diff --git a/cmd/recipe_bootstrap/main.go b/cmd/recipe_bootstrap/main.go
index 2b45196..b88dea8 100644
--- a/cmd/recipe_bootstrap/main.go
+++ b/cmd/recipe_bootstrap/main.go
@@ -79,8 +79,8 @@
 }
 
 // Calls a luciexe, attaching its steps to sr.Build.Steps.
-func (sr *bootstrapStepRunner) invoke(ctx context.Context, exePath string, opts *invoke.Options) error {
-	subprocess, err := invoke.Start(ctx, exePath, sr.build, opts)
+func (sr *bootstrapStepRunner) invoke(ctx context.Context, exeArgs []string, opts *invoke.Options) error {
+	subprocess, err := invoke.Start(ctx, exeArgs, sr.build, opts)
 	if err != nil {
 		return err
 	}
@@ -156,20 +156,20 @@
 	}
 	luciexePath := filepath.Join(cwd, cipdRoot, "luciexe")
 	// Invoke recipe bundle luciexe.
-	if err := sr.invoke(ctx, luciexePath, &invokeOpts); err != nil {
+	if err := sr.invoke(ctx, []string{luciexePath}, &invokeOpts); err != nil {
 		return err
 	}
 	return nil
 }
 
 func main() {
-	exe.Run(func(ctx context.Context, build *buildbucketpb.Build, send exe.BuildSender) error {
+	exe.Run(func(ctx context.Context, input *buildbucketpb.Build, userArgs []string, send exe.BuildSender) error {
 		logdogBootstrap, err := bootstrap.Get()
 		if err != nil {
 			return err
 		}
 		return bootstrapRecipe(ctx, &bootstrapStepRunner{
-			build:     build,
+			build:     input,
 			send:      send,
 			bootstrap: logdogBootstrap,
 		})
diff --git a/cmd/recipe_bootstrap/step.go b/cmd/recipe_bootstrap/step.go
index 18833ae..acedf28 100644
--- a/cmd/recipe_bootstrap/step.go
+++ b/cmd/recipe_bootstrap/step.go
@@ -19,5 +19,5 @@
 	runStep(ctx context.Context, name string, fn stepFunc) error
 
 	// Invoke calls a luciexe, attaching its Steps to Build.Steps.
-	invoke(ctx context.Context, exePath string, opts *invoke.Options) error
+	invoke(ctx context.Context, exeArgs []string, opts *invoke.Options) error
 }
diff --git a/cmd/recipe_bootstrap/step_test.go b/cmd/recipe_bootstrap/step_test.go
index 0437c2b..40facb1 100644
--- a/cmd/recipe_bootstrap/step_test.go
+++ b/cmd/recipe_bootstrap/step_test.go
@@ -19,7 +19,7 @@
 	return nil
 }
 
-func (sr *successfulStepRunner) invoke(ctx context.Context, exePath string, opts *invoke.Options) error {
+func (sr *successfulStepRunner) invoke(ctx context.Context, exeArgs []string, opts *invoke.Options) error {
 	return nil
 }
 
@@ -29,7 +29,7 @@
 	return errors.New("step failed")
 }
 
-func (sr *failingStepRunner) invoke(ctx context.Context, exePath string, opts *invoke.Options) error {
+func (sr *failingStepRunner) invoke(ctx context.Context, exeArgs []string, opts *invoke.Options) error {
 	return errors.New("invoke failed")
 }
 
