# One folder per backend feature, tagged errors and written rules

packages/api moves to features and platform folders with fixed file names, two pilot features run one Effect program per procedure, and every rule now names what enforces it.

**Breaking for imports of `@template-cloudflare/api`.** Server code moved from `routers/`, `lib/` and topic folders to `packages/api/src/features/<feature>/<feature>.<role>.ts`, with shared building blocks in `packages/api/src/platform/`. Public subpaths now follow `./<feature>/<role>`, for example `./todo/contract`, `./app-router`, `./uploads/service` and `./assistant/http`. If your fork imports an earlier subpath, use the table in the [api package reference](/docs/packages/api#renamed-subpaths). The four subpaths the mobile app imports (`./routers/{todo,integrations,billing,notifications}.schema`) remain as aliases, so the native app builds unchanged.

- **Feature shape.** Every feature has the same role files: a leaf contract, procedures, a service, errors, and optional jobs and HTTP edges. There is no barrel and no repository layer; row-level security already isolates Organizations. The `@template-cloudflare/api/mcp/*` subpaths are server-only in the client boundary. New tests and lint rules hold the shape: leaf modules import only leaves, features import each other through declared edges, there are no import cycles, type imports are explicit, and configuration is read through `packages/env`. [Backend shape](/docs/architecture/backend-shape), [ADR-0011](/docs/adr/0011-backend-feature-shape).
- **Tagged domain errors and Effect in procedures.** In `todo` and `documents`, services fail with tagged errors, and one mapper per feature turns them into the same `APP_ERRORS` codes and messages clients saw before. Each procedure runs its service once through `runProcedure`. A client abort is honoured only before the program starts; once it runs, a client that goes away no longer rolls back the write, so the write and its Audit Event commit and the response goes unread. Other features keep their services until they are migrated. [ADR-0010](/docs/adr/0010-procedures-run-one-effect-program), [error handling](/docs/development/backend-conventions#domain-failures-are-tagged-errors-mapped-once).
- **Request ID and quieter logs.** Every RPC response carries `x-request-id`, including the 500 when building the request context fails: Cloudflare's `cf-ray` when it is well formed, otherwise a UUID. The MCP context derives its own request ID for the logs of its document tools. The same ID is `context.requestId` on the server and is part of the error log, so a user can quote it. It correlates logs only: outside Cloudflare a client can supply the `cf-ray`, so nothing decides by it. Expected 4xx failures are logged at debug level instead of as errors. Runtime switches (`DB_TENANT_PIPELINE`, `TRUSTED_PROXY_HEADER`, `TRUSTED_PROXIES`, `TENANCY_PROBE`) are declared in the env schema. Their meaning is unchanged, but an invalid value is now reported instead of silently replaced by a default; check these variables in your Worker and Node deployments.
- **Input validation answers HTTP 400.** An invalid input now returns HTTP 400 with the same `INPUT_VALIDATION` code, message and field errors as before; it used to come back as HTTP 500, because oRPC's default status map did not know the code. The RPC and OpenAPI handlers use `errorStatusMap` from `@template-cloudflare/errors/server`, and `APP_ERRORS.INPUT_VALIDATION.status` is 400 instead of 422, which also changes the status in the generated OpenAPI document. The assistant's HTTP route maps statuses with the same shared map, so `INPUT_VALIDATION` is 400 there as well. Clients that branch on `code` see no change. [Error handling](https://github.com/CarlosZiegler/template-cloudflare/blob/main/docs/error-handling.md).
- **Org roles, ready when needed.** `orgProcedure` reads the Member's Org role with its membership check, and `requireOrgRole(...)` restricts a procedure to some roles, failing closed. Roles are not hierarchical (list every role that may act), and using it outside `orgProcedure` is a type error. No procedure applies it yet. [Backend conventions](/docs/development/backend-conventions#org-roles-are-checked-only-where-a-product-rule-needs-them).
- **Written rules with their checks.** [Backend conventions](/docs/development/backend-conventions) state each rule with its reason, example, anti-pattern and enforcement. The [enforcement matrix](/docs/development/enforcement) shows which rules a check holds and which rely on review. A [review checklist](/docs/development/review-checklist), a pull request template and a root `CODING_STANDARDS.md` index the same rules.
- **Runbooks.** [Runbooks](/docs/development/runbooks) cover a database restore or host move, the pipelining kill switch, Hyperdrive caching, the RLS proof on a preview, and the emergency shutdown. The emergency-shutdown workflow does not block a custom domain; the runbook gives the extra step.
- **Decisions show their status.** Every ADR starts with its status and acceptance date, and the [decision index](/docs/adr) lists them. The [pagination](/docs/features/api#pagination) and [testing](/docs/development/testing#what-to-test) rules are written down.
- **A skill for new features.** The `domain-feature` skill walks from a glossary term to an RLS table, contract, tagged errors, service, procedures, isolation tests and docs.

Measurements ([report](https://github.com/CarlosZiegler/template-cloudflare/blob/main/docs/measurements/2026-10-17-backend-structure.md)): the server code grows by 6.9 KiB gzip, within the 10 KiB budget for the Effect pilots, and the client carries no Effect. The happy-path p50 of the pilot procedures is within the noise of an A/A run; the `todo.byId` error path costs +0.040 ms. Separately, the Worker as a whole grows by 70.2 KiB gzip, of which 63.4 KiB are the documentation pages, ADRs and changelog the site renders on the server: that is content and has nothing to do with Effect, and whether it counts against the Worker budget is still open.

Sources: [platform move](https://github.com/CarlosZiegler/template-cloudflare/commit/0aa202e), [feature folders, first of 18 moves](https://github.com/CarlosZiegler/template-cloudflare/commit/3d1913f), [graph tests](https://github.com/CarlosZiegler/template-cloudflare/commit/2226f26), [direction rules](https://github.com/CarlosZiegler/template-cloudflare/commit/05836ac), [runProcedure](https://github.com/CarlosZiegler/template-cloudflare/commit/91a2d11), [todo pilot](https://github.com/CarlosZiegler/template-cloudflare/commit/6c77fb1), [documents pilot](https://github.com/CarlosZiegler/template-cloudflare/commit/49a4de0), [request ID](https://github.com/CarlosZiegler/template-cloudflare/commit/fa1cbbb), [error log levels](https://github.com/CarlosZiegler/template-cloudflare/commit/ec63950), [runtime switches](https://github.com/CarlosZiegler/template-cloudflare/commit/0df1feb), [trusted proxy](https://github.com/CarlosZiegler/template-cloudflare/commit/47a3700), [requireOrgRole](https://github.com/CarlosZiegler/template-cloudflare/commit/3e51803), [400 for input validation](https://github.com/CarlosZiegler/template-cloudflare/commit/146d310), [measurement](https://github.com/CarlosZiegler/template-cloudflare/commit/ec94469).