fix-investigate

name	fix-investigate
description	Investigate failing tests or CI divergence. Deep single-test root-cause analysis, or local-vs-CI pattern matching.
when_to_use	investigate failing test, why is this test failing, debug this test, test debugging, test broken, works locally not CI, CI failed but local passes, fix CI divergence, CI divergence.
argument-hint	[test name | CI error output | 'CI divergence']

Fix Investigate

You are a test-failure investigator. Run a deep investigation of failing tests or CI-vs-local divergence. For batch build error fixing, use /fix instead.

Step 0: Detect Mode

Input pattern	Mode
"works locally" / "CI only" / "CI failed but local"	CI Divergence
Single test name or pasted xUnit failure	Deep Investigation

---

Mode: CI Divergence

If the repo keeps local-vs-CI build notes (e.g. lode/infrastructure/local-vs-ci-build.md), read them first. Then match each error to a known divergence pattern:

Divergence Type	Typical Symptoms
Case sensitivity	File not found on Linux but exists on macOS
Missing using	CS0246 on a type resolved via macOS global usings
TFM-specific API	Method exists in local SDK but not CI target TFM
Nullable annotations	CI has stricter <Nullable>enable</Nullable>
Analyzer version	CI NuGet restore fetches newer analyzer
Path separator	\\ in hardcoded paths fails on Linux

For each error, explain the local-vs-CI gap, apply the fix, then validate with scripts/check.sh --all --no-format --json. If the divergence type is new and the repo keeps local-vs-CI notes, record it there.

---

Mode: Deep Investigation

Step 1: Extract test identifier

From $ARGUMENTS or conversation, identify the test class or method name.

Step 2: Investigate in parallel

Run these simultaneously:

1. scripts/test.sh {TestName} — capture assertion message, stack trace
2. Read test file — locate by {TestClass}Tests.cs in tests/
3. Read source under test — from test method, identify the SUT in src/

Categorize the failure:

Category	Indicators
Assertion mismatch	Expected X but got Y; test logic or implementation drift
Null reference / setup	NRE, missing mock setup, incorrect fixture
Flaky / race condition	Passes sometimes; async, timers, shared state
Missing implementation	NotImplementedException, method doesn't exist
Environment / config	Missing file, wrong path, env variable not set

Check sibling tests in the same class for shared root cause.

Step 3: Propose fix

Present the diagnosis with category, root cause, proposed code change, and affected sibling tests. Wait for user confirmation before applying.

For flaky async tests, flag the concurrency hazard (async/timers/shared state) and recommend a dedicated concurrency review before trusting the fix.

Step 4: Validate

After user-approved fix: scripts/test.sh {TestClass}

Common Pitfalls

CS0535 cascade

When implementing interface stubs for CS0535, expression-bodied members don't allow parameter references. Use block-bodied methods. Unused nullable params need GC.KeepAlive(param), non-nullable ref params need ArgumentNullException.ThrowIfNull(param).