Build Fix

/build-fix

What

The kit's autonomous iteration-loop skill. It drives a broken dotnet build (or failing dotnet test) to green by looping: run, parse failures, categorize by root cause, apply targeted fixes, re-run. It repeats until green or a guard fires — the same way an experienced developer works through a wall of red, but with hard limits that stop it from thrashing.

This is not a single-pass fix. It handles cascading errors where fixing one issue reveals the next.

When

• The build is broken and there are multiple compiler errors
• Tests are failing after code changes or a build-fix pass
• After a major refactor that touched type names, namespaces, or signatures
• After updating NuGet packages (especially major version bumps)
• After merging a branch with conflicts resolved but not compiled
• After scaffolding or code generation that needs manual adjustments
• User says: "fix the build", "make it compile", "make the tests pass", "keep going until it works", "keep fixing"

How

Loop Discipline (applies to every loop)

1. Bounded iteration, always — Default max 5 iterations, hard cap 10 (user "keep going" extends by 3, never past 10). If 5 iterations cannot solve it, the problem needs human judgment, not a 6th identical attempt.
2. Progress or exit — Each iteration must reduce the error/failure count. Same errors after a fix attempt = STUCK: stop, report, and re-plan with a different approach. Never retry the same fix that already failed.
3. Categorize before fixing — Group errors by root cause and fix the highest-leverage first (one missing using can erase a dozen downstream errors).
4. Transparency per iteration — Report what changed and why: Iteration 3/5: fixed CS0246 by adding using System.Text.Json, 2 remain. Never modify files silently.
5. Atomicity — Each iteration leaves the codebase no worse than before. If iteration 3 fails, the code stays in iteration 2's state.

Primary Flow: Build-Fix Loop (max 5 iterations)

1. Build — Run dotnet build, capture full error output

2. Parse — Extract every error CS#### with file, line, and message

3. Categorize — Group by root cause:

   Category	Codes	Fix strategy
   Missing using/reference	CS0246, CS0234	Add using, package, or project ref
   Type mismatch	CS0029, CS1503	Check expected type, cast or convert
   API change	CS0117, CS7036	Check new signature, update call sites
   Nullability	CS8600–CS8604	Add null check, ?. or ??
   Ambiguity / duplicate	CS0104, CS0121, CS0111	Qualify namespace, remove dupe
   Missing member	CS1061	Check spelling, verify member exists
   Missing implementation	CS0535	Implement interface/abstract members
   Obsolete API	CS0618	Replace with recommended alternative

4. Fix — Apply targeted fixes, root-cause/highest-leverage errors first

5. Rebuild — Run dotnet build again, compare error count

6. Evaluate — Zero errors: run dotnet test as a sanity check, report success. Fewer errors: continue. Same errors: STUCK — exit and re-plan. More errors: revert the iteration, report REGRESSION.

Variant: Test-Fix Loop (max 5; 3 if it follows a build-fix pass)

Same loop, same guards, with dotnet test --no-build as the runner and one critical extra step — diagnose before fixing:

1. Read the test — understand the assertion and setup
2. Read the production code — understand the actual behavior
3. Decide where the bug lives: wrong expectation → fix the test; production bug → fix the code; incomplete setup → fix the setup; contract changed → update the test to match
4. Never weaken an assertion to make a test pass. BAD: Assert.Equal(expected, actual) → Assert.NotNull(actual). GOOD: fix the production code so the original assertion passes.

Fail-Safe Guards (immediate exit)

• STUCK — same errors/failures after a fix, or count oscillates (3 → 2 → 3): report what could not be fixed and what a human should check
• REGRESSION — an iteration introduced more errors than it fixed: revert its changes, report
• Cascading failures — fixing one error spawns 3+ new ones twice in a row: the approach is wrong, stop
• Critical error — wrong SDK, missing project file, corrupted solution, or the test runner itself fails: human intervention needed, stop
• User interruption — finish the current iteration, report progress, ask how to proceed

Other Loops

The same discipline — bounded iterations, progress detection, fail-safe guards — governs refactor passes (/de-sloppify: verify build + tests after each target, revert on failure) and scaffolding (/scaffold: generate, then run nested build-fix and test-fix loops). Nested loops get a smaller budget (parent 5 → nested 3), max nesting depth 2, total budget 15.

Invokes

MCP Tools Used

• get_diagnostics — Compiler errors/warnings scoped to file or project
• find_symbol — Locate moved or renamed types
• find_references — Assess blast radius of a broken API change
• get_project_graph — Dependency order for fixing reference errors

Example

User: /build-fix

Claude: Running dotnet build...
  Found 12 errors across 4 files.

  Iteration 1/5:
  - 6 errors: Missing namespace (CS0246) — adding using directives
  - 3 errors: Type mismatch (CS1503) — updating method signatures
  - 3 errors: Interface not implemented (CS0738) — package API changed

  Rebuilding... 3 errors remaining.

  Iteration 2/5:
  - 3 errors: CS0738 after xunit.v3 upgrade
    - IAsyncLifetime.InitializeAsync now returns ValueTask (was Task in v2),
      and DisposeAsync comes from IAsyncDisposable
    - Updating 3 test fixtures to the ValueTask signatures

  Rebuilding... 0 errors. Build is green.

  Running dotnet test... All 47 tests passed.
  Added to Memory > Packages: "xunit.v3 IAsyncLifetime uses ValueTask signatures"

Related

• /verify — Full verification pass (build + test + format + diagnostics)
• /tdd — Red-green-refactor when building new features test-first
• /de-sloppify — Clean up code quality issues after the build is green