fix(staging): add isCPTemplateConfigFile filter to collectCPConfigFiles

Cherry-picks the filter from main commit 8fced202: only transport
config.yaml and files under prompts/ from the template directory to the
control plane. Arbitrary template files (adapter.py, Dockerfile, etc.)
are now excluded regardless of size, reducing the transport surface.

Also adds a test case verifying adapter.py is excluded even when within
the size limit.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

workspace-server/internal/provisioner/cp_provisioner.go

@@ -257,6 +257,16 @@ func (p *CPProvisioner) Start(ctx context.Context, cfg WorkspaceConfig) (string,
 
 const cpConfigFilesMaxBytes = 12 << 10
 
+// isCPTemplateConfigFile restricts which files from a template directory are
+// eligible for transport to the control plane. Only config.yaml (the runtime
+// entrypoint config) and files under prompts/ (system prompts) are needed;
+// shipping arbitrary files (e.g. adapter.py, Dockerfile) is both unnecessary
+// and a potential data-exfiltration surface.
+func isCPTemplateConfigFile(name string) bool {
+	name = filepath.ToSlash(filepath.Clean(name))
+	return name == "config.yaml" || strings.HasPrefix(name, "prompts/")
+}
+
 func collectCPConfigFiles(cfg WorkspaceConfig) (map[string]string, error) {
 	files := make(map[string]string)
 	total := 0
@@ -310,6 +320,9 @@ func collectCPConfigFiles(cfg WorkspaceConfig) (map[string]string, error) {
 			if err != nil {
 				return err
 			}
+			if !isCPTemplateConfigFile(rel) {
+				return nil
+			}
 			data, err := os.ReadFile(path)
 			if err != nil {
 				return err

workspace-server/internal/provisioner/cp_provisioner_test.go

@@ -1,6 +1,7 @@
 package provisioner
 
 import (
+	"bytes"
 	"context"
 	"encoding/base64"
 	"encoding/json"
@@ -291,6 +292,11 @@ func TestStart_CollectsConfigFiles(t *testing.T) {
 	if err := os.WriteFile(filepath.Join(tmpl, "config.yaml"), []byte("name: test\n"), 0o600); err != nil {
 		t.Fatal(err)
 	}
+	// adapter.py is within the size limit but is NOT config.yaml or prompts/,
+	// so isCPTemplateConfigFile must exclude it from the transport.
+	if err := os.WriteFile(filepath.Join(tmpl, "adapter.py"), bytes.Repeat([]byte("x"), cpConfigFilesMaxBytes), 0o600); err != nil {
+		t.Fatal(err)
+	}
 
 	var gotBody cpProvisionRequest
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -339,6 +345,12 @@ func TestStart_CollectsConfigFiles(t *testing.T) {
 	if !foundGenerated {
 		t.Errorf("ConfigFiles missing generated.json from ConfigFiles")
 	}
+	// adapter.py must NOT be in ConfigFiles — isCPTemplateConfigFile filters it out
+	for name := range gotBody.ConfigFiles {
+		if name == "adapter.py" {
+			t.Errorf("adapter.py should not be in ConfigFiles — isCPTemplateConfigFile must filter it out")
+		}
+	}
 }
 
 // TestStart_SymlinkTemplatePathError — a symlink TemplatePath should cause