Fix TC message log write failure preventing collection from opening (BL-16772)

[andrew-polk]

Problem: A user whose Team Collection's local folder contains read-only files could not open their collection at all. Bloom reported a raw UnauthorizedAccessException ("Access to the path ...log.txt is denied") and gave up, even though the TC code has a disconnected-mode fallback (added for BL-16227) designed to let the collection open with Team Collection features degraded.

Cause: When TC initialization failed (a sync write to the unwritable folder threw), the recovery path in the TeamCollectionManager constructor built a DisconnectedTeamCollection and then wrote an error message via TeamCollectionMessageLog.WriteMessage — which appends to log.txt in the same unwritable folder. That second exception escaped the constructor uncaught, killed the Autofac resolve, and prevented the whole ProjectContext from being created.

Fix: TeamCollectionMessageLog.WriteMessage now catches a failure to persist a message to log.txt, logs it via the SIL Logger, and continues. The message is already in the in-memory list and the Logger before the file write, so the current session still shows it; it just won't survive a restart. A regression test makes the log file read-only and verifies WriteMessage doesn't throw and keeps the message in memory. The PR targets Version6.4 directly (the affected user is on 6.4 Beta); the change is deliberately minimal. Version6.4 merges forward to 6.5/master per the usual flow.

Ref: https://issues.bloomlibrary.org/youtrack/issue/BL-16772

Devin review

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This change is 

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Devin review

[greptile-apps]

Greptile Summary

The PR prevents a Team Collection message-log persistence failure from aborting collection startup.

• Retains the message in memory and reports file-write failures through the SIL logger.
• Adds regression coverage using a read-only Team Collection log file.

Important Files Changed

Filename	Overview
src/BloomExe/TeamCollection/TeamCollectionMessageLog.cs	Handles message-log persistence failures without disrupting Team Collection initialization.
src/BloomTests/TeamCollection/TeamCollectionMessageLogTests.cs	Adds regression coverage confirming an unwritable log does not discard the in-memory message or throw.

_{Reviews (2): Last reviewed commit: "Fix BL-16772 TC message log write failur..." | Re-trigger Greptile}

[andrew-polk]

[Claude Fable 5] Consulted Devin on 2026-08-28 ~19:25 UTC up to commit 1798dbf. Result: no bugs, no Investigate flags; 1 informational note (confirming the message survives in memory/Logger when the file write fails). Nothing to mirror.

[andrew-polk]

[Claude Fable 5] Consulted Devin on 2026-08-28 ~20:20 UTC up to commit da662d8 (branch rebuilt on Version6.4). Result: no bugs, no Investigate flags; the same single informational note as before. Nothing to mirror.

[StephenMcConnel]

@StephenMcConnel reviewed 2 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on andrew-polk).