Early access WhatsApp messaging: add API reference, spec updates, guides

[hey-august]

Description

Adds WhatsApp as a messaging channel in both the REST API reference and the platform guides.

Outbound sends reuse the existing POST /api/messaging/messages endpoint. When the from number matches a connected WhatsApp number (identified by its whatsapp: prefix), it gets routed over Whatsapp. message_type selects a content message, and template_id selects a template.

This PR also adds three read/manage surfaces: WhatsApp Business Accounts, WhatsApp numbers, and message templates.

Alpha status

WhatsApp messaging is in alpha / early access. The guides explain this, and include links to the request form for customer Space enablement. The whatsapp_interactive_flow type is deliberately omitted because Flows are not part of the alpha program.

New pages (with linked previews)

API reference

• List WhatsApp Business Accounts
• Get a WhatsApp number
• List WhatsApp numbers
• Create a message template
• Delete a message template
• Get a message template
• List message templates
• Update a message template

Guides

• WhatsApp messaging overview
• Onboarding
• Receive messages
• Send messages
• Message templates

File changes

TypeSpec specs

• message-api/messages/models/whatsapp.tsp (new): Includes all WhatsApp send models. Has a shared WhatsAppSendBase, per-type content bodies (image, video, audio, sticker, document, location, contacts, reaction, interactive), the message_type-discriminated WhatsAppContentMessageRequest union, the WhatsAppTemplateMessageRequest, and the combined SendMessageRequest.
• message-api/messages/main.tsp: Sends now accept SendMessageRequest. Endpoint docs explain WhatsApp routing and the 24-hour window.
• message-api/messages/models/core.tsp: Adds whatsapp to MessageKind, and read to MessageStatus.
• message-api/whatsapp-businesses/ (new): Adds list_whatsapp_businesses plus the WhatsAppBusiness model and list response.
• message-api/whatsapp-numbers/ (new): Adds list/retrieve for numbers, with the WhatsAppNumber model (routing resource IDs, voice-capability flags) and responses.
• message-api/whatsapp-templates/ (new): Adds full CRUD (list/retrieve/create/update/delete), the WhatsAppTemplate model, category/format/status enums, and request/response models. Create returns 201, and delete returns 200 with a { success, errors } body.
• message-api/tags.tsp: Adds tag metadata for the three new WhatsApp tags.
• message-api/main.tsp / main.tsp: Wire up the new namespaces and register the tags on the service.

Generated reference

• fern/apis/signalwire-rest/openapi.yaml: Regenerated from the specs above.

Guides (fern/products/platform/pages/messaging/whatsapp/)

• overview.mdx: Introduces the alpha, its supported features, how it works, prerequisites, and how to request access.
• onboarding.mdx: How to connect a Meta-verified business number via embedded signup and verify it through the businesses/numbers endpoints.
• send-messages.mdx: Routing rules, the full message_type table, and text / interactive-reply-button / template examples.
• receive-messages.mdx: Describes inbound handling, message logs, and delivery-status semantics.
• message-templates.mdx: Components, parameters, categories, and the template lifecycle.

Navigation

• fern/products/apis/apis.yml: Adds a WhatsApp section referencing the businesses/numbers/templates packages.
• fern/products/platform/platform.yml: Adds a WhatsApp guide folder under Messaging.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Code cleanup / refactor

Related Issues

#447

Testing

• Added/updated unit tests
• Tested manually
• Tested with live SignalWire credentials (if applicable)

Checklist

• I have read the CONTRIBUTING guidelines
• My code follows the project's style guidelines
• I have added tests for my changes (if applicable)
• I have updated documentation (if applicable)
• All existing tests pass

[github-actions]

🌿 Preview

https://signalwire-preview-019f47cc-c036-77b9-82d6-af24b76fdde6.docs.buildwithfern.com/docs

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