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## 1.21.0

**`(feat):`** Add an opt-in `allowUserAgentAppInfo` config (default `false`). When enabled, the
generated client accepts an optional `app_info` keyword
(`{ name:, version:, comment: }`) whose product token is appended to the
`User-Agent` header for all three branches (the structured platform value, the
configured `user-agent` template value, and the default `{package}/{version}`),
producing e.g. `acme/0.0.1 partner-app/3.1.0 (+https://partner.example)` per
RFC 9110. Caller-supplied values are sanitized (name/version percent-encoded to
RFC 7230 tchars; comment delimiters and control characters escaped) and trimmed
before encoding, so untrusted values cannot inject additional header content. The
header is still overridable by an explicit `User-Agent` and suppressed by
`omitFernHeaders`. Default-off output is byte-identical.