Merge remote-tracking branch 'upstream/master' into fix/xds-resolver-close-drop-field-refs

# Conflicts:
#	internal/xds/resolver/xds_resolver.go

Author: sushanb

CONTRIBUTING.md

@@ -23,6 +23,29 @@ wanted"](https://github.com/grpc/grpc-go/issues?q=sort%3Aupdated-desc%20is%3Aiss
 are especially nice for first-time contributors, as they should be well-defined
 problems that already have agreed-upon solutions.
 
+## Generative AI Policy
+
+AI tools have the ability to produce more code than is possible for the gRPC
+team to read, understand, review, and accept into the repository.  For this
+reason, we request that all contributions adhere to the following rules:
+
+1. **No AI-Generated Interactions:** All communication in the repo must be
+   authored by a human.  _Exception: AIs may be used for directed writing
+   assistance or translation._  Absolutely no automated agents are allowed to
+   directly publish to GitHub.
+
+2. **Author Ownership and Accountability:** Code contributions are expected to
+   be fully owned and understood by the human contributor.  If the code was
+   produced by generative AI, the author is expected to have reviewed and
+   understood it in its entirety before submitting it for review.  This includes
+   all content: production code, tests, examples, tools, etc.
+
+In addition to the above requirements, any AI-assisted contributions must also
+comply with the [Linux Foundation Generative AI
+Policy](https://www.linuxfoundation.org/legal/generative-ai).  This includes
+confirming that all contributions are legally allowed to be contributed to the
+gRPC project under the applicable license terms.
+
 ## Code Style
 
 We follow [Google's published Go style

balancer/autosharding/autosharding.go

@@ -0,0 +1,79 @@
+/*
+ *
+ * Copyright 2026 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package autosharding implements the autosharding load balancing policy.
+package autosharding
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"google.golang.org/grpc/balancer"
+	iserviceconfig "google.golang.org/grpc/internal/serviceconfig"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+// Name is the name of the autosharding balancer.
+const Name = "autosharding_experimental"
+
+func init() {
+	balancer.Register(bb{})
+}
+
+// lbConfig is the balancer config for the autosharding balancer.
+type lbConfig struct {
+	serviceconfig.LoadBalancingConfig `json:"-"`
+
+	ChannelFactoryKey        string                  `json:"channelFactoryKey,omitempty"`
+	AutoShardingTarget       string                  `json:"autoshardingTarget,omitempty"`
+	KeyHeaderName            string                  `json:"keyHeaderName,omitempty"`
+	EnableFallback           bool                    `json:"enableFallback,omitempty"`
+	InitialAssignmentTimeout iserviceconfig.Duration `json:"initialAssignmentTimeout,omitempty"`
+}
+
+type bb struct{}
+
+func (bb) Name() string {
+	return Name
+}
+
+func (bb) ParseConfig(s json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
+	lbConfig := &lbConfig{InitialAssignmentTimeout: iserviceconfig.Duration(60 * time.Second)}
+	if err := json.Unmarshal(s, lbConfig); err != nil {
+		return nil, fmt.Errorf("autosharding: unable to unmarshal LBConfig: %v", err)
+	}
+	if lbConfig.ChannelFactoryKey == "" {
+		return nil, fmt.Errorf("autosharding: channelFactoryKey field is required")
+	}
+	if lbConfig.AutoShardingTarget == "" {
+		return nil, fmt.Errorf("autosharding: autoshardingTarget field is required")
+	}
+	if lbConfig.KeyHeaderName == "" {
+		return nil, fmt.Errorf("autosharding: keyHeaderName field is required")
+	}
+	return lbConfig, nil
+}
+
+func (bb) Build(balancer.ClientConn, balancer.BuildOptions) balancer.Balancer {
+	return &autoshardingBalancer{}
+}
+
+type autoshardingBalancer struct {
+	balancer.Balancer
+}

balancer/autosharding/autosharding_test.go

@@ -0,0 +1,144 @@
+/*
+ *
+ * Copyright 2026 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package autosharding
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+	"google.golang.org/grpc/internal/grpctest"
+	iserviceconfig "google.golang.org/grpc/internal/serviceconfig"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
+func (s) TestParseConfig_Success(t *testing.T) {
+	parser := bb{}
+	tests := []struct {
+		name    string
+		input   string
+		wantCfg serviceconfig.LoadBalancingConfig
+	}{
+		{
+			name: "all-fields",
+			input: `{
+				"channelFactoryKey": "factory-key",
+				"autoshardingTarget": "target",
+				"keyHeaderName": "header",
+				"enableFallback": true,
+				"initialAssignmentTimeout": "30s"
+			}`,
+			wantCfg: &lbConfig{
+				ChannelFactoryKey:        "factory-key",
+				AutoShardingTarget:       "target",
+				KeyHeaderName:            "header",
+				EnableFallback:           true,
+				InitialAssignmentTimeout: iserviceconfig.Duration(30 * time.Second),
+			},
+		},
+		{
+			name: "default-timeout",
+			input: `{
+				"channelFactoryKey": "factory-key",
+				"autoshardingTarget": "target",
+				"keyHeaderName": "header"
+			}`,
+			wantCfg: &lbConfig{
+				ChannelFactoryKey:        "factory-key",
+				AutoShardingTarget:       "target",
+				KeyHeaderName:            "header",
+				InitialAssignmentTimeout: iserviceconfig.Duration(60 * time.Second),
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			gotCfg, err := parser.ParseConfig(json.RawMessage(test.input))
+			if err != nil {
+				t.Fatalf("ParseConfig() error = %v, want nil", err)
+			}
+			if diff := cmp.Diff(test.wantCfg, gotCfg); diff != "" {
+				t.Errorf("ParseConfig() config diff (-want +got):\n%s", diff)
+			}
+		})
+	}
+}
+
+func (s) TestParseConfig_Failure(t *testing.T) {
+	parser := bb{}
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "invalid-json",
+			input: "{{invalidjson{{",
+		},
+		{
+			name: "invalid-duration",
+			input: `{
+				"channelFactoryKey": "factory-key",
+				"autoshardingTarget": "target",
+				"keyHeaderName": "header",
+				"initialAssignmentTimeout": "invalid"
+			}`,
+		},
+		{
+			name: "missing-channel-factory-key",
+			input: `{
+				"autoshardingTarget": "target",
+				"keyHeaderName": "header"
+			}`,
+		},
+		{
+			name: "missing-autosharding-target",
+			input: `{
+				"channelFactoryKey": "factory-key",
+				"keyHeaderName": "header"
+			}`,
+		},
+		{
+			name: "missing-key-header-name",
+			input: `{
+				"channelFactoryKey": "factory-key",
+				"autoshardingTarget": "target"
+			}`,
+		},
+		{
+			name:  "empty-config",
+			input: `{}`,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if _, err := parser.ParseConfig(json.RawMessage(test.input)); err == nil {
+				t.Fatalf("ParseConfig() succeeded, want error")
+			}
+		})
+	}
+}