[extension/datadog] Set os.type in resource attributes instead of os field (open-telemetry#46896)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Follow up to
open-telemetry#46881.
Set `os.type` to `runtime.GOOS` in the datadog extension if not already
present in resource attributes. Remove previous field for `OS`.

<!-- Issue number (e.g. open-telemetry#1234) or full URL to issue, if applicable. -->
#### Link to tracking issue

<!--Describe what testing was performed and which tests were added.-->
#### Testing
Unit tests

<!--Describe the documentation added.-->
#### Documentation

<!--Please delete paragraphs that you did not use before submitting.-->

Author: liustanley

.chloggen/stanley.liu_os-type.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. receiver/filelog)
+component: extension/datadog
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Set `os.type` resource attribute if not already present for Fleet Automation metadata.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [46896]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

extension/datadogextension/extension.go

@@ -5,6 +5,7 @@ package datadogextension // import "github.com/open-telemetry/opentelemetry-coll
 
 import (
 	"context"
+	"runtime"
 	"sync"
 	"time"
 
@@ -20,6 +21,7 @@ import (
 	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/service"
 	"go.opentelemetry.io/collector/service/hostcapabilities"
+	conventions "go.opentelemetry.io/otel/semconv/v1.38.0"
 	"go.uber.org/zap"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/extension/datadogextension/internal/componentchecker"
@@ -391,6 +393,10 @@ func newExtension(
 			return true
 		})
 	}
+	// Ensure os.type is always present; defer to any value already set by a resource detector
+	if _, ok := resourceMap[string(conventions.OSTypeKey)]; !ok {
+		resourceMap[string(conventions.OSTypeKey)] = runtime.GOOS
+	}
 
 	// configure payloadSender struct
 	ctxWithCancel, cancel := context.WithCancel(ctx)

extension/datadogextension/extension_test.go

@@ -6,6 +6,7 @@ package datadogextension
 import (
 	"context"
 	"errors"
+	"runtime"
 	"sync"
 	"testing"
 	"time"
@@ -227,9 +228,9 @@ func TestCollectorResourceAttributesArePopulated(t *testing.T) {
 	err = ext.NotifyConfig(t.Context(), conf)
 	require.NoError(t, err)
 
-	// Expect map with keys and values
+	// Expect map with keys and values (os.type is always injected as a fallback)
 	require.NotNil(t, ext.otelCollectorMetadata)
-	expected := map[string]string{"a_key": "1", "b_key": "2"}
+	expected := map[string]string{"a_key": "1", "b_key": "2", "os.type": runtime.GOOS}
 	assert.Equal(t, expected, ext.otelCollectorMetadata.CollectorResourceAttributes)
 
 	// Cleanup
@@ -274,12 +275,13 @@ func TestCollectorResourceAttributesWithMultipleKeys(t *testing.T) {
 	err = ext.NotifyConfig(t.Context(), conf)
 	require.NoError(t, err)
 
-	// Verify all resource attributes are collected
+	// Verify all resource attributes are collected (os.type is always injected as a fallback)
 	require.NotNil(t, ext.otelCollectorMetadata)
 	expected := map[string]string{
 		"deployment.environment.name": "prod",
 		"cloud.region":                "us-east",
 		"team.name":                   "backend",
+		"os.type":                     runtime.GOOS,
 	}
 	assert.Equal(t, expected, ext.otelCollectorMetadata.CollectorResourceAttributes)
 

extension/datadogextension/go.mod

@@ -27,6 +27,7 @@ require (
 	go.opentelemetry.io/collector/pdata v1.53.1-0.20260312222452-c212d203a110
 	go.opentelemetry.io/collector/service v0.147.1-0.20260312222452-c212d203a110
 	go.opentelemetry.io/collector/service/hostcapabilities v0.147.1-0.20260312222452-c212d203a110
+	go.opentelemetry.io/otel v1.42.0
 	go.uber.org/zap v1.27.1
 )
 
@@ -253,7 +254,6 @@ require (
 	go.opentelemetry.io/collector/receiver/xreceiver v0.147.1-0.20260312222452-c212d203a110 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.67.0 // indirect
 	go.opentelemetry.io/contrib/otelconf v0.22.0 // indirect
-	go.opentelemetry.io/otel v1.42.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc v0.18.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.18.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0 // indirect

extension/datadogextension/internal/httpserver/httpserver_test.go

@@ -228,7 +228,6 @@ const successfulInstanceResponse = `{
     "collector_resource_attributes": {},
     "collector_deployment_type": "unknown",
     "collector_installation_method": "",
-    "os": "",
     "ttl": 900000000000
   },
   "uuid": "test-uuid"

extension/datadogextension/internal/payload/payload.go

@@ -7,7 +7,6 @@ package payload // import "github.com/open-telemetry/opentelemetry-collector-con
 import (
 	"encoding/json"
 	"errors"
-	"runtime"
 
 	"github.com/DataDog/datadog-agent/pkg/serializer/marshaler"
 )
@@ -39,7 +38,6 @@ type OtelCollector struct {
 	CollectorResourceAttributes map[string]string  `json:"collector_resource_attributes"`
 	CollectorDeploymentType     string             `json:"collector_deployment_type"`     // deployment type: gateway, daemonset, or unknown
 	CollectorInstallationMethod string             `json:"collector_installation_method"` // installation method: kubernetes, bare-metal, docker, ecs-fargate, eks-fargate, or ""
-	OS                          string             `json:"os"`                            // runtime operating system (runtime.GOOS)
 	TTL                         int64              `json:"ttl"`
 }
 
@@ -110,7 +108,6 @@ func PrepareOtelCollectorMetadata(
 		FullConfiguration:           fullConfig,
 		CollectorDeploymentType:     deploymentType,
 		CollectorInstallationMethod: installationMethod,
-		OS:                          runtime.GOOS,
 		TTL:                         ttl,
 	}
 }

extension/datadogextension/internal/payload/payload_test.go

@@ -465,28 +465,6 @@ func TestPrepareOtelCollectorMetadata_DeploymentType(t *testing.T) {
 	}
 }
 
-func TestPrepareOtelCollectorMetadata_OS(t *testing.T) {
-	buildInfo := CustomBuildInfo{Command: "otelcol", Description: "Test Collector", Version: "1.0.0"}
-	metadata := PrepareOtelCollectorMetadata(
-		"test-host", "config", "test-uuid", "1.0.0", "datadoghq.com", "{}",
-		"unknown", "", buildInfo, int64(5*time.Minute*3),
-	)
-
-	assert.NotEmpty(t, metadata.OS)
-
-	payload := &OtelCollectorPayload{Hostname: "test-host", Timestamp: time.Now().UnixNano(), UUID: "test-uuid", Metadata: metadata}
-	jsonData, err := json.Marshal(payload)
-	require.NoError(t, err)
-
-	var jsonMap map[string]any
-	err = json.Unmarshal(jsonData, &jsonMap)
-	require.NoError(t, err)
-
-	metadataMap, ok := jsonMap["otel_collector"].(map[string]any)
-	require.True(t, ok)
-	assert.NotEmpty(t, metadataMap["os"])
-}
-
 func TestPrepareOtelCollectorMetadata_InstallationMethod(t *testing.T) {
 	tests := []struct {
 		name               string