Core: Handle BROWSER=none correctly and improve error messages

[jonathan-fulton]

Description

Fixes #24191

When the BROWSER environment variable is set to none, Storybook should not attempt to open a browser. This fix ensures the behavior is correct and improves error messages.

Changes

1. Properly handle openBrowser() return value: When openBrowser() returns false (indicating BROWSER=none was set intentionally), we now skip the fallback open() call entirely.

2. Improved error messages: When browser opening fails, the error message now includes the current BROWSER environment variable value if set, helping users diagnose issues like typos or invalid values.

Before this fix

Even when openBrowser() returned false for BROWSER=none, the code might still attempt the fallback browser opening with the open package.

After this fix

# This now works correctly - no browser opens, no error
BROWSER=none npx storybook dev

# Invalid values now show helpful error messages
BROWSER=invalid npx storybook dev
# Error: Could not open http://localhost:6006 inside a browser...
# Note: BROWSER environment variable is set to "invalid". 
# To disable browser opening, use BROWSER=none or the --ci flag.

Testing

• Tested with BROWSER=none - no browser opens, no error
• Tested with invalid BROWSER values - error message includes the value

Summary by CodeRabbit

• Bug Fixes
  • Improved error handling and messaging when browser fails to open.
  • Added support for BROWSER=none and --ci environment flags to prevent automatic browser opening.
  • Enhanced error messages with helpful guidance on controlling browser behavior.
  • Refined browser opening logic for more reliable execution.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR modifies the browser opening utility to handle cases where browser launching is explicitly disabled (BROWSER=none), adding an early return when the browser cannot open. It also corrects a variable name typo and improves error messages with environment variable guidance.

Changes

Cohort / File(s)	Summary
Browser Opening Logic code/core/src/core-server/utils/open-browser/open-in-browser.ts	Captures openBrowser result in new variable, adds early return when openBrowserResult is false, fixes typo (errorOccured→errorOccurred), enriches error messages with BROWSER environment hints (BROWSER=none or --ci).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• Dev: Improve the browser opening experience #32488: Introduced the boolean return type from openBrowser() API that this PR now checks and handles in the call site.
• Upgrade: Packages open #32484: Also modifies the same open-in-browser.ts file and openInBrowser behavior with browser-opening logic and error handling.
• Core: Honor BROWSER shell scripts before xdg-open #33292: Updates openBrowser's implementation in opener.ts to honor BROWSER environment scripts and throw BrowserEnvError, complementing this PR's error messaging improvements.

✨ Finishing touches

• 📝 Generate docstrings

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