feat(schema): allow template variables in transport URL field

[tadasant]

Authored by Claude Code Opus 4.5, steered/reviewed by me.

Summary

• Updated the URL regex pattern in StreamableHttpTransport and SseTransport to allow template variables like {baseUrl} as an alternative to requiring the https:// prefix
• This enables more flexible URL configuration in the remotes section of server.json

Changes

• Modified the url field pattern from ^https?://[^\s]+$ to ^(https?://[^\s]+|\{[a-zA-Z_][a-zA-Z0-9_]*\}[^\s]*)$
• Updated both openapi.yaml and the derived server.schema.json
• Added clarifying documentation that URL must start with http://, https://, or a template variable

Regex breakdown

^(https?://[^\s]+|\{[a-zA-Z_][a-zA-Z0-9_]*\}[^\s]*)$

Part	Meaning
^	Start of string
(	Begin alternation group
https?://[^\s]+	http:// or https:// followed by non-whitespace
|	OR
\{[a-zA-Z_][a-zA-Z0-9_]*\}	Template variable: { + valid identifier + }
[^\s]*	Optional path/query after template variable
)	End alternation group
$	End of string

Test cases

Should match ✓

• https://api.example.com/mcp
• http://localhost:8080/sse
• https://example.com/path?query=value
• {baseUrl}
• {baseUrl}/mcp
• {server_url}/api/v1
• {API_ENDPOINT}

Should NOT match ✗

• ftp://example.com — wrong protocol
• example.com — missing protocol or variable
• /relative/path — relative paths not allowed
• {invalid-name}/path — hyphens not valid in variable names
• {123invalid} — variables can't start with numbers

[tadasant]

cc @BobDickinson

[BobDickinson]

I like it