Impact Analysis with GitNexus

When to Use

• "Is it safe to change this function?"
• "What will break if I modify X?"
• "Show me the blast radius"
• "Who uses this code?"
• Before making non-trivial code changes
• Before committing — to understand what your changes affect

Workflow

1. impact({target: "X", direction: "upstream"}) or `node .gitnexus/run.cjs impact "X" --direction upstream --repo .`
2. READ gitnexus://repo/{name}/processes                   → Check affected execution flows
3. detect_changes({scope: "all"}) or `node .gitnexus/run.cjs detect-changes --scope all --repo .`
4. Assess risk and report to user

If "Index is stale" → run node .gitnexus/run.cjs analyze in terminal. If .gitnexus/run.cjs is missing, replace node .gitnexus/run.cjs with npx gitnexus in the fallback commands.

Checklist

- [ ] impact({target, direction: "upstream"}) or CLI fallback to find dependents
- [ ] Review d=1 items first (these WILL BREAK)
- [ ] Check high-confidence (>0.8) dependencies
- [ ] READ processes to check affected execution flows
- [ ] detect_changes({scope: "all"}) or CLI fallback for pre-commit check
- [ ] Assess risk level and report to user

Understanding Output

Risk Assessment

UNKNOWN is not a low rung on this scale — it means the walk could not answer. An empty caller set is equally consistent with "genuinely unused" and "the callers are not resolvable by the index" (plain-object property access, dynamic dispatch, cross-language calls), so few-callers ⇒ LOW does not apply. The result carries a riskNote saying so. Confirm with a text search before treating the symbol as safe to change or delete.

Tools

impact — the primary tool for symbol blast radius. If MCP is unavailable, use node .gitnexus/run.cjs impact <symbol> --direction upstream --repo . instead:

impact({
  target: "validateUser",
  direction: "upstream",
  minConfidence: 0.8,
  maxDepth: 3
})

→ d=1 (WILL BREAK):
  - loginHandler (src/auth/login.ts:42) [CALLS, 100%]
  - apiMiddleware (src/api/middleware.ts:15) [CALLS, 100%]

→ d=2 (LIKELY AFFECTED):
  - authRouter (src/routes/auth.ts:22) [CALLS, 95%]

detect_changes — git-diff based impact analysis. If MCP is unavailable, use node .gitnexus/run.cjs detect-changes --scope all --repo . instead:

detect_changes({scope: "all"})

→ Changed: 5 symbols in 3 files
→ Affected: LoginFlow, TokenRefresh, APIMiddlewarePipeline
→ Risk: MEDIUM

partial: true (a graph query failed) or truncated: true (the changed-symbol listing was capped) means the result is short of the truth, and reads like UNKNOWN above: a zero there means unseen, not unaffected. Re-run it rather than tick the pre-commit check.

Example: "What breaks if I change validateUser?"

1. impact({target: "validateUser", direction: "upstream"}) or `node .gitnexus/run.cjs impact "validateUser" --direction upstream --repo .`
   → d=1: loginHandler, apiMiddleware (WILL BREAK)
   → d=2: authRouter, sessionManager (LIKELY AFFECTED)

2. READ gitnexus://repo/my-app/processes
   → LoginFlow and TokenRefresh touch validateUser

3. Risk: 2 direct callers, 2 processes = MEDIUM