[andrew-polk]

Problem. On a computer whose regional format is Thai (probably Lao too), every Bloom operation that reads or writes the credits/license metadata inside an image fails with UnsupportedFormatException. That covers choosing a picture, editing its credits, anything that saves images with metadata, and every book's cover thumbnail: selecting a book replaces its thumbnail with the hazard sign (BL-16944; in a debug build it trips an assert and Bloom exits). The culture sweep's th-TH leg found it. Targets Version6.4.

Cause. When TagLib# isn't given a mime type, it works one out from the file name with a culture-sensitive LastIndexOf("."). Under Thai ICU collation the period is ignorable, so the extension comes out empty and the mime type is taglib/. libpalaso's ClearShare code and Bloom's own code both call TagLib.File.Create(path).

Fix.

• Bloom registers a TagLib# FileTypeResolver (TagLib's own extension point) at the top of Program.Main. When TagLib's mime type is unknown but the extension found with Path.GetExtension is known, the resolver creates the file with the right mime type. Otherwise it stays out of the way, so mislabeled and unsupported files behave as before. One registration covers libpalaso's calls and Bloom's own direct calls. It can be removed once a TagLib# release searches ordinally (upstream fix: Find the file extension ordinally in File.Create mono/taglib-sharp#381).
• BloomTests registers it in a [SetUpFixture], as Program does. New th-TH regression tests (PNG and JPEG) cover the libpalaso save/read path and Bloom's RobustFileIO.CreateTaglibFile. They first check that the runtime really ignores the period, so they can't pass for nothing.
• Verified in a real 6.4 Bloom forced to th-TH: with the resolver disabled, selecting a book wrote the hazard image over its thumbnail; with it enabled, both test books' thumbnails regenerated byte-for-byte identical to the originals.

Ref: https://issues.bloomlibrary.org/youtrack/issue/BL-16926

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Devin review

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This change is 

[andrew-polk]

[Claude Opus 5.5 from Andrew Polk's machine during preflight] Consulted Devin on 2026-09-25 22:25 UTC up to commit 8cd8588: no bugs, no flags.

[greptile-apps]

[Medium risk] Adds a workaround for image metadata handling on Thai-locale systems.

The PR appears safe to merge.

Summary

The PR registers a TagLib# file-type resolver at startup to restore image metadata handling under Thai collation.

• Adds PNG and JPEG regression tests for metadata reads and writes.
• Registers the resolver before tests run.

_{Reviews (3) · Last reviewed commit: "Fix image metadata on Thai-locale comput..."}

[andrew-polk]

[Claude Opus 5.5 from Andrew Polk's machine] Re Greptile's summary: added JPEG cases to both regression tests (amended into 2d22c56). Kept the NLS premise check as a hard failure on purpose: on a runtime whose Thai collation finds the period the tests couldn't reproduce the bug, and a loud failure beats a silent pass. .NET 8 on current Windows uses ICU.

[andrew-polk]

[Claude Opus 5.5 from Andrew Polk's machine] Consulted Devin on 2026-09-25 23:02 UTC up to commit 2d22c56: no bugs, no flags.

[andrew-polk]

[Claude Opus 5.5 from Andrew Polk's machine during preflight] Consulted Devin on 2026-09-29 16:16 UTC up to commit d23dd7c (the fix rebased onto Version6.4): no bugs, no flags.