From e78334682329f502afeb006fb315eac8cc31e16b Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Mon, 14 Sep 2026 11:11:34 -0700
Subject: [PATCH 1/6] fix(python): handle required etag headers

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../fix-required-etag-header-2026-09-14.md    |  8 ++++++++
 .../http-client-python/emitter/src/http.ts    |  6 +++++-
 .../emitter/test/http.test.ts                 | 19 +++++++++++++++++++
 ...ecial_headers_conditional_request_async.py |  5 +++++
 ...ure_special_headers_conditional_request.py |  4 ++++
 5 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 .chronus/changes/fix-required-etag-header-2026-09-14.md
 create mode 100644 packages/http-client-python/emitter/test/http.test.ts

diff --git a/.chronus/changes/fix-required-etag-header-2026-09-14.md b/.chronus/changes/fix-required-etag-header-2026-09-14.md
new file mode 100644
index 00000000000..46d5b15cc0d
--- /dev/null
+++ b/.chronus/changes/fix-required-etag-header-2026-09-14.md
@@ -0,0 +1,8 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Generate required `If-Match` headers as direct `if_match` parameters instead of
+the optional `etag` and `match_condition` convenience API.
diff --git a/packages/http-client-python/emitter/src/http.ts b/packages/http-client-python/emitter/src/http.ts
index e1fe7efb351..4831c8e9474 100644
--- a/packages/http-client-python/emitter/src/http.ts
+++ b/packages/http-client-python/emitter/src/http.ts
@@ -206,7 +206,11 @@ function isEtagType(type: SdkType): boolean {
   );
 }
 
-function getEtagRole(parameter: SdkHeaderParameter): string | undefined {
+export function getEtagRole(parameter: SdkHeaderParameter): string | undefined {
+  // The etag/match_condition convenience API can omit or redirect the wire
+  // header, so it is only valid when the TypeSpec header itself is optional.
+  if (!parameter.optional) return undefined;
+
   const name = parameter.name.toLowerCase();
   const wire = parameter.serializedName.toLowerCase();
   // Standard If-Match / If-None-Match headers work with any type
diff --git a/packages/http-client-python/emitter/test/http.test.ts b/packages/http-client-python/emitter/test/http.test.ts
new file mode 100644
index 00000000000..536d57d50c8
--- /dev/null
+++ b/packages/http-client-python/emitter/test/http.test.ts
@@ -0,0 +1,19 @@
+import type { SdkHeaderParameter } from "@azure-tools/typespec-client-generator-core";
+import { strictEqual } from "assert";
+import { describe, it } from "vitest";
+import { getEtagRole } from "../src/http.js";
+
+function createHeaderParameter(optional: boolean): SdkHeaderParameter {
+  return {
+    name: "ifMatch",
+    serializedName: "If-Match",
+    optional,
+  } as SdkHeaderParameter;
+}
+
+describe("typespec-python: HTTP parameters", () => {
+  it("only promotes optional If-Match headers to the conditional convenience API", () => {
+    strictEqual(getEtagRole(createHeaderParameter(true)), "ifMatch");
+    strictEqual(getEtagRole(createHeaderParameter(false)), undefined);
+  });
+});
diff --git a/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py b/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py
index 264cc71cdb3..e1f7ae821b9 100644
--- a/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py
+++ b/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py
@@ -21,6 +21,11 @@ async def test_post_if_match(client: ConditionalRequestClient):
     await client.post_if_match(etag="valid", match_condition=MatchConditions.IfNotModified)
 
 
+@pytest.mark.asyncio
+async def test_post_required_if_match(client: ConditionalRequestClient):
+    await client.post_required_if_match(if_match='"required"')
+
+
 @pytest.mark.asyncio
 async def test_post_if_none_match(client: ConditionalRequestClient):
     await client.post_if_none_match(etag="invalid", match_condition=MatchConditions.IfModified)
diff --git a/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py b/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py
index dacd7ba07f0..a54cc1baa75 100644
--- a/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py
+++ b/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py
@@ -19,6 +19,10 @@ def test_post_if_match(client: ConditionalRequestClient):
     client.post_if_match(etag="valid", match_condition=MatchConditions.IfNotModified)
 
 
+def test_post_required_if_match(client: ConditionalRequestClient):
+    client.post_required_if_match(if_match='"required"')
+
+
 def test_post_if_none_match(client: ConditionalRequestClient):
     client.post_if_none_match(etag="invalid", match_condition=MatchConditions.IfModified)
 

From e28762d9882dc15d251abc7958f380364e5f9e2e Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Mon, 14 Sep 2026 12:53:49 -0700
Subject: [PATCH 2/6] test(python): remove unavailable required etag scenario

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../test_azure_special_headers_conditional_request_async.py  | 5 -----
 .../azure/test_azure_special_headers_conditional_request.py  | 4 ----
 2 files changed, 9 deletions(-)

diff --git a/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py b/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py
index e1f7ae821b9..264cc71cdb3 100644
--- a/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py
+++ b/packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py
@@ -21,11 +21,6 @@ async def test_post_if_match(client: ConditionalRequestClient):
     await client.post_if_match(etag="valid", match_condition=MatchConditions.IfNotModified)
 
