Introduced a per-coin locked unit reserve mechanism that allows withdrawals from PaymentHub even when channels are active, provided sufficient unlocked balance remains.

Changes

• Global configuration: Added PaymentHubConfig with per-coin locked_unit_per_coin table
• Unlocked balance calculation: withdraw_from_hub now checks unlocked_balance = total_balance - (locked_unit × active_channel_count) instead of blocking all withdrawals
• Admin API: set_locked_unit<CoinType> configures reserve per coin type with monotonic non-decreasing enforcement
• Event emission: LockedUnitConfigUpdatedEvent tracks config changes
• View helpers: get_unlocked_balance_in_hub, get_required_locked_for_owner, get_locked_unit
• Code cleanup: Removed unnecessary copy operations and redundant wrapper functions

Behavior

Before: Any active channel blocks all withdrawals
After: Withdrawals allowed up to unlocked balance, maintaining locked_unit × active_channels reserve

// User has 1000 coins, 2 active channels, locked_unit = 100
// Required locked: 100 × 2 = 200
// Unlocked balance: 1000 - 200 = 800
// Can withdraw up to 800 coins

Overflow protection relies on Move's built-in abort; governance expected to set reasonable locked_unit values.

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.