GeezerVison

chatd can now move a root chat, together with its subagent chats, into a project, to another project, or out of its project. Nothing calls this yet. #30894 adds the API.

Stack (moving chats between projects, bottom first):

1. This PR: the move in chatd
2. feat: move chats between projects through the chat update API #30894: PATCH /api/v2/chats/{chat} takes project_id
3. feat(site/src): move chats between projects from the chat menu #30895: Move to project in the chat menu
4. feat(site): drag chats onto project folders in the sidebar #30795: drag a chat onto a project folder in the sidebar

Why: today a chat keeps the project it was created with. A move must follow the family rules of archiving, because a step that runs during a move would still have the memory tools of the old project.

• chatstate.Tx.SetProject runs only from W, E0 and E1, like SetArchived. SetFamilyProject() locks the root row before its subagents, in the same order as archiving, so a busy family gets ErrTransitionNotAllowed and nothing changes.
• A move to the project the chat is already in changes nothing, even while the chat runs. The check reads the locked root row, so it waits for a move that is still in flight.
• Only the root row stores project_id, and subagents use the project of the root. After the commit, chatd publishes a new project_change watch event for each chat of the family. The move keeps updated_at, so lists keep their order.
• A root chat outside a project now has an empty memory index. When a chat leaves its project, or its project is deleted, its next turn start commits one memory index update that removes the memories the model saw there.

What to scrutinize: the lock order and the same-project check under the lock in SetFamilyProject() (chatstate/family.go), the turn-start condition in memoryIndexMessage() (memory.go), and whether the ARCHITECTURE.md text matches them.

Generated (make gen): queries.sql.go, querier.go, dbmock and dbmetrics come from queries/chats.sql. coderd/apidoc, docs/reference/api/schemas.md and typesGenerated.ts come from the new watch event kind, which is also why two chats.test.ts fixtures gain project_change: false.

Architecture doc: coderd/x/chatd/ARCHITECTURE.md lists SetProject among the transitions and in the execution state diagram (W, E0 and E1 back to themselves). It also says that a root chat's project can change after creation, and that a moved chat's next turn starts with a memory index update from the old project to the new one.

Testing

• make pre-commit passes. go test passes for coderd/x/chatd/chatstate, coderd/database/dbauthz (TestMethodTestSuite) and the chatd memory tests.
• TestSetFamilyProjectLocksRootFirst fails with 55P03 when a subagent row is locked first. TestSetFamilyProjectKeepsTheCurrentProject covers the same-project move during a run. The transition matrix test gains SetProject cases for W, E0 and E1.
• TestMovedChatUsesNewProject runs two real turns around a move: the second turn uses the instructions and memories of the new project, and OutOfProject fails without the memory index removal.

Xum opened this PR on behalf of @ibetitsmike.