Problem

Coder workspace apps with long hostnames were failing silently due to DNS hostname segment length limitations (63 characters per RFC 1035). When the combined length of app name + agent name + workspace name + username exceeded the DNS limit in any segment, apps would return empty responses without any user-visible indication of the problem.

The hostname format is: {APP_SLUG}--{AGENT_NAME}--{WORKSPACE_NAME}--{USERNAME}

Solution

This PR adds hostname length validation during the workspace app conversion process and marks apps as "unhealthy" when they exceed DNS limits, replacing silent failures with clear visual feedback and educational tooltips.

Key Changes

1. Added hostname validation function (validateAppHostnameLength) that checks each hostname segment against the 63-character DNS limit
2. Modified app health logic in the Apps() conversion function to set health to unhealthy when hostname segments are too long
3. Enhanced frontend tooltips to educate users about hostname length issues with actionable guidance
4. Only affects subdomain apps - path-based apps remain unaffected since they don't use hostname-based routing

User Experience Enhancement

Before this fix, users would see apps marked as "unhealthy" with no explanation. Now they receive clear, educational tooltips:

• Generic unhealthy apps: "Unhealthy" (unchanged behavior)
• Hostname length issues: "App name too long for DNS hostname. Please use a shorter app name, workspace name, or username."

Example Behavior

// Before: App fails silently with empty response
app := WorkspaceApp{
    Slug: "very-long-application-name-that-exceeds-dns-limits-and-causes-failures",
    Subdomain: true,
    Health: "healthy", // Misleading - app actually doesn't work
}

// After: App shows clear unhealthy status with educational tooltip
app := WorkspaceApp{
    Slug: "very-long-application-name-that-exceeds-dns-limits-and-causes-failures", 
    Subdomain: true,
    Health: "unhealthy", // Clear indication with helpful tooltip explaining the issue
}

Testing

• Added comprehensive test coverage for edge cases and various hostname lengths
• Added Storybook story demonstrating the enhanced tooltip behavior
• Verified existing functionality remains unchanged
• Manual testing confirms unhealthy apps are properly marked while valid apps remain healthy

Users will now see workspace apps with hostname length issues marked as "unhealthy" in the UI with clear guidance on how to resolve the problem, instead of experiencing silent failures.

Fixes #15178.

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