Document GET /fin_voice/conversation/{conversation_id}

[salmanbshah]

Why?

GET /fin_voice/conversation/{conversation_id} was implemented in FinVoiceController as collect_by_conversation_id but missing from all specs. The other four fin_voice lookup endpoints (/collect/{id}, /external_id/{id}, /phone_number/{number}, /register) were already documented — this was a gap in an otherwise complete resource.

How?

Added the missing endpoint to both Unstable and v2.15 specs, modeled after the adjacent GET /fin_voice/phone_number/{phone_number} endpoint. Returns an array of ai_call_response (a conversation can have multiple associated calls).

Decisions

• Backfilled to v2.15: Unlike data_connectors, the fin_voice resource is fully present in v2.15. Keeping this endpoint Unstable-only while the other four lookups are in v2.15 would be inconsistent and confusing for customers.
• Array response: Returns an array rather than a single object because one conversation can have multiple Fin Voice calls.

Implementation Plan

API Documentation Gap Plan

Confirmed Gaps (this PR covers gap #2)

#	Controller	Missing Endpoints	Spec Target
1	api/v3/data_connectors_controller.rb	GET /data_connectors/{id}	Unstable only
2	api/v3/fin_voice_controller.rb	GET /fin_voice/conversation/{conversation_id}	Unstable + v2.15
3	api/v3/conversation_parts_controller.rb	PUT /conversations/{conversation_id}/conversation_parts/{id}	Unstable only
4	api/v3/messages_controller.rb	GET /messages/whatsapp/status	Unstable only

Skipped (feature-flagged, not yet GA)

• fin/tasks_controller.rb — ai_answers_billing_feature
• fin/api_controller.rb — fin-agent-api
• procedures_controller.rb — ProcedureRuns::Constants::FEATURE_FLAG

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