 
-@pytest.mark.asyncio
-async def test_post_required_if_match(client: ConditionalRequestClient):
-    await client.post_required_if_match(if_match='"required"')
-
-
 @pytest.mark.asyncio
 async def test_post_if_none_match(client: ConditionalRequestClient):
     await client.post_if_none_match(etag="invalid", match_condition=MatchConditions.IfModified)
diff --git a/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py b/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py
index a54cc1baa75..dacd7ba07f0 100644
--- a/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py
+++ b/packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py
@@ -19,10 +19,6 @@ def test_post_if_match(client: ConditionalRequestClient):
     client.post_if_match(etag="valid", match_condition=MatchConditions.IfNotModified)
 
 
-def test_post_required_if_match(client: ConditionalRequestClient):
-    client.post_required_if_match(if_match='"required"')
-
-
 def test_post_if_none_match(client: ConditionalRequestClient):
     client.post_if_none_match(etag="invalid", match_condition=MatchConditions.IfModified)
 

From f0f45252b859561bd4eceb6e784fdee00fca15e1 Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Tue, 15 Sep 2026 09:43:01 -0700
Subject: [PATCH 3/6] fix(python): process etags in nested operation groups

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../fix-required-etag-header-2026-09-14.md    |  3 +-
 .../http-client-python/emitter/src/http.ts    |  6 +-
 .../emitter/test/http.test.ts                 | 19 ----
 .../generator/pygen/preprocess/__init__.py    | 23 ++++-
 .../tests/unit/test_preprocess_etag.py        | 99 ++++++++++++-------
 5 files changed, 83 insertions(+), 67 deletions(-)
 delete mode 100644 packages/http-client-python/emitter/test/http.test.ts

diff --git a/.chronus/changes/fix-required-etag-header-2026-09-14.md b/.chronus/changes/fix-required-etag-header-2026-09-14.md
index 46d5b15cc0d..30a45960e55 100644
--- a/.chronus/changes/fix-required-etag-header-2026-09-14.md
+++ b/.chronus/changes/fix-required-etag-header-2026-09-14.md
@@ -4,5 +4,4 @@ packages:
   - "@typespec/http-client-python"
 ---
 
-Generate required `If-Match` headers as direct `if_match` parameters instead of
-the optional `etag` and `match_condition` convenience API.
+Generate complete ETag handling for operations in nested operation groups.
diff --git a/packages/http-client-python/emitter/src/http.ts b/packages/http-client-python/emitter/src/http.ts
index 4831c8e9474..e1fe7efb351 100644
--- a/packages/http-client-python/emitter/src/http.ts
+++ b/packages/http-client-python/emitter/src/http.ts
@@ -206,11 +206,7 @@ function isEtagType(type: SdkType): boolean {
   );
 }
 
-export function getEtagRole(parameter: SdkHeaderParameter): string | undefined {
-  // The etag/match_condition convenience API can omit or redirect the wire
-  // header, so it is only valid when the TypeSpec header itself is optional.
-  if (!parameter.optional) return undefined;
-
+function getEtagRole(parameter: SdkHeaderParameter): string | undefined {
   const name = parameter.name.toLowerCase();
   const wire = parameter.serializedName.toLowerCase();
   // Standard If-Match / If-None-Match headers work with any type
diff --git a/packages/http-client-python/emitter/test/http.test.ts b/packages/http-client-python/emitter/test/http.test.ts
deleted file mode 100644
index 536d57d50c8..00000000000
--- a/packages/http-client-python/emitter/test/http.test.ts
+++ /dev/null
@@ -1,19 +0,0 @@
-import type { SdkHeaderParameter } from "@azure-tools/typespec-client-generator-core";
-import { strictEqual } from "assert";
-import { describe, it } from "vitest";
-import { getEtagRole } from "../src/http.js";
-
-function createHeaderParameter(optional: boolean): SdkHeaderParameter {
-  return {
-    name: "ifMatch",
-    serializedName: "If-Match",
-    optional,
-  } as SdkHeaderParameter;
-}
-
-describe("typespec-python: HTTP parameters", () => {
-  it("only promotes optional If-Match headers to the conditional convenience API", () => {
-    strictEqual(getEtagRole(createHeaderParameter(true)), "ifMatch");
-    strictEqual(getEtagRole(createHeaderParameter(false)), undefined);
-  });
-});
diff --git a/packages/http-client-python/generator/pygen/preprocess/__init__.py b/packages/http-client-python/generator/pygen/preprocess/__init__.py
index 1a5f815e030..0a93215f211 100644
--- a/packages/http-client-python/generator/pygen/preprocess/__init__.py
+++ b/packages/http-client-python/generator/pygen/preprocess/__init__.py
@@ -286,6 +286,21 @@ def _process_operation_etag_headers(
         client["hasEtag"] = True
 
