feat: language preference persistence per channel

[STRRL]

Summary

Implements automatic language preference persistence for each channel. When a user selects a language for a video from a specific channel, the app remembers and auto-applies that preference to future videos from the same channel.

Implementation

• Extended Settings struct with ChannelLanguagePrefs map
• Added GetChannelLanguagePreference() and SetChannelLanguagePreference() backend methods
• Modified StartTranscription() to save preferences automatically
• Updated NewTranscriptionPage to query and auto-select saved language preferences

Behavior

• New channels default to global SourceLang setting
• Preferences stored as {platform}:{channelID} with fallback to channel name
• Settings persisted to ~/.config/TransCube/settings.json
• Backward compatible with existing settings files

🤖 Generated with Claude Code

[mesa-dot-dev]

Mesa Description

TL;DR

Implements automatic language preference persistence for each channel. When a user selects a language for a video from a specific channel, the app remembers and auto-applies that preference to future videos from the same channel.

What changed?

• Extended Settings struct with ChannelLanguagePrefs map
• Added GetChannelLanguagePreference() and SetChannelLanguagePreference() backend methods
• Modified StartTranscription() to save preferences automatically
• Updated NewTranscriptionPage to query and auto-select saved language preferences
• New channels default to global SourceLang setting
• Preferences stored as {platform}:{channelID} with fallback to channel name
• Settings persisted to ~/.config/TransCube/settings.json
• Backward compatible with existing settings files

^{Description generated by Mesa. Update settings}

[mesa-dot-dev]

Performed full review of b9beb81...076eb7b

Analysis

1. Unbounded Storage Growth: The map-based storage for channel language preferences has no eviction policy, potentially causing unlimited growth for users who watch many channels.

2. Frontend Race Condition: Platform detection happens asynchronously, but preference lookup occurs immediately when metadata loads, which could lead to using 'unknown' as the platform identifier.

3. No User Interface for Management: Users cannot view or clear their saved channel preferences through any UI, limiting control over accumulated preferences.

4. Preference Saving Before Validation: Language preferences are saved in StartTranscription() before the transcription task begins, meaning preferences will be persisted even for failed transcriptions.

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^{0 files reviewed | 2 comments | Edit Agent Settings • Read Docs}

[mesa-dot-dev]

The platform variable may still be 'unknown' when this executes. Platform detection runs asynchronously via DetectPlatform(url), but there's no guarantee it completes before handleMetadataLoaded is called. If metadata loads first, the preference lookup will use 'unknown' as the platform key, likely returning no saved preference. Consider adding a check like if (platform === 'unknown') return or ensuring platform detection completes before querying preferences.

Agent: ⚛️ React •  • 

Prompt for Agent

Task: Address review feedback left on GitHub.
Repository: STRRL/transcube-webapp#26
File: frontend/src/pages/NewTranscriptionPage.tsx#L189
Action: Open this file location in your editor, inspect the highlighted code, and resolve the issue described below.

Feedback:
The `platform` variable may still be `'unknown'` when this executes. Platform detection runs asynchronously via `DetectPlatform(url)`, but there's no guarantee it completes before `handleMetadataLoaded` is called. If metadata loads first, the preference lookup will use `'unknown'` as the platform key, likely returning no saved preference. Consider adding a check like `if (platform === 'unknown') return` or ensuring platform detection completes before querying preferences.

[mesa-dot-dev]

Race condition: If the user manually selects a different source language while GetChannelLanguagePreference is still pending, the delayed setSourceLang(preferredLang) will overwrite the user's manual selection. Consider tracking whether the user has made a manual selection (e.g., via a ref or flag) and skip the auto-selection if they have, or use an AbortController to cancel the pending update.

Agent: ⚛️ React •  • 

Prompt for Agent

Task: Address review feedback left on GitHub.
Repository: STRRL/transcube-webapp#26
File: frontend/src/pages/NewTranscriptionPage.tsx#L195
Action: Open this file location in your editor, inspect the highlighted code, and resolve the issue described below.

Feedback:
Race condition: If the user manually selects a different source language while `GetChannelLanguagePreference` is still pending, the delayed `setSourceLang(preferredLang)` will overwrite the user's manual selection. Consider tracking whether the user has made a manual selection (e.g., via a ref or flag) and skip the auto-selection if they have, or use an AbortController to cancel the pending update.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Memoize metadata handler to avoid endless metadata refetches

VideoPreview’s useEffect depends on the onMetadataLoaded prop, so when this page now passes an inline handleMetadataLoaded function that is recreated every render, the effect reruns on every render even when the URL is unchanged (see VideoPreview.tsx where the effect depends on onMetadataLoaded). Each rerender schedules another ParseVideoUrl call and preference lookup every ~500 ms, producing continuous metadata fetches and state churn once the first metadata load updates state. The handler should be memoized (e.g., useCallback) or the dependency removed to prevent repeated backend calls.

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