C2: typecheck materialization through the local store

[briansrls]

Auto-opened by session-dashboard for session valiant-hawk-763.
Pushing to session/valiant-hawk-763 advances this PR.

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[gunbai-bot]

Superseded by #13482 (C2 survivor). Distinct ensure/lookup/commit and digest-keyed requests were ported there; this duplicate is closed so there is one C2 PR.