refactor: centralize LLM prompt templates and transcript utilities

[vegerot]

• Extract shared prompt templates into LLMPromptTemplates (GeminiPromptPreferences.swift)
• Add VideoPromptPreferences/VideoPromptOverrides/VideoPromptSections types,
  replacing GeminiPromptPreferences/GeminiPromptOverrides/GeminiPromptSections
• Centralize transcript JSON decoding and observation conversion in
  LLMTranscriptUtilities (TimeParsing.swift) for reuse across providers
• Refactor GeminiDirectProvider to use LLMPromptTemplates and LLMTranscriptUtilities
• Refactor TestConnectionView to accept a provider parameter with
  finishFailure/finishSuccess helpers for clean multi-provider support
• Fix OnboardingLLMSelectionView card-width calculation to be dynamic
  based on card count rather than hard-coded divisor of 3
• Update SettingsProvidersTabView and ProvidersSettingsViewModel to use
  new VideoPrompt* types

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

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• feat: add Doubao (Ark) LLM provider #212
• fix: stop settings hang caused by blocking XPC call on main thread #252
• feat: add option to disable automatic updates #250
• feat: mirror analytics events to stdout and OSLog #228
• feat: use structured output to improve responses #227
• -> refactor: centralize LLM prompt templates and transcript utilities #226

[Copilot]

Pull request overview

This PR centralizes prompt templates and transcript utilities used by LLM providers in Dayflow. Previously, GeminiDirectProvider contained large inline prompt strings and private timestamp/validation helpers; these are now extracted into shared types (LLMPromptTemplates, LLMTranscriptUtilities, LLMVideoTimestampUtilities, LLMTimelineCardValidation) for reuse across providers. Additionally, the Gemini-specific prompt preference types are renamed to provider-agnostic names (VideoPromptOverrides, VideoPromptPreferences, VideoPromptSections), TestConnectionView is made provider-aware, and the onboarding card-width calculation is made dynamic.

Changes:

• Extract inline prompt strings from GeminiDirectProvider into LLMPromptTemplates and centralize transcript/timestamp utilities into LLMTranscriptUtilities / LLMVideoTimestampUtilities / LLMTimelineCardValidation in TimeParsing.swift
• Rename GeminiPromptPreferences/Overrides/Sections to VideoPromptPreferences/Overrides/Sections, and refactor TestConnectionView to accept an LLMProviderID provider parameter with shared finishFailure/finishSuccess helpers
• Add local OSLog logging to AnalyticsService alongside PostHog capture via a new captureToPostHogAndLocal helper; fix dynamic card-width calculation in OnboardingLLMSelectionView

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
GeminiPromptPreferences.swift	Renames Gemini-specific prompt types to Video* prefix; adds LLMPromptTemplates with shared prompt-generating functions
TimeParsing.swift	Adds LLMVideoTimestampUtilities, LLMTimelineCardValidation, and LLMTranscriptUtilities enums centralizing timestamp parsing, validation, and transcript decoding
GeminiDirectProvider.swift	Replaces inline prompt strings and private helpers with calls to the new shared utilities
TestConnectionView.swift	Adds provider: LLMProviderID parameter and shared finishFailure/finishSuccess helpers for multi-provider support
AnalyticsService.swift	Adds captureToPostHogAndLocal helper with OSLog local logging; consolidates all capture calls through it
ProvidersSettingsViewModel.swift	Updates to use VideoPromptPreferences/VideoPromptOverrides
SettingsProvidersTabView.swift	Passes explicit .gemini provider to updated TestConnectionView
OnboardingLLMSelectionView.swift	Makes card-width calculation dynamic based on providerCards.count

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[Copilot]

The new LLMTimelineCardValidation.formatTimestampForPrompt method at line 83 creates a new DateFormatter on each call. The file already demonstrates the pattern of caching DateFormatter instances (see cachedHMMAFormatters at lines 4-17) with a comment explaining "creating DateFormatters is expensive (ICU initialization)". This method should either use a cached DateFormatter or call LLMVideoTimestampUtilities utilities to be consistent — though note that DateFormatter is not thread-safe, so a cached shared instance would need care if called from multiple threads.

Suggested change

	static func formatTimestampForPrompt(_ unixTime: Int) -> String {
	let date = Date(timeIntervalSince1970: TimeInterval(unixTime))
	let formatter = DateFormatter()
	formatter.dateFormat = "h:mm a"
	formatter.locale = Locale(identifier: "en_US_POSIX")
	formatter.timeZone = TimeZone.current
	return formatter.string(from: date)
	/// Cached formatter for human-readable prompt timestamps.
	/// Access to this formatter is synchronized because DateFormatter is not thread-safe.
	private static let promptTimeFormatter: DateFormatter = {
	let formatter = DateFormatter()
	formatter.dateFormat = "h:mm a"
	formatter.locale = Locale(identifier: "en_US_POSIX")
	formatter.timeZone = TimeZone.current
	return formatter
	}()
	private static let promptTimeFormatterQueue = DispatchQueue(label: "LLMTimelineCardValidation.promptTimeFormatter")
	static func formatTimestampForPrompt(_ unixTime: Int) -> String {
	let date = Date(timeIntervalSince1970: TimeInterval(unixTime))
	return promptTimeFormatterQueue.sync {
	promptTimeFormatter.string(from: date)
	}

[vegerot]

Good point, but this code isn't hot enough to make a big difference

[Copilot]

The file GeminiPromptPreferences.swift now contains VideoPromptOverrides, VideoPromptPreferences, VideoPromptSections, and LLMPromptTemplates — types that are no longer Gemini-specific. The filename no longer reflects the contents of the file. Consider renaming it to something like LLMPromptPreferences.swift or VideoPromptPreferences.swift to match the types it now defines.

[vegerot]

I agree with this, and initially did name it something else, but it made keeping track of upstream too hard. Once this patch lands I'll open another one to do the rename

[vegerot]

@JerryZLiu Would you please review this PR? This doesn't change any behavior, but makes adding new video providers in my fork easier