fix(core): parse screenshot MIME in GoogleCUAClient function responses

[yawbtng]

why

Closes #2046. GoogleCUAClient builds function-response image parts with inlineData.mimeType = "image/png" and strips the data URL prefix using a PNG-only regex. If a screenshot is JPEG/WebP (or anything non-PNG), the metadata is wrong and the regex no-ops — the whole data URL ends up as the payload.

what changed

• Added parseImageDataUrl(input) helper that extracts { mimeType, data } from an image/<type> data URL, falling back to image/png + the raw input for unrecognized formats (preserves prior behavior).
• Replaced the hardcoded PNG strip + hardcoded mimeType at the function-response call site with the helper's parsed values.
• No change to captureScreenshot() — it still normalizes raw provider input to PNG data URLs, matching the issue's stated current contract.

test plan

New packages/core/tests/unit/google-cua-client.test.ts covering:

• PNG data URL → image/png + base64 payload
• JPEG data URL → image/jpeg + base64 payload
• WebP data URL → image/webp + base64 payload
• Raw base64 → fallback to image/png with the input as data
• Non-image data URL (e.g. text/plain) → fallback to image/png

Also ran pnpm run typecheck and pnpm run eslint in packages/core — both clean.

---

Summary by cubic

Fixes screenshot MIME parsing in GoogleCUAClient function responses by deriving the type and base64 payload from image data URLs, including newline-wrapped payloads. Addresses Linear issue #2046 and ensures JPEG/WebP screenshots set the correct inlineData.mimeType, with a PNG fallback for raw inputs.

• Bug Fixes
  • Added parseImageDataUrl(input) to extract { mimeType, data } from data:image/*;base64,..., handling newline-wrapped base64.
  • Replaced PNG-only strip and hardcoded mimeType with parsed values.
  • Added unit tests for PNG, JPEG, WebP, newline-wrapped data, raw base64, and non-image data URLs.

^{Written for commit 246ef50. Summary will update on new commits. Review in cubic}

[changeset-bot]

🦋 Changeset detected

Latest commit: 246ef50

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/browse-cli	Patch
@browserbasehq/stagehand-evals	Patch
@browserbasehq/stagehand-server-v3	Patch

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[github-actions]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle newline-wrapped base64 data URLs

The new parser regex uses (.*) for the payload, but . does not match newlines in JavaScript regexes, so valid data:image/...;base64,... strings that contain line breaks will fail to match and fall back to returning the entire data URL as inlineData.data. In that case Google receives data:image/...;base64,... instead of raw base64 bytes, which can break function-response image decoding. This is a regression from the previous replace(/^data:image\/png;base64,/, "") behavior, which stripped the prefix regardless of payload newlines.

Useful? React with 👍 / 👎.

[yawbtng]

Good catch — fixed in 246ef50. Switched (.*) to ([\s\S]*) so the payload group captures newline-wrapped (MIME-style) base64, and added a regression test (parses a PNG data URL with newline-wrapped base64 (MIME-style)) so this can't drift back. The new behavior is now a strict superset of the previous replace(/^data:image\/png;base64,/, "") — wrapped payloads, JPEG/WebP, raw base64, and unrecognized URLs all handled. 6/6 tests pass locally.

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}