Shared Helper Changed For One Caller

What goes wrong

A shared helper or accessor is changed to suit one caller — a different field, a hard-coded constant, its own ordering — without checking who else calls it, so the other callers silently show a different number or inherit a limit or order that is wrong for them.

Example

The price formatter is tweaked to drop cents for the cart summary; the product catalogue, using the same helper, now shows rounded prices too.

Not to be confused with

One shared body, not two copies that drift apart (Hand Copy Of Canonical Rule); not a policy missing on one entrypoint (Sibling entrypoint skips the policy) and not an aggregate over the wrong population.

Discovered by

@sks24git GitHub

Field notes · 6

@sks24git2026-11-02beat 2 review rounds

A filter that hides free text on button answers sits in the shared reader, not in the math that needs it. The review screen reads the same data, so the client words vanish where a human checks the choice.

Filter at the consumer that needs it. A shared reader feeds screens you did not test.
Check every caller before you narrow a reader. A fix for one caller can blind another.

@sks24git2026-10-29beat 2 review rounds

A fix widened a shared fetch to return every attempt of a check, to help one caller. Another caller demands that every attempt pass, so one failed try that a retry fixed now blocks it.

Scope a widened query to the caller that needs it. Shared helpers have readers with other rules.
a search tool every caller before you change what a helper returns.

@sks24git2026-10-29beat 1 review round

A fix widened what a stored field means for one report, while another reader still trusted the old status field. Items the report now counts as done vanish from the board, and the bundle that carried them counts twice.

a search tool every reader before you widen a field's meaning. One updated reader makes the rest disagree.
Put shared filters in one place. Copies drift on the next change.

@sks24git2026-10-21beat 1 review round

A retry rule moved a failed request to any free worker, but some requests are bound to one worker by contract. For those the move is forbidden, so one passing error became a hard failure instead of a retry.

List every kind of binding before changing who may move. One label can hide two contracts.
Build test fixtures through the real code path. A hand-made state passes where production fails.

@sks24git2026-10-13beat 1 review round

Several path parsers are merged into one, built and tested to match just one of the old patterns. A caller whose old pattern handled quoted names now cuts those names in the middle.

Diff-test a merged parser against every parser it replaces. One oracle covers one caller.
Keep each caller's odd cases as tests. They are why the old code differed.

@sks24git2026-09-02beat 3 review rounds

One accessor served two questions — what an account holds and what it may spend — and the operator screen was wired to the spend side. When expiry arms, held money shows the operator 0.00, flagged as a genuine zero.

Kill the short name, don't alias it. Every reader must say which question it asks; a compiler enforces that, a tool does not.
Make one fixture where the fields differ. Equal ones hide a swap.