Merge branch 'main' into feature/graphql

Author: FionaBronwen

.chronus/changes/external-type-python-2025-9-20-14-28-41.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http-client-python"
+---
+
+Support SDK users defined customized serialization/deserialization function for external models

.chronus/changes/fionabronwen-mutator-framework-2025-11-3-22-19-48.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: feature
+packages:
+  - "@typespec/mutator-framework"
+---
+
+Add `EnumMutation` and `EnumMemberMutation` to the Mutator Framework

.chronus/changes/fix-encode-duration-tests-2025-11-25-04-18-59.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-specs"
+---
+
+Fix EncodeDuration tests with larger unit durations being too strict by making query parameter expectations match input types as numbers instead of strings

.chronus/changes/fix-signature-help-test-slow-2025-10-14-2-25-10.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: internal
+packages:
+  - "@typespec/compiler"
+---
+
+Fix signature help test super slow

.chronus/changes/mictaylor-json-schema-discriminator-circular-ref-fix-2025-10-21-6-44-36.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/json-schema"
+---
+
+avoid circular references in discriminated unions with polymorphic-models-strategy

.chronus/changes/mictaylor-json-schema-open-discriminator-support-2025-11-2-20-20-32.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/json-schema"
+---
+
+add support for open discriminators

.chronus/changes/named-unions-response-doc-2025-10-10-16-34-57.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http"
+---
+
+support documentation on union variants for response descriptions

.chronus/changes/python-backcompatTspPadding-2025-10-18-17-23-22.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Keep original client name for backcompat reasons when the name is only padded for tsp generations

.chronus/changes/python-fix-optional-properties-2025-11-3-16-16-35.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fix for optional properties in flatten model to keep compatibility

.chronus/changes/python-flatten-model-initialization-test-2025-11-1-8-33-43.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/http-client-python"
+---
+
+Add test case for flatten model initialization to check compatibility