 
+def _process_operation_group_etag_headers(
+    operation_groups: list[dict[str, Any]],
+    client: dict[str, Any],
+    version_tolerant: bool,
+) -> None:
+    for operation_group in operation_groups:
+        for operation in operation_group.get("operations", []):
+            _process_operation_etag_headers(operation, client, version_tolerant)
+        _process_operation_group_etag_headers(
+            operation_group.get("operationGroups", []),
+            client,
+            version_tolerant,
+        )
+
+
 def headers_convert(yaml_data: dict[str, Any], replace_data: Any) -> None:
     if isinstance(replace_data, dict):
         for k, v in replace_data.items():
@@ -607,9 +622,11 @@ def update_client(self, yaml_data: dict[str, Any]) -> None:
         if prop_name.endswith("Client"):
             prop_name = prop_name[: len(prop_name) - len("Client")]
         yaml_data["builderPadName"] = to_snake_case(prop_name)
-        for og in yaml_data.get("operationGroups", []):
-            for o in og["operations"]:
-                _process_operation_etag_headers(o, yaml_data, self.version_tolerant)
+        _process_operation_group_etag_headers(
+            yaml_data.get("operationGroups", []),
+            yaml_data,
+            self.version_tolerant,
+        )
 
         # add client signature cloud_setting for arm
         if self.azure_arm and yaml_data["parameters"]:
diff --git a/packages/http-client-python/tests/unit/test_preprocess_etag.py b/packages/http-client-python/tests/unit/test_preprocess_etag.py
index f631f71ba51..69038b61f34 100644
--- a/packages/http-client-python/tests/unit/test_preprocess_etag.py
+++ b/packages/http-client-python/tests/unit/test_preprocess_etag.py
@@ -20,12 +20,18 @@ def _plugin() -> PreProcessPlugin:
     )
 
 
-def _header_param(client_name: str, wire_name: str, etag_role: str | None) -> dict:
+def _header_param(
+    client_name: str,
+    wire_name: str,
+    etag_role: str | None,
+    *,
+    optional: bool = True,
+) -> dict:
     p: dict = {
         "clientName": client_name,
         "wireName": wire_name,
         "location": "header",
-        "optional": True,
+        "optional": optional,
         "implementation": "Method",
         "type": {"type": "string"},
     }
@@ -59,6 +65,47 @@ def _get_op(client: dict) -> dict:
     return client["operationGroups"][0]["operations"][0]
 
 
+def test_etag_headers_in_nested_operation_group_are_processed():
+    """Nested ETag operations get their partner parameter and enable client helpers."""
+    if_match = _header_param(
+        "if_match",
+        "If-Match",
+        "ifMatch",
+        optional=False,
+    )
+    operation = {
+        "name": "remove",
+        "parameters": [if_match],
+    }
+    client = _client_yaml([])
+    client["operationGroups"] = [
+        {
+            "operations": [],
+            "operationGroups": [
+                {
+                    "operations": [operation],
+                }
+            ],
+        }
+    ]
+
+    plugin = _plugin()
+    plugin.update_client(client)
+
+    assert client["hasEtag"] is True
+    assert operation["hasEtag"] is True
+    assert len(operation["parameters"]) == 2
+    assert operation["parameters"][0]["etagRole"] == "ifMatch"
+    assert operation["parameters"][1]["etagRole"] == "ifNoneMatch"
+
+    for parameter in operation["parameters"]:
+        plugin.update_parameter(parameter)
+    assert [parameter["clientName"] for parameter in operation["parameters"]] == [
+        "etag",
+        "match_condition",
+    ]
+
+
 def test_etag_role_preserved_when_only_standard_pair_present():
     """Standard If-Match/If-None-Match keep their etagRole."""
     if_match = _header_param("if_match", "If-Match", "ifMatch")
@@ -78,9 +125,7 @@ def test_etag_role_preserved_when_only_standard_pair_present():
 def test_etag_role_preserved_when_only_custom_pair_present():
     """Custom etag headers alone are promoted to the etag/match_condition slot."""
     source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
-    source_none = _header_param(
-        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
-    )
+    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
     client = _client_yaml([source_match, source_none])
 
     _plugin().update_client(client)
@@ -98,12 +143,8 @@ def test_standard_etag_wins_over_custom_when_both_present():
     Regression test for PR #10494 which caused operations like Storage's copyFromUrl
     to emit two parameters named "etag" and two named "match_condition".
     """
-    source_match = _header_param(
-        "source_if_match", "x-ms-source-if-match", "ifMatch"
-    )
-    source_none = _header_param(
-        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
-    )
+    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
+    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
     if_match = _header_param("if_match", "If-Match", "ifMatch")
     if_none_match = _header_param("if_none_match", "If-None-Match", "ifNoneMatch")
 
