Connector-centric registry: one place to add an integration

[alexeygrigorev]

Full analysis in docs/architecture-review.md. The trigger→action engine is sound; what doesn't scale is that connector knowledge lives in four hand-maintained registries across two languages.

Problem

Adding one action today touches:

1. src/dapier/engine/actions/<x>.py
2. the run_x import + if/elif dispatch in src/dapier/engine/__init__.py
3. ACTION_SPECS validation in src/dapier/triggers/email_triggers.py
4. the hand-mirrored designer/src/catalog.ts (comment says "Mirrors the run_* dispatch")

Adding one trigger source touches:

1. worker.normalize_payload branches
2. template.yaml (per-source queue/table/env)
3. api/router.py hook routing
4. a load_workflows() hook in matching.all_workflows

Nothing links these copies; they drift silently. Related structural limits: no data flow between steps (blocks #6, #7, #12), O(all-workflows) resolution per event (published-table scan capped at 200, silently), and per-action auth folklore (credential_id vs connection_id vs auth_secret_id).

Proposal

• src/dapier/connectors/<name>/ — one package per integration: a manifest (label, events, actions + field schema), normalize(raw) -> event per ingress it owns, and run(action, ctx) per action. A connectors/registry.py replaces the dispatch chain, ACTION_SPECS, and the trigger-load hooks.
• GET /api/catalog — serve the manifests as JSON; the designer renders palette/inspector from it (keep catalog.ts as a dev fallback). One registry, three consumers: engine dispatch, validation, UI.
• ActionContext — ctx.connection(name) → live token (auto-refreshed), plus event, workflow, run id, and a steps namespace so later steps can template earlier outputs (first enabler for Step-to-step data mapping + Formatter #6).
• One workflows table with a connector#event GSI — merge the published/email/hook/schedule stores; matching becomes a query per event instead of four scans + a linear pass. Instant-publish semantics unchanged.
• Generic ingress — a route/queue/source → connector mapping with one ingress handler; per-connector queues become declared resources instead of template.yaml surgery.

Migration order (incremental, no big bang)

1. Registry wrapping the existing run_* functions; dispatch reads the registry. Tests keep passing.
2. Move normalize_payload branches into connectors; keep the SQS contract.
3. /api/catalog; designer consumes it; delete the TS mirror and ACTION_SPECS duplication.
4. ActionContext + steps + unified connection_id (keep credential_id/auth_secret_id as deprecated aliases).
5. Single workflows table + trigger GSI.
6. Then Step-to-step data mapping + Formatter #6/In-workflow logic: filter steps, branching, delays, loops #7/Test-before-publish: run a workflow against a sample event #10 become small changes on top instead of structural ones.

The 23 src/*.py back-compat shims are already removed (2026-09-25); make test was 426 passing at filing time.