Reuse Check (Polar)

The handle is the diff. The evidence is new code that duplicates something the repo
already has, with the import that replaces it.

This is the most common substantive comment in Polar reviews: 84 of ~1,100 human review
comments from Feb to Aug 2026 point at an existing helper the author did not know about. It
is also the one category where grep beats a human reviewer, and it got worse once agents
started writing the code, because an agent that does not search first writes its own helper.

Scope

Run on any diff that adds a function, constant, Annotated type, validator, enum, model
property, repository method, React component, or hook. Skip deletions, renames, config and
lockfiles.

Owned elsewhere: agent noise → slop-check; API contract → api-surface-review; deploy
safety → ship-safety; billing behaviour → billing-review.

Method

For each new symbol:

1. Name search — rg -n "def <name>|<Name>\b" server/polar clients/packages, plus obvious
   synonyms (normalize/sanitize/clean, fetch/get/load).
2. Behaviour search — the distinctive part of the body: a regex literal, a library call
   (urlparse, pycountry, stdnum, slugify), a magic constant.
3. Inventory — check the list below.

Report only when you can name the existing symbol and its import path. A hunch is not a
finding. Always show what you searched for, so a false positive is cheap to dismiss.

Inventory

Home	Holds
polar/kit/schemas.py	Schema, IDSchema, TimestampedSchema, EmptyStrToNone, SlugValidator, StripValidator, HttpsUrl, HttpUrlToStr, Int32, ClassName, MergeJSONSchema, SetSchemaReference, MultipleQueryFilter, *_ID_EXAMPLE
polar/kit/http.py	get_safe_return_url (open redirect), get_ip_address, add_query_parameters, get_content_disposition, is_localhost, SSRF-safe crawling (SSRFBlockedError, UnsafeCrawlableUrl, UrlReachability)
polar/kit/currency.py, money.py, math.py	get_currency_decimal_factor (zero-decimal currencies), get_minimum_currency_amount, get_maximum_currency_amount, format_currency, get_presentment_currency, get_cents_in_dollar_string, polar_round, non_negative_running_sum
polar/kit/pagination.py	ListResource, Pagination, PaginationParams, count_subquery
polar/kit/repository/base.py	get_base_statement, get_one_or_none, get_all, paginate, create, update, from_session, stream
polar/kit/ (rest)	address, anonymization, crypto, csv, db, email (EmailStrDNS), encryption, html, json, jwk, jwt, locale, metadata, operator, routing, services, sorting, time_queries, trial, utils, visibility
server/scripts/helper.py	run_batched_update
polar/backoffice/forms.py	Form builder classes. Pattern: polar/backoffice/orders/endpoints.py
clients/packages/orbit/src/components	Alert, Avatar, Box, Button, ButtonGroup, Checkbox, Grid, GridItem, InlineModal, Input, List, ListGroup, Modal, Pill, SegmentedControl, Select, Spinner, Status, Subnav, Switch, Tabs, Text, TextArea, Tooltip, Truncated, datatable
Libraries already in use	stdnum (tax IDs), pycountry (country names), slugify, email_validator

Also grep the model. A lot of duplicated logic is a property that already exists:
Organization.is_payout_ready, Organization.can_authenticate, ProductPrice.is_free,
Checkout.is_free_product_price, Payment.UNRECOVERABLE_DECLINE_CODES.

The ones people actually miss

• A hand-written "empty string means null" validator instead of EmptyStrToNone.
• A keyset loop over UUIDs instead of RepositoryBase.stream, which batches implicitly.
• Fetching rows only to count them, instead of an existence query.
• Hand-rolled cents conversion or currency rounding.
• A country-code table or slug regex instead of pycountry / slugify.
• A hand-built HTMX form in a new backoffice view.
• A hand-styled div that duplicates an Orbit primitive.

Output

## Reuse

### 🟠 Should fix
- `file:line` — <what the new code does>. Fix: `from polar.kit.schemas import EmptyStrToNone`
  (searched: `rg "empty_str|strip_to_none" server/polar`)

### 🟡 Question
- `file:line` — <question>

### Verdict
✅ Nothing reinvented  |  ❌ n duplicates