Auto derived format

src/data_value.rs

@@ -33,6 +33,14 @@ pub struct ParamDeclaration {
     /// regex/JSON-field extraction.
     #[serde(default)]
     pub elapsed_since_last: bool,
+    /// Set when this param was discovered by `crate::engine::auto_declare_params` (a nom-based
+    /// `key=value` scan run on every ingested line) rather than declared through `POST /api/params`.
+    /// `declare_param` refuses to overwrite an auto-derived param by name, and it's never persisted
+    /// to a profile — see `crate::engine::declare_param` and `crate::api::reload_engine_declarations`.
+    /// `#[serde(default)]` so profiles/requests saved before this field existed still load as
+    /// ordinary (non-auto) params.
+    #[serde(default)]
+    pub auto_derived: bool,
 }
 
 /// Reads a value out of a JSON object by dot-separated field path (e.g. `"foo.bar"`), for