Guard home tab selection against stale/invalid tab query params

[Copilot]

In some new-study/Firebase setups, the home page could render top tabs but no study cards. The root cause is a stale or invalid ?tab= value selecting a tab that is not currently available after visibility filtering.

• Root cause addressed

  • ConfigSwitcher previously trusted searchParams.get('tab') without validating it against tabs that actually exist for the current user/storage-mode visibility state.
  • When the requested tab had no corresponding rendered panel, the page appeared empty despite valid studies being present.

• Implementation

  • Added a small resolver to validate requested tab selection and fall back to the first available tab:
    • resolveHomeTab(requestedTab, availableTabs, fallbackTab)
  • Computed availableTabs from currently rendered tab groups (Others, Demos, Examples, Tutorials, Tests, Libraries).
  • Switched tab selection logic to use the resolver instead of raw query-param value.

• Regression coverage

  • Added focused unit tests for:
    • invalid tab → fallback tab
    • valid tab → preserved
    • null tab → fallback tab

export function resolveHomeTab(
  requestedTab: string | null,
  availableTabs: string[],
  fallbackTab: string,
) {
  if (requestedTab && availableTabs.includes(requestedTab)) {
    return requestedTab;
  }
  return fallbackTab;
}

• • 

Original prompt

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This section details on the original issue you should resolve

<issue_title>New study creation can trigger missing studies bug</issue_title>
<issue_description>Describe the bug

When creating a new study repo clone and setting up Firebase, sometimes the user will encounter the study homepage with the tabs at the top, but with no studies shown underneath.

To Reproduce
Steps to reproduce the behavior:

Fork repo, add new study, push, link up firebase. (I think this is mostly what leads to it)

Expected behavior
The studies should show. Maybe has to do with config hashing?

Work around
If you go to a known url like /demo-html/ it will load the study. Then when you go to the homepage it will work again and show all the studies that are available in the deployment.

<agent_instructions>Please provide some clarity as to what the issue is here. Could it be to do with the currentParticipant parameter or something else from localstorage?</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes New study creation can trigger missing studies bug #1103

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