Apply audio's brand-based provider-options extraction to TTS, Transcription, Summarize

[tombeckenham]

Background

Commit 603d4abe (#564) fixed AudioProviderOptions in packages/typescript/ai/src/activities/generateAudio/index.ts:

// Before — collapsed to `object` for any concrete provider options interface
export type AudioProviderOptions<TAdapter> =
  TAdapter extends AudioAdapter<any, any>
    ? TAdapter['~types']['providerOptions']
    : object

// After — brand-based structural infer
export type AudioProviderOptions<TAdapter> =
  TAdapter extends { '~types': { providerOptions: infer P extends object } }
    ? P
    : object

The same broken pattern still exists in three sibling activities.

Affected files

Activity	File	Helper
TTS	packages/typescript/ai/src/activities/generateSpeech/index.ts:30	TTSProviderOptions
Transcription	packages/typescript/ai/src/activities/generateTranscription/index.ts:30	TranscriptionProviderOptions
Summarize	packages/typescript/ai/src/activities/summarize/index.ts:28	SummarizeProviderOptions

All three use the same extends *Adapter<any, any> ? T['~types']['providerOptions'] : object shape that was just fixed in audio.

Why this is silent today

Audio surfaced because FalAudioProviderOptions<'fal-ai/minimax-music/v2'> has a required field (lyrics_prompt). The contravariance check on generateAudio's parameter only fires when the concrete provider options has a required field.

Concrete options for the other three activities (OpenAITTSProviderOptions, OpenAITranscriptionProviderOptions, etc.) are all-optional, so the constraint check coincidentally passes — but modelOptions at user call sites is silently typed as object, meaning users get no autocomplete or validation on modelOptions for these activities.

Add a single required field to any concrete *ProviderOptions and these would break the same way ai-fal did.

Fix

For each of the three helpers, apply the same swap:

export type TTSProviderOptions<TAdapter> =
  TAdapter extends { '~types': { providerOptions: infer P extends object } }
    ? P
    : object

Note on Summarize: in addition to the helper, SummarizeActivityOptions and its three function-signature constraints at summarize/index.ts:45, 153, 299 currently use extends SummarizeAdapter<string, object> — the broken contravariant form. These should switch to the F-bounded extends SummarizeAdapter<string, SummarizeProviderOptions<TAdapter>> shape (matching audio's pattern) once the helper is fixed.

Acceptance criteria

• TTSProviderOptions, TranscriptionProviderOptions, SummarizeProviderOptions rewritten to use brand-based infer P extends object.
• Summarize constraints switched from <string, object> to F-bounded form.
• pnpm test:types green across the workspace (the existing ai-openai/ai-fal/ai-anthropic adapter tests are the regression net).
• No new anys introduced.
• Per .agent/self-learning/coupling.json triggers: update packages/typescript/ai/skills/ai-core/media-generation/SKILL.md if any user-visible typing guidance changes; update relevant docs/media/** pages if modelOptions examples are shown.

Out of scope (separate follow-ups)

• Image / Video constraint cleanup: generateImage/index.ts and generateVideo/index.ts use 4-generic adapters with <string, any, any, any> constraints throughout. Their *ProviderOptions helpers happen to extract correctly (via infer'd positions), but the surrounding any placeholders deserve a tightening pass.
• Chat (TextAdapter) AnyTextAdapter removal: chat's surface uses extends AnyTextAdapter = TextAdapter<any, any, any, any, any, any, any> at every call site (chat/index.ts:84, 244, 289, 303, 1633). Replacing with an F-bounded constraint is materially different work — likely half a day to a day — and warrants its own issue.