@@ -128,15 +169,9 @@ def test_standard_etag_wins_over_custom_when_both_present():
 def test_first_custom_pair_chosen_when_multiple_custom_pairs_present():
     """With multiple custom etag pairs and no standard pair, the first candidate wins."""
     blob_match = _header_param("blob_if_match", "x-ms-blob-if-match", "ifMatch")
-    blob_none = _header_param(
-        "blob_if_none_match", "x-ms-blob-if-none-match", "ifNoneMatch"
-    )
-    source_match = _header_param(
-        "source_if_match", "x-ms-source-if-match", "ifMatch"
-    )
-    source_none = _header_param(
-        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
-    )
+    blob_none = _header_param("blob_if_none_match", "x-ms-blob-if-none-match", "ifNoneMatch")
+    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
+    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
     client = _client_yaml([blob_match, blob_none, source_match, source_none])
 
     _plugin().update_client(client)
@@ -153,9 +188,7 @@ def test_synthetic_partner_still_works_with_only_one_custom_etag():
     synthetic-partner code path still creates a matching ifNoneMatch (or ifMatch)
     copy. The fix must not regress this behavior.
     """
-    source_match = _header_param(
-        "source_if_match", "x-ms-source-if-match", "ifMatch"
-    )
+    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
     client = _client_yaml([source_match])
 
     _plugin().update_client(client)
@@ -175,12 +208,8 @@ def test_full_update_yaml_does_not_collide_client_names():
     Without the fix, both source_if_match and if_match end up with clientName="etag",
     and both source_if_none_match and if_none_match end up with clientName="match_condition".
     """
-    source_match = _header_param(
-        "source_if_match", "x-ms-source-if-match", "ifMatch"
-    )
-    source_none = _header_param(
-        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
-    )
+    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
+    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
     if_match = _header_param("if_match", "If-Match", "ifMatch")
     if_none_match = _header_param("if_none_match", "If-None-Match", "ifNoneMatch")
     client = _client_yaml([source_match, source_none, if_match, if_none_match])
@@ -193,9 +222,7 @@ def test_full_update_yaml_does_not_collide_client_names():
         plugin.update_parameter(p)
 
     client_names = [p["clientName"] for p in op["parameters"]]
-    assert len(client_names) == len(set(client_names)), (
-        f"Duplicate clientNames after preprocess: {client_names}"
-    )
+    assert len(client_names) == len(set(client_names)), f"Duplicate clientNames after preprocess: {client_names}"
     # The standard pair was promoted; the custom pair retains its natural names.
     assert "etag" in client_names
     assert "match_condition" in client_names
@@ -214,9 +241,7 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     If-Match gets a synthetic If-None-Match partner instead.
     """
     if_match = _header_param("if_match", "If-Match", "ifMatch")
-    source_none = _header_param(
-        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
-    )
+    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
     client = _client_yaml([if_match, source_none])
 
     plugin = _plugin()
@@ -239,9 +264,7 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     for p in op["parameters"]:
         plugin.update_parameter(p)
     client_names = [p["clientName"] for p in op["parameters"]]
-    assert len(client_names) == len(set(client_names)), (
-        f"Duplicate clientNames: {client_names}"
-    )
+    assert len(client_names) == len(set(client_names)), f"Duplicate clientNames: {client_names}"
 
 
 def test_standard_if_none_match_not_paired_with_custom_if_match():

From d30cd1fac7cacc64ceb044ceebd5ee8d1a0e86ce Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Tue, 15 Sep 2026 09:43:43 -0700
Subject: [PATCH 4/6] chore(python): keep etag test diff focused

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../tests/unit/test_preprocess_etag.py        | 48 ++++++++++++++-----
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/packages/http-client-python/tests/unit/test_preprocess_etag.py b/packages/http-client-python/tests/unit/test_preprocess_etag.py
index 69038b61f34..2f1cdaf9b15 100644
--- a/packages/http-client-python/tests/unit/test_preprocess_etag.py
+++ b/packages/http-client-python/tests/unit/test_preprocess_etag.py
@@ -125,7 +125,9 @@ def test_etag_role_preserved_when_only_standard_pair_present():
 def test_etag_role_preserved_when_only_custom_pair_present():
     """Custom etag headers alone are promoted to the etag/match_condition slot."""
     source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
-    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
+    source_none = _header_param(
+        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
+    )
     client = _client_yaml([source_match, source_none])
 
     _plugin().update_client(client)
@@ -143,8 +145,12 @@ def test_standard_etag_wins_over_custom_when_both_present():
     Regression test for PR #10494 which caused operations like Storage's copyFromUrl
     to emit two parameters named "etag" and two named "match_condition".
     """
-    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
-    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
+    source_match = _header_param(
+        "source_if_match", "x-ms-source-if-match", "ifMatch"
+    )
+    source_none = _header_param(
+        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
+    )
     if_match = _header_param("if_match", "If-Match", "ifMatch")
     if_none_match = _header_param("if_none_match", "If-None-Match", "ifNoneMatch")
 
@@ -169,9 +175,15 @@ def test_standard_etag_wins_over_custom_when_both_present():
 def test_first_custom_pair_chosen_when_multiple_custom_pairs_present():
     """With multiple custom etag pairs and no standard pair, the first candidate wins."""
     blob_match = _header_param("blob_if_match", "x-ms-blob-if-match", "ifMatch")
-    blob_none = _header_param("blob_if_none_match", "x-ms-blob-if-none-match", "ifNoneMatch")
-    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
-    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
+    blob_none = _header_param(
+        "blob_if_none_match", "x-ms-blob-if-none-match", "ifNoneMatch"
+    )
+    source_match = _header_param(
+        "source_if_match", "x-ms-source-if-match", "ifMatch"
+    )
+    source_none = _header_param(
+        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
+    )
     client = _client_yaml([blob_match, blob_none, source_match, source_none])
 
