# Deburr Edge Cases Skill: Make coding agents systematize their local code > Source: > Published: 2026-06-28 02:44:14+00:00 | name | deburr-edge-cases | |---|---| | description | Strip AI-codegen cruft from a branch — defensive checks the type system should make unrepresentable, redundant validation, speculative abstraction, no-op wrappers — while preserving load-bearing seams. Use after a feature lands and before merge, when asked to "simplify", "de-ornament", "remove cruft", "make erroneous states unrepresentable", or "clean up" a diff. | A structured pass to remove accumulated cruft from a branch — particularly the failure mode where code solves, at a narrow local layer, a problem that should be addressed globally or structurally. The canonical example: instead of enforcing design intent in the type system (making erroneous states unrepresentable), the code accumulates defensive runtime checks to *detect* and flag bad states that a better type would forbid at compile time. This is a **quality** pass, not a bug hunt. Every change must be behavior-preserving, with the existing test suite as the safety net. It complements a correctness-focused review (which hunts bugs); route bug findings there, not here. If you trip over a genuine correctness bug mid-pass, note and surface it separately — do not fix it as part of this pass. A recognizable shape — an `unwrap_or` , a single-`impl` trait — is a prompt to ask whether the construct earns its keep *here*, not a finding in itself. Reason about intent and invariants, not form. - After a feature branch lands, before merge — especially work assembled by several contributors or agents, which tends to accrete per-phase scaffolding that reads as cruft once the whole is in view. - When the user asks to "simplify", "de-ornament", "remove cruft / ceremony / boilerplate", "make bad states unrepresentable", "tighten the types", or "clean up" a set of changes. **Defensive coding the type system should forbid.** Runtime checks, branches, or asserts guarding states a tighter type would make unrepresentable — for example a tri-state`Option` , a sentinel (`""` /`-1` /`0` ) standing in for an`Option` /enum, a field validated on every read rather than made unconstructable-when-invalid, or a "this can't happen" guard.**Redundant / over-eager validation.** Re-checking an invariant already guaranteed upstream (e.g. re-validating what a parse step already proved).**Speculative generality / over-abstraction.** A trait, generic, indirection layer, config knob, or helper with a single call site and no second implementor in view. No-op wrapper methods that just forward to another method with no distinct behavior.**Ornamental error handling.** Error/diagnostic variants for conditions that cannot occur, or a fan-out of variants where one would do.**Dead-but-dressed-up scaffolding** that is*not*a deliberate, documented forward seam. Do not strip things that earn their keep. Call them out as intentional rather than flagging them: **Genuine architectural seams**: a trait that is the documented extension point for future implementors (even with one impl today), mirroring an established pattern in the codebase.**The sole enforcement point**: input validation that is the*only*guard (e.g. validating tool-call arguments when the schema is advisory and never enforced at the boundary).**Concurrency primitives** matching the actual ownership (an`AtomicBool` guard through a shared`&self` can't be replaced by take-by-value`Option` if the caller holds`&self` ).**Test seams**: a generalization (e.g. over`AsyncWrite` ) that has a real second caller in tests.**Required safety rails**: a bound or check mandated by a spec/requirement is not "added cruft" even if the current structure makes it hard to hit — keep it.- A DI/context struct that is over-built today but has a confirmed near-term second consumer. When unsure whether something is cruft or load-bearing: **it is load-bearing until proven otherwise.** Default to keeping. Finding no ornamentation is a valid and common result — especially on small or already-tight diffs. Report "clean" rather than inventing a finding to justify the pass. Run the steps directly, or route the fan-out and edits through whatever review/delegation process the repo otherwise follows. Keep edits one-at-a-time and behavior-preserving, and review each before moving on. Match effort to the diff: for a few files, scan and fix directly; the clustering and per-cluster fan-out below are for large, multi-author branches. Compute the cumulative branch diff against the merge base and list the changed source files, excluding generated/state files (lockfiles, task-tracker state) unless relevant. This is the review surface. Partition the changed files