test-manage-missed.sh

Live staging validation covered:

• Docker service health for broker, gatekeeper, Paymentalist, PostgreSQL, and proxy.
• Bitcoin Core and Elements RPC connectivity on mainnet/Liquid mainnet.
• Gatekeeper action inventory and authorization matrix coverage.
• Bitcoin and Elements watch/missed-confirmation regression paths.

Notes for reviewers

• This is a draft PR so review can happen before the final merge decision.
• The new readiness scripts are not product runtime dependencies; they are repeatable gates for local and staging verification.