Propagate converter exceptions instead of hanging indefinitely

[matt-ramotar]

Closes #660

Problem

When Converter.fromNetworkToLocal() throws an exception, store.stream() and store.get() hang indefinitely instead of emitting an error.

Root Cause

Conversion happens inside the Multicaster's onEach callback. Exceptions there propagate to the internal actor, which terminates and closes downstream channels silently. This means no error signal reaches collectors.

Solution

Move conversion and SourceOfTruth writes from onEach into the source flow's map operator. Exceptions are now caught and emitted as StoreReadResponse.Error.Exception, allowing callers to handle them appropriately.

---

Note

Addresses hanging when Converter.fromNetworkToLocal() throws by handling conversion inside the fetcher source and emitting errors.

• In FetcherController, move conversion and SOT writes from onEach to the source map with try/catch; rethrow CancellationException, emit StoreReadResponse.Error.Exception on failure; no-op onEach to avoid actor shutdowns
• In RealStore, adjust disk/network merge: unlock disk on network Data/NoNewData/Error; track networkErrorWithNoFallback to suppress SOT emissions for fresh requests when fallback is disabled; preserve fetcher name in origins
• Add tests validating error emission, fetcher name propagation, flow completion on fresh, fallback enabled/disabled behavior, and recovery when conversion later succeeds

^{Written by Cursor Bugbot for commit 50dc877. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.76%. Comparing base (d4e94b4) to head (50dc877).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ilenativefoundation/store/store5/impl/RealStore.kt	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #728      +/-   ##
==========================================
+ Coverage   79.17%   79.76%   +0.58%     
==========================================
  Files          42       42              
  Lines         941      919      -22     
  Branches      169      172       +3     
==========================================
- Hits          745      733      -12     
+ Misses        120      111       -9     
+ Partials       76       75       -1     

Files with missing lines	Coverage Δ
...efoundation/store/store5/impl/FetcherController.kt	98.14% <100.00%> (ø)
...ilenativefoundation/store/store5/impl/RealStore.kt	89.39% <88.88%> (+0.67%)	⬆️

... and 9 files with indirect coverage changes

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