fix(openapi): declare the mirror replay 200 of a medication create

A mirror create re-posting a pair the caller already holds has always
answered the existing medication with 200, as the description says; only
the 201 was declared.

docs/api/openapi.yaml

@@ -6585,6 +6585,13 @@ paths:
             schema:
               $ref: "#/components/schemas/CreateMedicationRequest"
       responses:
+        "200":
+          description: "A mirror create re-posting an `(externalSource, externalId)` pair the caller already holds: the existing
+            medication, nothing written."
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/CreateMedicationResponse"
         "201":
           description: Created medication with its schedules.
           content:

src/lib/openapi/routes/medications/paths.ts

@@ -255,6 +255,13 @@ const medicationIntakeImportJobStatusEnvelope = dataEnvelope(
   "MedicationIntakeImportJobStatusEnvelope",
 );
 
+// Shared by the create's 201 and its mirror-replay 200: the envelope id is
+// registered once.
+const createMedicationResponse = dataEnvelope(
+  medicationDetailEntry,
+  "CreateMedicationResponse",
+);
+
 export const medicationPaths: NonNullable<ZodOpenApiObject["paths"]> = {
   "/api/medications/intake": {
     get: {
@@ -969,12 +976,14 @@ export const medicationPaths: NonNullable<ZodOpenApiObject["paths"]> = {
         "201": {
           description: "Created medication with its schedules.",
           content: {
-            "application/json": {
-              schema: dataEnvelope(
-                medicationDetailEntry,
-                "CreateMedicationResponse",
-              ),
-            },
+            "application/json": { schema: createMedicationResponse },
+          },
+        },
+        "200": {
+          description:
+            "A mirror create re-posting an `(externalSource, externalId)` pair the caller already holds: the existing medication, nothing written.",
+          content: {
+            "application/json": { schema: createMedicationResponse },
           },
         },
         ...stdResponses,