tapchannel: fix immediate force-close proof sync and sweep anchoring

[GeorgeTsagk]

Description

This PR fixes immediate post-funding (N=0) force-close recovery by correctly re-syncing active vPacket outputs with re-anchored proofs when anchor indices are stale, and hardens anchor resolution to return explicit errors instead of panicking on out-of-range indices.

It also adds an integration test that force-closes right after funding confirmation and verifies the swept assets remain spendable via an onward transfer to a third node.

Depends on lightningnetwork/lnd#10804

[gemini-code-assist]

Summary of Changes

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This pull request improves the reliability of asset channel force-closes, particularly in scenarios where a channel is closed immediately after funding. It introduces mechanisms to re-sync proofs and re-anchor outputs correctly, while also hardening the code against potential panics during anchor resolution. These changes ensure that assets remain recoverable and spendable even under edge-case timing conditions.

Highlights

• Immediate Force-Close Recovery: Fixed post-funding (N=0) force-close recovery by ensuring active vPacket outputs are correctly re-synced with re-anchored proofs.
• Anchor Resolution Hardening: Replaced potential panics with explicit error handling for out-of-range anchor indices, improving system stability.
• Proof Metadata Persistence: Added support for storing witness scripts and control blocks in proof metadata, enabling reliable sweeps for commitment outputs.
• Integration Testing: Added a new integration test to verify that assets remain spendable after an immediate force-close.

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[gemini-code-assist]

Code Review

This pull request introduces support for immediate force-closing of asset channels by adding a new test case and updating the auxiliary sweeper and commitment logic to handle the necessary proof metadata and script key synchronization. The review comment regarding the robustness of the confirmation fallback logic in waitForTransferTxConf is valid and provides an actionable improvement, so it has been retained.

[gemini-code-assist]

The fallback confirmation logic might not be robust enough if no height hint is provided. If scanHeight is 0, startHeight is set to currentHeight, meaning only the current block is scanned. If the transaction was confirmed in a recent block (e.g., currentHeight - 1) and the primary notification was missed, this fallback will not find it, as scanHeight will be updated to currentHeight + 1 and the missed block will never be scanned.

To make this fallback more reliable, consider scanning a few recent blocks when no height hint is available.

                if startHeight == 0 {
			const rescanDepth = 6
			if currentHeight > rescanDepth {
				startHeight = currentHeight - rescanDepth
			} else {
				startHeight = 1
			}
		} else if startHeight > currentHeight {
			startHeight = currentHeight
		}