Handle no-object act inference failures

[monadoid]

Why

• A customer reported stagehand.act surfacing an HTTP error after Gemini returned a schema-invalid action object with an empty elementId.
• The AI SDK correctly raises NoObjectGeneratedError, but that previously bypassed ActHandler's existing No action found result path.

What changed

• Catch AI SDK NoObjectGeneratedError at the ActHandler inference boundary using NoObjectGeneratedError.isInstance(error).
• Convert only that structured-output failure into the existing success: false result, while rethrowing other LLM/provider errors.

// before
const response = await actInference(...);

// after
try {
  response = await actInference(...);
} catch (error) {
  if (NoObjectGeneratedError.isInstance(error)) return {};
  throw error;
}

Testing

• Added a regression test for NoObjectGeneratedError returning Failed to perform act: No action found.
• Added a guard test that ordinary LLM errors still reject.
• Ran pnpm --filter @browserbasehq/stagehand run test:core -- packages/core/dist/esm/tests/unit/timeout-handlers.test.js and pnpm --filter @browserbasehq/stagehand run typecheck.

---

Summary by cubic

Prevents HTTP errors when act inference returns no schema-valid action. ActHandler now maps NoObjectGeneratedError to the existing “No action found” result and rethrows other provider errors.

• Bug Fixes
  • Catch NoObjectGeneratedError at the ActHandler boundary, log it, and return the “No action found” path instead of surfacing an HTTP error.
  • Added tests and a changeset to ship a patch for @browserbasehq/stagehand; non-structured-output errors still reject.

^{Written for commit 91de32e. Summary will update on new commits. Review in cubic}

[changeset-bot]

🦋 Changeset detected

Latest commit: 91de32e

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

This PR includes changesets to release 4 packages

Name	Type
@browserbasehq/stagehand	Patch
@browserbasehq/stagehand-evals	Patch
@browserbasehq/stagehand-server-v3	Patch
@browserbasehq/stagehand-server-v4	Patch

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