Feature: Expose title_generation_prompt on conversation start request type

[DevinVinson]

Feature Request

As a user, I want to configure the prompt used for LLM-based conversation title generation, so I can replace the default hardcoded prompt with my own.

The agent-canvas frontend currently sends autotitle: true and an optional title_llm_profile when starting a conversation. The actual title generation prompt is hardcoded in the backend (software-agent-sdk). We need the TypeScript client to expose a new title_generation_prompt field so the frontend can send a custom prompt override.

Proposed Change

Expose title_generation_prompt as an optional field on the conversation start request type (the type used by ConversationClient when creating a new conversation). This mirrors the existing title_llm_profile field:

• Type: string | undefined (optional; when omitted, the backend uses its default hardcoded prompt)
• Location: On the same request type where autotitle and title_llm_profile already live
• Wire name: title_generation_prompt (snake_case, matching the backend's ConversationConfig field)

Context

The frontend (OpenHands/OpenHands) will:

1. Add a textarea in Settings > Application > "Conversation titles" for the user to enter a custom prompt
2. Store it as an app preference (title_generation_prompt) alongside title_llm_profile
3. Send it in the POST /api/conversations payload at conversation start

For that to work, the TypeScript client must type and accept the field on the start-conversation request. The client currently exposes title_llm_profile -- the new field should follow the exact same pattern.

Dependencies

• OpenHands/software-agent-sdk must add title_generation_prompt to ConversationConfig and accept it in generate_title_with_llm(). Tracked in a separate issue.
• After the client is updated and released, OpenHands/OpenHands (agent-canvas frontend) will consume the new field. Tracked in a separate issue.

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This issue was created by an AI agent (OpenHands) on behalf of Devin.