fix(agent): minimal env and explicit project dir for compose, resolve every config file's symlinks (#7)

internal/agent/updater/compose.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"os/exec"
 	"strings"
 	"time"
@@ -43,10 +44,29 @@ func ExecDocker(ctx context.Context, dir string, out io.Writer, args ...string)
 	cmd.Dir = dir
 	cmd.Stdout = out
 	cmd.Stderr = out
+	cmd.Env = dockerEnv()
 	cmd.WaitDelay = 10 * time.Second
 	return cmd.Run()
 }
 
+// dockerEnvVars are the only variables from the agent's environment that
+// reach docker compose. Compose prefers process variables over the stack's
+// .env file when it interpolates, so passing the agent's own (HOSTNAME,
+// AGENT_TOKEN, ...) would change stack configuration and expose the token.
+var dockerEnvVars = []string{"PATH", "HOME", "DOCKER_HOST", "DOCKER_CONFIG", "DOCKER_TLS_VERIFY", "DOCKER_CERT_PATH"}
+
+// dockerEnv returns the allowed variables that are set in the agent's
+// environment, as KEY=value pairs.
+func dockerEnv() []string {
+	var env []string
+	for _, k := range dockerEnvVars {
+		if v := os.Getenv(k); v != "" {
+			env = append(env, k+"="+v)
+		}
+	}
+	return env
+}
+
 // ComposeDocker is the subset of the Docker SDK ComposeExecutor needs.
 type ComposeDocker interface {
 	SelfInspector
@@ -115,7 +135,9 @@ func (e *ComposeExecutor) Execute(ctx context.Context, job protocol.JobStart, ou
 		return "", err
 	}
 
-	base := []string{"compose", "-p", project}
+	// --project-directory is explicit because, with -f, compose would take it
+	// from the first file, which differs for stacks started with the flag.
+	base := []string{"compose", "-p", project, "--project-directory", workingDir}
 	for _, f := range files {
 		base = append(base, "-f", f)
 	}