fix: separate historical session capacity audits from execution sizing

crates/fidc-core/src/execution_capacity.rs

@@ -12,6 +12,19 @@ pub enum VolumeCapacityMode {
     SessionCapacityAudit,
 }
 
+impl VolumeCapacityMode {
+    pub fn validate(self, enabled: bool, has_execution_observations: bool) -> Result<(), CapacityError> {
+        if !enabled { return Ok(()); }
+        match self {
+            Self::ExecutionObservation if !has_execution_observations => Err(CapacityError::MissingObservation),
+            Self::CompletedBar => Err(CapacityError::MissingCompletedBar),
+            _ => Ok(()),
+        }
+    }
+
+    pub fn limits_execution_quantity(self) -> bool { self != Self::SessionCapacityAudit }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Error)]
 pub enum CapacityError {
     #[error("execution capacity ratio must be finite and in (0, 1]")]
@@ -26,6 +39,28 @@ pub enum CapacityError {
     WrongSession,
     #[error("execution-time capacity is missing; daily session volume cannot size an earlier fill")]
     MissingObservation,
+    #[error("completed_bar capacity requires declared bar end and availability; an undated daily total is not a completed observation")]
+    MissingCompletedBar,
+}
+
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CapacityAuditSummary {
+    pub mode: VolumeCapacityMode,
+    pub enabled: bool,
+    pub participation_rate: f64,
+    pub audited_symbol_sessions: usize,
+    pub failed_symbol_sessions: usize,
+    pub audit_passed: Option<bool>,
+    pub execution_time_capacity_proven: bool,
+}
+
+impl CapacityAuditSummary {
+    pub fn observe(&mut self, audit: &SessionCapacityAudit) {
+        self.audited_symbol_sessions += 1;
+        self.failed_symbol_sessions += usize::from(!audit.passed);
+        self.audit_passed = Some(self.failed_symbol_sessions == 0);
+    }
 }
 
 /// Decimal semantics of the frozen JSON rate, evaluated without a float product.