Plan: Extension API wiring and public handoff UX

[codethor0]

Goal

Plan how the MV3 extension hands off job URLs when a public backend exists. No extension network calls in this issue.

Current state

• Extension opens local frontend with ?posting_url= only
• No backend API calls from extension
• Issue Design review: future URL validation API integration #5 covers URL validation API design separately

Deliverables

1. Target popup UX (normalized URL, provider hint, link to public Form vs in-app report)
2. Config strategy: public API base URL vs local dev
3. Auth model for extension (read-only lookup first)
4. Manifest permissions review before any network access
5. Test strategy (unit + manual)

Constraints

• Design/planning only until public backend hosting is approved
• No new dependencies without approval

Related

• Issue Design review: future URL validation API integration #5 (URL validation API integration)
• docs/post-launch-roadmap.md Track 3