     _plugin().update_client(client)
@@ -188,7 +200,9 @@ def test_synthetic_partner_still_works_with_only_one_custom_etag():
     synthetic-partner code path still creates a matching ifNoneMatch (or ifMatch)
     copy. The fix must not regress this behavior.
     """
-    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
+    source_match = _header_param(
+        "source_if_match", "x-ms-source-if-match", "ifMatch"
+    )
     client = _client_yaml([source_match])
 
     _plugin().update_client(client)
@@ -208,8 +222,12 @@ def test_full_update_yaml_does_not_collide_client_names():
     Without the fix, both source_if_match and if_match end up with clientName="etag",
     and both source_if_none_match and if_none_match end up with clientName="match_condition".
     """
-    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
-    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
+    source_match = _header_param(
+        "source_if_match", "x-ms-source-if-match", "ifMatch"
+    )
+    source_none = _header_param(
+        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
+    )
     if_match = _header_param("if_match", "If-Match", "ifMatch")
     if_none_match = _header_param("if_none_match", "If-None-Match", "ifNoneMatch")
     client = _client_yaml([source_match, source_none, if_match, if_none_match])
@@ -222,7 +240,9 @@ def test_full_update_yaml_does_not_collide_client_names():
         plugin.update_parameter(p)
 
     client_names = [p["clientName"] for p in op["parameters"]]
-    assert len(client_names) == len(set(client_names)), f"Duplicate clientNames after preprocess: {client_names}"
+    assert len(client_names) == len(set(client_names)), (
+        f"Duplicate clientNames after preprocess: {client_names}"
+    )
     # The standard pair was promoted; the custom pair retains its natural names.
     assert "etag" in client_names
     assert "match_condition" in client_names
@@ -241,7 +261,9 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     If-Match gets a synthetic If-None-Match partner instead.
     """
     if_match = _header_param("if_match", "If-Match", "ifMatch")
-    source_none = _header_param("source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch")
+    source_none = _header_param(
+        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
+    )
     client = _client_yaml([if_match, source_none])
 
     plugin = _plugin()
@@ -264,7 +286,9 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     for p in op["parameters"]:
         plugin.update_parameter(p)
     client_names = [p["clientName"] for p in op["parameters"]]
-    assert len(client_names) == len(set(client_names)), f"Duplicate clientNames: {client_names}"
+    assert len(client_names) == len(set(client_names)), (
+        f"Duplicate clientNames: {client_names}"
+    )
 
 
 def test_standard_if_none_match_not_paired_with_custom_if_match():

From d88ac8362c336f43e90c5caaa7adf7980f289ade Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Tue, 15 Sep 2026 11:18:32 -0700
Subject: [PATCH 5/6] Default match conditions for required ETag headers

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../fix-required-etag-header-2026-09-14.md    |  3 +-
 .../generator/pygen/preprocess/__init__.py    | 18 +++-
 .../tests/unit/test_preprocess_etag.py        | 93 +++++++++++++++----
 3 files changed, 89 insertions(+), 25 deletions(-)

diff --git a/.chronus/changes/fix-required-etag-header-2026-09-14.md b/.chronus/changes/fix-required-etag-header-2026-09-14.md
index 30a45960e55..dcfc261e072 100644
--- a/.chronus/changes/fix-required-etag-header-2026-09-14.md
+++ b/.chronus/changes/fix-required-etag-header-2026-09-14.md
@@ -4,4 +4,5 @@ packages:
   - "@typespec/http-client-python"
 ---
 
-Generate complete ETag handling for operations in nested operation groups.
+Generate complete ETag handling for operations in nested operation groups and
+default synthesized match conditions for required ETag headers.
diff --git a/packages/http-client-python/generator/pygen/preprocess/__init__.py b/packages/http-client-python/generator/pygen/preprocess/__init__.py
index 0a93215f211..609dc4c36b3 100644
--- a/packages/http-client-python/generator/pygen/preprocess/__init__.py
+++ b/packages/http-client-python/generator/pygen/preprocess/__init__.py
@@ -264,9 +264,6 @@ def _process_operation_etag_headers(
     if_match_candidates: list[dict[str, Any]] = []
     if_none_match_candidates: list[dict[str, Any]] = []
     for p in operation["parameters"]:
-        wire_name_lower = get_wire_name_lower(p)
-        if p["location"] == "header" and wire_name_lower == "client-request-id":
-            client["requestIdHeaderName"] = wire_name_lower
         if version_tolerant and p["location"] == "header":
             role = _get_etag_role(p)
             if role == "ifMatch":
@@ -274,9 +271,17 @@ def _process_operation_etag_headers(
             elif role == "ifNoneMatch":
                 if_none_match_candidates.append(p)
 
