fix: harden handlers API response

[chubes4]

Summary

• Normalize handler definitions before enriching /datamachine/v1/handlers responses so missing optional keys do not emit PHP notices into REST output.
• Drop malformed non-array handler registrations from the discovery response instead of letting them contaminate JSON output.
• Add a smoke regression covering JSON-safe /handlers output with incomplete and malformed handler registrations.

Fixes #1959.

Testing

• homeboy lint --path /Users/chubes/Developer/data-machine@fix-handlers-invalid-json --changed-since origin/main
• homeboy test --path /Users/chubes/Developer/data-machine@fix-handlers-invalid-json --changed-since origin/main
• php tests/handlers-api-json-safe-smoke.php
• npm run build

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Investigated the /handlers invalid JSON evidence, drafted the focused REST response hardening and smoke coverage, and ran local verification. Chris remains responsible for review and merge.

[homeboy-ci]

Homeboy Results — data-machine

Lint

✅ lint — passed

ℹ️ Full options: homeboy docs commands/lint
Deep dive: homeboy lint data-machine --changed-since e0c4f30

Test

✅ test — passed

ℹ️ Auto-fix lint issues: homeboy refactor data-machine --from lint --write
ℹ️ Collect coverage: homeboy test data-machine --coverage
ℹ️ Pass args to test runner: homeboy test -- [args]
ℹ️ Full options: homeboy docs commands/test
Deep dive: homeboy test data-machine --changed-since e0c4f30

Audit

✅ audit — passed

• requested_detectors — 5 finding(s)
• intra-method-duplication — 1 finding(s)
• Total: 6 finding(s)

Deep dive: homeboy audit data-machine --changed-since e0c4f30

Tooling versions

• Homeboy CLI: homeboy 0.175.0+638659dd
• Extension: wordpress from https://github.com/Extra-Chill/homeboy-extensions
• Extension revision: 83a0f27
• Action: unknown@unknown