Merge ticket/015-json-field-param-metric-declaration

Resolves conflicts with ticket 018 (boolean param kind) in
src/engine.rs, webapp/src/lib/api.ts, and Params.tsx: boolean-kind
params and JSON-field-path extraction now coexist as independent
extraction modes alongside regex capture groups.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

src/profile.rs

@@ -64,6 +64,10 @@ pub struct ParamDeclarationRecord {
     pub name: String,
     pub message_match_regex: String,
     pub capture_group: String,
+    /// See `crate::data_value::RegexToMetricPrimitiveMatcher::json_field_path`; `#[serde(default)]`
+    /// so profiles saved before this field existed still load as plain regex-capture-group params.
+    #[serde(default)]
+    pub json_field_path: Option<String>,
     pub kind: ProfileMetricPrimitiveKind,
 }
 
@@ -73,6 +77,7 @@ impl From<&DeclareParamRequest> for ParamDeclarationRecord {
             name: request.name.clone(),
             message_match_regex: request.message_match_regex.clone(),
             capture_group: request.capture_group.clone(),
+            json_field_path: request.json_field_path.clone(),
             kind: request.kind.into(),
         }
     }
@@ -84,6 +89,7 @@ impl From<&ParamDeclarationRecord> for DeclareParamRequest {
             name: record.name.clone(),
             message_match_regex: record.message_match_regex.clone(),
             capture_group: record.capture_group.clone(),
+            json_field_path: record.json_field_path.clone(),
             kind: record.kind.into(),
         }
     }
@@ -94,6 +100,10 @@ impl From<&ParamDeclarationRecord> for DeclareParamRequest {
 pub struct MetricParamRecord {
     pub param_name: String,
     pub capture_group: String,
+    /// See `crate::data_value::RegexToMetricPrimitiveMatcher::json_field_path`; `#[serde(default)]`
+    /// so profiles saved before this field existed still load as plain regex-capture-group matchers.
+    #[serde(default)]
+    pub json_field_path: Option<String>,
     pub kind: ProfileMetricPrimitiveKind,
     /// See `ParamRole`; `#[serde(default)]` so profiles saved before this field existed still load, defaulting to `Label`.
     #[serde(default)]
@@ -125,6 +135,7 @@ impl From<&DeclareMetricRequest> for MetricDeclarationRecord {
                 .map(|matcher| MetricParamRecord {
                     param_name: matcher.param_name.clone(),
                     capture_group: matcher.capture_group.clone(),
+                    json_field_path: matcher.json_field_path.clone(),
                     kind: matcher.kind.into(),
                     role: matcher.role,
                 })
@@ -148,6 +159,7 @@ impl From<&MetricDeclarationRecord> for DeclareMetricRequest {
                 .map(|param| RegexToMetricPrimitiveMatcher {
                     param_name: param.param_name.clone(),
                     capture_group: param.capture_group.clone(),
+                    json_field_path: param.json_field_path.clone(),
                     kind: param.kind.into(),
                     role: param.role,
                 })
@@ -630,6 +642,7 @@ mod tests {
             name: name.to_string(),
             message_match_regex: pattern.to_string(),
             capture_group: capture_group.to_string(),
+            json_field_path: None,
             kind: MetricPrimitiveKind::String,
         }
     }
@@ -643,6 +656,7 @@ mod tests {
             params: vec![RegexToMetricPrimitiveMatcher {
                 param_name: param_name.to_string(),
                 capture_group: capture_group.to_string(),
+                json_field_path: None,
                 kind: MetricPrimitiveKind::Number,
                 role: ParamRole::Label,
             }],