Bug hunt 24: sixteen fixes from random-file sampling

[niksedk]

Twenty-fourth bug hunt: seeded random shuffle of all C# sources, five parallel reviewers over 24-file slices, plus a solo fractional-ms / comma-culture round-trip sweep over every text format. Every finding below was confirmed by execution before fixing.

Format writers/readers that could not round-trip their own output

• FLVCoreCuePoints, HoliStar JSON, JSON Type 5/7/17, OpenDVT wrote milliseconds with the current culture (1500,5 under da-DK etc.); their integer readers dropped the cue or split on the comma. Now write whole ms invariantly.
• Unknown 2 wrote hundredths where the sample and reader expect ms (1.520 s reloaded as 1.052 s).
• Unknown 4 read the two-digit fraction as ms (00:00:22.50 → 22.050 s).
• Unknown 3 wrote frame counts where the sample and reader expect ms (1.520 s reloaded as 0.036 s).
• Unknown 31 scaled the frames-within-foot field by the frame rate; the reader adds it straight to 16 * footage.
• Unknown 45 formatted the seconds double with {0:00000}, rounding 1.52 s up to 00002 and then appending the frames of the 520 ms (→ 2.5 s).
• Unknown 50 read the frames field as ms.
• Unknown 60 wrote an end-time line that the start-only reader took as the next cue's start, so every cue reloaded at its old end time.
• Unknown 105 wrote [WAIT] before its text, but the reader pairs text with the following wait, so every cue took the next cue's timing. The writer now also emits the first cue's offset.
• YouTube transcript one line: 1:01:01 text matched the minutes regex first and loaded as 1:01 with :01 text as the text.

Other

• ASSA style picker "Usages" column was bound to FontSize; both callers also dropped the count when converting to SsaStyle, so "Take usages from…" showed font sizes.
• Matroska TextST track → Export built the decoded cues and then threw them away; the helper's own load has no TextST branch and wrote the raw payload as text.
• AssaDraw DrawShape.ToAssa serialized a mixed line/bezier shape as one b run, turning straight points into bezier control points and shifting every later triplet.
• HtmlUtil.FixInvalidItalicTags "FALCONE:" branch did Substring(0, -1) for a bare \n on Windows; the sibling branches were already guarded for the same crash.
• PodcastIndexer read speaker raw although ToText JSON-escapes it (like body).
• DcPropertiesSmpte read every value raw although Save JSON-escapes them (C:\fonts\a.ttf reloaded doubled).

Tests

• tests/libse/SubtitleFormats/BugHunt24Test.cs (18 tests)
• tests/UI/Features/Assa/DrawShapeToAssaTests.cs (3 tests)

Full libse suite green locally (1934 tests).

🤖 Generated with Claude Code