test(handlers): OFFSEC-001 — harden RecallMemory_GlobalScope test (mc#693)

Sibling of #680 (CommitMemory). The recall path exercises the same dispatchRPC
scrub path as commit, but the previous test only asserted `resp.Error != nil`.

Changes:
- Renamed TestMCPHandler_RecallMemory_GlobalScope_Blocked → ..._ScrubsInternalError
- Added OFFSEC-001 scrub contract assertions:
  1. resp.Error.Code == -32000 (server error, not generic -32600)
  2. resp.Error.Message == "tool call failed" (constant, no "GLOBAL" leak)
  3. Defence-in-depth: strings.Contains guard rejects original error keywords

Issue: #693

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/handlers/mcp_test.go

@@ -548,7 +548,12 @@ func TestMCPHandler_CommitMemory_CleanContent_PassesThrough(t *testing.T) {
 // tools/call — recall_memory
 // ─────────────────────────────────────────────────────────────────────────────
 
-func TestMCPHandler_RecallMemory_GlobalScope_Blocked(t *testing.T) {
+// TestMCPHandler_RecallMemory_GlobalScope_ScrubsInternalError verifies C3 is
+// enforced and the OFFSEC-001 scrub contract is applied. The tool returns a
+// descriptive error mentioning GLOBAL scope; dispatchRPC must replace it with
+// a constant "tool call failed" message so internal implementation details
+// never reach the caller.
+func TestMCPHandler_RecallMemory_GlobalScope_ScrubsInternalError(t *testing.T) {
 	h, mock := newMCPHandler(t)
 	// No DB expectations — handler must abort before touching the DB.
 
@@ -568,7 +573,20 @@ func TestMCPHandler_RecallMemory_GlobalScope_Blocked(t *testing.T) {
 	var resp mcpResponse
 	json.Unmarshal(w.Body.Bytes(), &resp)
 	if resp.Error == nil {
-		t.Error("expected JSON-RPC error for GLOBAL scope recall, got nil")
+		t.Fatal("expected JSON-RPC error for GLOBAL scope recall, got nil")
+	}
+	// OFFSEC-001 scrub contract: error code is -32000 (server error).
+	if resp.Error.Code != -32000 {
+		t.Errorf("expected error code -32000, got %d", resp.Error.Code)
+	}
+	// Message must be the constant scrubbed string — no "GLOBAL" or bridge
+	// implementation details leaked to the caller.
+	if resp.Error.Message != "tool call failed" {
+		t.Errorf("error message should be constant 'tool call failed', got: %q", resp.Error.Message)
+	}
+	// Defence-in-depth: the original error body must not appear in the response.
+	if strings.Contains(resp.Error.Message, "GLOBAL") || strings.Contains(resp.Error.Message, "bridge") {
+		t.Error("scrubbed error message must not contain original error keywords")
 	}
 	if err := mock.ExpectationsWereMet(); err != nil {
 		t.Errorf("unexpected DB calls on GLOBAL scope block: %v", err)