[AI Chapters] Show indicator until fingerprinting settles

[sztomek]

Description

This is a follow-up of #5445
Now we show an indicator on the top of the chapters page until fingerprinting settles.

Fixes PCDROID-616 https://linear.app/a8c/issue/PCDROID-616/show-indicator-while-fingerprinting-is-in-progress

Testing Instructions

1. Find a podcast episode with generated chapters (e.g. The Daily episodes)
2. Open an episode
3. Select the Chapters tab
4. Hit a chapter to play
5. Notice the indicator
6. Wait a bit until the fingerprinting finishes
7. Notice the indicator disappearing

Screenshots or Screencast

Checklist

• If this is a user-facing change, I have added an entry in CHANGELOG.md
• Ensure the linter passes (./gradlew spotlessApply to automatically apply formatting/linting)
• I have considered whether it makes sense to add tests for my changes
• All strings that need to be localized are in modules/services/localization/src/main/res/values/strings.xml
• Any jetpack compose components I added or changed are covered by compose previews
• I have updated (or requested that someone edit) the Event Horizon schema to reflect any new or changed analytics.

[Copilot]

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[geekygecko]

Thanks for making this change. I have asked the designers for feedback here p1782174481298809-slack-C05RR9P9RAT

[wpmobilebot]

Version 8.15 has now entered code-freeze, so the milestone of this PR has been updated to 8.16.

[claude]

Claude finished @sztomek's task in 2m 18s —— View job

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PR Review — AI Chapters fingerprinting indicator

I reviewed the diff, the touched files, and FingerprintTimingManager for context. Overall this is a clean, well-tested change — the state derivation is correct for the common path, the feature is properly gated behind SYNCED_TRANSCRIPTS + AppPlatform.Phone, and the four new ViewModel tests cover the meaningful branches (preparing/generated, embedded chapters, other episode, non-phone). Nice work. A few notes below.

🟡 Suggestions

1. Missing Compose preview (inline)
AligningChaptersRow has no @Preview, while ChapterRow and ChaptersHeader in the same package each ship a full themed set. The checklist ticks "compose components… covered by compose previews," so this seems like an oversight. It also reads LocalChaptersTheme.current, so a preview would validate the theme wiring.

2. activeEpisodeUuid read is not reactive (inline)
activeEpisodeUuid is a @Volatile var read inside map on stateFlow, so the derived flag only recomputes on a stateFlow emission. It works today because prepareForEpisode() sets activeEpisodeUuid before flipping the state to Preparing, but that ordering is an implicit contract worth a comment (or derive the active episode from a flow). Not blocking.

🔵 Questions / minor

• "Preparing" ≠ "aligning chapters" in every case. The indicator shows for any State.Preparing on an episode with generated chapters, but the full-timeline chapter alignment only runs when shouldRunEagerPass is true (hasGeneratedChapters && (isDownloaded || unmetered)). For a streaming episode on a metered connection, preparation is playhead-following (transcript highlighting) rather than a full chapter re-align, yet the copy still reads "Aligning chapters…". Is showing it there intended, or should the indicator track the eager pass specifically?
• Never-settling case. If a stream never reaches MINIMUM_COVERAGE_FOR_ACTIVE (and never fails/goes unavailable), Preparing persists and so does the spinner. Probably acceptable, just flagging the UX edge.
• Accessibility (nit): the CircularProgressIndicator has no semantics/contentDescription. The adjacent TextP50 label carries the meaning, so this is low priority.
• Material2 CircularProgressIndicator/Divider usage is consistent with the rest of this (not-yet-migrated) module, so that's fine per the guidelines.

None of these are blockers — (1) and (2) are the ones I'd address before merge.

[claude]

Every other composable in this package (ChapterRow, ChaptersHeader) ships a full set of themed @Previews, and the PR checklist claims "Any jetpack compose components I added or changed are covered by compose previews." AligningChaptersRow has none. Since it reads LocalChaptersTheme.current, a preview would also catch the theme wiring. Consider adding one (matching the existing Light/Dark/etc. set) so the indicator is visually verifiable.

[claude]

activeEpisodeUuid is a plain @Volatile var, not part of a flow, but it's read inside map on stateFlow. This means the derived boolean only recomputes when stateFlow emits — a change to activeEpisodeUuid alone will not re-trigger it.

This happens to work today because FingerprintTimingManager.prepareForEpisode() sets activeEpisodeUuid = episodeUuid (line 396) before setting _stateFlow.value = State.Preparing (line 422). But it's fragile: if the manager ever switches episodes while remaining in Preparing (e.g. resetState() nulls activeEpisodeUuid without changing the state, then a new prepare sets Preparing again — which MutableStateFlow dedups, emitting nothing), an already-subscribed consumer wouldn't observe the episode change. Worth a comment noting the ordering dependency, or better, deriving the active episode from the flow itself.