into coherent clusters (e.g. parse/types, registry/storage, config/state-modeling, wiring/transport). Take one cluster at a time — or, if the repo supports parallel read-only reviewers, one reviewer per cluster. For each, apply: - the precise lens above (the five ornamentation categories + the preserve list), - the file cluster and the specific suspects to scrutinize, **verify suspicious editor diagnostics against** before reporting,`cargo check --all-targets` - a consistent finding shape: one-line title; confidence (high/med/low that it's a real simplification, not a behavior change); `file:location` ; the specific cruft; a crisp remedy (prefer "replace runtime check X with type Y"); behavior-preserving vs. behavior-changing. Separate **clear wins** from **judgment calls**, and name anything judged **intentional / load-bearing** so it is not re-litigated. The review stage reports findings only — it does not edit. Merge the findings. Drop: - anything behavior-changing that isn't clearly an improvement, - anything that removes a spec-required rail, - low-value cosmetic churn. Keep the type-system wins and genuine no-op removals. The headline finding is usually a single structural remodel (e.g. tri-state `Option` →`Option` so the bad state is unrepresentable); the rest are small isolated cleanups. Take one finding (or one tightly-coupled pair) at a time. **Pin the exact contract** before editing — especially for a structural refactor, write the target type design and the invariant truth-table the change must preserve, plus a test-migration map (migrate tests to the new shape; never weaken assertions to pass). Execute in **increasing invasiveness**: small, isolated, behavior-preserving cleanups first; the big structural remodel last, on an already-cleaned base. After each change, verify cargo and review it before moving on. If no existing test exercises the changed path, the suite is not a safety net for it — add a characterization test first, or lower the finding's confidence and flag the gap. Before deleting a "no-op", confirm it is one. A classic trap: a `let _ = (&field, …)` discard or an `#[allow]` that *looks* ornamental but actually suppresses a real `dead_code` /lint warning (e.g. `#[derive(Deserialize)]` does not count as a read, and `#[derive(Debug)]` is ignored by dead-code analysis — so fields only read via derives genuinely warn). If removing the "cruft" produces a warning or breaks a check, **restore it and report** rather than deleting into a broken build. Don't trade ornament for a warning. Run the full check suite on the whole de-ornamented stack: `cargo fmt --check` , `cargo clippy --all-targets --all-features` , `cargo nextest run` , `ratchets check` . Confirm no assertion was weakened or deleted to make a change pass — tests that only covered genuinely-removed code may go with it, but everything else must be migrated, not loosened. **Tri-state collapse → unrepresentable bad state.**`enabled: Option` rewritten`None → Some(true)` at assembly and read via`unwrap_or(false)` , then carried*dead*into a component that only exists when enabled. Fix: split the parse DTO from a resolved type; make the consumer field`Option` with**no**, so "disabled" =`enabled` field`None` by construction. Deletes the rewrite, the accessor, the`unwrap_or` , the dead field, and the explanatory comments that existed only to compensate for the confusing type.**Sentinel →** A helper returning an owned`Option` .`String` with`""` meaning "absent", forcing a downstream`!is_empty() && …` guard. Fix: return`Option<&str>` ; the guard and an allocation vanish.**Namespacing struct → free function.** A zero-field`struct FooThing;` whose only purpose is to host one associated`fn` that is never called on an instance and implements no trait. Fix: make it a module-level free`fn` , delete the struct/impl. (Distinguish from the*real*seam — the trait + concrete type it delegates to — which stays.)**No-op wrapper method.** A trait default`summarize()` that just returns`self.list()` , with no override and one caller. Fix: delete it; the caller uses`list()` . Reintroduce only if a second, genuinely-distinct behavior ever materializes. - Deleting something into a compiler/clippy warning (verify first; restore if it warns). - Removing a spec-mandated safety bound because the current structure makes it hard to hit. - Stripping a documented forward seam or the sole enforcement point of an invariant. - Weakening or deleting test assertions to make a refactor pass — migrate them instead. - Doing the big structural remodel first, or batching everything into one giant unreviewable commit. - Treating the pass as a bug hunt — it is quality-only; route correctness findings to a dedicated bug-hunting review.