engineering-bar

name	engineering-bar
description	Use when implementing or reviewing any non-trivial change and you need the canonical engineering quality bar — default biases, definition of done, and reviewable expectations — or when authoring a project's about/craft-and-care pillar that should reference this bar instead of restating it.
metadata	{"owner":"tze","authors":["tze","Claude Fable 5","OpenAI Codex"],"status":"active","last_reviewed":"2026-08-02"}

Engineering Bar

Canonical default quality bar for implementation work. Projects adopt it by reference from about/craft-and-care/ and override individual biases there; when a project pillar exists, the pillar wins. Everything here is a reviewable expectation: a reviewer can reject a change for violating it.

Use This Skill When

• Implementing a non-trivial change, deciding what "done" requires
• Reviewing a change holistically before merge
• Resolving a conflict between subdomain findings (e.g. readability vs. observability) — biases set the tiebreak
• Authoring or updating a project's about/craft-and-care/ pillar (via /th-projects project-shape) — reference this bar, restate nothing

Example trigger phrasings: "hold this to the engineering bar", "is this change done", "is this good enough to merge", "what does done require here", "set the quality bar for this project".

Do Not Use This Skill For

• Deep work in one subdomain — route to the sibling subskill (code-readability, test-rigor, dependency-hygiene, cruft-cleanup)
• Project-level governance, specs, or repo-wide audits — /th-projects

Default Engineering Biases

Unless a project's about/craft-and-care/ explicitly overrides them, these biases apply:

1. Prefer cleanup over same-repo compatibility cruft — When a refactor, rename, or migration completes atomically inside the same repo, delete retired wrappers, aliases, fallback branches, dead flags, and unused paths rather than preserving them "just in case." Preserve backward compatibility only for a verified external consumer or real cross-repo migration constraint. (cruft-cleanup operationalizes this.)
2. Prefer readability and simplicity over cleverness — When two approaches achieve equal correctness and reliability, take the simpler, more readable one. Dense, overly abstract, or surprising code needs strong justification. (code-readability operationalizes this.)
3. Bias toward observability — Failure paths must be diagnosable. Logs on failure-prone paths carry enough structured context to narrow plausible causes, not merely report that something failed.
4. Prefer durable fixes over expedient patches — Don't optimize for "clear the error for now" when a correct, maintainable fix is tractable. Assume engineering time is available; optimize for correctness, reliability, long-term maintainability.
5. Prefer explicitness over magic — Visible control flow, explicit data movement, and obvious invariants beat hidden side effects, surprising framework behavior, and implicit coupling.
6. Prefer fail-fast over silent fallback — Unless graceful degradation is explicitly required by doctrine, specs, or design contracts, surface incorrect assumptions and invalid states loudly rather than masking them behind quiet fallback.
7. Prefer same-change documentation and contract updates — When behavior, assumptions, interfaces, or standards change, update the relevant docs, specs, RFCs, or standards in the same change. "We'll update the docs later" is a violation, not a plan. (documentation operationalizes this, including the code-citation discipline that makes doc claims re-verifiable.)
8. Prefer verification depth over throughput — Verification is deliberate and risk-scaled. Re-check important changes before merge rather than assuming the first pass sufficed. Evidence (command output, test runs, rendered artifacts) beats assertion. (test-rigor operationalizes the testing half.)
9. Take pride in the work, but evaluate feedback on merit — Defend good work with rigor, not ego. Incorporate valid feedback quickly, stay humble about blind spots, push back clearly on incorrect, weak, or scope-distorting claims.

Definition of Done

A non-trivial change is complete when all of these hold:

• Behavior verified — the change was exercised (tests, run, render), evidence stated, not implied.
• No retired paths left behind — every callsite, import, and test uses the new interface; the old one is gone (bias 1).
• Failure paths covered — new failure modes either fail fast or log with diagnostic context (biases 3, 6).
• Docs and contracts current — specs, READMEs, and standards the change touches are updated in the same change (bias 7).
• Regression protected — bugfixes ship with a test that fails on the old behavior (bias 8).
• Test delta accounted — added tests pass the worth-adding bar (each catches a bug no existing test catches) and net suite growth is stated; adds-only growth in a mature area is reviewed, not waved through (bias 8; test-rigor operationalizes).
• A reviewer can follow it — naming, structure, and commit message let a reviewer reconstruct intent without the author present (bias 2).

Applying the Bar in Review

• Cite the bias or done-criterion a finding violates, with file:line evidence.
• Severity follows blast radius: silent fallback in a money path outranks a vague name in a test helper.
• When two biases tension (e.g. explicitness vs. simplicity), prefer the one protecting future readers and operators; say which you chose and why.
• Classify findings before changing scope:
  • Small, local violations clearly inside the approved outcome (naming, fixture clarity, missing focused assertion, dead local cruft) get fixed in the current change by its implementation owner, not filed separately.
  • Missing correctness for the accepted outcome remains in the active task/PR; repeated corrections rewrite the acceptance/failure matrix before more work.
  • A new subsystem, process-global state decision, trust boundary, migration, concurrency model, or other risk-class change becomes a linked prerequisite and returns to /th-projects at the earliest governing spec/allocation gate.
  • New behavior is spec-first; duplicates link to existing work.
• Preserve independent review. "Fix now" does not turn the reviewer into the implementation owner. If the reviewer authors semantic code, require fresh independent review of the exact resulting head.