/clear + /clear N — core context trim infrastructure #83

Parent

Parent PRD: #82

What to build

Full end-to-end implementation of the /clear and /clear N slash commands. When a user types /clear (wipe everything) or /clear 3 (keep last 3 turns), the system prunes conversation context, inserts a visual trim point divider in the chat timeline, and restarts the provider session so the agent forgets the trimmed history.

This slice covers every layer: schema contracts, server-side CQRS (command dispatch, event sourcing, read model update), provider session restart, WebSocket dispatch, the composer slash command registration, and the UI divider component.

After this slice, a user can type /clear and see a collapsed divider marking trimmed history. /clear N works identically but preserves the last N turns as bootstrap context for the new session. Git checkpoints for trimmed turns are preserved (not deleted) so undo still works.

Acceptance criteria

• thread.context.trim command schema defined in contracts (with optional keepLastNTurns field)
• thread.trim-point-created domain event schema defined in contracts
• OrchestrationThread read model gains a contextTrimPoints: Array<ContextTrimPoint> field (ordered array with id, createdAt, beforeEntryId, prunedMessageCount, prunedTurnIds)
• Decider validates thread exists, determines trim boundary (last message before trim, or last N turns boundary), emits thread.trim-point-created
• Projector appends trim point to thread read model and updates derived timeline state
• Trim command triggers provider session restart: current session is stopped, new session starts with resume cursor past trim boundary. Surviving messages (for /clear N) are sent as bootstrap context.
• /clear and /clear [N] parse correctly in the composer slash command system and dispatch thread.context.trim
• ContextTrimPointDivider component renders in the timeline at the trim boundary, showing "Earlier messages" label and pruned message count, always in collapsed state
• deriveTimelineEntries() produces context-trim entries from the read model
• deriveMessagesTimelineRows() handles the trim entry as a divider row
• Git checkpoints for pruned turns remain available (no cleanup of projection_turns rows or git refs)
• Idempotent: dispatching a trim command on a thread with no messages or no turns produces a no-op trim point (prunedMessageCount = 0)
• Tests cover: command → event → read model, timeline derivation with trim points, slash command parsing

Blocked by

None — can start immediately