fix(sandbox): cap the Go daemon's fs route request bodies

packages/sandbox/daemon-go/internal/routes/fs.go

@@ -42,11 +42,18 @@ func (d FsDeps) notifyWrite(path string) {
 	}
 }
 
+// decodeBody caps the request body at maxTransferBytes: without a limit, a
+// misbehaving or malicious caller could stream an unbounded body into memory
+// and crash the daemon, tearing down the sandbox pod on the next missed
+// health probe. The cap matches the daemon's other file-transfer bound.
 func decodeBody(r *http.Request, out any) error {
-	raw, err := io.ReadAll(r.Body)
+	raw, err := io.ReadAll(io.LimitReader(r.Body, maxTransferBytes+1))
 	if err != nil {
 		return fmt.Errorf("Failed to parse body: %s", err.Error())
 	}
+	if len(raw) > maxTransferBytes {
+		return fmt.Errorf("Request body exceeded %d bytes", maxTransferBytes)
+	}
 	if err := json.Unmarshal(raw, out); err != nil {
 		return fmt.Errorf("Failed to parse body: %s", err.Error())
 	}

packages/sandbox/daemon-go/internal/routes/fs_test.go

@@ -3,10 +3,12 @@ package routes
 import (
 	"bytes"
 	"encoding/json"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -30,6 +32,32 @@ func seedBlocks(t *testing.T) FsDeps {
 	return FsDeps{AppRoot: filepath.Dir(repoDir), RepoDir: repoDir}
 }
 
+// infiniteReader never hits EOF; it lets a test drive decodeBody's cap
+// without pre-allocating the oversized body it's rejecting.
+type infiniteReader struct{}
+
+func (infiniteReader) Read(p []byte) (int, error) {
+	for i := range p {
+		p[i] = 'a'
+	}
+	return len(p), nil
+}
+
+// Without a cap, decodeBody's io.ReadAll(r.Body) would buffer an unbounded
+// request body into memory and could crash the daemon, tearing down the
+// sandbox pod on the next missed health probe.
+func TestDecodeBodyRejectsOversizedRequest(t *testing.T) {
+	req := httptest.NewRequest(http.MethodPost, "/write", io.NopCloser(infiniteReader{}))
+	var out map[string]any
+	err := decodeBody(req, &out)
+	if err == nil {
+		t.Fatal("expected decodeBody to reject an oversized body, got nil error")
+	}
+	if !strings.Contains(err.Error(), "exceeded") {
+		t.Fatalf("expected a size-limit error, got: %v", err)
+	}
+}
+
 func readReq(t *testing.T, deps FsDeps, path string) *httptest.ResponseRecorder {
 	t.Helper()
 	body, _ := json.Marshal(map[string]any{"path": path, "full": true})