gitnexus-debugging

# Debugging with GitNexus ## When to Use - "Why is this function failing?" - "Trace where this error comes from" - "Who calls this method?" - "This endpoint returns 500" - Investigating bugs, errors, or unexpected behavior ## Bind the repository first A root cause traced in the wrong repository is a wrong root cause. Call `list_repos {}` before the first tool call. With one indexed repository, use the examples below as written. With more than one, pass `repo` on every call: an omitted `repo` normally errors, but under an MCP policy with a configured default it resolves to that default silently. If you cannot tell which repository is meant, stop and ask. This matters most for `cypher`, whose statement carries no in-band hint of which database it ran against. `list_repos` is paginated, so page with `offset: pagination.nextOffset` until `hasMore` is false before concluding a repository is absent. A stale index describes the code from before your bug, so refresh before trusting a trace, and state the repository and index freshness with the diagnosis. ## Workflow ``` 0. list_repos {} → Bind repo 1. query({search_query: "<error or symptom>"}) → Find related execution flows 2. context({name: "<suspect>"}) → See callers/callees/processes 3. READ gitnexus://repo/{name}/process/{name} → Trace execution flow 4. cypher({statement: "MATCH path..."}) → Custom traces if needed ``` > If "Index is stale" → run `node .gitnexus/run.cjs analyze` in terminal. > Hot-tool `staleness` names which index answered (`branch`/`lastCommit`) and how fresh it is (`status`). Re-analyze only for `behind` or `diverged` — `current` is identity, `unknown` is unmeasurable. ## Checklist ``` - [ ] list_repos {} — bind repo; explicit repo when >1 indexed, ask if ambiguous - [ ] Understand the symptom (error message, unexpected behavior) - [ ] query for error text or related code - [ ] Identify the suspect function from returned processes - [ ] context to see callers and callees - [ ] Trace execution flow via process resource if applicable - [ ] cypher for custom call chain traces if needed - [ ] Read source files to confirm root cause - [ ] State the repository and index freshness with the diagnosis ``` ## Debugging Patterns | Symptom | GitNexus Approach | | -------------------- | ---------------------------------------------------------- | | Error message | `query` for error text → `context` on throw sites | | Wrong return value | `context` on the function → trace callees for data flow | | Intermittent failure | `context` → look for external calls, async deps | | Performance issue | `context` → find symbols with many callers (hot paths) | | Recent regression | `detect_changes` to see what your changes affect — pass `worktree` for a linked worktree | | "How does A reach B?" | `trace` between the two symbols — shortest call chain in one call | ## Tools **query** — find code related to error: ``` query({search_query: "payment validation error", repo: "my-app"}) → Processes: CheckoutFlow, ErrorHandling → Symbols: validatePayment, handlePaymentError, PaymentException ``` **context** — full context for a suspect: ``` context({name: "validatePayment", repo: "my-app"}) → Incoming calls: processCheckout, webhookHandler → Outgoing calls: verifyCard, fetchRates (external API!) → Processes: CheckoutFlow (step 3/7) ``` **cypher** — custom call chain traces. Pass `repo` alongside the statement; the Cypher text itself names no repository, so the result is unattributable without it: ```cypher MATCH path = (a)-[:CodeRelation {type: 'CALLS'}*1..2]->(b:Function {name: "validatePayment"}) RETURN [n IN nodes(path) | n.name] AS chain ``` **trace** — shortest call chain between two symbols ("how does A reach B?"), one call instead of chaining `context` hops: ``` trace({ from: "processCheckout", to: "fetchRates", repo: "my-app" }) → status: ok, hopCount: 3 → hops: processCheckout → validatePayment → verifyCard → fetchRates → edges: CALLS (1.0), CALLS (0.95), CALLS (1.0) ``` When no path exists, `trace` reports the furthest reachable node — exactly where the chain breaks (dynamic dispatch, reflection, or an external boundary). ## Example: "Payment endpoint returns 500 intermittently" ``` 0. list_repos {} → total: 2 (my-app, billing-api) — bind my-app explicitly on every call 1. query({search_query: "payment error handling", repo: "my-app"}) → Processes: CheckoutFlow, ErrorHandling → Symbols: validatePayment, handlePaymentError 2. context({name: "validatePayment", repo: "my-app"}) → Outgoing calls: verifyCard, fetchRates (external API!) 3. READ gitnexus://repo/my-app/process/CheckoutFlow → Step 3: validatePayment → calls fetchRates (external) 4. Root cause: fetchRates calls external API without proper timeout Repository: my-app Index: current ``` With a single indexed repository, step 0 returns `total: 1` and the `repo` argument drops out of every call above.