Event Modeling — implement

Goal: turn a single ready-to-implement slice into merged, verified code — the one phase where the agent builds rather than facilitates.

Read reference/implement.md before doing any implement work and follow it as the contract. In short: gate on em validate <model>.em --slice-ready <key> (stop and hand back if it fails — never edit the doc to make the gate pass); read the project's implementation constitution before writing code and stay inside its rules; before a project's first slice PR, land a one-time foundation PR holding every model event (plus the shared interface shell) so slices only ever import contracts, never invent or reach into a sibling's; build in dependency order from em query upstream, not timeline order; treat the slice doc as the spec (read-only, except the merge-time status/implementedIn flip); implement exactly one slice doc per PR — a covers: doc's two keys ship together in that one PR, and an again view instance is a continuation of its originating slice (no doc, status, or PR of its own — it ships in the originating doc's PR); ship the endpoint a ui-triggered command or ui-consumed view obligates, and surface — never invent — one the model doesn't show; surface every gap to the user instead of deciding it silently; cover every INV-<MNEMONIC>-n and every scenario with tests, proving the citations before merge with em coverage <model>.em --slice <key> --tests <dir> --strict (the default form skips a ready-to-implement slice); write or update the slice's conformance/bindings/<key>.yaml (GH #450, docs/bindings.md's schema) and verify it with em conform bindings check <model>.em --repo <path> --slice <key> --exit-code before calling the slice done; in spec-kit projects, allocate via em-sdd-bridge (redirect mode) and never run /speckit.specify.

Gate: no constitution, no first slice. The constitution is the project's ratified house rules — stack and architectural shape (including which implementation skill each slice pattern routes to), code style, testing norms, NFR baselines, review/merge norms. It lives at .specify/memory/constitution.md in a spec-kit project (when that file exists), otherwise constitution.md beside the model; em status reports which, and whether it's there. If it's missing — or its ratifiedBy: is empty, meaning nobody has signed it off — run reference/implement.md §7 ("Before the first slice: the constitution") first: ask its questions conversationally, write the answers in, and have a human ratify them. Don't decide the project's stack or style yourself to get moving.

That contract applies to any implementing agent, whether or not the session started from /event-modeling — em contract prints it to stdout with no .claude/ awareness required, for an agent that can run a shell but isn't Claude Code.

If the project ships pattern-specific implementation skills (for example an Axon/DCB skill set keyed on a slice doc's pattern: frontmatter), route by the slice's pattern and follow those — reference/implement.md §2 explains where that hand-off happens, and the constitution's routing table (§7) is what names the skill set for each pattern.

Preconditions (tool check, model location) are the same as every other phase — see ../event-modeling-shared/reference/operating-principles.md — but this phase additionally requires the target slice to already be ratified; if it isn't, stop and say so rather than starting on unratified work. The one documented exception is inline ratification (GH #399, reference/implement.md §1a): for an internal (non-public-touching, non-engagement) slice whose doc is already reviewed, drafting code on the same branch ahead of the human's em slice ratify is sanctioned — provided you never flip the gate yourself and re-confirm --slice-ready reads true before treating the slice as done. event-modeling-engagement is unchanged by this: it still requires every dispatched slice ratified before its branch is cut.

End of phase: PR merged, slice doc flipped to status: implemented with implementedIn filled, em slice index <model-name>.em run to refresh README.md's Slices table. Implement doesn't chain to another phase — run it once per ratified slice; event-modeling-conform's conform phase later checks the result against the model.