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## 1.55.0

**`(feat):`** Add opt-in `allowUserAgentAppInfo` config. When enabled, generated clients expose an
`option.WithUserAgentAppInfo(name, version, comment string)` client option whose sanitized
product token is appended to whatever `User-Agent` the SDK would otherwise send
(`{sdk}/{version} ... {product}/{product-version} ({comment})`), following RFC 9110.
Disabled by default, so existing generated output is byte-identical, and it composes with
`includePlatformHeaders`, the configured `user-agent` template value, and the default
`{package}/{version}` value. Caller-supplied values are trimmed before the blank check and
before encoding (blank name/version/comment are dropped rather than encoded into whitespace
tokens), then name/version are percent-encoded to RFC 7230 `tchar` and comment delimiters
`(`, `)`, `\` and control characters (incl. CR/LF) are escaped, so untrusted values cannot
inject header content. Still overridable by an explicit `User-Agent` header and suppressed
by `omitFernHeaders`. The `AppInfo` type, the `AppInfoOption`, and the emitted
`appendAppInfoToUserAgent` helper are only generated when the flag is on, so the shared
core-utilities are never modified. No IR change.