Fix Python codegen so ReasoningSummary import is not shadowed

The 1.0.60 schema introduces OptionsUpdateReasoningSummary and
SessionOpenOptionsReasoningSummary, structurally identical to the shared
ReasoningSummary enum. quicktype's enum-merging path (independent of
combineClasses) collapsed them into a single locally-defined
`class ReasoningSummary(Enum)` that shadowed the import from
session_events at the top of rpc.py. ModelSwitchToRequest.to_dict()
then called `to_enum(ReasoningSummary, x)` against the local class
while session.py constructed values via the imported one, so the
isinstance check inside to_enum failed and the unit test
TestSessionConfigForwarding.test_set_model_sends_correct_rpc broke.

Add a small post-processing step that strips locally-emitted enum
classes whose name and value set exactly match a name imported from
.session_events. The existing aliases at the end of rpc.py
(OptionsUpdateReasoningSummary = ReasoningSummary etc.) now resolve to
the imported enum, restoring isinstance equality across the SDK.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

python/copilot/generated/rpc.py

@@ -1177,6 +1177,60 @@ function removeRequiredAnyDefaultsForPython(
     });
 }
 
+/**
+ * Remove locally-emitted Enum class definitions whose name already comes from
+ * a `.session_events` import.
+ *
+ * Quicktype's enum-merging path collapses structurally-identical enums (even
+ * with `combineClasses: false`, which only governs class merging). When the
+ * RPC schema gains sibling enums like `OptionsUpdateReasoningSummary` and
+ * `SessionOpenOptionsReasoningSummary` whose value set matches the shared
+ * `ReasoningSummary` enum, quicktype picks `ReasoningSummary` as the merged
+ * canonical name. That local class then shadows the import we add at the top
+ * of `rpc.py`, breaking `isinstance` checks against the canonical enum used
+ * elsewhere in the SDK.
+ *
+ * The fix: detect such shadowed enum definitions, verify the local values
+ * exactly match the imported enum's values in the session-events schema, and
+ * strip the local class so references resolve to the import.
+ */
+function removeShadowedSessionEventEnumsForPython(
+    code: string,
+    importedFromSessionEvents: Set<string>,
+    sessionEventsSchema: JSONSchema7 | undefined
+): string {
+    if (importedFromSessionEvents.size === 0 || !sessionEventsSchema) return code;
+    const seDefs = collectDefinitionCollections(sessionEventsSchema as Record<string, unknown>);
+    const enumBlockRe =
+        /(?:^|\n)class\s+(\w+)\s*\(Enum\):\s*\r?\n([\s\S]*?)(?=\nclass\s+\w|\n@dataclass\b|\ndef\s+\w|$)/g;
+    return code
+        .replace(enumBlockRe, (match: string, className: string, body: string) => {
+            if (!importedFromSessionEvents.has(className)) return match;
+            const seDef = seDefs.definitions[className] ?? seDefs.$defs[className];
+            const seResolved = seDef ? resolveSchema(seDef, seDefs) ?? seDef : undefined;
+            if (
+                !seResolved?.enum ||
+                !Array.isArray(seResolved.enum) ||
+                !seResolved.enum.every((value) => typeof value === "string")
+            ) {
+                return match;
+            }
+            const localValues = new Set<string>();
+            const valueRe = /^\s+\w+\s*=\s*"([^"]*)"/gm;
+            let vm: RegExpExecArray | null;
+            while ((vm = valueRe.exec(body)) !== null) {
+                localValues.add(vm[1]);
+            }
+            const seValues = new Set(seResolved.enum as string[]);
+            if (localValues.size !== seValues.size) return match;
+            for (const value of localValues) {
+                if (!seValues.has(value)) return match;
+            }
+            return "";
+        })
+        .replace(/\n{3,}/g, "\n\n");
+}
+
 function reorderPythonDataclassFields(code: string): string {
     const fieldRe =
         /^    \w+: (?:Any|bool|int|float|str|dict|list|ClassVar|[A-Z_]\w*|['"][A-Z_]\w*)(?:[^=]*)?(?: = .*)?$/;
@@ -2896,6 +2950,11 @@ async function generateRpc(schemaPath?: string, sessionEventsSchema?: JSONSchema
     typesCode = collapsePlaceholderPythonDataclasses(typesCode, knownDefNames);
     typesCode = postProcessExternalUnionAliasesForPython(typesCode, externalUnionAliases);
     typesCode = postProcessExternalRefsForPython(typesCode, externalRefs.placeholderNames, externalEnumNames);
+    typesCode = removeShadowedSessionEventEnumsForPython(
+        typesCode,
+        externalRefs.imports.get(".session_events") ?? new Set<string>(),
+        sessionEventsSchema
+    );
     const { code: typesCodeAfterUnions, unions: refBasedUnions } = postProcessRefBasedDiscriminatedUnionsForPython(
         typesCode,
         allDefinitions,