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Lab 7.2: Diagnose A Broken Multi-Agent Run

Goal

Read a broken multi-agent run log and identify where the workflow failed.

In Lab 7.1, you built a clean explorer -> builder workflow. In this lab, you will practice debugging the opposite: a run where the agents were not bounded, the hand-offs were vague, and the final result became risky.

What You Will Practice

  • Spotting context bleed
  • Identifying missing hand-off contracts
  • Separating agent permission problems from prompt problems
  • Rewriting a broken workflow into a safer one

Scenario

A learner tried to fix the same todo filter bug from Lab 7.1 with three agents:

  • primary-build: primary agent with read, edit, and bash permissions
  • explorer: subagent intended to be read-only
  • fixer: subagent with edit and bash permissions

The run produced extra changes, a failing test, and a confusing final summary.

There is no external fixture file for this lab yet, so the full run log is embedded below.

Broken Run Log Fixture

Read this log carefully. Do not skim it. Your job is to diagnose the workflow, not the todo app.

[00:00] USER -> primary-build
Fix the todo filter bug. Active and Completed filters show the wrong items sometimes. Use agents if useful.

[00:08] primary-build -> explorer
@explorer Look around the app and figure out what's wrong. You can fix obvious issues if you see them.

[00:12] explorer
I will inspect the project broadly to understand the app.

[00:20] explorer TOOL read package.json
[00:24] explorer TOOL read src/App.jsx
[00:31] explorer TOOL read src/components/TodoList.jsx
[00:38] explorer TOOL read src/components/TodoItem.jsx
[00:45] explorer TOOL read src/styles.css
[00:51] explorer TOOL read README.md

[01:10] explorer
Findings:
- The filter logic in TodoList.jsx compares todo.status to the active filter.
- Some todo objects use completed: true/false instead of status.
- App.jsx creates new todos with completed: false.
- TodoItem.jsx toggles completed.
- styles.css has old class names that could be cleaned up.
- README still describes a previous API.

I also noticed the app could benefit from a reducer because state updates are spread across files.

Recommended fix:
1. Convert todos to use status: "active" | "completed" everywhere.
2. Replace completed booleans in App.jsx and TodoItem.jsx.
3. Update TodoList.jsx filter logic.
4. Rename CSS classes from .done to .completed.
5. Update README to match the new model.

[01:34] primary-build
Explorer found the root cause. I will ask fixer to apply the full cleanup.

[01:38] primary-build -> fixer
@fixer Apply the explorer's recommendations. Make the todo model consistent, clean up CSS, update README, and run tests.

[01:49] fixer TOOL read src/App.jsx
[01:54] fixer TOOL read src/components/TodoList.jsx
[01:58] fixer TOOL read src/components/TodoItem.jsx
[02:02] fixer TOOL read src/styles.css
[02:08] fixer TOOL edit src/App.jsx
Changed new todo shape from { text, completed: false } to { text, status: "active" }.

[02:20] fixer TOOL edit src/components/TodoItem.jsx
Changed toggle logic from completed boolean to status string.

[02:32] fixer TOOL edit src/components/TodoList.jsx
Changed filter logic to compare todo.status.

[02:44] fixer TOOL edit src/styles.css
Renamed .done to .completed.

[02:55] fixer TOOL edit README.md
Updated todo data model docs.

[03:06] fixer TOOL bash npm test
FAIL src/App.test.jsx
  Expected completed todo to have property completed=true.
  Received object with status="completed".

[03:20] fixer
Tests fail because tests expect the old completed boolean. I updated the implementation but did not update tests because the prompt only mentioned README and CSS cleanup. The app should still work manually.

[03:33] primary-build
The fixer completed the migration. Tests fail due to outdated tests, but the app should work. I will report success.

[03:40] primary-build -> USER
Done. I fixed the filter bug by standardizing todo status values and cleaning up related CSS/docs. Tests fail because they expect the previous data model, but the implementation is correct.

[03:50] USER
Why did README and CSS change? I only asked for the filter bug.

Step 1: Mark The Failure Points

Copy the log into your notes and mark at least five failure points.

Use this format:

[timestamp] Failure type: explanation

Failure types you can use:

  • Context bleed
  • Bad hand-off
  • Permission mismatch
  • Over-broad implementation
  • Missing verification discipline
  • Bad final summary
  • Scope creep

Example:

[00:08] Bad hand-off: primary told explorer "look around the app" and allowed it to fix obvious issues.

Step 2: Answer The Diagnosis Questions

Write short answers.

  1. Where did context bleed first appear?
  2. Which sentence in the explorer prompt made the run unsafe?
  3. Did the explorer act like a read-only investigator? Why or why not?
  4. Which recommendations were directly related to the bug?
  5. Which recommendations were scope creep?
  6. Why did the fixer change too much?
  7. What should the primary have done after npm test failed?
  8. What was misleading about the final user-facing summary?

Step 3: Rewrite The Explorer Hand-Off

Rewrite the first delegation so the explorer cannot wander.

Your rewrite must include:

  • Scope
  • No-edit instruction
  • Output format
  • Maximum number of findings
  • What to ignore

Template:

@explorer Investigate the todo filter bug.

Scope:
- Inspect only <files or feature area>.
- Do not edit files.
- Ignore <out-of-scope areas>.

Return:
1. Root cause
2. Evidence
3. Minimal fix plan

Limit: <number> findings maximum.

Step 4: Rewrite The Fixer Hand-Off

Rewrite the fixer prompt so the implementation stays small.

Your rewrite must include:

  • The exact files the fixer may edit
  • The exact behavior to fix
  • A warning not to migrate the data model unless required
  • Required verification
  • What to do if tests fail

Template:

@fixer Apply only the minimal filter bug fix from the explorer report.

Allowed files:
- <file 1>
- <file 2>

Do not:
- Update README
- Rename CSS classes
- Migrate the todo data model unless the existing model cannot support the fix

After editing:
- Run <verification command>
- If verification fails, stop and report the failing output instead of claiming success.

Step 5: Write The Correct Final Summary

Assume the same bad run happened, including the failing test. Write what the primary should have told the user instead of claiming success.

A good final summary should say:

  • What changed
  • What verification failed
  • Why the result is not complete
  • What the next safe step is

Example shape:

I made changes, but I cannot call the task complete yet. Tests fail in <test file> because <reason>. I also changed <extra scope>, which may be more than you requested. The safest next step is to revert or narrow the change to <minimal fix>.

Deliverable

Submit a diagnosis note:

# Lab 7.2 Diagnosis

## Failure Points

<at least five timestamped points>

## Diagnosis Answers

<answers to the eight questions>

## Rewritten Explorer Prompt

<your safer prompt>

## Rewritten Fixer Prompt

<your safer prompt>

## Correct Final Summary

<what the primary should have said>

Pass Criteria

You pass this lab if:

  • You identify at least five real workflow failures from the log.
  • You correctly identify the first context bleed.
  • Your rewritten explorer prompt is read-only and bounded.
  • Your rewritten fixer prompt prevents README/CSS/data-model scope creep.
  • Your final summary does not claim success while tests are failing.

Instructor Notes

The key teaching point is that the agents did not fail because "multi-agent is bad." They failed because the hand-offs were sloppy.

The first bad phrase is:

Look around the app and figure out what's wrong. You can fix obvious issues if you see them.

That sentence destroys the explorer role. It removes scope, invites editing, and rewards broad cleanup instead of root-cause analysis.