Validate scroll deltas and live-screen input on the Bot computer

[Ayush7614]

What this changes

Two related holes on the Bot computer, both the same bug class already fixed for navigate URLs and exec timeouts (400 naming the field, not a 502 reading as a broken computer):

1. Scroll deltas: /scroll, /human/scroll (and the internal fallbacks) accepted any typeof === number. Infinity (valid JSON: 1e999) travelled into mouse.wheel and came back as a 502. New parseScrollDelta (mirroring parseExecTimeout) requires a finite number; absent still means the endpoint default (600 Bot / 400 human). Edge returns 400 with the same message the server gateway uses; the performers also refuse defensively.
2. Live-screen socket: any JSON object passed the cast and fell through to Input.insertText({ text: undefined }), or forwarded wrong-typed x/y/key/code into CDP. New parseInputMessage discriminates mouse/wheel/key/text, requires events, finite coordinates/deltas, and non-empty key/code/text; malformed frames get an error reply and never reach CDP.

Where it runs

The computer process holding one Bot browser. No shared state: each computer validates its own requests.

• New state that outlives a request? None. Per-request validation.
• What happens on the second replica? Same 400/error on every computer: pure function of the request/frame. No cross-computer coordination.
• Anything serialised? No.
• Anything fanned out to a browser? Validation happens before Playwright/CDP calls, on the computer that owns that browser.
• New listener, port, or schedule? No.

Postgres is already there and is the default answer to all of the above: nothing here needs it.

Boundary and audit

• Every acting call still goes through the gateway: resolve, decide, audit, then act. The computer holds no policy engine; this checks well-formedness only, same as the existing navigate/timeout checks.
• New refusals and new failures each write a row. N/A on this process: 400s here are caller errors answered at the edge, matching the existing navigate/timeout behaviour; gateway audit ordering is untouched.
• Nothing new is trusted from the client that the server can resolve itself. Stricter: fewer shapes reach Playwright/CDP.

Changelog

• A line in CHANGELOG.md under Unreleased: scroll/input validation entry.

Proof

• bun test agent-computer/tests/request-validation.test.ts: 44 pass (scroll absent/finite/infinite/string/null/boolean/object; mouse/wheel/key/text well-formed and malformed cases).
• bun run format:check: clean. bun run lint: clean.
• Server/worker typecheck pass; app has the pre-existing embla-carousel-react failure identical on clean upstream main.

[davidmckayv]

Deep-reviewed clean (validation, no secret leak, fail-closed, agrees with existing layers). CI green.