Subagents Discipline

Implementation Principles

Rule 0: Read the Bead First

Before implementing anything, read the bead comments for context:

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bd show {BEAD_ID}
bd comments {BEAD_ID}

The orchestrator's dispatch prompt is automatically logged as a DISPATCH comment on the bead. This contains:

• The investigation findings
• Root cause analysis (file, function, line)
• Related files that may need changes
• Gotchas and edge cases

Use this context. Don't re-investigate. The comments contain everything you need to implement confidently.

If no dispatch or context comments exist, ask the orchestrator to provide context before proceeding.

Rule 1: Look Before You Code

Before writing code that touches external data (API, database, file, config):

1. Fetch/read the ACTUAL data - run the command, see the output
2. Note exact field names, types, formats - not what docs say, what you SEE
3. Code against what you observed - not what you assumed

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WITHOUT looking first:
  Assumed: column is "reference_images"
  Reality: column is "reference_image_url"
  Result:  Query fails

WITH looking first:
  Ran: SELECT column_name FROM information_schema.columns WHERE table_name = 'assets';
  Saw: reference_image_url
  Coded against: reference_image_url
  Result: Works

Rule 2: Test Functionally (Close the Loop)

Principle: Optimize for the fastest way to verify your work actually works.

Two strategies:

1. User Journey Tests — Test actual behavior as a user experiences it:

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   # API: curl with real data
   curl -X POST localhost:3000/api/users -d '{"name":"test"}' -H "Content-Type: application/json"
   
   # CLI: run the command
   bd create "Test" -d "Testing" && bd list
   
   # Error case: curl with invalid auth
   curl -X POST localhost:3000/api/users -H "Authorization: Bearer invalid"
   

2. Component Tests — Supplement for regression prevention when fast verification isn't possible:

   • Complex logic with many edge cases
   • Code that runs in environments you can't easily replicate
   • Shared libraries used by multiple consumers

"Close the Loop" principle: Run the actual thing. Verify it works. Check error cases.

Good: "Curled endpoint with invalid auth, got 401 as expected" Bad: "Wrote tests, they compile"

Rule 3: Use Your Tools

Before claiming you can't fully test:

1. Check what MCP servers you have access to - list available tools
2. If any tool can help verify the feature works, use it
3. Be resourceful - browser automation, database inspection, API testing tools

Rule 4: Log Your Approach (Optional)

If you deviated from the orchestrator's suggestion, found a better path, or made a choice future maintainers might question:

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bd comment {BEAD_ID} "APPROACH: Used X instead of Y because Z"

When to log:

• Deviated from the suggested fix
• Multiple valid solutions, chose one for a specific reason
• Future maintainers might question the approach

Skip if the code is self-explanatory. This is not enforced.

For Epic Children

If your BEAD_ID contains a dot (e.g., BD-001.2), you're implementing part of a larger feature:

1. Check for design doc: bd show {EPIC_ID} --json | jq -r '.[0].design'
2. Read it if it exists - this is your contract
3. Match it exactly - same field names, same types, same shapes

Red Flags - Stop and Verify

When you catch yourself thinking:

• "This should work..." → run it and see
• "I assume the field is..." → look at the actual data
• "I'll test it later..." → test it now
• "It's too simple to break..." → verify anyway