claude
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Sync course wiki / sync-wiki (push) Successful in 4s
Co-authored-by: claude <claude@jpaul.io> Co-committed-by: claude <claude@jpaul.io>
44 lines
2.7 KiB
Markdown
44 lines
2.7 KiB
Markdown
# Skill: Safe scoped change
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A safe-change playbook (a Module 21 skill) for modifying a codebase you don't fully understand.
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Use it only **after** `map-this-repo` has produced an architecture summary. The whole bet of this
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skill is: small, scoped, tested, reviewable, never a sweeping rewrite.
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## When to use
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When making a concrete change to an unfamiliar repo.
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## Rules
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- **One change, one branch.** Create a branch first (Module 6). Never work on the default branch.
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- **Smallest diff that solves it.** Touch the fewest files possible. If the change wants to sprawl,
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stop and re-scope; sprawl in code you don't understand is how you break things invisibly.
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- **No drive-by edits.** Do not reformat, rename, or "clean up" unrelated code. Those bury the real
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change and make the diff unreviewable (Module 10).
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- **Match local conventions.** Mirror the surrounding code's style, naming, and patterns, not your
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own defaults.
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- **Tests are the contract.** A change isn't done until it's covered (Module 13) and the existing
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suite still passes.
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## Steps
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1. **State the change in one sentence** and the acceptance criterion ("done when X").
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2. **Find the blast radius first:** search for every caller/usage of what you're about to touch.
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List them. If you can't enumerate them, you're not ready to change it.
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3. **Install the project's dependencies, then run the existing tests before touching anything**;
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establish a green baseline. Tell two failures apart: if the suite errors with missing imports,
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"no module named …", or "no tests ran," that's an **unconfigured environment**, not a baseline.
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Finish the documented install (and pick a different repo if it still won't go green on a clean
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clone). A genuine **pre-existing failure** (install succeeded, but a real test fails) is the other
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case: note it so it doesn't get blamed on you, and don't build on top of it.
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4. **Make the minimal edit.** Keep it to the files identified in step 2.
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5. **Add or extend a test** that fails without your change and passes with it.
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6. **Run the full suite.** All green, including the baseline tests.
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7. **Self-review the diff** as if reviewing someone else's PR (Module 10): is every changed line
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necessary and explained? Revert anything that isn't.
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8. **Write the PR description:** what changed, why, blast radius, how it was tested, what you did
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NOT touch and why.
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## Stop conditions (escalate to a human instead of pushing on)
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- The change requires touching more than ~3 files or a "core" file from the architecture summary.
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- You can't enumerate the callers of what you're changing.
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- A test you don't understand starts failing.
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- The fix needs a design decision the existing code doesn't settle.
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