@@ -73,7 +73,7 @@
 		} else if !test.expectedRunStepErr {
 			t.Fatalf("got unexpected error %v", err)
 		}
-		err = test.sr.invoke(ctx, "", &invoke.Options{})
+		err = test.sr.invoke(ctx, []string{}, &invoke.Options{})
 		if err == nil {
 			if test.expectedInvokeErr {
 				t.Fatalf("expected error, got nil")
diff --git a/go.mod b/go.mod
index 6325974..b5fd797 100644
--- a/go.mod
+++ b/go.mod
@@ -10,7 +10,7 @@
 	github.com/docker/go-units v0.3.3 // indirect
 	github.com/gogo/protobuf v1.1.1 // indirect
 	github.com/golang/mock v1.4.0
-	github.com/golang/protobuf v1.3.3
+	github.com/golang/protobuf v1.4.1
 	github.com/google/go-cmp v0.4.0
 	github.com/google/subcommands v1.0.1
 	github.com/google/uuid v1.1.1
@@ -27,7 +27,7 @@
 	github.com/smartystreets/goconvey v0.0.0-20190330032615-68dc04aab96a // indirect
 	github.com/texttheater/golang-levenshtein v0.0.0-20180516184445-d188e65d659e // indirect
 	go.chromium.org/gae v0.0.0-20190826183307-50a499513efa // indirect
-	go.chromium.org/luci v0.0.0-20200502172955-ba1dbf255208
+	go.chromium.org/luci v0.0.0-20200618184218-0a74025c6b50
 	go.fuchsia.dev/fuchsia v0.0.0-20200428055653-c6718692bc20
 	go.fuchsia.dev/tools v0.0.0-20190902223517-00b2baf53fff
 	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550
@@ -36,8 +36,9 @@
 	golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae
 	golang.org/x/time v0.0.0-20191024005414-555d28b269f0
 	google.golang.org/api v0.18.0
-	google.golang.org/genproto v0.0.0-20200224152610-e50cd9704f63
+	google.golang.org/genproto v0.0.0-20200526211855-cb27e3aa2013
 	google.golang.org/grpc v1.29.1
+	google.golang.org/protobuf v1.24.0 // indirect
 )
 
