Amend the OpenZeppelin Canton Ecosystem Stack proposal

This PR amends the approved OpenZeppelin Canton Ecosystem Stack proposal. The proposal was accepted on 13 May 2026, and delivery work began on 14 May 2026. The amendments record the actual engagement start and the payment and review mechanics agreed after approval. All other text is unchanged.

Summary of amendments

Security (Workstream C)

• Add an Independent Third-Party Review clause. The review starts after OpenZeppelin delivers its own audit report, is procured by the Canton Foundation, and is funded outside this grant.
• Add the Audit and Review Cadence. Each milestone's code is audited during the following milestone's development window, and the audit report ships with the following milestone's submission. Milestone 1's submission carries no audit report.

Milestones

• Record the engagement start on 14 May 2026 and shift every milestone window by 13 days.
• Add a Submission Date row to each milestone table.
• Remove the Milestone 1 audit deliverable, because the audit of Milestone 1 code runs in the Milestone 2 window.
• Add a project-specific condition: the third-party review is not an acceptance criterion, and milestone acceptance proceeds without it when the report is outstanding.

Funding

• Add the Milestone Payment Structure: from Milestone 2 onward, each delivery payment is released 90% on acceptance and 10% on delivery of the third-party review, with a sixty-day release clause. Milestone 1 is paid in full on acceptance. Adoption-gated payments at Milestones 4 and 8 are not split.
• Replace the payment breakdown table with a per-milestone tranche table in USD and indicative CC.
• Replace the quarterly rebase with a rebase at each payment release, based on the 30-day moving average price before release.
• Update the early completion bonus amounts and the billing terms to match the two-stage release.