[GrantFox][High] Make optimistic portfolio mutations rollback-safe

Summary

Make optimistic portfolio mutations rollback-safe

Why this matters

A failed prediction or claim can leave the portfolio visually overstated.

Scope

Track operation identity, apply one optimistic change, and reconcile or rollback from authoritative state.

Acceptance criteria

• Failure rolls back exactly once.
• Concurrent operations do not overwrite one another.
• Confirmed state comes from authoritative data.
• Tests cover failure, retry, refresh, and delayed responses.

Validation

Add regression coverage for existing behavior, failure modes, authorization boundaries, and compatibility. The implementation must pass the repository CI checks.

Non-goals

• Typo-only, formatting-only, or documentation-only changes.
• Unrelated refactors or dependency upgrades.
• Weakening existing security, authorization, CI, or production safeguards.

Contributor application

Before implementation, comment with relevant experience, a 1–4 bullet approach, and an estimate for opening the first draft PR. Wait for maintainer assignment before coding.

PR requirements

Use a feature branch, include Closes #<issue-number>, check every acceptance criterion, link criteria to code/tests, explain security and failure-mode considerations, and pass CI.

Reward-readiness

This is a substantive GrantFox campaign issue. Merge and CI success do not by themselves guarantee reward eligibility; final reward-readiness is determined by campaign review.

Start by locating the portfolio mutation entry points and existing regression coverage for prediction and claim operations. Trace the current optimistic update flow, then add coverage for failure, retry, refresh, delayed responses, concurrency, and authorization boundaries. Done means the acceptance criteria pass and the repository CI checks succeed.