mint dev: empty navbar/sidebar when selected version differs from the first version block containing the current page

[seb86]

Environment

• mint CLI 4.2.696 (also reproduces after downgrading the CLI to 4.2.667 — the locally downloaded preview client in ~/.mintlify appears to be what regressed, not the CLI package; cache cleared and re-downloaded 2026-07-15)
• Windows 11 Pro, Node 24.18.0
• Local preview only — the identical navigation pattern works correctly on our hosted site (docs.cocartapi.com, config with 138 pages shared between two versions; version switching works fine there)

Summary
When docs.json uses navigation.versions and the same page path is listed in more than one version's navigation, mint dev renders that page with an empty navbar (no tabs) and an empty sidebar whenever the active version is not the first version block in the array that contains the page. Page content, search, banner, and the "On this page" TOC all render normally — only navigation disappears.

Minimal reproduction (4 files)

docs.json:

{
  "$schema": "https://mintlify.com/docs.json",
  "theme": "mint",
  "name": "Version Repro",
  "colors": { "primary": "#6a42d7" },
  "navigation": {
    "versions": [
      {
        "version": "v1",
        "default": true,
        "groups": [{ "group": "Guides", "pages": ["shared", "v1-only"] }]
      },
      {
        "version": "v2",
        "groups": [{ "group": "Guides", "pages": ["shared", "v2-only"] }]
      }
    ]
  }
}

Plus three trivial MDX pages: shared.mdx, v1-only.mdx, v2-only.mdx (frontmatter title/description only).

Steps

1. mint dev
2. Open /shared — renders correctly with full sidebar (v1 is first/default).
3. Use the version dropdown to switch to v2 while on /shared.

Expected: sidebar shows v2's navigation (shared, v2-only).
Actual: the tab row disappears and the sidebar is empty except the version switcher. Navigating to /v2-only directly renders fine, and switching versions from there works — the failure occurs only on pages listed in multiple version blocks.

Additional observations

• The failing side flips with array order: if the shared page's first containing version is not the active one, nav dies. With v2 listed first, /shared breaks on v1 instead.
• Real-world impact: our docs share ~170 general guide pages between a "community" and a "latest" version; every shared page rendered with no navigation until we reordered the version blocks, and the non-first version still breaks on shared pages when selected explicitly.
• The same configuration renders and version-switches correctly on Mintlify hosting, so this looks like a regression scoped to the local preview client bundle.