fix(remote-config): Remote-config fixes/improvements

[tonidero]

Hardening fixes from a review pass over the remote-config stack.

Changes

• Malformed topic item no longer crashes the app: ConfigItemSerializer throws SerializationException (instead of the .jsonObject accessor's IllegalStateException, which escaped the manager's catch) for a non-object item, making it a recoverable parse failure.
• Crash-safe blob writes: RemoteConfigBlobStore writes via AtomicFile (same scheme as the disk cache), so a process kill can never leave a partial blob file under a valid ref.
• In-memory snapshot in RemoteConfigDiskCache: hot-path reads (topic()/blobData(), blob-source lookups per download) stop re-reading + re-parsing the file and recomputing contentHash on every call.

Tests

• Non-object topic item: parse fails with SerializationException; manager keeps the cache, releases the guard, no crash.
• Interrupted blob write leaves no readable blob; the .new orphan is pruned by retainOnly.
• Disk-cache snapshot is served without file re-reads and dropped on clear(); fresh instances still read from disk.
• A failed refresh does not stamp the staleness window (next check retries); the rate-limited syncAttributesAndOfferings branch does not force a refresh.
• Persisted-file forward-compat: unknown keys are tolerated.
• Concurrency stress: 8 readers × 50 iterations racing clearCache + refreshes all complete, manager stays functional.

---

Note

Medium Risk
Changes affect on-disk config/blob caching and config parse error handling on a hot SDK path; behavior is defensive and well-covered by tests, but incorrect snapshot or atomic-write semantics could cause stale config or missed updates.

Overview
Hardens the remote-config persistence and parsing stack so bad payloads and crashes are handled safely, and hot-path disk access is cheaper.

ConfigItemSerializer now throws SerializationException when a topic item is not a JSON object (instead of IllegalStateException from .jsonObject), so RemoteConfigManager can treat malformed config as a recoverable parse failure without crashing.

RemoteConfigBlobStore switches blob persistence to AtomicFile (same pattern as the disk cache), so a killed process cannot leave a partial file under a valid ref; retainOnly docs/tests now cover <ref>.new orphans instead of rc_blob_*.tmp.

RemoteConfigDiskCache adds a synchronized in-memory snapshot: read() loads from disk once (including caching a miss), write() updates the snapshot only after a durable write, and clear() resets the snapshot before deleting the file.

Tests cover interrupted blob writes, snapshot behavior, forward-compatible persisted JSON, failed refresh / rate-limited sync not over-refreshing, non-object topic items, and a concurrency stress run over clearCache + refreshes + topic() reads.

^{Reviewed by Cursor Bugbot for commit a031979. Bugbot is set up for automated code reviews on this repo. Configure here.}

[tonidero]

• fix(remote-config): Remote-config fixes/improvements #3714 👈 (View in Graphite)
• refactor(remote-config): Disable in CEC mode + add observability logs #3705
• refactor(remote-config): add RemoteConfigManager read facade (topic/body) #3703 : 1 other dependent PR (#3708 )
• refactor(remote-config): Disable /v1/config for the session on a 4xx response #3700
• refactor(remote-config): Re-arm blob sources only when exhausted + in-memory blob-store index #3698
• refactor(remote-config): Wire the blob fetcher into RemoteConfigManager (prefetch, re-arm, clear) #3683
• refactor(remote-config): Add RemoteConfigBlobFetcher #3679 : 1 other dependent PR (#3682 )
• refactor(remote-config): user-scoped invalidation #3621
• refactor(remote-config): persist the full topic index as the source of truth #3673
• main

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[codecov]

Codecov Report

❌ Patch coverage is 74.19355% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.57%. Comparing base (693d387) to head (a031979).

Files with missing lines	Patch %	Lines
...hases/common/remoteconfig/RemoteConfigBlobStore.kt	57.14%	3 Missing ⚠️
...hases/common/remoteconfig/RemoteConfigDiskCache.kt	84.21%	2 Missing and 1 partial ⚠️
...rchases/common/remoteconfig/RemoteConfiguration.kt	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3714      +/-   ##
==========================================
+ Coverage   80.56%   80.57%   +0.01%     
==========================================
  Files         398      398              
  Lines       16473    16488      +15     
  Branches     2356     2356              
==========================================
+ Hits        13271    13286      +15     
- Misses       2265     2266       +1     
+ Partials      937      936       -1     

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[ajpallares]

Nice improvements indeed!