Browser pane prepends https:// to file:// URLs, breaking local file navigation

[addisonlynch]

Summary

When I navigate the cmux browser pane to a file:// URL (e.g. by clicking a link in a terminal pane, or pasting into the address bar), cmux strips the file:// scheme and prepends https:// instead. The browser then tries to resolve the path's first segment as a hostname, which fails.

Repro

1. In a terminal pane, output a file:// URL such as file:///Users/me/some-file.html (e.g. an Open it at file:///… message from a tool).
2. Click the URL, or copy it and paste into the browser pane's address bar.

Expected

Browser loads the local file at /Users/me/some-file.html.

Actual

Address bar shows https://Users/me/some-file.html (or, in my case, https://raw/pipeline/observability-diagrams/exec-summary.html — the leading /Users/admin/berkshire-vault/ was also stripped along with the scheme).

Page shows: "Can't reach this page — https://… refused to connect. Check that a server is running on this address."

Why this matters

Local HTML previews are a common workflow — agents generate static HTML reports/dashboards into the workspace and the natural next step is to open them in the cmux browser pane. With this bug, the only workaround is to open them in an external browser, which loses the in-cmux workflow.

Environment

• cmux desktop app (recent build, May 2026)
• macOS (Darwin 24.1.0)