[anomalydetection] gate recorder on python build tag (mirror observer)

Move recorder/fx-noop into recorder/fx/fx_noop.go with //go:build !python,
and add //go:build python to recorder/fx/fx.go. Same package, mutually
exclusive build tags — Go and Bazel rules_go pick the right Module()
implementation per flavor.

This matches the pattern observer (#50430) and logssource use: the
"python" tag is a proxy for "full agent, not IoT agent" — same import
path everywhere, build system decides whether arrow-go gets linked.

Result by flavor:
- agent_* / docker_agent_* (have python): real fx.go, arrow-go linked,
  recorder operational at runtime when recording.enabled=true.
- iot_agent_* / dogstatsd_* / cluster_agent_* (no python): fx_noop.go,
  empty fx options, no arrow-go in dep closure.

Resolves the worst static-quality-gate failures on iot_agent flavors
(+37-43% increase becomes 0). agent_* flavors still ship arrow-go and
need a size-gate exception filed separately — that is the unavoidable
cost of "recorder must run inside the agent at runtime", which is by
design (observer #50599 declares Recorder option.Option[Component]).

Also removes the now-redundant recorder/fx-noop and recorder/impl-noop
directories; cmd/agent's recorderfx import is unchanged.

Author: ellataira

comp/anomalydetection/observer/AGENTS.md

@@ -37,18 +37,18 @@ comp/anomalydetection/
     impl/
     impl-testbench/
     mock/
-  recorder/     ← parquet recorder for scenario capture
+  recorder/     ← parquet recorder for live scenario capture
     def/
-    fx/         ← full implementation (parquet, heavy deps)
-    fx-noop/    ← stub wired in the main agent build
+    fx/         ← fx.go (//go:build python) + fx_noop.go (//go:build !python)
     impl/
-    impl-noop/
 ```
 
-The **production agent** wires `reporter/fx-noop` and `recorder/fx-noop` to
-keep those heavy dependencies out of the agent binary. The
-**testbench** (`internal/qbranch/anomalydetection-testbench/`) wires the full
-`fx` + `impl` variants.
+The recorder is gated on the `python` build tag, used as a proxy for "full
+agent, not IoT agent" — same pattern as `observer/fx`. Full agent and
+docker agent flavors compile `recorder/fx/fx.go` and link `apache/arrow-go`;
+IoT, dogstatsd-only, cluster-agent, and serverless flavors compile
+`recorder/fx/fx_noop.go` and ship no parquet dependencies. The reporter
+component still uses a separate `reporter/fx-noop` package for now.
 
 ## Architecture
 

comp/anomalydetection/recorder/fx-noop/BUILD.bazel

@@ -2,12 +2,16 @@ load("@rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "fx",
-    srcs = ["fx.go"],
+    srcs = [
+        "fx.go",
+        "fx_noop.go",
+    ],
     importpath = "github.com/DataDog/datadog-agent/comp/anomalydetection/recorder/fx",
     visibility = ["//visibility:public"],
     deps = [
         "//comp/anomalydetection/recorder/def",
         "//comp/anomalydetection/recorder/impl",
         "//pkg/util/fxutil",
+        "@org_uber_go_fx//:fx",
     ],
 )

comp/anomalydetection/recorder/fx-noop/fx_noop.go

@@ -3,9 +3,13 @@
 // This product includes software developed at Datadog (https://www.datadoghq.com/).
 // Copyright 2016-present Datadog, Inc.
 
+// The `python` build tag is used here as a proxy for "full agent, not IoT agent".
+// See comp/anomalydetection/recorder/fx/fx_noop.go for the stub used in IoT agent
+// and other size-sensitive builds, which avoids linking apache/arrow-go.
+
+//go:build python
+
 // Package fx provides the fx module for the recorder component.
-// Wire this module when full parquet recording is needed (e.g. in the testbench).
-// For the main agent build, use recorder/fx-noop instead.
 package fx
 
 import (

comp/anomalydetection/recorder/fx/BUILD.bazel

@@ -0,0 +1,25 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2016-present Datadog, Inc.
+
+//go:build !python
+
+// Package fx provides the fx module for the recorder component.
+package fx
+
+import (
+	"go.uber.org/fx"
+
+	"github.com/DataDog/datadog-agent/pkg/util/fxutil"
+)
+
+// Module is a no-op for builds without Python support (e.g. IoT agent).
+// Returning empty fx options avoids linking apache/arrow-go into binaries
+// that do not need parquet recording. Consumers of recorder.Component are
+// expected to gate on the same `python` tag — see observer/fx for the
+// matching shape that ensures observer's optional Recorder dependency is
+// only declared when the real recorder Module is wired.
+func Module() fxutil.Module {
+	return fxutil.Module{Option: fx.Options()}
+}

comp/anomalydetection/recorder/fx/fx.go

@@ -6,6 +6,7 @@ require (
 	github.com/DataDog/datadog-agent/comp/anomalydetection/recorder/def v0.0.0-00010101000000-000000000000
 	github.com/DataDog/datadog-agent/comp/anomalydetection/recorder/impl v0.0.0-00010101000000-000000000000
 	github.com/DataDog/datadog-agent/pkg/util/fxutil v0.73.0-rc.5
+	go.uber.org/fx v1.24.0
 )
 
 require (
@@ -90,7 +91,6 @@ require (
 	go.opentelemetry.io/otel/trace v1.43.0 // indirect
 	go.uber.org/atomic v1.11.0 // indirect
 	go.uber.org/dig v1.19.0 // indirect
-	go.uber.org/fx v1.24.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	go.uber.org/zap v1.28.0 // indirect
 	go.yaml.in/yaml/v2 v2.4.4 // indirect