Single responsibility as one reason to change

A village cricket club prints one membership form. The treasurer sets its fee bands, the junior coach its age groups and training nights, and the welfare officer its consent wording.

At the cricket club	In code
three officers each change a part of one form	one module that three groups specify (steps 1, 3)
the treasurer adds a family rate, and the coach's age-group boxes slide off the page	one group's edit changes another group's output (step 4)
the secretary fixes a typo	a bug fix, which is not a reason to change (step 2)
a fee schedule, a team sheet and a consent form, one per officer	a split by who asks (steps 3, 6)
age groups and training nights stay on the coach's sheet	one group's code kept together (step 7)
one sheet per age group, so each new season means six edits	a split that went too far (step 7)

In real terms: for each request, find who sent it and which files it edits; a file that two groups' requests edit, or a request that edits many files, is the signal.

Breaks down when: a form's sections sit visibly apart on the page, while two groups' functions in code can share one helper that nobody sees; on paper, nothing behaves like a shared function (step 4).

Contrasting case: a club with one officer who does everything has one asker; one form is right until a second officer takes over a part of it.

4.1 ExamHall EXH-2520: one results service, three groups asking

GET /results/:attemptId was served by one provider. Three requests arrived in one sprint: the mobile app team renames scorePercent to percent, the exam board raises the pass mark from 50 to 60, and the platform team renames the table attempt_scores to scores.

@Injectable()
export class ResultsService {
  constructor(private readonly db: Db) {}
  async result(attemptId: string) {
    const row = await this.db.one('SELECT score, max_score FROM attempt_scores WHERE attempt_id = $1', [attemptId]);
    if (!row) throw new NotFoundException();
    const percent = Math.round((100 * row.score) / row.max_score);
    return { attempt: attemptId, scorePercent: percent, passed: percent >= 50 };
  }
}

4.1 EXH-2520 results.service.ts as written: mobile team edits results.service.ts · exam board edits results.service.ts · platform team edits results.service.ts
4.1 MR !2820 controller, grading rules and repository: mobile team edits results.controller.ts · exam board edits grading-rules.ts · platform team edits results.repository.ts
4.1 MR !2820 same replies before and after the split: a-1 200 {"attempt":"a-1","scorePercent":72,"passed":true} · a-9 404

All three requests edited one file, so each edit sat beside the other groups' code (steps 4, 9). MR !2820 gives each group its own file: a controller that shapes the reply, plain grading functions and a repository that owns the SQL (steps 10–12). Here each layer happens to have one asker; a second group's rules would need a second rules file (step 3).

4.2 ExamHall EXH-2521: the results screen

ExamResultsComponent fetched an exam's attempts, worked out the median and the 90th percentile, and drew the bars. The backend team renames score to percent in the attempts API, the exam board moves to the 95th percentile, and the designer recolours the bars.

export function ExamResultsComponent({ examId }: { examId: string }) {
  const [rows, setRows] = useState<AttemptRow[]>([]);
  useEffect(() => { fetch(`/api/exams/${examId}/attempts`).then((r) => r.json()).then(setRows); }, [examId]);
  const scores = rows.map((r) => r.score).sort((a, b) => a - b);
  const at = (p: number) => scores[Math.max(0, Math.ceil(p * scores.length) - 1)] ?? 0;
  return (
    <figure>
      {scores.map((s, i) => <div key={i} style={{ height: s, background: '#9aa5b1' }} />)}
      <figcaption>median {at(0.5)} · high {at(0.9)}</figcaption>
    </figure>
  );
}

4.2 EXH-2521 ExamResults.tsx as written: backend team edits ExamResults.tsx · exam board edits ExamResults.tsx · designer edits ExamResults.tsx
4.2 MR !2821 data hook, statistics file and chart: backend team edits use-exam-results.ts · exam board edits exam-stats.ts · designer edits ResultsChart.tsx
4.2 MR !2821 after the backend's rename, files tsc names outside use-exam-results.ts: none

MR !2821 splits the screen by who asks: a data hook turns the API's rows into plain scores, so the backend's rename stops there; the statistics and the bars each get their own file (step 13).