When extra.base_url is set in the Telegram platform config, use it as
the base URL for all Telegram API requests instead of api.telegram.org.
This allows agents to route Telegram traffic through the credential
proxy, which injects the real bot token — the VM never sees it.
Also supports extra.base_file_url for file downloads (defaults to
base_url if not set separately).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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