fix(mql): terminate parse loop on quoted value as final token

mql/parser.go

@@ -178,9 +178,16 @@ func (p *Parser) parseValueFromPos(startPos int) string {
 		}
 		if endIdx < len(p.input) {
 			val := p.input[startIdx+1 : endIdx]
-			// Advance scanner past the quoted string
+			// Advance scanner past the quoted string. When the closing quote is
+			// the final character, the scanner is already at EOF and next() no
+			// longer advances its offset, so guard on forward progress to avoid
+			// looping forever (issue #221).
 			for p.s.Pos().Offset-1 < endIdx+1 {
+				prev := p.s.Pos().Offset
 				p.next()
+				if p.s.Pos().Offset == prev {
+					break // scanner reached EOF, no further progress possible
+				}
 			}
 			return val
 		}

mql/parser_test.go

@@ -0,0 +1,59 @@
+package mql
+
+import (
+	"testing"
+	"time"
+)
+
+// TestParseQuotedValueAsFinalToken guards against a regression where a quoted
+// value appearing as the final token of the input caused Parser.Parse to spin
+// forever in parseValueFromPos: at EOF the scanner stops advancing its offset,
+// so the scanner-advance loop's condition never becomes false (issue #221).
+//
+// Each case is parsed in a goroutine so the test fails via timeout instead of
+// hanging the whole suite if the loop ever regresses.
+func TestParseQuotedValueAsFinalToken(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		key   string
+		value string
+	}{
+		{"single-char quoted final value", `k:"v"`, "k", "v"},
+		{"word quoted final value", `name:"alice"`, "name", "alice"},
+		{"quoted final value with space", `k:"hello world"`, "k", "hello world"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			type parseResult struct {
+				expr Expr
+				err  error
+			}
+			done := make(chan parseResult, 1)
+			go func() {
+				expr, err := NewParser(tt.input).Parse()
+				done <- parseResult{expr, err}
+			}()
+
+			select {
+			case r := <-done:
+				if r.err != nil {
+					t.Fatalf("Parse(%q) returned error: %v", tt.input, r.err)
+				}
+				term, ok := r.expr.(*TermExpr)
+				if !ok {
+					t.Fatalf("Parse(%q) = %T, want *TermExpr", tt.input, r.expr)
+				}
+				if term.Key != tt.key {
+					t.Errorf("Parse(%q) key = %q, want %q", tt.input, term.Key, tt.key)
+				}
+				if term.Value != tt.value {
+					t.Errorf("Parse(%q) value = %v, want %q", tt.input, term.Value, tt.value)
+				}
+			case <-time.After(2 * time.Second):
+				t.Fatalf("Parse(%q) did not terminate within 2s (infinite loop)", tt.input)
+			}
+		})
+	}
+}