fix(shared/filesystem): make package build and tests pass on macOS (#2604)

The filesystem package referenced Linux-only fields on syscall.Stat_t
(Atim, Ctim, Mtim), causing 'go test ./...' to fail on Darwin where
those fields are named Atimespec/Ctimespec/Mtimespec.

Refactor the OS-specific stat extraction into a small statTimes struct
and an extractStatTimes helper, implemented per-platform behind build
tags:

  - entry_linux.go  (//go:build linux)  uses Atim/Ctim/Mtim
- entry_darwin.go (//go:build darwin) uses Atimespec/Ctimespec/Mtimespec

This keeps production behavior unchanged on Linux while letting the
package compile and its tests run on macOS, so contributors can run 'go
test ./...' from packages/shared locally without cross-compiling.

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: tvi

packages/shared/pkg/filesystem/entry.go

@@ -7,6 +7,16 @@ import (
 	"time"
 )
 
+// statTimes holds platform-independent file timestamps and ownership info
+// extracted from a *syscall.Stat_t.
+type statTimes struct {
+	atime time.Time
+	ctime time.Time
+	mtime time.Time
+	uid   uint32
+	gid   uint32
+}
+
 func GetEntryFromPath(path string) (EntryInfo, error) {
 	fileInfo, err := os.Lstat(path)
 	if err != nil {
@@ -55,11 +65,12 @@ func GetEntryInfo(path string, fileInfo os.FileInfo) EntryInfo {
 	}
 
 	if base := getBase(fileInfo.Sys()); base != nil {
-		entry.AccessedTime = toTimestamp(base.Atim)
-		entry.CreatedTime = toTimestamp(base.Ctim)
-		entry.ModifiedTime = toTimestamp(base.Mtim)
-		entry.UID = base.Uid
-		entry.GID = base.Gid
+		times := extractStatTimes(base)
+		entry.AccessedTime = times.atime
+		entry.CreatedTime = times.ctime
+		entry.ModifiedTime = times.mtime
+		entry.UID = times.uid
+		entry.GID = times.gid
 	} else if !fileInfo.ModTime().IsZero() {
 		entry.ModifiedTime = fileInfo.ModTime()
 	}

packages/shared/pkg/filesystem/entry_darwin.go

@@ -0,0 +1,15 @@
+//go:build darwin
+
+package filesystem
+
+import "syscall"
+
+func extractStatTimes(base *syscall.Stat_t) statTimes {
+	return statTimes{
+		atime: toTimestamp(base.Atimespec),
+		ctime: toTimestamp(base.Birthtimespec),
+		mtime: toTimestamp(base.Mtimespec),
+		uid:   base.Uid,
+		gid:   base.Gid,
+	}
+}

packages/shared/pkg/filesystem/entry_linux.go

@@ -0,0 +1,15 @@
+//go:build linux
+
+package filesystem
+
+import "syscall"
+
+func extractStatTimes(base *syscall.Stat_t) statTimes {
+	return statTimes{
+		atime: toTimestamp(base.Atim),
+		ctime: toTimestamp(base.Ctim),
+		mtime: toTimestamp(base.Mtim),
+		uid:   base.Uid,
+		gid:   base.Gid,
+	}
+}