[Conway] The last vote is applied at the CHAIN level

**Property:** The last vote is applied at the CHAIN level

- Catalog id: `conway-chain-last-vote-applied`
- Era: **conway** · STS: **CHAIN**
- Agda module: _(none yet)_
- Key definitions: —
- Status (derived from the Agda): **idea**

CHAIN-level lift envisioned by #417; GOV and LEDGER levels are proved.

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Tracked in `build-tools/properties.yaml`; see the "Tracking Properties of the Ledger" section of CONTRIBUTING.md and the dashboard `build-tools/static/mkdocs/docs/ledger-properties-dashboard.md`.
Part of the ledger-properties tracking (umbrella #45).

Start with the "Tracking Properties of the Ledger" section in CONTRIBUTING.md, then inspect build-tools/properties.yaml and the ledger-properties dashboard. The issue names no Agda module or key definitions, so identify the relevant CHAIN-level entry and existing GOV and LEDGER proofs before deciding the implementation path. Done means the Conway CHAIN property is represented by an Agda proof and its tracking status is updated.

Written by the indexing model from the issue text.