codehub-debugging

name	codehub-debugging
description	Use when the user is debugging a bug, tracing an error, or asking why something fails. Examples: "Why is X failing?", "Where does this error come from?", "Trace this bug", "This endpoint returns 500".

Debugging with OpenCodeHub

When to Use

• "Why is this function failing?"
• "Trace where this error comes from."
• "Who calls this method?"
• "This endpoint returns 500 intermittently."
• Investigating bugs, errors, test failures, or unexpected behaviour.

Workflow

1. mcp__codehub__detect_changes                              → Is this a recent regression?
2. mcp__codehub__query({ query: "<error or symptom>" })      → Find code related to the symptom
3. mcp__codehub__context({ name: "<suspect>" })              → Callers, callees, processes, cochanges
4. mcp__codehub__sql for a process trace                     → Ordered PROCESS_STEP chain
5. mcp__codehub__list_findings                               → SARIF findings that already flagged the area
6. Read source files only after the graph has narrowed the suspect set

If the context envelope warns the index is stale, run codehub analyze first — stale graphs point at the wrong suspect.

Checklist

- [ ] Capture the symptom (error text, stack frame, failing assertion, wrong output)
- [ ] mcp__codehub__detect_changes({ scope: "unstaged" | "staged" })
      — if non-empty, recent edits are the primary suspect
- [ ] mcp__codehub__query for the error text or related concept
- [ ] mcp__codehub__context on the suspect symbol
- [ ] Read confidenceBreakdown — if unknown > 0, an LSP contradicted a heuristic edge;
      the suspect may be a stale or dead reference
- [ ] Review cochanges (git-history signal, NOT call deps) — files historically edited
      together often point at the hidden collaborator
- [ ] Trace the execution via mcp__codehub__sql on PROCESS_STEP edges
- [ ] mcp__codehub__list_findings to see if a scanner already flagged the area
- [ ] Read source to confirm root cause

Debugging Patterns

Symptom	OpenCodeHub path
Error message	query for the error text → context on every throw site it returned
Wrong return value	context on the function → trace outgoing CALLS for the data flow
Intermittent failure	context → look for outgoing FETCHES (external I/O) + cochanges
Performance issue	impact (downstream) → find symbols with many outbound CALLS (hot paths)
Recent regression	detect_changes → symbols touched in the working tree or staged diff
Failing scanner gate	list_findings({ severity: "error" }) → read the rule + the hit line

Tools

mcp__codehub__query — find code related to the error

mcp__codehub__query({ query: "payment validation error", repo })

→ results: validatePayment, handlePaymentError, PaymentException
→ processes: CheckoutFlow (populated when PROCESS_STEP edges exist)

mcp__codehub__context — full context for a suspect

mcp__codehub__context({ name: "validatePayment", repo })

→ incoming.CALLS: [processCheckout, webhookHandler]
→ outgoing.CALLS: [verifyCard, fetchRates]          ← fetchRates is external I/O — likely culprit
→ outgoing.FETCHES: [POST https://api.stripe.com/...]
→ processes: [{process: "CheckoutFlow", step: 3}]
→ confidenceBreakdown: {confirmed: 3, heuristic: 1, unknown: 0}
→ cochanges: [src/payments/refund.ts (lift 4.2)]   (git history, NOT call deps)

The cochanges section frequently surfaces the hidden collaborator a heuristic call graph misses. Always label it as git-history signal so the user does not treat it as a dependency.

mcp__codehub__sql — custom call-chain trace

Two-hop upstream trace for every caller of validatePayment:

WITH direct AS (
  SELECT src, dst, 1 AS depth
  FROM edges
  WHERE type = 'CALLS'
    AND dst IN (SELECT id FROM nodes WHERE name = 'validatePayment' AND kind = 'Function')
),
indirect AS (
  SELECT e.src, d.dst, 2 AS depth
  FROM edges e
  JOIN direct d ON d.src = e.dst
  WHERE e.type = 'CALLS'
)
SELECT caller.name, caller.file_path, caller.start_line, u.depth
FROM (SELECT * FROM direct UNION ALL SELECT * FROM indirect) u
JOIN nodes caller ON caller.id = u.src
ORDER BY u.depth ASC, caller.name;

mcp__codehub__list_findings — scanner hits in the suspect area

mcp__codehub__list_findings({
  repo,
  severity: "error",
  path_prefix: "src/payments"
})

→ [{rule, severity, message, file, line, snippet}]

Use it early — a scanner often has the bug pre-labelled.

Example: "Payment endpoint returns 500 intermittently"

1. mcp__codehub__detect_changes({ scope: "staged", repo: "my-app" })
   → empty. Not a recent regression.

2. mcp__codehub__query({ query: "payment error handling", repo: "my-app" })
   → results: validatePayment, handlePaymentError, PaymentException
   → processes: [CheckoutFlow (7 steps), ErrorHandling (4 steps)]

3. mcp__codehub__context({ name: "validatePayment", repo: "my-app" })
   → outgoing.CALLS: [verifyCard, fetchRates]
   → outgoing.FETCHES: [GET https://rates.example.com/v1/latest]   ← external I/O
   → confidenceBreakdown: {confirmed: 3, heuristic: 0, unknown: 0}
   → cochanges: [src/utils/http-client.ts (lift 5.1)]              ← investigate this file

4. mcp__codehub__list_findings({
     repo: "my-app",
     path_prefix: "src/utils/http-client"
   })
   → security-rule "missing-request-timeout" at src/utils/http-client.ts:42 (error)

5. Root cause: `fetchRates` uses a shared HTTP client with no timeout configured;
   Stripe rate endpoint occasionally hangs, caller returns 500.