cyclone/.superpowers/skills/cyclone-api-router/SKILL.md

name, description

name	description
cyclone-api-router	Cyclone FastAPI router conventions (api_routers/, api_helpers.py, response shapes, error envelopes). Use when: adding or changing an HTTP endpoint, splitting a route out of api.py, or wiring a new helper into api_helpers.py.

cyclone-api-router

Cyclone splits its FastAPI surface two ways: small resource-group routers live in backend/src/cyclone/api_routers/<topic>.py and are mounted bare into api.py; the high-traffic streaming and parse endpoints still live as top-level decorators in api.py itself. This skill codifies the conventions so additions stay consistent with the four routers already shipped (acks, admin, health, ta1_acks).

As of this writing: 4 router modules under backend/src/cyclone/api_routers/, one shared helpers module at backend/src/cyclone/api_helpers.py (248 lines, NDJSON primitives + content negotiation + tail_events), and ~30 routes still inlined in backend/src/cyclone/api.py. The next refactor target is the parse endpoints.

When to use

• Adding an endpoint. You're adding a new GET / POST handler — you need to know whether it belongs in api.py (parse / streaming) or in a new router under api_routers/, and what the response shape and test file conventions look like.
• Splitting a route. You're moving a route out of api.py into a dedicated api_routers/<topic>.py module and need the import / mounting rules (from cyclone.api_routers import <topic> then app.include_router(<topic>.router)).
• Adding a helper. You're wiring a new function into api_helpers.py (NDJSON primitive, content-negotiation probe, tail-event helper) and need to keep it private to the API layer.
• Defining an error response. You're raising from a route handler and need the conventional HTTPException(status_code=..., detail=...) shape used everywhere else in the API surface.

Conventions

1. No new top-level routes in api.py for resource groups. Any endpoint grouped under a resource (/api/<resource> and its /{id} detail) lives in backend/src/cyclone/api_routers/<topic>.py as an APIRouter. The streaming list endpoints (/api/claims/stream, /api/remittances/stream, /api/activity/stream) and the parse endpoints (/api/parse-*) currently stay in api.py because they span multiple store modules — don't move them unless you're also restructuring the store split.
2. Reuse api_helpers.py. NDJSON primitives (ndjson_line, ndjson_stream_list, ndjson_stream_837, ndjson_stream_835), content negotiation (client_wants_json, wants_ndjson), the strict / raw_segments rewrites (strict_rewrite_837, strict_rewrite_835, drop_raw_segments_837, drop_raw_segments_835), and the shared live-tail generator (tail_events, heartbeat_seconds) all live there. Don't duplicate them in a router. The module's docstring (api_helpers.py:1-18) declares it private to the API layer — no business logic, no DB writes.
3. Response shape. Every successful response is a plain dict produced by a per-router <entity>_to_ui(row) helper (see _ack_to_ui at api_routers/acks.py:29-48 and _ta1_to_ui at api_routers/ta1_acks.py:23-37). This dict shape must match the matching <entity>_written event payload so live-tail pages don't drift (see cyclone-store for the serializer contract). Errors use FastAPI's HTTPException with a detail dict of the form {"error": "<Title>", "detail": "<message>"} — acks.py:85-88, ta1_acks.py:72. There is no shared ErrorEnvelope Pydantic model; the detail dict is the contract.
4. Mounting. Routers are mounted bare in api.py:251-256 — app.include_router(<name>.router) with no prefix= argument. Each @router.<verb> decorator carries the full /api/<resource> path itself (see acks.py:51,75, ta1_acks.py:49,67, admin.py:23, health.py:28). The router = APIRouter() declaration carries no tags= either — keep it minimal.
5. Streaming endpoints. Use StreamingResponse(media_type="application/x-ndjson") and feed it either ndjson_stream_list(items, total, returned, has_more) (for list pages) or tail_events(request, bus, kinds) (for live-tail pages). See acks.py:62-66 for the list-stream skeleton and api.py:1357-1401 for the full live-tail pattern (snapshot → snapshot_end → subscription → heartbeats). See cyclone-tail for the wire format.
6. Tests. Every new endpoint gets a test_api_<topic>_<verb>.py under backend/tests/ (see cyclone-tests for the naming convention + autouse conftest.py). Existing examples: test_api_validate_provider.py (admin), test_api_parse_persists_ack.py (acks).

Patterns

A new APIRouter skeleton

Pattern from backend/src/cyclone/api_routers/acks.py:1-72. Module docstring names the resource, imports the shared helpers, declares router = APIRouter() with no prefix, and defines a _foo_to_ui(row) mapper at module scope.

