fix(tanstack-ai): handle image ContentPart in workers-ai adapter

[mdhruvil]

Fix: Workers AI adapter drops type: "image" content parts

Closes #431

Problem

TanStack AI's multimodal content uses ContentPart types where images are represented as:

{
  type: "image",
  source: { type: "url" | "data", value: string, mimeType?: string }
}

The workers-ai adapter's buildUserContent function only handled the legacy type: "image_url" format (workers-ai.ts#L98-L122), which TanStack AI never sends. This caused all image parts to be silently dropped from user messages.

The detection logic on line 98 correctly checked for both type: "image_url" and type: "image", but the conversion logic on lines 112-122 only handled type: "image_url" — so images were detected as present but never converted.

Solution

Rewrote the message-building helpers to use TanStack AI's canonical types directly, following the patterns from the reference OpenAI adapter (as recommended by TanStack's community adapter guide).

Type changes

• Removed the ad-hoc MessageLike interface — replaced with ModelMessage from @tanstack/ai
• Removed the inline Array<{ type: string; content?: string; image_url?: unknown }> content type — replaced with ModelMessage["content"] which is string | null | Array<ContentPart>
• Imported ContentPart and ModelMessage from @tanstack/ai (already a peer dependency)

convertContentPart (new)

Extracted a dedicated function that converts a single ContentPart → OpenAI.Chat.ChatCompletionContentPart:

Input	Output
type: "text"	{ type: "text", text: part.content }
type: "image", source.type: "url"	{ type: "image_url", image_url: { url: source.value } }
type: "image", source.type: "data"	{ type: "image_url", image_url: { url: "data:{mimeType};base64,{value}" } }
audio / video / document	console.warn + skip (Workers AI chat API doesn't support these)

Includes a guard against source.value already containing a data: prefix (matching the reference adapter's pattern) to prevent malformed double-prefixed URIs.

Files changed

File	Change
packages/tanstack-ai/src/adapters/workers-ai.ts	Core fix: use ContentPart/ModelMessage, handle type: "image"
packages/tanstack-ai/test/message-builder.test.ts	Update image tests to ContentPart format
packages/tanstack-ai/test/workers-ai-adapter.test.ts	Update image integration test, add data source test

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