Two independent defects broke /mcp reauth against S256-only providers on
Windows boxes whose PATH no longer references System32:
1. openPath spawned bare rundll32 and swallowed the
`Executable not found in $PATH` throw with a bare `catch {}`, so the MCP
controller's outer try/catch was dead and the transcript unconditionally
claimed "Opening browser automatically...".
2. TUI#prepareLine silently truncates any composed row wider than the
viewport. MCPAuthorizationLinkPrompt rendered `Copy URL: <full URL>` as a
single ~271-column line whose trailing parameter is
code_challenge_method=S256. On the reporter's 270-col terminal the cut
landed inside that parameter, dropping the method while keeping
code_challenge — which RFC 7636 §4.3 treats as plain PKCE, which Linear
correctly rejects with "The plain PKCE method is not allowed. Use S256
instead."
OAuthCallbackFlow now hosts a `GET /launch` route on the same loopback
callback server it already runs; the route 302-redirects to the pending
authorization URL and is advertised as `OAuthAuthInfo.launchUrl` — a
~30-char copy target no viewport can meaningfully truncate. The MCP OAuth
fallback, /login, setup wizard, auth-broker CLI, and login-dialog all
prefer the launch URL for the visible copy target, keep the full URL in
the OSC 8 hyperlink for click-through, and the MCP flow additionally
stages the copy target on the clipboard via OSC 52 (same pattern the
setup wizard uses).
openPath now resolves rundll32.exe through %SystemRoot%\System32 (with a
C:\Windows fallback when SystemRoot is unset) and logs both synchronous
spawn throws and non-zero exits via the shared logger, so silent
misconfigurations show up in ~/.omp/logs/omp.*.log. The dead try/catch
around openPath in the MCP controller is removed.
Fixes#4418
roboomp
97c1d08cce