refactor(remote-config): Re-arm blob sources only when exhausted + in-memory blob-store index

[tonidero]

Changes

• Add restartIfExhausted(purpose) to the source provider: re-arms a purpose only if it is currently exhausted, otherwise a no-op that preserves failover progress.
• On-demand ensureDownloaded now re-arms exhausted blob sources before enqueuing, so a read after a prior cycle drained the sources retries instead of failing silently.
• RemoteConfigManager.prefetchBlobs re-arms blob sources only when exhausted rather than unconditionally every sync.
• RemoteConfigBlobStore keeps an in-memory index of on-disk refs so contains/cachedRefs no longer stat the disk on every call.

---

Note

Medium Risk
Changes hot-path blob cache checks and network source selection for remote config; behavior shifts from always retrying primary blob sources each sync to preserving failover state, which could delay recovery if exhaustion detection is wrong.

Overview
Remote config blob source failover no longer resets every sync or on every download. restartIfExhausted re-winds blob (and API) sources to the first entry only when that purpose has no healthy source left; otherwise failover progress is kept so a known-bad primary is not retried on each sync.

On-demand ensureDownloaded calls restartIfExhausted before enqueueing a missing blob so reads after an exhausted cycle can retry recovered sources. Sync prefetch uses the same conditional re-arm instead of unconditional restart. Individual download workers still do not restart inside the failover loop (one re-arm per on-demand request or prefetch cycle).

RemoteConfigBlobStore maintains a synchronized in-memory ref index (lazy one-time disk scan, updated on write / retainOnly / clear). contains and cachedRefs avoid per-call disk stats; read drops stale index entries when the file is missing. retainOnly still scans the blobs directory so orphan temp and invalid-named files are removed.

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[tonidero]

• refactor(remote-config): add RemoteConfigManager read facade (topic/body) #3703 : 2 dependent PRs (#3705 , #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 👈 (View in Graphite)
• 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 82.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.55%. Comparing base (b9cc466) to head (fa9c39d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...hases/common/remoteconfig/RemoteConfigBlobStore.kt	74.07%	0 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3698      +/-   ##
==========================================
+ Coverage   80.52%   80.55%   +0.03%     
==========================================
  Files         395      395              
  Lines       16278    16300      +22     
  Branches     2315     2318       +3     
==========================================
+ Hits        13108    13131      +23     
+ Misses       2244     2243       -1     
  Partials      926      926              

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[rickvdl]

Awesome! Thanks for iterating 🫶