diff --git a/go/engine/php/workspace.go b/go/engine/php/workspace.go
index 035d425..7ff26c8 100644
--- a/go/engine/php/workspace.go
+++ b/go/engine/php/workspace.go
@@ -2,7 +2,6 @@ package php
 
 import (
 	core "dappco.re/go"
-	"dappco.re/go/io"
 	"gopkg.in/yaml.v3"
 )
 
@@ -24,19 +23,31 @@ func defaultWorkspaceConfig() *workspaceConfig {
 
 // loadWorkspaceConfig tries to load workspace.yaml from the given directory's .core subfolder.
 // Returns nil if no config file exists.
+//
+// The probe walks UP an arbitrary ancestor chain, so it is deliberately
+// not coreio.Local: since go-io v0.15.2 the local medium routes through
+// os.Root, which by design refuses any path leaving its root — including
+// one that merely traverses a symlink. Correct for sandboxed media,
+// wrong for a search that is unbounded by construction. Reached through
+// a symlinked project directory (an ordinary macOS layout), Local.Read
+// fails "path escapes from parent" AND Local.IsFile returns false, so
+// this walked past a config that exists and reported the workspace as
+// unconfigured. The os-level core.Stat / core.ReadFile are the right
+// tool for probing; coreio media stay correct for sandboxed I/O.
 func loadWorkspaceConfig(dir string) (*workspaceConfig, error) { // Result boundary
 	path := core.PathJoin(dir, ".core", "workspace.yaml")
-	data, err := io.Local.Read(path)
-	if err != nil {
-		if !io.Local.IsFile(path) {
+	readResult := core.ReadFile(path)
+	if !readResult.OK {
+		if stat := core.Stat(path); !stat.OK {
 			parent := core.PathDir(dir)
 			if parent != dir {
 				return loadWorkspaceConfig(parent)
 			}
 			return nil, nil
 		}
-		return nil, core.Errorf("failed to read workspace config: %w", err)
+		return nil, core.Errorf("failed to read workspace config: %w", readResult.Err())
 	}
+	data := string(readResult.Value.([]byte))
 
 	config := defaultWorkspaceConfig()
 	if err := yaml.Unmarshal([]byte(data), config); err != nil {
@@ -60,7 +71,9 @@ func findWorkspaceRoot() (string, error) { // Result boundary
 	dir, _ := cwdResult.Value.(string)
 
 	for {
-		if io.Local.IsFile(core.PathJoin(dir, ".core", "workspace.yaml")) {
+		// os-level stat, for the same reason as loadWorkspaceConfig: this
+		// walks up to the filesystem root, so no medium root can contain it.
+		if isRegularFile(core.PathJoin(dir, ".core", "workspace.yaml")) {
 			return dir, nil
 		}
 
@@ -73,3 +86,16 @@ func findWorkspaceRoot() (string, error) { // Result boundary
 
 	return "", core.Errorf("not in a workspace")
 }
+
+// isRegularFile reports whether path names an existing non-directory,
+// following symlinks. Uses core.Stat (os.Stat) rather than a coreio
+// medium because the callers probe ancestor directories that no medium
+// root contains — see loadWorkspaceConfig.
+func isRegularFile(path string) bool {
+	result := core.Stat(path)
+	if !result.OK {
+		return false
+	}
+	info, ok := result.Value.(core.FsFileInfo)
+	return ok && !info.IsDir()
+}
diff --git a/go/engine/php/workspace_symlink_test.go b/go/engine/php/workspace_symlink_test.go
new file mode 100644
index 0000000..4206fb4
--- /dev/null
+++ b/go/engine/php/workspace_symlink_test.go
@@ -0,0 +1,116 @@
+// SPDX-Licence-Identifier: EUPL-1.2
+
+package php
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// TestLoadWorkspaceConfig_ThroughSymlink pins the go-io v0.15.2
+// regression this code used to sit on.
+//
+// Since v0.15.2 the coreio local medium routes through os.Root, which by
+// design refuses a path that leaves its root — including one that merely
+// traverses a symlink. loadWorkspaceConfig probes ancestor directories,
+// so no medium root can contain it: reached through a symlinked project
+// directory (an ordinary macOS layout, and what any worktree or
+// /tmp-based test produces), Local.Read failed "path escapes from
+// parent" AND Local.IsFile returned false, so the walk continued past a
+// config that exists and reported the workspace as unconfigured.
+//
+// The config must be found through the symlink exactly as through the
+// real path.
+func TestLoadWorkspaceConfig_ThroughSymlink(t *testing.T) {
+	base := t.TempDir()
+	real := filepath.Join(base, "project")
+	if err := os.MkdirAll(filepath.Join(real, ".core"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	body := "version: 1\nactive: web\npackages_dir: ./pkgs\n"
+	if err := os.WriteFile(filepath.Join(real, ".core", "workspace.yaml"), []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	link := filepath.Join(base, "linked-project")
+	if err := os.Symlink(real, link); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+
+	for _, tc := range []struct{ name, dir string }{
+		{"direct", real},
+		{"through_symlink", link},
+		{"child_through_symlink", filepath.Join(link, "nested")},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			if tc.name == "child_through_symlink" {
+				if err := os.MkdirAll(tc.dir, 0o755); err != nil {
+					t.Fatal(err)
+				}
+			}
+			config, err := loadWorkspaceConfig(tc.dir)
+			if err != nil {
+				t.Fatalf("loadWorkspaceConfig: %v", err)
+			}
+			if config == nil {
+				t.Fatal("config not found; a symlinked path must resolve like the real one")
+			}
+			if config.Active != "web" || config.PackagesDir != "./pkgs" {
+				t.Fatalf("config = %+v, want active=web packages_dir=./pkgs", config)
+			}
+		})
+	}
+}
+
+// TestLoadWorkspaceConfig_Absent asserts a genuinely missing config
+// still walks to the root and reports nothing, rather than erroring.
+func TestLoadWorkspaceConfig_Absent(t *testing.T) {
+	dir := t.TempDir()
+	config, err := loadWorkspaceConfig(dir)
+	if err != nil {
+		t.Fatalf("loadWorkspaceConfig: %v", err)
+	}
+	if config != nil {
+		t.Fatalf("config = %+v, want nil for a directory with no workspace", config)
+	}
+}
+
+// TestIsRegularFile covers the probe's three answers: a file, a
+// directory, and an absent path — including each reached via a symlink,
+// which is the case the coreio medium refuses.
+func TestIsRegularFile(t *testing.T) {
+	base := t.TempDir()
+	file := filepath.Join(base, "workspace.yaml")
+	if err := os.WriteFile(file, []byte("version: 1\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	dir := filepath.Join(base, "subdir")
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	link := filepath.Join(base, "link")
+	if err := os.Symlink(base, link); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+
+	cases := []struct {
+		name string
+		path string
+		want bool
+	}{
+		{"file", file, true},
+		{"directory", dir, false},
+		{"absent", filepath.Join(base, "nope.yaml"), false},
+		{"file_via_symlink", filepath.Join(link, "workspace.yaml"), true},
+		{"directory_via_symlink", filepath.Join(link, "subdir"), false},
+		{"empty", "", false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := isRegularFile(tc.path); got != tc.want {
+				t.Fatalf("isRegularFile(%q) = %v, want %v", tc.path, got, tc.want)
+			}
+		})
+	}
+}