#2478 chore: restore v4 generated artifact checks

Summary

• replace the remaining z.object(...).strict() protocol schemas with the equivalent z.strictObject(...) form
• regenerate the Go protocol models to remove an unreachable generated catalog field
• refresh the deterministic Stagehand extension archive embedded by the Go SDK

These files drifted out of sync while the v4 SDK stack landed, causing unrelated pull requests against v4-spike to fail the TypeScript, Python build, and Go generation checks.

E2E Test Matrix

Command / flow	Observed output	Confidence / sufficiency
corepack pnpm build && git diff --exit-code -- packages/protocol/stagehand.v4.json && corepack pnpm check && corepack pnpm exec vitest run	Builds and checks passed; generated protocol JSON remained unchanged; 119 test files passed, 1 skipped, with 1,093 tests passed.	Covers the complete TypeScript CI path that previously rejected the noncanonical strict schemas.
uv --directory packages/sdk-python run --locked python scripts/generate.py --check plus Ruff, ty, and pytest	Generation, formatting, lint, and type checks passed; 196 tests passed.	Confirms the protocol cleanup does not make the generated Python SDK stale or invalid.
Build the Python wheel, install it into an isolated environment, and run packages/sdk-python/scripts/smoke.py with local Chrome	The installed wheel initialized Stagehand, navigated a real headless Chrome page, verified its title, and closed cleanly.	Exercises the packaged extension through a real browser, beyond static generation checks.
Go generation check, gofmt, vet, example compilation, package tests with local Chrome, generator tests, and build	All commands passed; the Stagehand package and extension packages passed their test suites.	Covers the complete Go CI path and proves the regenerated model and embedded extension compile and run together.
Rebuild the server extension and rerun go generate ./... twice	The generated Go model and embedded extension SHA-256 hashes were identical across runs, with no additional diff.	Confirms the checked-in binary artifact is deterministic rather than a one-off local build.

Tracking

STG-2724

---

Summary by cubic

Restores v4-spike generated artifacts and strict schemas to bring CI back to green. Addresses STG-2724 by syncing TypeScript, Python, and Go SDK outputs and making the embedded Stagehand extension deterministic.

• Refactors
  • Replace remaining z.object(...).strict() with z.strictObject(...) in packages/protocol/schemas.ts.
  • Regenerate Go protocol models to drop unreachable __schema8 from generatedModelCatalog.
  • Refresh the embedded Stagehand extension archive at packages/sdk-go/internal/extensionassets/stagehand-extension.zip to the deterministic build.