[api-sync 2026-07-31] gradientlabs-go: split outbound conversation start into chat/email/phone

[gmtuca]

⚠️ Breaking change — version 0.4.0

POST /outbound/conversations has been removed from the public API and replaced by three channel-specific endpoints. This SDK follows suit:

Removed	Added
Client.StartOutboundConversation	Client.StartOutboundChatConversation → POST /outbound/conversations/chat
	Client.StartOutboundEmailConversation → POST /outbound/conversations/email
	Client.StartOutboundPhoneConversation → POST /outbound/conversations/phone

Also removed: StartOutboundConversationParams and the CustomerSource type/constants (the field has no replacement in the new API). SupportPlatform and its constants are unchanged, just moved to support_platform.go now that they outlive the outbound start params. StartOutboundConversationResponse is kept as the shared {conversation_id} response of all three methods.

Migration

Old Channel	New method
ChannelVoice	StartOutboundPhoneConversation
ChannelEmail	StartOutboundEmailConversation
ChannelWeb	StartOutboundChatConversation

• CustomerSource has no replacement. CustomerID is now always your own customer ID — the one echoed back in tool and webhook payloads. Identifiers for third-party platforms move to CustomerSupportPlatformIdentifiers (the existing CustomerSupportPlatformIdentifier type already used by StartConversation), keyed by platform. Zendesk requires type zendesk_support_user; Salesforce requires salesforce_contact_id.
• SupportPlatform is now required on chat and email. The API no longer auto-selects the highest-priority connected platform.
• Phone has no support platform or channel field at all — the backend pins the call to voice/livekit. It gains required ToPhoneNumber and FromPhoneNumber (E.164; the from number must already be provisioned for your company).
• Email's Subject and Body are required together and forbidden individually. Chat takes Body only.
• Resources is now map[string]any rather than json.RawMessage, matching StartConversationParams.Resources.

Version

version.go: 0.3.1 → 0.4.0 (minor bump, by request — note this is still a breaking change for callers, so the version alone will not signal it). The module stays pre-1.0, so go.mod needs no /vN suffix. No tag is created by this PR.

Two notes for whoever tags the release:

• version.go on main had already drifted from the tag line — it said 0.3.1 while the latest tag is v0.3.11.
• Version collision: the unmerged branch api-client-sync/2026-07-22 also bumps version.go to 0.4.0. Whichever of the two lands second must be re-bumped to 0.5.0.

Verification

gofmt -l . is empty; go build ./... && go vet ./... && go test ./... all pass (the repo has no test files).

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