Fixes https://github.com/coder/internal/issues/1436
* Adds organization_id to chats with backfill (workspace org → user org membership → default org)
* No support yet for ACLs (follow-up issue)
- Cross-org workspace binding rejected (both in `CreateChatRequest` and in `create_workspace` tool
- Adds `OrganizationAutocomplete` to `AgentCreateForm`
- Docs updated with `organization_id` in chats-api.md
> 🤖 Written by a Coder Agent. Reviewed by many humans and many agents.
---------
Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>
Adds a `system_prompt` field to `CreateChatRequest` that allows API
consumers to provide custom instructions when creating a chat. The
per-chat prompt is stored as a separate system message (`role=system`,
`visibility=model`) in the `chat_messages` table, inserted between the
deployment system prompt and the workspace awareness message.
Also moves deployment system prompt resolution from the HTTP handler
(`resolvedChatSystemPrompt`) into `chatd.CreateChat` where it belongs.
The handler no longer assembles system prompts —
`CreateOptions.SystemPrompt` is now purely the per-chat user prompt, and
the deployment prompt is resolved internally by chatd.
No database schema changes required.
**Message insertion order:**
1. Deployment system prompt (resolved by chatd, existing)
2. Per-chat user system prompt (new, from `CreateOptions.SystemPrompt`)
3. Workspace awareness (existing)
4. Initial user message (existing)
🤖 Generated with [Coder Agents](https://coder.com/agents)
- Moves `coderd/chatd/`, `coderd/gitsync/`, `enterprise/coderd/chatd/`
under `x/` parent directories to signal instability
- Adds `Experimental:` glue code comments in `coderd/coderd.go`
> 🤖 This PR was created with the help of Coder Agents, and was
reviewed by my human. 🧑💻
Cian Johnston