harness-tools/docs/fast-browser-prototype-plan.md

Fast Browser prototype

Historical first-slice plan. The unattended-session plan supersedes its approval, credential and configuration requirements.

Branch: feat/fast-browser. Package/extension directory: extensions/fast-browser. User-approved scope: bounded local-browser Pi extension, same-host Chrome, JEV decisions, literal filling and optional small-model text generation. See browser-use-jev-feasibility.md for research.

Status: first slice implemented and offline-validated. See validation results and remaining live-test work.

First slice

• Typed observe, act, and close bridge operations; no arbitrary model-generated Python/JS/CDP.
• Explicit loopback Chrome endpoint, dedicated test profile recommended. Do not auto-open or connect to a user's default browser.
• Extract actionable candidates with stable observation IDs and tab/frame/document identity. Revalidate before action and reject stale/changed targets.
• A supplied sequence of bounded click/fill steps, rather than an unconstrained autonomous agent. JEV picks a candidate or abstains. Literal text bypasses generation; composition uses the configured Pi auxiliary model.
• Every live mutation requires a Pi UI confirmation of the exact action/payload. Noninteractive sessions fail closed. Offline controller tests inject approval. We will not silently trade away approval overhead for speed.
• TypeScript controller owns step/time budgets, cancellation, strict JEV response validation, approval, postconditions and compact timings. No blind action retries.
• Browser-harness runs through a restricted Python worker. No cloud APIs, telemetry, update checks, recording, profile sync, arbitrary network fetch or raw execution tools exposed.
• Companion skill and README describe experimental limits and setup. No automatic global installation/config edits.

Validation

Offline TypeScript tests with fake browser/JEV/text adapters, Python bridge tests without Chrome, package checks and typecheck. Local live smoke tests only after explicit safe endpoint/test fixture setup; live inference only with approved use of credentials. Record actual failures encountered in docs/todos.md when not fixed immediately.

Deferred

General autonomous planning, screenshot/vision fallback, automatic site-specific helper writing, DOM-independent actions, remote browser hosts, multi-browser concurrency, uploads/downloads, submission/Enter shortcuts, implicit bulk approval, and any efficacy claim without benchmarks.