-    property_if_match, property_if_none_match = _resolve_etag_pair(if_match_candidates, if_none_match_candidates)
+    default_match_condition = None
+    if len(if_match_candidates) == 1 and not if_none_match_candidates and not if_match_candidates[0]["optional"]:
+        default_match_condition = "MatchConditions.IfNotModified"
+    elif len(if_none_match_candidates) == 1 and not if_match_candidates and not if_none_match_candidates[0]["optional"]:
+        default_match_condition = "MatchConditions.IfModified"
 
+    property_if_match, property_if_none_match = _resolve_etag_pair(if_match_candidates, if_none_match_candidates)
     if property_if_match and property_if_none_match:
+        if default_match_condition:
+            property_if_none_match["clientDefaultValue"] = default_match_condition
+
         etag_params = {id(property_if_match), id(property_if_none_match)}
         operation["parameters"] = [item for item in operation["parameters"] if id(item) not in etag_params] + [
             property_if_match,
@@ -622,6 +627,11 @@ def update_client(self, yaml_data: dict[str, Any]) -> None:
         if prop_name.endswith("Client"):
             prop_name = prop_name[: len(prop_name) - len("Client")]
         yaml_data["builderPadName"] = to_snake_case(prop_name)
+        for operation_group in yaml_data.get("operationGroups", []):
+            for operation in operation_group.get("operations", []):
+                for parameter in operation["parameters"]:
+                    if parameter["location"] == "header" and get_wire_name_lower(parameter) == "client-request-id":
+                        yaml_data["requestIdHeaderName"] = "client-request-id"
         _process_operation_group_etag_headers(
             yaml_data.get("operationGroups", []),
             yaml_data,
diff --git a/packages/http-client-python/tests/unit/test_preprocess_etag.py b/packages/http-client-python/tests/unit/test_preprocess_etag.py
index 2f1cdaf9b15..ad7b85e2dd4 100644
--- a/packages/http-client-python/tests/unit/test_preprocess_etag.py
+++ b/packages/http-client-python/tests/unit/test_preprocess_etag.py
@@ -4,6 +4,8 @@
 # license information.
 # --------------------------------------------------------------------------
 """Tests for etag-typed header handling in the preprocess plugin."""
+import pytest
+
 from pygen.preprocess import PreProcessPlugin
 
 
@@ -65,38 +67,51 @@ def _get_op(client: dict) -> dict:
     return client["operationGroups"][0]["operations"][0]
 
 
-def test_etag_headers_in_nested_operation_group_are_processed():
+@pytest.mark.parametrize(
+    ("client_name", "wire_name", "etag_role", "match_condition_default"),
+    [
+        ("if_match", "If-Match", "ifMatch", "MatchConditions.IfNotModified"),
+        ("if_none_match", "If-None-Match", "ifNoneMatch", "MatchConditions.IfModified"),
+    ],
+)
+def test_etag_headers_in_nested_operation_group_are_processed(
+    client_name: str,
+    wire_name: str,
+    etag_role: str,
+    match_condition_default: str,
+):
     """Nested ETag operations get their partner parameter and enable client helpers."""
-    if_match = _header_param(
-        "if_match",
-        "If-Match",
-        "ifMatch",
+    etag_parameter = _header_param(
+        client_name,
+        wire_name,
+        etag_role,
         optional=False,
     )
     operation = {
         "name": "remove",
-        "parameters": [if_match],
+        "parameters": [etag_parameter],
     }
     client = _client_yaml([])
-    client["operationGroups"] = [
-        {
-            "operations": [],
-            "operationGroups": [
-                {
-                    "operations": [operation],
-                }
-            ],
-        }
-    ]
+    parent_group = {
+        "operations": [],
+        "operationGroups": [
+            {
+                "operations": [operation],
+            }
+        ],
+    }
+    client["operationGroups"] = [parent_group]
 
     plugin = _plugin()
     plugin.update_client(client)
 
     assert client["hasEtag"] is True
+    assert "hasEtag" not in parent_group
     assert operation["hasEtag"] is True
     assert len(operation["parameters"]) == 2
     assert operation["parameters"][0]["etagRole"] == "ifMatch"
     assert operation["parameters"][1]["etagRole"] == "ifNoneMatch"
+    assert operation["parameters"][1]["clientDefaultValue"] == match_condition_default
 
     for parameter in operation["parameters"]:
         plugin.update_parameter(parameter)
@@ -260,9 +275,12 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     The fix demotes the custom header (strips etagRole) so the standard
     If-Match gets a synthetic If-None-Match partner instead.
     """
-    if_match = _header_param("if_match", "If-Match", "ifMatch")
+    if_match = _header_param("if_match", "If-Match", "ifMatch", optional=False)
     source_none = _header_param(
-        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
+        "source_if_none_match",
+        "x-ms-source-if-none-match",
+        "ifNoneMatch",
+        optional=False,
     )
     client = _client_yaml([if_match, source_none])
 
