Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@_bruno/Flows/Get` Flows by Product.yml:
- Around line 53-58: The example response for the "Get Flows by Product" flow is
missing the product_id field; update the sample JSON object (the Flow example
with keys id, name, description, created_at, updated_at) to include the
product_id property with an appropriate sample value so the documented response
shape matches the endpoint contract.

In `@internal/flow/handler_test.go`:
- Around line 315-323: The test case named "No Flows Found" in
internal/flow/handler_test.go is asserting a 404 but the handler should return
200 with an empty array when the product exists but has no flows; update that
case so mockFlowQuerier.getFlowsByProductFunc returns (nil, nil) and
expectedStatus is http.StatusOK and assert an empty JSON array response. Also
add a new case (e.g., "Product Not Found") where
mockFlowQuerier.getFlowsByProductFunc returns (nil, pgx.ErrNoRows) and
expectedStatus is http.StatusNotFound to cover the missing-product contract.

In `@internal/flow/handler.go`:
- Around line 88-90: The handler currently treats pgx.ErrNoRows as "product not
found" and returns 404; instead distinguish the two cases by changing the data
layer/query and the handler: have the data function (e.g., GetFlowsByProduct)
return an explicit sentinel error ErrProductNotFound when the product row itself
is missing, and return an empty slice (and nil error) when the product exists
but has zero flows; then update the handler to check for errors.Is(err,
ErrProductNotFound) to call internal.HandleHttpError(..., http.StatusNotFound)
and otherwise treat a nil error with an empty slice as a 200 + [] response,
removing the current errors.Is(err, pgx.ErrNoRows) 404 branch.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@internal/flow/service.go`:
- Around line 47-51: The GetFlowsByProduct return can propagate a nil []Flow
which JSON-encodes to null; after calling s.queries.GetFlowsByProduct(ctx, id)
and before returning, ensure the returned flows slice is normalized to an empty
slice when nil (e.g., if flows == nil then set flows = make([]Flow, 0)) so the
method (in service.go) always returns an empty array instead of null while
preserving the existing error handling around s.queries.GetFlowsByProduct.
- Around line 20-23: The current error branch checks errors.Is(err,
pgx.ErrNoRows) but INSERT ... RETURNING foreign-key failures surface as
*pgconn.PgError with SQLSTATE "23503", so replace the pgx.ErrNoRows check with
logic that type-asserts err to *pgconn.PgError and, when pgErr.Code == "23503"
(optionally also checking pgErr.Constraint or Detail for the product FK name),
return Flow{}, internal.NewNotFoundError(id, "Product"); otherwise fall back to
the existing fmt.Errorf("failed to create flow: %w", err) handling. Ensure you
import github.com/jackc/pgconn if not already.

In `@internal/response_test.go`:
- Around line 76-79: The test branch for encoding failures currently only checks
status and Content-Type; update the case where tt.expectedStatus ==
http.StatusInternalServerError to also decode the response body (w.Body.Bytes())
as JSON and assert the problem+json payload contains a "detail" field with the
expected error message (or at least that it contains text indicating an encoding
failure) so the contract produced by HandleHttpError is validated; use the same
test table entry's expected message or a concrete substring and reference w,
tt.expectedStatus, and HandleHttpError/response writer usage to locate where to
add the JSON decode and assertion.

---

Nitpick comments:
In `@internal/flow/handler_test.go`:
- Around line 304-311: The test's success assertions only check len(flows) and
omit verifying the response includes the product_id; update the tests that use
m.getFlowsByProductFunc (the success cases around the existing blocks returning
[]Flow) to decode the handler response JSON and assert that the top-level
"product_id" equals the requested product (e.g., 1). Locate the test cases
referencing m.getFlowsByProductFunc and Flow, parse the response body into the
expected response struct or map, and add an assertion for product_id in both
success scenarios (the blocks around the current getFlowsByProductFunc stubs,
including the other case around lines 365-372).

In `@internal/flow/service_test.go`:
- Around line 92-150: The tests for the service are missing coverage for several
error and edge branches: add unit tests that use the mockFlowQuerier to simulate
(1) a generic DB error returned from GetFlowById (not pgx.ErrNoRows) and assert
the propagated error, (2) a generic DB error from GetProductById and assert
propagation when calling the service method that depends on product lookup, (3)
a generic DB error from GetFlowsByProduct and assert the service surfaces that
error, and (4) a case where a product exists but GetFlowsByProduct returns an
empty slice — assert the service returns an empty slice (not nil) to preserve
the contract; implement these by adding table-driven test cases similar to
TestService_GetFlowById that set
mockFlowQuerier.getFlowFunc/getProductFunc/getFlowsByProductFunc to return the
desired errors or empty slice and verify expected error messages or empty slice
results.