feat(observability): expose pool write-block diagnostics (#7417)

* feat(observability): expose pool write-block diagnostics

* fix(error): merge equivalent api message branches

Combine the MaxVersionsExceeded and internal IO message branches so Clippy no longer flags identical if blocks while preserving the existing response messages.

Co-Authored-By: heihutu <heihutu@gmail.com>

Co-Authored-By: zhi22915 <qiuzgang@gmail.com>

* fix(heal): cleanup consumed MRF replay journals

Do not retain Accepted or Merged replay intents as startup anchors after they have been handed to the heal manager. Only refused or still-pending replay records keep the journal on disk until a successor snapshot can persist them.

This keeps successor snapshots limited to the pending queue, which lets successful replay remove both authoritative and legacy journal paths and restores the crash-boundary tests around successor flush.

Co-Authored-By: heihutu <heihutu@gmail.com>

Co-Authored-By: zhi22915 <qiuzgang@gmail.com>
(cherry picked from commit d5b8f49c9d)

---------

Signed-off-by: houseme <housemecn@gmail.com>
Co-authored-by: houseme <housemecn@gmail.com>
Co-authored-by: zhi22915 <qiuzgang@gmail.com>
Co-authored-by: Zhengchao An <anzhengchao@gmail.com>

docs/testing/distributed-e2e.md

@@ -29,7 +29,7 @@ The expansion fixture is an all-current-binary fleet, so it initializes pool met
 - Object Lock COMPLIANCE, GOVERNANCE and bypass, legal hold, bucket default retention, and non-lock bucket rejection
 - Versioning, exact historical reads, delete-marker removal, and suspended null-version overwrite semantics
 - Bucket replication between two 4-node clusters, including metadata/tags and target-outage retry; hard quota admission and absence of rejected keys
-- Ready/live probes on every node, exact 4-server/16-disk inventory, realtime metrics on every node, and correlated audit-webhook delivery
+- Ready/live probes on every node, exact 4-server/16-disk inventory, realtime metrics on every node, and correlated audit-webhook delivery. The observability case runs at WARN and suspends two node processes to model nonresponsive peers: cached drives become unknown immediately, exact per-node HTTP PUT deltas expose sub-quorum failures, the local metadata snapshot does not invent a write latch, and resumed peers allow new writes and byte-identical reads from every node. This models stalled processes, not a physical network partition.
 - Pool expand, decommission, rebalance, checksum integrity, versioned and multipart data, and S3 during active movement
 - Bidirectional site-replication convergence plus enabled/synchronized peer state on both sites
 - A 24-worker mixed PUT/HEAD/GET/COPY/DELETE workload; concurrent PUT during active decommission