@@ -278,6 +296,7 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     assert last_two[0]["wireName"] == "If-Match"
     assert last_two[1]["etagRole"] == "ifNoneMatch"
     assert last_two[1]["wireName"] == "if-none-match"  # synthetic
+    assert "clientDefaultValue" not in last_two[1]
 
     # The custom header should NOT have been promoted — etagRole stripped.
     assert "etagRole" not in source_none
@@ -298,8 +317,18 @@ def test_standard_if_none_match_not_paired_with_custom_if_match():
     The custom header should be demoted; the standard If-None-Match gets a
     synthetic If-Match partner.
     """
-    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
-    if_none_match = _header_param("if_none_match", "If-None-Match", "ifNoneMatch")
+    source_match = _header_param(
+        "source_if_match",
+        "x-ms-source-if-match",
+        "ifMatch",
+        optional=False,
+    )
+    if_none_match = _header_param(
+        "if_none_match",
+        "If-None-Match",
+        "ifNoneMatch",
+        optional=False,
+    )
     client = _client_yaml([source_match, if_none_match])
 
     plugin = _plugin()
@@ -313,5 +342,29 @@ def test_standard_if_none_match_not_paired_with_custom_if_match():
     assert last_two[0]["wireName"] == "if-match"  # synthetic
     assert last_two[1]["etagRole"] == "ifNoneMatch"
     assert last_two[1]["wireName"] == "If-None-Match"
+    assert "clientDefaultValue" not in last_two[1]
 
     assert "etagRole" not in source_match
+
+
+def test_required_match_condition_default_not_added_for_multiple_candidates():
+    """A default is only safe when exactly one conditional header is declared."""
+    first_match = _header_param(
+        "first_if_match",
+        "x-ms-first-if-match",
+        "ifMatch",
+        optional=False,
+    )
+    second_match = _header_param(
+        "second_if_match",
+        "x-ms-second-if-match",
+        "ifMatch",
+        optional=False,
+    )
+    client = _client_yaml([first_match, second_match])
+
+    _plugin().update_client(client)
+
+    synthetic_none_match = _get_op(client)["parameters"][-1]
+    assert synthetic_none_match["etagRole"] == "ifNoneMatch"
+    assert "clientDefaultValue" not in synthetic_none_match

From af3c0916619393e04cd844de77c0de2b8d0d73c3 Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Wed, 16 Sep 2026 09:29:39 -0700
Subject: [PATCH 6/6] Remove required ETag match condition defaults

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../fix-required-etag-header-2026-09-14.md    |  3 +-
 .../generator/pygen/preprocess/__init__.py    |  9 ---
 .../tests/unit/test_preprocess_etag.py        | 75 +++----------------
 3 files changed, 13 insertions(+), 74 deletions(-)

diff --git a/.chronus/changes/fix-required-etag-header-2026-09-14.md b/.chronus/changes/fix-required-etag-header-2026-09-14.md
index dcfc261e072..30a45960e55 100644
--- a/.chronus/changes/fix-required-etag-header-2026-09-14.md
+++ b/.chronus/changes/fix-required-etag-header-2026-09-14.md
@@ -4,5 +4,4 @@ packages:
   - "@typespec/http-client-python"
 ---
 
-Generate complete ETag handling for operations in nested operation groups and
-default synthesized match conditions for required ETag headers.
+Generate complete ETag handling for operations in nested operation groups.
diff --git a/packages/http-client-python/generator/pygen/preprocess/__init__.py b/packages/http-client-python/generator/pygen/preprocess/__init__.py
index 609dc4c36b3..1e0a8a82579 100644
--- a/packages/http-client-python/generator/pygen/preprocess/__init__.py
+++ b/packages/http-client-python/generator/pygen/preprocess/__init__.py
@@ -271,17 +271,8 @@ def _process_operation_etag_headers(
             elif role == "ifNoneMatch":
                 if_none_match_candidates.append(p)
 
-    default_match_condition = None
-    if len(if_match_candidates) == 1 and not if_none_match_candidates and not if_match_candidates[0]["optional"]:
-        default_match_condition = "MatchConditions.IfNotModified"
-    elif len(if_none_match_candidates) == 1 and not if_match_candidates and not if_none_match_candidates[0]["optional"]:
-        default_match_condition = "MatchConditions.IfModified"
-
     property_if_match, property_if_none_match = _resolve_etag_pair(if_match_candidates, if_none_match_candidates)
     if property_if_match and property_if_none_match:
-        if default_match_condition:
-            property_if_none_match["clientDefaultValue"] = default_match_condition
-
         etag_params = {id(property_if_match), id(property_if_none_match)}
         operation["parameters"] = [item for item in operation["parameters"] if id(item) not in etag_params] + [
             property_if_match,
diff --git a/packages/http-client-python/tests/unit/test_preprocess_etag.py b/packages/http-client-python/tests/unit/test_preprocess_etag.py
index ad7b85e2dd4..319b2311e76 100644
--- a/packages/http-client-python/tests/unit/test_preprocess_etag.py
+++ b/packages/http-client-python/tests/unit/test_preprocess_etag.py
@@ -4,8 +4,6 @@
 # license information.
 # --------------------------------------------------------------------------
 """Tests for etag-typed header handling in the preprocess plugin."""
-import pytest
-
 from pygen.preprocess import PreProcessPlugin
 
