Drop a trailing period from a suggested file name [patch]

[matt-edmondson]

Fixes #196

What was wrong

Models often end their answer with a full stop, even when asked for just a file name. Scan.SanitizeFileName kept that period at every step. Path.GetExtension("sunset.") is empty, . is a legal character, and the final trim removed only - and space. So:

model answer	before	after
sunset-over-the-lake.	sunset-over-the-lake..jpg	sunset-over-the-lake.jpg
photo.jpg. (to .png)	photo.jpg..png	photo.png
...	....jpg	unnamed.jpg

A suggestion is stored once per hash and never regenerated, so the bad name stayed in the database for good.

Change

• Trim trailing periods and spaces right after the quote and backtick trim, before the extension check. This also lets photo.jpg. lose its image extension.
• Add . to the final trim set. A name made only of dots now falls back to unnamed. So does a period left at the end once the final trim removes a trailing hyphen (sunset.- gives sunset.jpg).
• Dots inside a name are unchanged: the st.-louis-arch-at-dusk and sunset-at-5.30pm tests still pass.

Tests

New ScanTests cases: SanitizeFileNameDropsTrailingPeriod (4 rows), SanitizeFileNameStripsImageExtensionFollowedByPeriod, SanitizeFileNameReturnsUnnamedForOnlyPeriods (3 rows), and SanitizeFileNameDropsPeriodLeftBeforeTrimmedHyphen.

• With the fix reverted, all 9 new cases fail.
• With it applied, the full suite passes: 117 passed and 1 skipped. The skip is ScanForImagesSkipsUnreadableSubdirectories, which is inconclusive when run as root.
• CI is green on Ubuntu, macOS and Windows.

Not covered: names already stored with .. are not rewritten. The triage note suggests a one-off cleanup or a re-suggest path for those, which is a separate change. I've also left alone a Windows-only crash that already exists on main: an extension that Windows rejects, such as .?, throws inside IsImageExtension. It is described in the comment below.

🤖 Generated with Claude Code

https://claude.ai/code/session_01URmxVUpdaWCEUSPudDfLsq

[matt-edmondson]

The first push failed Test on windows-latest in SanitizeFileNameDropsPeriodLeftBeforeReplacedCharacter, which threw ArgumentException: Cannot convert ".?" to FileExtension. On Windows, Path.GetExtension("sunset.?") returns .?. ImageScanner.IsImageExtension then converts that to a FileExtension, which refuses ?. de7f220 swaps the input for sunset.-, which exercises the same trailing-period trim on every platform. Against the code before this PR, the renamed case fails; with the fix, it passes.

Not fixed here, because it is outside this PR's scope: the same crash exists on main today. On Windows, any suggestion whose text after its last dot contains a character Windows rejects (for example what is this.? or a.b:c) makes SanitizeFileName throw before the replacement step runs. One possible fix is to run the extension check after the character replacement, or to have IsImageExtension return false for an extension that isn't valid. Either would fit with #171.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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