Static-only review of the full authoritative diff found six issues that should be addressed before merge (five P1, one P2).

Review-cycle status: incomplete after the three-round cap. Both normal agents returned NO_NEW_VALUABLE_FINDINGS in Round 3, but the risk-focused agent found a final FE-side scope correction that was independently verified and merged into the token round-trip comment; the review contract does not permit a fourth round. All currently known candidates are nevertheless adjudicated and included below.

Critical checkpoint conclusions:

• Data correctness: failed. Session-token credentials are dropped/staled across FE DDL and meta-service paths, and Recycler exists status mapping can turn real provider failures into false not-found results.
• Concurrency and lifecycle: delete-task ownership, executor waiting, batch clamping, and error propagation are sound; request admission during recursive deletion is not.
• Configuration and dynamic behavior: Recycler rate limiting and PUT fault injection are bypassed for the actual recursive-delete SDK requests; AWS provider precedence, refresh-capable providers, and client cache identity otherwise remain compatible.
• Compatibility and rolling behavior: the optional protobuf field is wire-compatible, but the Recycler 0/1/negative adapter contract and GCS iterator migration are broken.
• Parallel paths: BE/Recycler and S3/Azure/GCS paths were traced; the GCS path has an unconditional compile failure and Recycler differs from the preserved BE admission behavior.
• Tests and validation: no builds or tests were run, as required by the review prompt. Existing S3 accessor tests still require 1 for not-found, and there is no end-to-end token persistence/redaction/rotation coverage; the GCS compile error is statically evident.
• Observability and security: the session token lacks SK-equivalent encryption/log/display handling, and successful S3 writes now log at INFO on the hot path. This is credential-secret handling within authenticated control paths; no unsupported cross-tenant vulnerability claim is made.
• Persistence and recovery: token-bearing vault/stage records can either lose the token or retain it plaintext, so persistence round trips are not safe.
• Performance: recursive deletion can evade Recycler request controls, while per-write INFO logging adds log I/O proportional to storage QPS; page and provider batch limits themselves are sound.

User focus: review_focus.txt supplied no additional focus, so the entire PR was reviewed without narrowing scope.

Review opinion

Request changes. The shared object-storage refactor is largely coherent, but it narrows the Azure exception boundary for multipart upload and HEAD. A standard exception from successful-response parsing can now escape the facade; on the BE upload pool that can terminate the process instead of completing the upload buffer with an error. I left one P1 inline comment.

Critical checkpoint conclusions

1. Goal and proof: The PR consistently moves BE and Recycler S3/Azure behavior behind shared backends, authentication factories, admission control, and recursive-delete orchestration. The migration is mostly achieved, but the accepted Azure exception-boundary regression means the goal is not safely complete. The changed unit/mocked tests cover many facade, limiter, writer, credential, and recursive-delete paths, but no negative test proves conversion of non-RequestFailedException SDK failures.
2. Focus and clarity: Although large, the change is focused on removing duplicate object clients and relocating their callers/tests. The new facade/backend split is understandable, and no unrelated production change survived the full review.
3. Concurrency: I traced the BE upload pool, client cache/reset locking, request admission, and Recycler executor submission, bounded backpressure, cancellation, waits, and first-error settlement. Locks remain scoped around lightweight shared state and no new lock-order/deadlock issue was found. The blocker is the uncaught Azure standard exception crossing the upload-worker boundary.
4. Lifecycle and static state: Backend/client/credential shared ownership, AWS SDK/static lifetime, executor reset, Azure shared-key/SAS lifetime, and cross-library bvar/CMake ownership were checked. No circular ownership, shutdown leak, or cross-TU initialization-order defect was found.
5. Configuration: No new configuration item is introduced. Existing endpoint, TLS/CA, credential-provider, limiter, and internal-bucket settings are propagated through the new factories; no additional dynamic-reload defect was found.
6. Compatibility: No storage format, persisted metadata, FE-BE protocol, or externally serialized value is changed. Numeric status conventions, namespace aliases, request fields, and provider behavior were traced; no rolling-upgrade compatibility issue was found.
7. Parallel paths: S3/Azure/GCS, AWS V1/V2 and credential modes, BE/Recycler, synchronous/executor deletion, and reader/writer/list/delete/HEAD paths were compared. The accepted Azure upload_part/head_object boundary is the only uncovered distinct regression; other concerns are already in live threads or were dismissed with code evidence.
8. Conditionals: Provider selection, BUILD_AZURE/USE_AZURE, NOT_FOUND mapping, page termination, capability batching, and credential branches were checked against siblings. No additional incorrect or unexplained special condition was found.
9. Test coverage: The PR updates broad C++ unit/mock coverage, including the facade, rate limiting, writers, credentials, and recursive deletion. It lacks a negative test for an ordinary exception from Azure successful-response parsing; existing live review threads already cover other missing executor/provider cases. No new end-to-end regression test is added.
10. Test results: No result/golden files are changed. I did not run local builds or tests under this review-only bundle. At submission time Cloud UT and FE UT pass; Clang Formatter fails; BE UT, macOS BE UT, compile, performance, and this review check are still pending.
11. Observability: Provider errors, request IDs, HTTP status, TLS context, and bvars were traced before Recycler response collapse. Apart from concerns already raised in live threads, no additional production observability gap survived; the suspected Azure ListBlobs gap was dismissed because the pinned storage exception already includes provider message and request ID in what().
12. Transactions and persistence: No EditLog, transaction-state, master-failover, or persistent-storage schema change is introduced.
13. Data writes, atomicity, and crashes: Multipart PUT, completion, reads, batch deletes, recursive deletion, retry/idempotency, and partial-failure settlement were traced. No new atomicity issue was found, but the accepted Azure exception path can escape the upload worker and terminate the BE instead of returning an error, so this checkpoint is blocking.
14. FE-BE variables: No new variable or thrift/protobuf value needs propagation between FE and BE.
15. Performance: Page and provider batch sizes, bounded streaming deletion, admissions, cache reuse, allocations, and hot-path logging were reviewed. No additional substantiated CPU, memory, complexity, or redundant-work regression was found beyond concerns already covered in live threads.
16. Other issues: Authentication and cloud trust-boundary changes were checked against SECURITY.md and the threat model; no new distinct security issue survived deduplication. No additional nullability, ownership, memory-safety, or stale-symbol defect was found.

Review completion and focus

The focus file contains no extra user guidance, so I reviewed the entire 64-file PR. Three full convergence rounds completed; all final reviewers returned NO_NEW_VALUABLE_FINDINGS against the same frozen one-comment set. Every candidate is accepted, merged, duplicated, already covered, or dismissed with concrete evidence. Immediately before submission, the live head/base still matched 5f7c022169e34d78936527cd3a653d2bb564f93b / 07ba0d1e448be58bef46e17c01498cb3d9864891, and no live review, inline, or issue comment duplicated the accepted finding.