 
@@ -67,29 +65,17 @@ def _get_op(client: dict) -> dict:
     return client["operationGroups"][0]["operations"][0]
 
 
-@pytest.mark.parametrize(
-    ("client_name", "wire_name", "etag_role", "match_condition_default"),
-    [
-        ("if_match", "If-Match", "ifMatch", "MatchConditions.IfNotModified"),
-        ("if_none_match", "If-None-Match", "ifNoneMatch", "MatchConditions.IfModified"),
-    ],
-)
-def test_etag_headers_in_nested_operation_group_are_processed(
-    client_name: str,
-    wire_name: str,
-    etag_role: str,
-    match_condition_default: str,
-):
+def test_etag_headers_in_nested_operation_group_are_processed():
     """Nested ETag operations get their partner parameter and enable client helpers."""
-    etag_parameter = _header_param(
-        client_name,
-        wire_name,
-        etag_role,
+    if_match = _header_param(
+        "if_match",
+        "If-Match",
+        "ifMatch",
         optional=False,
     )
     operation = {
         "name": "remove",
-        "parameters": [etag_parameter],
+        "parameters": [if_match],
     }
     client = _client_yaml([])
     parent_group = {
@@ -111,7 +97,8 @@ def test_etag_headers_in_nested_operation_group_are_processed(
     assert len(operation["parameters"]) == 2
     assert operation["parameters"][0]["etagRole"] == "ifMatch"
     assert operation["parameters"][1]["etagRole"] == "ifNoneMatch"
-    assert operation["parameters"][1]["clientDefaultValue"] == match_condition_default
+    assert all(parameter["optional"] is False for parameter in operation["parameters"])
+    assert all("clientDefaultValue" not in parameter for parameter in operation["parameters"])
 
     for parameter in operation["parameters"]:
         plugin.update_parameter(parameter)
@@ -275,12 +262,9 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     The fix demotes the custom header (strips etagRole) so the standard
     If-Match gets a synthetic If-None-Match partner instead.
     """
-    if_match = _header_param("if_match", "If-Match", "ifMatch", optional=False)
+    if_match = _header_param("if_match", "If-Match", "ifMatch")
     source_none = _header_param(
-        "source_if_none_match",
-        "x-ms-source-if-none-match",
-        "ifNoneMatch",
-        optional=False,
+        "source_if_none_match", "x-ms-source-if-none-match", "ifNoneMatch"
     )
     client = _client_yaml([if_match, source_none])
 
@@ -296,7 +280,6 @@ def test_standard_if_match_not_paired_with_custom_if_none_match():
     assert last_two[0]["wireName"] == "If-Match"
     assert last_two[1]["etagRole"] == "ifNoneMatch"
     assert last_two[1]["wireName"] == "if-none-match"  # synthetic
-    assert "clientDefaultValue" not in last_two[1]
 
     # The custom header should NOT have been promoted — etagRole stripped.
     assert "etagRole" not in source_none
@@ -317,18 +300,8 @@ def test_standard_if_none_match_not_paired_with_custom_if_match():
     The custom header should be demoted; the standard If-None-Match gets a
     synthetic If-Match partner.
     """
-    source_match = _header_param(
-        "source_if_match",
-        "x-ms-source-if-match",
-        "ifMatch",
-        optional=False,
-    )
-    if_none_match = _header_param(
-        "if_none_match",
-        "If-None-Match",
-        "ifNoneMatch",
-        optional=False,
-    )
+    source_match = _header_param("source_if_match", "x-ms-source-if-match", "ifMatch")
+    if_none_match = _header_param("if_none_match", "If-None-Match", "ifNoneMatch")
     client = _client_yaml([source_match, if_none_match])
 
     plugin = _plugin()
@@ -342,29 +315,5 @@ def test_standard_if_none_match_not_paired_with_custom_if_match():
     assert last_two[0]["wireName"] == "if-match"  # synthetic
     assert last_two[1]["etagRole"] == "ifNoneMatch"
     assert last_two[1]["wireName"] == "If-None-Match"
-    assert "clientDefaultValue" not in last_two[1]
 
     assert "etagRole" not in source_match
-
-
-def test_required_match_condition_default_not_added_for_multiple_candidates():
-    """A default is only safe when exactly one conditional header is declared."""
-    first_match = _header_param(
-        "first_if_match",
-        "x-ms-first-if-match",
-        "ifMatch",
-        optional=False,
-    )
-    second_match = _header_param(
-        "second_if_match",
-        "x-ms-second-if-match",
-        "ifMatch",
-        optional=False,
-    )
-    client = _client_yaml([first_match, second_match])
-
-    _plugin().update_client(client)
-
-    synthetic_none_match = _get_op(client)["parameters"][-1]
-    assert synthetic_none_match["etagRole"] == "ifNoneMatch"
-    assert "clientDefaultValue" not in synthetic_none_match