"""``/api/foo`` — list & detail endpoints for <topic>."""
from __future__ import annotations

from fastapi import APIRouter, HTTPException, Query, Request
from fastapi.responses import StreamingResponse

from cyclone.api_helpers import ndjson_stream_list, wants_ndjson
from cyclone.store import store

router = APIRouter()


def _foo_to_ui(row) -> dict:
    """Map a Foo ORM row to the UI shape used by ``/api/foo``."""
    return {"id": row.id, "name": row.name}


@router.get("/api/foo")
def list_foo(
    request: Request,
    limit: int = Query(100, ge=1, le=1000),
):
    """Return the list of persisted Foo rows, newest first."""
    rows = store.list_foo()
    items = [_foo_to_ui(r) for r in rows[:limit]]
    total = len(rows)
    returned = len(items)
    has_more = total > returned
    if wants_ndjson(request):
        return StreamingResponse(
            ndjson_stream_list(items, total, returned, has_more),
            media_type="application/x-ndjson",
        )
    return {"items": items, "total": total, "returned": returned, "has_more": has_more}

A get_<topic> detail endpoint with 404

Pattern from api_routers/acks.py:75-104 and ta1_acks.py:67-76. Path param is <entity>_id (not id) so it doesn't shadow FastAPI's internal id and the OpenAPI docs stay self-describing.

@router.get("/api/foo/{foo_id}")
def get_foo(foo_id: int) -> dict:
    """Return one persisted Foo row with its parsed detail.

    Path param is ``foo_id`` (not ``id``) to avoid shadowing
    FastAPI's internal ``id`` name and to keep OpenAPI docs
    self-describing. Returns 404 when the row is missing — never 500.
    """
    row = store.get_foo(foo_id)
    if row is None:
        raise HTTPException(
            status_code=404,
            detail={"error": "Not found", "detail": f"Foo {foo_id} not found"},
        )
    return _foo_to_ui(row)

Mounting in api.py

Pattern from backend/src/cyclone/api.py:246-256. The block lives just after middleware registration and just before the first @app.<verb> decorator.

# Resource-group routers. Each module owns its own APIRouter and is
# registered below. New resources go in `cyclone.api_routers.<name>`
# and are wired in here.
from cyclone.api_routers import acks, admin, health, ta1_acks  # noqa: E402

app.include_router(health.router)
app.include_router(acks.router)
app.include_router(ta1_acks.router)
app.include_router(admin.router)

Anti-patterns

• Don't import from cyclone.api into a router — the dependency runs the other way. Routers are mounted into api.py (api_routers/acks.py etc. know nothing about cyclone.api). A circular import would silently break the from cyclone.api_routers import ... block at api.py:251.
• Don't introduce Pydantic response models where the codebase returns dicts. Every existing list / detail endpoint returns a plain dict produced by a <entity>_to_ui(row) helper (see acks.py:29-48, ta1_acks.py:23-37). That dict shape is the event payload that <entity>_written carries — see cyclone-store. Introducing a Pydantic model on one side drifts the event payload from the list shape and silently breaks live-tail dedup.
• Don't bypass CycloneStore to query the ORM directly from a route. Always call store.<method>(...) (store.list_acks(), store.get_ta1_ack(ack_id)) so the read path picks up the same session + snapshot serializer as the live-tail subscriber. A raw with db.SessionLocal()() as s: s.get(Foo, foo_id) in a handler bypasses the serializer contract and breaks the event-payload match. See cyclone-store.
• Don't set prefix= on APIRouter. Mount the router bare (app.include_router(<name>.router)) and put the full /api/<resource> path in the decorator. Mixing the two styles scatters the URL across two files and breaks grep "/api/foo" audits.

Related skills

• cyclone-store — most routes call store.<method>(...) and the dict payload is the <entity>_written event payload; load when adding a route so the read path stays aligned with the pubsub contract.
• cyclone-tail — streaming endpoints (/api/<resource>/stream) and the NDJSON wire format; load when adding a live-tail route or changing the wire format.
• cyclone-edi — parse endpoints (/api/parse-837, /api/parse-835, /api/parse-999, /api/parse-ta1, /api/parse-277ca) currently live in api.py; load when adding or changing a parse endpoint.
• cyclone-tests — endpoint tests follow the test_api_<topic>_<verb>.py naming under backend/tests/; load when writing the test for a new endpoint.