diff --git a/internal/loader/artifact_cache.go b/internal/loader/artifact_cache.go
index e920d5a..ff3f753 100644
--- a/internal/loader/artifact_cache.go
+++ b/internal/loader/artifact_cache.go
@@ -20,10 +20,10 @@ import (
 	"encoding/hex"
 	"go/token"
 	"go/types"
+	"io"
 	"os"
 	"path/filepath"
 	"runtime"
-	"strconv"
 
 	"golang.org/x/tools/go/gcexportdata"
 )
@@ -62,7 +62,7 @@ func loaderArtifactPath(env []string, meta *packageMeta, isLocal bool) (string,
 
 func loaderArtifactKey(meta *packageMeta, isLocal bool) (string, error) {
 	sum := sha256.New()
-	sum.Write([]byte("wire-loader-artifact-v3\n"))
+	sum.Write([]byte("wire-loader-artifact-v4\n"))
 	sum.Write([]byte(runtime.Version()))
 	sum.Write([]byte{'\n'})
 	sum.Write([]byte(meta.ImportPath))
@@ -73,26 +73,15 @@ func loaderArtifactKey(meta *packageMeta, isLocal bool) (string, error) {
 		sum.Write([]byte(meta.Export))
 		sum.Write([]byte{'\n'})
 		if meta.Export != "" {
-			info, err := os.Stat(meta.Export)
+			h, err := hashFileContent(meta.Export)
 			if err != nil {
 				return "", err
 			}
-			sum.Write([]byte(strconv.FormatInt(info.Size(), 10)))
-			sum.Write([]byte{'\n'})
-			sum.Write([]byte(strconv.FormatInt(info.ModTime().UnixNano(), 10)))
+			sum.Write([]byte(h))
 			sum.Write([]byte{'\n'})
 		} else {
-			for _, name := range metaFiles(meta) {
-				info, err := os.Stat(name)
-				if err != nil {
-					return "", err
-				}
-				sum.Write([]byte(name))
-				sum.Write([]byte{'\n'})
-				sum.Write([]byte(strconv.FormatInt(info.Size(), 10)))
-				sum.Write([]byte{'\n'})
-				sum.Write([]byte(strconv.FormatInt(info.ModTime().UnixNano(), 10)))
-				sum.Write([]byte{'\n'})
+			if err := hashMetaFiles(sum, metaFiles(meta)); err != nil {
+				return "", err
 			}
 		}
 		if meta.Error != nil {
@@ -101,19 +90,35 @@ func loaderArtifactKey(meta *packageMeta, isLocal bool) (string, error) {
 		}
 		return hex.EncodeToString(sum.Sum(nil)), nil
 	}
-	for _, name := range metaFiles(meta) {
-		info, err := os.Stat(name)
-		if err != nil {
-			return "", err
-		}
+	if err := hashMetaFiles(sum, metaFiles(meta)); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(sum.Sum(nil)), nil
+}
+
+// hashFileContent returns the hex-encoded SHA-256 of the file content.
+func hashFileContent(path string) (string, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	h := sha256.Sum256(data)
+	return hex.EncodeToString(h[:]), nil
+}
+
+// hashMetaFiles writes content-based hashes for each file into sum.
+func hashMetaFiles(sum io.Writer, names []string) error {
+	for _, name := range names {
 		sum.Write([]byte(name))
 		sum.Write([]byte{'\n'})
-		sum.Write([]byte(strconv.FormatInt(info.Size(), 10)))
-		sum.Write([]byte{'\n'})
-		sum.Write([]byte(strconv.FormatInt(info.ModTime().UnixNano(), 10)))
+		h, err := hashFileContent(name)
+		if err != nil {
+			return err
+		}
+		sum.Write([]byte(h))
 		sum.Write([]byte{'\n'})
 	}
-	return hex.EncodeToString(sum.Sum(nil)), nil
+	return nil
 }
 
 func readLoaderArtifact(path string, fset *token.FileSet, imports map[string]*types.Package, pkgPath string) (*types.Package, error) {
diff --git a/internal/loader/discovery_cache.go b/internal/loader/discovery_cache.go
index 1151853..6d59a22 100644
--- a/internal/loader/discovery_cache.go
+++ b/internal/loader/discovery_cache.go
@@ -28,10 +28,11 @@ type discoveryLocalPackage struct {
 }
 
 type discoveryFileMeta struct {
-	Path    string
-	Size    int64
-	ModTime int64
-	IsDir   bool
+	Path        string
+	Size        int64
+	ModTime     int64  // deprecated: kept for gob compat, not used for matching
+	ContentHash string // sha256 of file content
+	IsDir       bool
 }
 
 type discoveryDirMeta struct {
@@ -44,7 +45,7 @@ type discoveryFileFingerprint struct {
 	Hash string
 }
 
-const discoveryCacheVersion = 3
+const discoveryCacheVersion = 4
 
 func readDiscoveryCache(req goListRequest) (map[string]*packageMeta, bool) {
 	entry, err := loadDiscoveryCacheEntry(req)
@@ -121,10 +122,16 @@ func validateDiscoveryCacheEntry(entry *discoveryCacheEntry) bool {
 	return true
 }
 
+const discoveryCacheDirEnv = "WIRE_DISCOVERY_CACHE_DIR"
+
 func discoveryCachePath(req goListRequest) (string, error) {
-	base, err := os.UserCacheDir()
-	if err != nil {
-		return "", err
+	dir := os.Getenv(discoveryCacheDirEnv)
+	if dir == "" {
+		base, err := os.UserCacheDir()
+		if err != nil {
+			return "", err
+		}
+		dir = filepath.Join(base, "wire", "discovery-cache")
 	}
 	sumReq := struct {
 		Version      int
@@ -147,7 +154,7 @@ func discoveryCachePath(req goListRequest) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	return filepath.Join(base, "wire", "discovery-cache", key+".gob"), nil
+	return filepath.Join(dir, key+".gob"), nil
 }
 
 func loadDiscoveryCacheEntry(req goListRequest) (*discoveryCacheEntry, error) {
@@ -188,11 +195,19 @@ func statDiscoveryFile(path string) (discoveryFileMeta, bool) {
 	if err != nil {
 		return discoveryFileMeta{}, false
 	}
+	h := ""
+	if !info.IsDir() {
+		var err error
+		h, err = hashFileContent(path)
+		if err != nil {
+			return discoveryFileMeta{}, false
+		}
+	}
 	return discoveryFileMeta{
-		Path:    canonicalLoaderPath(path),
-		Size:    info.Size(),
-		ModTime: info.ModTime().UnixNano(),
-		IsDir:   info.IsDir(),
+		Path:        canonicalLoaderPath(path),
+		Size:        info.Size(),
+		ContentHash: h,
+		IsDir:       info.IsDir(),
 	}, true
 }
 
@@ -201,7 +216,7 @@ func matchesDiscoveryFile(fm discoveryFileMeta) bool {
 	if !ok {
 		return false
 	}
-	return cur.Size == fm.Size && cur.ModTime == fm.ModTime && cur.IsDir == fm.IsDir
+	return cur.ContentHash == fm.ContentHash && cur.IsDir == fm.IsDir
 }
 
 func statDiscoveryDir(path string) (discoveryDirMeta, bool) {