Add maximum chapter duration cap when splitting by chapter (#1680)

[CryptoJones]

Summary

• Adds MaximumFileDuration configuration setting (in seconds, default 0 = disabled)
• When Split files by chapter is enabled and MaximumFileDuration > 0, any chapter longer than the limit is divided into equal-length parts
• Part titles are suffixed with (Part N of M) — e.g. Chapter 3 (Part 1 of 2)
• Offsets and durations are calculated exactly; the final part absorbs any remainder

Changes

• Configuration.PersistentSettings.cs — new MaximumFileDuration property
• Configuration.HelpText.cs — help/tooltip text for the new setting
• DownloadOptions.Factory.cs — new splitLongChapters() method; called after combineShortChapters() in the split-by-chapter pipeline
• SettingsDialog.Designer.cs / SettingsDialog.AudioSettings.cs — WinForms UI: label + NumericUpDown in the audiobook fixups group, enabled/disabled with the Split by chapter checkbox
• AudioSettingsVM.cs / Audio.axaml — Avalonia MVVM binding and NumericUpDown row in the split-by-chapter grid
• DownloadDecryptBookTests.cs — 6 new unit tests for splitLongChapters

Test plan

• splitLongChapters unit tests pass (no chapter split, exact limit, even split, uneven split, offset preservation, mixed-length list)
• WinForms: Maximum duration NUD appears beneath Minimum duration, enabled only when Split by chapter is checked
• Avalonia: same control visible in Audio settings, bound correctly
• Setting persists across app restarts
• Downloading an audiobook with a chapter exceeding the limit produces multiple files with correct part titles and durations

Closes #1680

🤖 Generated with Claude Code

[rmcrackan]

Thank you for the PR. The feature is scoped well: persistence, pipeline placement after combineShortChapters, shared configuration/help, both UIs wired with the same bounds and enable rules, and solid unit tests for splitLongChapters. That makes it much easier to review and merge with confidence.

Please address before merge

• WinForms layout: Move stripUnabridgedCbox and stripAudibleBrandingCbox (and tweak vertical spacing in the Audiobook Fix-ups group as needed) so they no longer sit on the same row as the new max-duration controls. Right now maxFileDurationNud is at the same Y as stripUnabridgedCbox, and the max label overlaps that row.
• Help text units: Update the new MaximumFileDuration help copy so it says seconds, not minutes, so it matches [Description], the NumericUpDown, and * 1000 in DownloadOptions.Factory. While you are in that dictionary entry, consider correcting MinimumFileDuration help text too (it already says minutes on master but the setting is seconds).
• User-facing accuracy: Align PR description / help wording with behavior: chapters are split into segments of at most the limit, with the last segment shorter when there is a remainder, not necessarily mathematically equal-length parts across the whole chapter.

[rmcrackan]

After making the layout fixes, please run classic (winforms) and chardonnay (avalonia) locally to get human eyes on it. AI can sometimes have a hard time getting visual/layout stuff correct.

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[CryptoJones]

Apologies for the delay — I've pushed a fix commit that addresses all three items:

WinForms layout: Moved stripUnabridgedCbox (Y 63 → 92) and stripAudibleBrandingCbox (Y 88 → 118) below the max-duration row so they no longer share a row with maxFileDurationNud / maxFileDurationLbl.

Help text units: Both MinimumFileDuration and MaximumFileDuration now say seconds instead of minutes.

User-facing accuracy: MaximumFileDuration help copy now reads: "Chapters longer than this duration will be split into segments of at most this length; the last segment will be shorter if the chapter does not divide evenly." — no more "equal-length parts" language.

Verifying the layout visually now and will report back.

[CryptoJones]

Please hold this merge until human verification has been completed.

[CryptoJones]

Visual verification complete — ran all three builds on a Windows 11 QEMU VM.

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Baseline Main/Master

(no Max File Duration field — clean reference)

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Smoothbrain Claude's Original PR

(Max File Duration field overlapping the Strip checkboxes — the layout bug)

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Slightly Less Smooth-Brained PR (mine)

(fixed: checkboxes pushed down, no overlap)

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The layout is correct. All three reviewer requests (layout, help text units, behavioral accuracy wording) are addressed in commit 77a4997b.

[CryptoJones]

Now manually testing Chardonnay.

[CryptoJones]

Chardonnay (Avalonia) visual verification — same Windows 11 QEMU VM.

Note: the Avalonia UI uses Grid row definitions in AXAML (not fixed pixel coordinates), so there was never a layout overlap in Chardonnay — the Max Duration row slots in correctly by construction.

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Chardonnay — Baseline Main/Master

(no Max File Duration field)

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Chardonnay — Fixed PR

(Max File Duration in its own row, no overlap)

[CryptoJones]

Sorry for all the hassle with this PR. I have locked that Claude instance into a virtual environment where it plays Maria Carry's "All I want for Christmas" on a loop for eternity.

[CLHatch]

I've sworn like a sailor to Gemini myself. :-D Lately to Claude as well, I've noticed the quality went down on it's coding lately.

[rmcrackan]

Thank you for all the effort you put into this one.

Heads up that I don't know when I'll be able to give it a proper review. I spent a lot of time on Libation last week so I'm falling behind on some stuff. It's my own fault. Now I need to play catch-up for a bit before doing the next big Libation thing.

[wtanksleyjr]

Does this change increase the minimum screen height? This Settings window cannot be resized beyond a certain point, we don't want to make it worse than it is.

[rmcrackan]

@wtanksleyjr Valid concern. I don't want to derail his work-in-progress. Would it be acceptable if I:

• Review (and hopefully accept) this PR, even if it exceeds desired height
• After: I can open a new bug for myself: that it's time to put all settings into a resize-able box with scrollbar(s)?

[wtanksleyjr]

That's the ideal solution I think.