feat: support deterministic actions without a model

[shrey150]

Summary

• allow structured Stagehand.act(Action) values to execute deterministically without configuring a model
• preserve the model requirement for natural-language instructions
• route CLI selector click and fill through the typed Action path and surface unsuccessful action results as command failures
• keep select, upload, highlight, coordinates, and capability-gap behavior inherited unchanged from the parent runtime PR

Refreshed on 2026-08-10 against the current parent and v4-spike commit d7556e9a.

Contract

Surface	Result
Structured Stagehand.act(Action) without a model	Executes once without inference or model-backed self-healing
Natural-language Stagehand.act("instruction") without a model	Continues to return the missing-model error
CLI click and fill syntax/results	Unchanged; implementation uses structured Actions
Other CLI page commands	Unchanged from the parent PR

Release boundary

The already-published Stagehand 4.0.0 does not contain this PR's extension change. A clean registry-backed install therefore supports open/snapshot/status but rejects model-free click/fill with the pre-fix missing-model error. This PR includes patch changesets for @browserbasehq/stagehand, @browserbasehq/stagehand-extension, @browserbasehq/stagehand-go, and browse, so release automation versions every embedded runtime and publishes the Stagehand patch before or alongside the Browse patch. Keeping workspace:* preserves that ordering; pinning Browse to 4.0.0 would ship an incompatible pair.

E2E Test Matrix

Command / flow	Observed output	Confidence / sufficiency
2026-08-10 cumulative stack refresh on Chrome Stable 151	pnpm build passed 6/6 tasks; pnpm check passed 11/11 tasks with 0 errors; the full pnpm test graph exited 0, including 17/17 protocol browser tests and 15/15 local SDK browser tests	Proves the updated six-PR stack is compatible with v4-spike d7556e9a across build, static checks, unit tests, and real-browser suites.
Clean coordinated-release tarball consumer at the cumulative tip	Packed workspace Stagehand and Browse, installed both into an empty npm project, opened example.com, produced a snapshot, clicked through to IANA, filled an injected input, and read back published-v4-ok	Proves the intended co-published artifacts work outside the monorepo with a real Chrome session; it does not substitute for a credentialed Browserbase smoke.
Clean packed Browse against registry Stagehand 4.0.0	Install, open, snapshot, and status passed; model-free click returned the pre-fix An LLM was not configured error	Confirms the cross-package patch and coordinated release are required rather than optional.
corepack pnpm exec vitest run packages/extension/tests/act.test.ts	1 file passed; 13/13 tests passed	Covers model-free Action execution, no-inference behavior, disabled self-healing without a model, and natural-language rejection.
corepack pnpm --filter browse test:unit	25 files passed; 380/380 tests passed	Covers CLI Action construction, selected-page routing, successful results, failure propagation, and the refreshed parent contract.
Real managed-local synthetic form → fill and click without model configuration	Filled hello-v4-final; click set document.body.dataset.clicked to yes	Proves the real bundled extension executes typed Actions without an LLM in Chrome Stable 151.
Extension archive drift check	Built artifact and Go embedded ZIP had the same SHA-256; go run ./internal/extensionpack --check passed	Proves the merged source and embedded Go asset are synchronized.
Go 1.26.5 tests with Chrome Stable 151	Root, extension asset, extension pack, and generator packages passed	Exercises the rebuilt extension through live Chrome in the Go SDK.
Remote Browserbase action rerun	Not run: no BROWSERBASE_API_KEY is available in this environment	Remaining live verification; GitHub CI is the next credentialed gate. Previous pre-refresh remote evidence is not counted for the new head.
Final repository gates	6/6 build tasks; 11/11 checks; 400 warnings and 0 errors	Proves the SDK, extension, CLI, and repository gates pass together.

Includes patch changesets for @browserbasehq/stagehand, @browserbasehq/stagehand-extension, @browserbasehq/stagehand-go, and browse because the existing typed Action contract now works without a model and the extension is embedded in both TypeScript and Go.

Final release validation (2026-08-10)

At the cumulative stack tip:

• release validation now recognizes public browse changesets
• a Changesets version dry run resolves browse 0.9.7, Stagehand 4.0.1, extension 1.0.1, and Go 4.0.1
• the packed Browse 0.9.7 manifest rewrites workspace:* to exact Stagehand 4.0.1
• a clean npm consumer installed those versioned tarballs and completed real-Chrome open, snapshot, model-free click, URL read, and stop with zero audit vulnerabilities

[changeset-bot]

🦋 Changeset detected

Latest commit: 9512209

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@browserbasehq/stagehand	Patch
browse	Patch

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[shrey150]

The CLI intent here is superseded by #2834, but the core Stagehand patch is intentionally not carried forward. Browse now executes deterministic click/fill operations through V4 locators directly, so those paths do not call act() and do not require a model. Closing this draft with no standalone core replacement.