feat(vault): reconcile an epoch once it settles

[hpmaxi]

Summary

Flooring the epoch total and then each claim left a remainder that was never reconciled. It is now. Each epoch records what pricing promised and what has been paid; when its last request settles, the remainder leaves pending_mint_shares and committed, stays in the reserve as fund money, and EpochReconciled says how much. Every subtraction from a running total is checked.

Changes

• Per-epoch settlement record, view get_epoch_settlement, event EpochReconciled.
• Checked subtraction everywhere a total goes down (AccountingMismatch, 6070).
• Two tests pin why the wind-down remainder stays owed.
• A test pins that an epoch with a request that can never settle stays open.

Deviations

• The first plan gave wind-down owed "the same treatment on the last claim". That is not safe: a later round needs those units. The remainder stays (at most one unit per holder), and a test shows why.

Acceptance criteria

• Each epoch records promised and settled shares and assets, and its open requests
• The last settled request clears the remainder and emits EpochReconciled
• An epoch with no requests reconciles when priced
• Every subtraction from a running total is checked
• A test shows the wind-down remainder stays bounded and is needed later

Test plan

Automated tests

1. SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2=1 nix develop -c cargo test --locked -p async-vault settlement wind_down
2. The property test runs 24 random epochs, with the claims in a random order.

Manual verification

None.

Breaking changes

None for callers; a new view and a new event. This version must be deployed fresh, or reached by upgrade only when no request is open: the settlement record counts requests from the moment it exists, so upgrading a vault in place while a request is open would under-count its open epochs, reverting claims from epochs priced before the upgrade and risking an early reconcile of a mixed epoch.

Checklist

• Self-reviewed my own diff
• Tests added or updated
• Docs updated (if applicable)
• No unrelated changes bundled in

Screenshots

None.

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Project	Deployment	Actions	Updated
strata-vault-kit-app	Ready	Preview	Oct 17, 2026 5:10am UTC