Fix Jev response fallbacks and redundant completion turn

[esokullu]

The fast Jev path could send target questions containing only the fallback none choice. The service still billed those HTTP 200 responses, but the client rejected their answer shape and silently returned to the main model on every changed snapshot. Browser actions that successfully navigated could also leave generic plan-execution evidence unresolved, forcing a second done model turn after the results page had already been read.

This change omits unsupported operations and their degenerate target questions, gives response-contract failures bounded reason codes, and stops further Jev calls for the run after the first billable malformed response. It also reconciles a successful, verified, URL-changing action with a later successful read of that exact resulting page. Submit, send, publish, payment, and site-workflow completion contracts keep their existing evidence requirements.

Chrome and Firefox implementations, regression tests, architecture, privacy, security, and the Jev test guide are updated together. No live or paid Jev calls were made.

Validation:

• npm run test:systemone — 26/26 pass
• npm run test:systemone:fast — 30/30 unit tests, 20 cumulative real-browser assertions, and 3/3 workflow fixtures pass
• npm run test:security — 60/60 pass
• selection-scope restoration and offline relevance checks pass
• test/run.js — 2,393 pass; its only two failures are existing release artifacts: the changelog remains at 36.7.0 while the package is 36.7.4, and dist/webbrain-chrome-36.7.4.zip is absent

[vercel]

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Project	Deployment	Actions	Updated
webbrain	Ready	Preview	Sep 19, 2026 6:01pm UTC