Stack Debugging Skill | Agent Skills

Stack Debugging

Troubleshoot @outfitter/* package issues.

Result Issues

Always Getting Error

Symptom: Result is err when it should be ok.

Check validation:

const inputResult = validateInput(rawInput);
if (inputResult.isErr()) {
  console.log("Validation failed:", inputResult.error.details);
  return inputResult;
}

Check async:

// BAD: Missing await
const result = getUser(id);  // Promise, not Result!

// GOOD
const result = await getUser(id);

Type Narrowing Broken

Symptom: TypeScript doesn't know type after isOk().

// BAD: Reassigning breaks narrowing
let result = await getUser(id);
if (result.isOk()) {
  result = await updateUser(result.value);  // Breaks!
}

// GOOD: Separate variables
const getResult = await getUser(id);
if (getResult.isErr()) return getResult;
const updateResult = await updateUser(getResult.value);

Error Type Lost

Use _tag for narrowing:

if (result.isErr()) {
  switch (result.error._tag) {
    case "ValidationError":
      console.log(result.error.details);
      break;
    case "NotFoundError":
      console.log(result.error.resourceId);
      break;
  }
}

MCP Issues

Tool Not Appearing

server.registerTool(myTool);
server.start();  // After registration!

Check schema is valid Zod with .describe():

const schema = z.object({
  query: z.string().describe("Required for AI"),
});

Tool Invocation Failing

Verify handler is async:

handler: async (input) => {  // Not sync!
  return Result.ok(data);
}

Return Result, not raw value:

// BAD
return { data: "value" };

// GOOD
return Result.ok({ data: "value" });

CLI Output Issues

JSON Not Printing

Force mode:
```
await output(data, { mode: "json" });
```

Check environment:

OUTFITTER_JSON=1 myapp list
OUTFITTER_JSON=0 myapp list --json  # Forces human!

Await output:

// BAD
output(data);
process.exit(0);  // May exit before output!

// GOOD
await output(data);

Wrong Exit Code

Use exitWithError:

// BAD
process.exit(1);

// GOOD
exitWithError(result.error);

Exit code table:

| Category | Exit | |----------|------| | validation | 1 | | not_found | 2 | | conflict | 3 | | permission | 4 | | timeout | 5 | | rate_limit | 6 | | network | 7 | | internal | 8 | | auth | 9 | | cancelled | 130 |

Logging Issues

Redaction Not Working

const logger = createLogger({
  redaction: { enabled: true },  // Must be true!
});

// Custom patterns
const logger = createLogger({
  redaction: {
    enabled: true,
    patterns: ["password", "apiKey", "myCustomSecret"],
  },
});

Missing Context

import { createChildLogger } from "@outfitter/logging";

const requestLogger = createChildLogger(ctx.logger, {
  requestId: ctx.requestId,
  handler: "myHandler",
});

requestLogger.info("Processing", { data });  // Includes requestId

Wrong Level

const logger = createLogger({
  level: process.env.LOG_LEVEL || "info",
});

// Hierarchy: trace < debug < info < warn < error < fatal
// "info" hides trace and debug

Debugging Tools

Trace Result Chain

function traceResult<T, E>(name: string, result: Result<T, E>): Result<T, E> {
  console.log(`[${name}]`, result.isOk() ? "OK:" : "ERR:",
    result.isOk() ? result.value : result.error);
  return result;
}

const result = traceResult("getUser", await getUser(id));

Inspect Context

console.log("Context:", {
  requestId: ctx.requestId,
  hasLogger: !!ctx.logger,
  hasConfig: !!ctx.config,
  hasSignal: !!ctx.signal,
  cwd: ctx.cwd,
});

Validate Zod Schema

const parseResult = schema.safeParse(rawInput);
if (!parseResult.success) {
  console.log("Zod errors:", parseResult.error.issues);
}

Related Skills

outfitter-stack:stack-patterns — Correct patterns
outfitter-stack:stack-review — Systematic audit

Agent Skills: Stack Debugging

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