cable-sizing: return 400 instead of 500 for an unknown context circuitId/projectId

context.circuitId/projectId are caller-supplied audit-log metadata, not
used in the calculation itself. A stale or unknown id (e.g. a circuit
deleted between page load and this request) violated the foreign key
and fell through to the generic 500 handler; catch it and report it as
a normal validation error instead.

src/server/controllers/cable-sizing.controller.ts

@@ -26,15 +26,34 @@ export async function calculateCableSizingHandler(req: Request, res: Response) {
   const result = calculateCableSizing(input);
   const alerts = buildCableSizingAlerts(input, result);
 
-  const entry = await cableSizingCalculationRepository.create({
-    id: randomUUID(),
-    projectId: context?.projectId ?? null,
-    circuitId: context?.circuitId ?? null,
-    equipmentIdentifier: context?.equipmentIdentifier ?? null,
-    input,
-    result,
-    appliedToCircuit: 0,
-  });
+  let entry;
+  try {
+    entry = await cableSizingCalculationRepository.create({
+      id: randomUUID(),
+      projectId: context?.projectId ?? null,
+      circuitId: context?.circuitId ?? null,
+      equipmentIdentifier: context?.equipmentIdentifier ?? null,
+      input,
+      result,
+      appliedToCircuit: 0,
+    });
+  } catch (error) {
+    // context.circuitId/projectId are caller-supplied and only used for the
+    // audit-log entry, not the calculation itself - a stale or unknown id
+    // (e.g. a circuit deleted between page load and this request) should be
+    // a normal 400, not a raw 500 from the foreign-key constraint.
+    if (
+      error &&
+      typeof error === "object" &&
+      "code" in error &&
+      (error as { code?: string }).code === "SQLITE_CONSTRAINT_FOREIGNKEY"
+    ) {
+      return res
+        .status(400)
+        .json({ error: "Unknown context.projectId or context.circuitId" });
+    }
+    throw error;
+  }
 
   return res.status(201).json({ calculationId: entry.id, result, alerts });
 }