docs: AGENTS.md for agents working in jig

AGENTS.md

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+# jig — agent instructions
+
+jig is a local-first software factory: one Go binary (control plane, worker,
+CLI) plus a React UI that is committed pre-built and embedded. Read
+`README.md` for the model (definition → run → job → attempt → phases) and
+`docs/plans/` for the design records (KTD/R/U numbers cited in code and
+commits).
+
+## Layout
+
+| Path | What |
+|---|---|
+| `cmd/jig/` | CLI entry points (`start`, `serve`, `worker`, `run`, `def`, `trigger`, `report`) |
+| `internal/protocol/` | Definition schema and save-time validation |
+| `internal/engine/` | Phase engine: chain, gates, repair edges, parallel group |
+| `internal/controlplane/` | HTTP API, SQLite ledger, queue, reports |
+| `internal/worker/` | Claims jobs, runs attempts, publishes via `gh` |
+| `internal/runtime/` | Agent CLI adapters (`claudecode`, `codex`) |
+| `migrations/` | SQLite migrations |
+| `web/src/` | UI source; `web/dist/` is the committed build |
+| `examples/definitions/` | Stock definitions, validated in CI |
+
+## Commands
+
+Go (from the repo root):
+
+| Command | Runs |
+|---|---|
+| `just check` | format-check, vet, boundary, definitions, test, build — what CI runs |
+| `just test-race` | Race suite: controlplane, worker, engine, runtime |
+| `just test` | `go test -timeout 5m ./...` |
+| `go test ./internal/engine/ -run <Name>` | One test while iterating |
+
+UI (from `web/`):
+
+| Command | Runs |
+|---|---|
+| `npm run typecheck` | `tsc -b` over app and vite config |
+| `npm test` | vitest |
+| `npm run build` | Rebuilds `web/dist/` |
+
+## Rules
+
+- **Commit the rebuilt bundle.** Any change under `web/src/` needs
+  `npm run build` and the resulting `web/dist/` committed; CI fails if the
+  rebuild differs from the tree.
+- **Every module the UI imports must be in `web/package.json`.** This Mac has
+  a `~/node_modules` (including `@types/node`) that tsc and Node fall back
+  to, so a missing dependency passes locally and fails in CI.
+- **The worker never imports the control plane** (`just boundary`, KTD1).
+- **Definition changes are validated at save time.** A new definition field
+  or rule goes in `internal/protocol/definition.go` with a test, and the stock
+  definitions must still pass `just definitions`.
+- **Parallel-group members are read-only and concurrent.** Anything that
+  dispatches or replays phases must not run a member outside the group.
+- Work on a branch in a sibling worktree, open a PR, never push to `main`.
+- `gofmt` everything; match the surrounding comment style, which explains
+  why and cites the plan ID.