Do external package manager check only at startup

We were doing the check for external package manager use when validating
vars for the platform, which happens on every configuration reload. I've
made this an attribute of the platform instead, and it's now only
checked on startup.

changelog/fragments/1733131399-vars-for-platform.yaml

@@ -0,0 +1,32 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: feature
+
+# Change summary; a 80ish characters long description of the change.
+summary: Do the external package manager check only at startup
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+# NOTE: This field will be rendered only for breaking-change and known-issue kinds at the moment.
+#description:
+
+# Affected component; usually one of "elastic-agent", "fleet-server", "filebeat", "metricbeat", "auditbeat", "all", etc.
+component: elastic-agent
+
+# PR URL; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+#pr: https://github.com/owner/repo/1234
+
+# Issue URL; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+#issue: https://github.com/owner/repo/1234

pkg/component/component.go

@@ -15,7 +15,6 @@ import (
 	"github.com/elastic/elastic-agent-libs/logp"
 
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
-	"github.com/elastic/elastic-agent/internal/pkg/agent/install/pkgmgr"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/transpiler"
 	"github.com/elastic/elastic-agent/internal/pkg/core/monitoring/config"
 	"github.com/elastic/elastic-agent/internal/pkg/eql"
@@ -682,7 +681,7 @@ type outputI struct {
 func varsForPlatform(platform PlatformDetail) (*transpiler.Vars, error) {
 	return transpiler.NewVars("", map[string]interface{}{
 		"install": map[string]interface{}{
-			"in_default": paths.ArePathsEqual(paths.Top(), paths.InstallPath(paths.DefaultBasePath)) || pkgmgr.InstalledViaExternalPkgMgr(),
+			"in_default": paths.ArePathsEqual(paths.Top(), paths.InstallPath(paths.DefaultBasePath)) || platform.IsInstalledViaExternalPkgMgr,
 		},
 		"runtime": map[string]interface{}{
 			"platform":    platform.String(),

pkg/component/platforms.go

@@ -6,6 +6,7 @@ package component
 
 import (
 	"fmt"
+	"github.com/elastic/elastic-agent/internal/pkg/agent/install/pkgmgr"
 	goruntime "runtime"
 	"strings"
 
@@ -114,7 +115,8 @@ type PlatformDetail struct {
 	Major      int
 	Minor      int
 
-	User UserDetail
+	IsInstalledViaExternalPkgMgr bool
+	User                         UserDetail
 }
 
 // PlatformModifier can modify the platform details before the runtime specifications are loaded.
@@ -155,6 +157,7 @@ func LoadPlatformDetail(modifiers ...PlatformModifier) (PlatformDetail, error) {
 		User: UserDetail{
 			Root: hasRoot,
 		},
+		IsInstalledViaExternalPkgMgr: pkgmgr.InstalledViaExternalPkgMgr(),
 	}
 	for _, modifier := range modifiers {
 		detail = modifier(detail)