 go 1.13
diff --git a/go.sum b/go.sum
index 3a32837..9f9b2b9 100644
--- a/go.sum
+++ b/go.sum
@@ -71,6 +71,13 @@
 github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.3.3 h1:gyjaxf+svBWX08ZjK86iN9geUJF0H6gp2IRKX6Nf6/I=
 github.com/golang/protobuf v1.3.3/go.mod h1:vzj43D7+SQXF/4pzW/hwtAqwc6iTitCiVSaWz5lYuqw=
+github.com/golang/protobuf v1.4.0-rc.1/go.mod h1:ceaxUfeHdC40wWswd/P6IGgMaK3YpKi5j83Wpe3EHw8=
+github.com/golang/protobuf v1.4.0-rc.1.0.20200221234624-67d41d38c208/go.mod h1:xKAWHe0F5eneWXFV3EuXVDTCmh+JuBKY0li0aMyXATA=
+github.com/golang/protobuf v1.4.0-rc.2/go.mod h1:LlEzMj4AhA7rCAGe4KMBDvJI+AwstrUpVNzEA03Pprs=
+github.com/golang/protobuf v1.4.0-rc.4.0.20200313231945-b860323f09d0/go.mod h1:WU3c8KckQ9AFe+yFwt9sWVRKCVIyN9cPHBJSNnbL67w=
+github.com/golang/protobuf v1.4.0/go.mod h1:jodUvKwWbYaEsadDk5Fwe5c77LiNKVO9IDvqG2KuDX0=
+github.com/golang/protobuf v1.4.1 h1:ZFgWrT+bLgsYPirOnRfKLYJLvssAegOj/hgyMFdJZe0=
+github.com/golang/protobuf v1.4.1/go.mod h1:U8fpvMrcmy5pZrNK1lt4xCsGvpyWQ/VVv6QDs8UjoX8=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/btree v1.0.0/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
@@ -150,6 +157,8 @@
 go.chromium.org/gae v0.0.0-20190826183307-50a499513efa/go.mod h1:ypuIZj/TmtaQgUYPNNu0iKlsUkuv10PROeqHCNrqrog=
 go.chromium.org/luci v0.0.0-20200502172955-ba1dbf255208 h1:ZhAof78/orfTT3L0crZ5Kr/K1dIqktuttZEVlkrdHyg=
 go.chromium.org/luci v0.0.0-20200502172955-ba1dbf255208/go.mod h1:MIQewVTLvOvc0UioV0JNqTNO/RspKFS0XEeoKrOxsdM=
+go.chromium.org/luci v0.0.0-20200618184218-0a74025c6b50 h1:5UP/hlkUwUM36dYoSVR7XzydvHLkblFprg5UfQ+RVlU=
+go.chromium.org/luci v0.0.0-20200618184218-0a74025c6b50/go.mod h1:MIQewVTLvOvc0UioV0JNqTNO/RspKFS0XEeoKrOxsdM=
 go.fuchsia.dev/fuchsia v0.0.0-20200428055653-c6718692bc20 h1:eDwOWbKauksACQGG3csBzFxPeGFy7Wag83ba6D8EvRw=
 go.fuchsia.dev/fuchsia v0.0.0-20200428055653-c6718692bc20/go.mod h1:UW6wH97UX+1WpRyT15aaOnHLqC1nGmmxF1GGmHXP8kc=
 go.fuchsia.dev/tools v0.0.0-20190902223517-00b2baf53fff h1:FKDLyKcMCfPoFxjcNp97H5t4T2Zr2pKt+e4e9PGW+2g=
@@ -320,6 +329,8 @@
 google.golang.org/genproto v0.0.0-20200212174721-66ed5ce911ce/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200224152610-e50cd9704f63 h1:YzfoEYWbODU5Fbt37+h7X16BWQbad7Q4S6gclTKFXM8=
 google.golang.org/genproto v0.0.0-20200224152610-e50cd9704f63/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
+google.golang.org/genproto v0.0.0-20200526211855-cb27e3aa2013 h1:+kGHl1aib/qcwaRi1CbqBZ1rk19r85MNUf8HaBghugY=
+google.golang.org/genproto v0.0.0-20200526211855-cb27e3aa2013/go.mod h1:NbSheEEYHJ7i3ixzK3sjbqSGDJWnxyFXZblF3eUsNvo=
 google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
 google.golang.org/grpc v1.20.1/go.mod h1:10oTOabMzJvdu6/UiuZezV6QK5dSlG84ov/aaiqXj38=
 google.golang.org/grpc v1.21.1 h1:j6XxA85m/6txkUCHvzlV5f+HBNl/1r5cZ2A/3IEFOO8=
@@ -331,6 +342,15 @@
 google.golang.org/grpc v1.27.1/go.mod h1:qbnxyOmOxrQa7FizSgH+ReBfzJrCY1pSN7KXBS8abTk=
 google.golang.org/grpc v1.29.1 h1:EC2SB8S04d2r73uptxphDSUG+kTKVgjRPF+N3xpxRB4=
 google.golang.org/grpc v1.29.1/go.mod h1:itym6AZVZYACWQqET3MqgPpjcuV5QH3BxFS3IjizoKk=
+google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
+google.golang.org/protobuf v0.0.0-20200221191635-4d8936d0db64/go.mod h1:kwYJMbMJ01Woi6D6+Kah6886xMZcty6N08ah7+eCXa0=
+google.golang.org/protobuf v0.0.0-20200228230310-ab0ca4ff8a60/go.mod h1:cfTl7dwQJ+fmap5saPgwCLgHXTUD7jkjRqWcaiX5VyM=
+google.golang.org/protobuf v1.20.1-0.20200309200217-e05f789c0967/go.mod h1:A+miEFZTKqfCUM6K7xSMQL9OKL/b6hQv+e19PK+JZNE=
+google.golang.org/protobuf v1.21.0/go.mod h1:47Nbq4nVaFHyn7ilMalzfO3qCViNmqZ2kzikPIcrTAo=
+google.golang.org/protobuf v1.22.0/go.mod h1:EGpADcykh3NcUnDUJcl1+ZksZNG86OlYog2l/sGQquU=
+google.golang.org/protobuf v1.23.1-0.20200526195155-81db48ad09cc/go.mod h1:EGpADcykh3NcUnDUJcl1+ZksZNG86OlYog2l/sGQquU=
+google.golang.org/protobuf v1.24.0 h1:UhZDfRO8JRQru4/+LlLE0BRKGF8L+PICnvYZmx/fEGA=
+google.golang.org/protobuf v1.24.0/go.mod h1:r/3tXBNzIEhYS9I1OUVjXDlt8tc493IdKGjtUeSXeh4=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=