reviewing-module-design

name	reviewing-module-design
description	Reviews module and type design: cohesion and coupling (via connascence), encapsulation, hard-to-misuse interfaces, and making illegal states unrepresentable. Use when reviewing class/module structure, interfaces, type or data modeling, coupling, or API ergonomics for callers.
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reviewing-module-design

Are the boundaries right? Coupling, encapsulation, interfaces that are hard to misuse, illegal states unrepresentable.

When to use

Reviews module and type design: cohesion and coupling (via connascence), encapsulation, hard-to-misuse interfaces, and making illegal states unrepresentable. Use when reviewing class/module structure, interfaces, type or data modeling, coupling, or API ergonomics for callers.

Shape: diff — design-capable. Also works on design docs and plans: apply the same checks to the proposed states, data flows, and failure paths before any code exists. When the design doc is specifically a decision record (an ADR, RFC, or adoption/deprecation plan), also run the shared decision-record checklist on top of this lens's own topical checks: is the rationale actually recorded (not just the outcome); are the stated assumptions still current; is there a revisit-trigger; is an exit, rollback, or sunset path defined; were real alternatives weighed, not just the chosen option justified after the fact? A gap here is this lens's finding, reported the same way as a topical one — not a separate report.

Reviewer discipline

Report only real problems. If the code correctly handles the case, reply "No findings" and stop — do not invent issues. This guards against false positives on correct code; still report every genuine issue you do find, with its full detail.

Defects are the default; improvements are opt-in. By default this lens is defect-only: do not suggest changes to code that is already correct. When the team has opted up into improvement suggestions, a finding on already-correct code is admissible only as nit-severity, route: implementer (the author applies, defers, or ignores), and must clear the non-configurable anti-churn floor: it must genuinely improve — never offer a merely equivalent alternative — and must converge (once a dimension is as good as you can confidently make it, stop; never oscillate A→B then B→A, never re-order to an equivalent state). Defects keep the strict bar above regardless of this setting.

Team preferences. If the reviewed repo has .code-quality-atlas/preferences.md, apply it before reporting: a repo's .code-quality-atlas/preferences.md may set/tune this lens's thresholds or selection, and — being preference-tier — may suppress one of its findings outright (it never surfaces). Its improvement-valence directive is also what decides whether the "opted up" improvement-suggestion behavior above is active for this review. Absent the file, apply this lens's defaults exactly as written above.

Pre-existing defects in touched code are surfaceable, not yours to fix. When you notice a genuine defect this change did not introduce but that sits in the code this PR actually touches — the edited function or immediately adjacent lines — you may surface it, tagged "pre-existing — not introduced by this change." Like improvements it is opt-in and default-quiet (off unless the team opts up), route: implementer, and non-blocking: it informs the author's fix-now / file-a-ticket / ignore call and never sets this PR's verdict, because the diff did not cause it. Stay scoped to code the change touches — a repo-wide hunt is the audits' job, not this review — and never let it expand the PR's scope.

Top checks

The head of the full checklist — enough for a first pass without opening any reference file:

• Is it hard to misuse — invalid argument/call-sequence prevented by types, not docs (caller ergonomics / pit of success)?
• Does the unit have one clear responsibility (high cohesion)? State its job in a sentence without "and."
• Is the interface narrow relative to the behavior behind it (deep module), or a shallow pass-through adding no value?
• What is the strongest connascence crossing the boundary, and is it local? (Position/Algorithm connascence across modules is a smell; prefer Name/Type.)
• Does it hide its implementation so internals can change without breaking callers?
• Are invalid states representable? Could you construct a value the domain forbids (an order both draft and shipped)? Model with a tagged union / state machine instead.
• Is untrusted input parsed into a precise type at the boundary (parse-don't-validate), or validated then passed onward as raw primitives (re-validatable downstream)?
• Primitive obsession: are domain concepts (email, money, id, %) raw string/number, or wrapped in domain types carrying invariants/units (cross #4)?
• Are optional/nullable fields modeled explicitly (Option/Maybe/| null) rather than sentinel values (-1, "")?

Mechanizing these checks

Where a finding here is one a tool can catch deterministically, surface that as an advisory route: implementer note next to the finding: the hand review caught it this time, and wiring the matching tool from reference/tool-rules.md into CI gates it going forward. This is a suggestion to mechanize, not a defect — it never blocks a verdict, and it falls away on a repo that already runs the tool.

Process notes. If this lens misfired on this change — flagged correct code, missed an obvious issue squarely in its own scope, or its checklist didn't fit the change shape — say so in one line under synthesizing-review-findings's Process notes appendix; that is not a defect finding. Say nothing if the lens worked as intended — never invent a process note to fill the section.

Going deeper

• reference/heuristics.md — the full checklist; open it when the change sits squarely in this lens's domain.
• examples.md — concrete good/bad findings, and the output format to match.
• reference/tool-rules.md — static-analysis rules covering the mechanical subset; for wiring up linters, not needed for the judgment review itself.
• reference/sources.md — the research behind each check; for provenance, not needed during a review.