Retry an after-response write that loses its CAS #1553

Follow-up from PR #1487.

Description

The after-response write re-reads the row and writes once. A conflict, often with this navigation's own pull-sync or another write, drops the results, and the vendor is asked again on the next navigation.

Proposed direction: Measure the conflict rate, then allow one bounded re-read and re-plan on Conflict, keeping the single-permit rule.

Done when

• The after-response CAS conflict rate is measured (log or metric).
• On Conflict, one bounded re-read and re-plan is attempted, keeping the single-permit rule.
• Tests cover a conflict followed by a successful retry and a second conflict that gives up.

Affected area

Core (Edge Cookies, GDPR)

Code: crates/trusted-server-core/src/ec/after_response.rs (commit_after_response_lookups); ec/kv.rs (commit_after_response).

Review threads

• Collect server-side identity provider EIDs in a single page-load write #1487 (comment)