Introduces the persistence layer for the upcoming Agent feature: an LLM
persona pinned to a specific Llm, optionally attached to a Project, with
persisted chat threads/messages so conversations survive REPL exits.
Constraint shape:
- Agent.llm uses ON DELETE RESTRICT — deleting an Llm in active use fails.
- Agent.project uses ON DELETE SET NULL — agents survive project deletion.
- ChatThread → ChatMessage cascade so deleting an agent purges its history.
- ChatMessage @@unique([threadId, turnIndex]) gives append ordering even
under racing writers (services retry on collision).
LiteLLM-style per-call overrides will live in Agent.defaultParams (Json);
the loose extras Json field is reserved for future LoRA/tool-allowlist work.
Pinned vitest fileParallelism=false in @mcpctl/db: all suites share the
same Postgres, and adding a second suite exposed FK contention between a
clearAllTables in one file and a create in another. Per-test isolation
still comes from beforeEach.
Tests: 8/8 green in src/db/tests/agent-schema.test.ts (defaults, name
uniqueness, llm-in-use Restrict, project-delete SetNull, agent-delete
cascade, duplicate (threadId, turnIndex) blocked, tool-call payload
round-trip, lastTurnAt DESC ordering).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
