[Pigbibi]

The P1 hosted engineering-review draft currently stages only repository Release assets. This stacked draft adds an optional GCS source for approved private input bundles without using a server directory.

• HOSTED_INPUT_FETCH_ENABLED defaults off. When enabled on main on a GitHub-hosted runner, fetch exactly one pinned object generation, validate metadata/size/SHA256, and reuse existing safe ZIP extraction. Reject wildcards, oversized inputs, stale destinations and digest errors; never fall back after a cloud failure.
• Preserve the existing release-ready, hosted-acceptance, first-attempt, concurrency, timeout and task-service gates. No GCP authentication configuration, IAM, variables or secrets are changed. The current job has no GCP auth step; approved keyless authentication, the actual bundle and durable task resume remain blockers.
• Keep private inputs in approved cloud storage. Tests use synthetic bytes and fake commands only.

TRADING_DIFF: No order execution, broker configuration, strategy limits, release or deployment behavior changes. If separately enabled after approval, the review input source changes from a Release asset to an immutable GCS object. Failed reads stop the review. No live workflow has been dispatched.

Depends on #674; this PR targets its existing branch and does not modify that branch. Keep both drafts until their distinct runtime prerequisites are accepted.

Validation: 8 fetch tests with 20 subtests; 5 existing offline ZIP-staging cases; actionlint for the review and staging workflows; git diff --check. Cloud fetch, OIDC/WIF admission and business execution are not validated.