[tompro]

Summary

Expose LndApi::get_transaction(&str) using WalletKit.GetTransaction so callers can retrieve one wallet transaction by txid instead of scanning wallet history.

• Pin fedimint-tonic-lnd to immutable commit 86fde7f1928d06ec57d843e919e7b62b2858df70 from chore: sync upstream LND RPC definitions tonic_lnd#2.
• Return lnrpc::Transaction, including wallet-owned output details and unconfirmed transactions.
• Cap decoded transaction responses at 4 MiB and release the shared client mutex before awaiting the RPC.
• Preserve typed UNIMPLEMENTED as Error::NodeApiUnsupported; retain existing error handling for other statuses. No error-text matching, retry or wallet-history fallback.
• Existing TLS/PEM configuration is unchanged.

Dependency / rollout

Depends on tonic_lnd PR #2. This is intended for https://github.com/The-Bitcoin-Company/tbc-rust/pull/652. Requires LND >= 0.18 with WalletKit and onchain:read permission. Callers retain responsibility for their RPC timeout.

Validation

Using the TBC Rust Nix development shell:

• 35 relevant tests passed: 15 payday_core + 20 payday_node_lnd.
• Workspace all-target check passed.
• Relevant crate Clippy with -D warnings passed.
• Focused tests cover exact txid, unconfirmed/output details, typed status mapping (including misleading error text), and mockable lookup without history calls.
• No live LND/TLS tests performed.