test(agentcompat): add agent runtime harness

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

integration/agentcompat/internal/agent/fm_observer.go

@@ -0,0 +1,92 @@
+//go:build linux
+
+package agent
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+type FMProducerSample struct {
+	RunID     string `json:"run_id"`
+	AgentUUID string `json:"agent_uuid"`
+	SessionID string `json:"session_id"`
+	Phase     string `json:"phase"`
+	Active    int64  `json:"active"`
+}
+
+type FMProducerObserver struct {
+	listener net.Listener
+	samples  chan FMProducerSample
+	done     chan struct{}
+	once     sync.Once
+}
+
+func newFMProducerObserver(socketPath string) (*FMProducerObserver, error) {
+	listener, err := net.Listen("unix", socketPath)
+	if err != nil {
+		return nil, fmt.Errorf("listen for FM producer observations: %w", err)
+	}
+	observer := &FMProducerObserver{listener: listener, samples: make(chan FMProducerSample, 16), done: make(chan struct{})}
+	go observer.accept()
+	return observer, nil
+}
+
+func (observer *FMProducerObserver) accept() {
+	defer close(observer.done)
+	for {
+		connection, err := observer.listener.Accept()
+		if err != nil {
+			if errors.Is(err, net.ErrClosed) {
+				return
+			}
+			continue
+		}
+		var sample FMProducerSample
+		err = json.NewDecoder(connection).Decode(&sample)
+		_ = connection.Close()
+		if err == nil {
+			observer.samples <- sample
+		}
+	}
+}
+
+func (observer *FMProducerObserver) Await(ctx context.Context, match func(FMProducerSample) bool) (FMProducerSample, error) {
+	for {
+		select {
+		case sample := <-observer.samples:
+			if match(sample) {
+				return sample, nil
+			}
+		case <-ctx.Done():
+			return FMProducerSample{}, ctx.Err()
+		}
+	}
+}
+
+func (observer *FMProducerObserver) Close() error {
+	var closeErr error
+	observer.once.Do(func() {
+		closeErr = observer.listener.Close()
+		<-observer.done
+	})
+	return closeErr
+}
+
+func fmObserverSocketPath(workspaceRoot string) string {
+	return filepath.Join(workspaceRoot, "fm-observer.sock")
+}
+
+func removeFMObserverSocket(path string) error {
+	err := os.Remove(path)
+	if errors.Is(err, os.ErrNotExist) {
+		return nil
+	}
+	return err
+}