Review the actual R5 implementation independently for correctness and regressions, using Claude Opus 5 at max effort. This is a read-only final code review after an already recorded two-round plan consensus. Do not edit files. Do not simulate tests or claim you executed them. Read the relevant source and evidence yourself; focus on material blockers and minimal compatible fixes.

Working tree: /Users/vonng/.codex/worktrees/77ad/silo
Base dependency commit: dbcf8dec589deb5d91e17d295cb70997635f5b55 (R4 KMS timestamp field, one production addition)
R5 plan v2 SHA256: 5a782acf3f285b23d1ae43a73481c4eb772a9a6d917fc5a550ecfc7cbf7446ca
R5 implementation patch SHA256: 8f6f76ee874c43b0827fde272e8a947f118efb1c1af92bf4a02ef88f93554c1b
Manifest: /Users/vonng/.codex/worktrees/77ad/silo/docs/investigations/r5/implementation-manifest.json
Frozen review patch (7 production files + 2 new tests): /Users/vonng/tmp/silo-r5-20260915-77ad/implementation-v1.patch
Plan: /Users/vonng/.codex/worktrees/77ad/silo/docs/investigations/r5/plan-v2.md
Prior actual review: /Users/vonng/.codex/worktrees/77ad/silo/docs/investigations/r5/opus-v2-review.md
Consensus and disagreements: /Users/vonng/.codex/worktrees/77ad/silo/docs/investigations/r5/consensus.md, /Users/vonng/.codex/worktrees/77ad/silo/docs/investigations/r5/opus-v1-response.md
Baseline reproduction: /Users/vonng/.codex/worktrees/77ad/silo/docs/investigations/r5/reproduction.md
Latest new regression run: /Users/vonng/tmp/silo-r5-20260915-77ad/fixed-targeted-latest.log (PASS, 9.161s; signed HTTP and actual storage on single/16 disks, null/UUID, COPY default and REPLACE, PUT/multipart, KMS plaintext GET, SSE-C rotation, multi-pool, retry and stale source ACK; test names and details in source.)
Additional related suite and race/static validation are ongoing and are not yet accepted. An expanded suite hit existing TestReplicationResync initialization panic before R5 tests; baseline isolation is ongoing. Do not treat that as a proven R5 regression or a passing test.

Research and implementation points to scrutinize:
1. Empty tag values are ordered states only with recorded timestamp; no fabricated tombstone for empty legacy object. Nonempty legacy sender falls back to ModTime. Malformed stored timestamp fails PUT and metadata COPY sender construction.
2. Local PUT/DELETE tagging timestamps are unconditional, advance under existing storage locks; pooled mutation computes a single revision > every copy; do not mutate caller map. Replicas keep source ordering and equal timestamp stored-wins.
3. Actual sender getCopyObjMetadata + minio Core.CopyObject sends tagging REPLACE with no metadata directive; peers may also send metadata REPLACE. Capture stored timestamp before reconstruction, accept incoming empty value, prevent stale SSE-C encMetadata snapshot overwrite, keep existing storage rechecks.
4. PUT/multipart init persist parsed trusted timestamp. Matching ETag/version no-op is relaxed only for trusted newer tag revision, retaining explicit client preconditions and SSE-C behavior. Multipart completion rechecks revision under lock.
5. Equal visible tag values can hide a newer deletion/re-addition revision, so scheduled metadata/heal work with recorded timestamp sends metadata. Preserve existing Completed/scanner and incoming no-reschedule gates.
6. Replication status ACK no longer writes old queued ri.UserTags over the current tags. Preserve current value/timestamp under metadata lock including multi-pool.
7. Scope explicitly excludes tag-filter target eligibility changes, historical tombstone recovery, arbitrary independent unversioned content replacements, clock skew consensus, and production multi-site acceptance. R4 owns object-api-options.go; it is not in this R5 diff.

There was an earlier KMS test-only fixture error: it assigned a single-PUT ETag to a multipart-layout retransmission; corrected by seeding a real multipart source and using its actual ETag/layout (full latest run passes plaintext read). Inspect the fixture rather than inferring production encryption correctness solely from prior failed test output.

Return a clear GO / GO_WITH_NONBLOCKING_NOTES / REQUEST_CHANGES verdict; blocking count; concrete source locations with cause, trigger and effect for any blockers; tests/coverage limitations if material. State which baseline, plan hash and patch hash you reviewed (you may quote supplied hash, but cannot independently compute with Read/Grep/Glob). Do not demand unrelated broad redesign. Distinguish actual source defect from nonblocking improvement or scope limitation.