feat: add TestNoRawTimeFormats audit check

Catches raw Go time layout strings in time.Parse, time.Format,
and time.AppendFormat calls. All layouts must use config/time
constants. Zero violations found; pure guardrail.

Signed-off-by: Jose Alekhinne <jose@ctx.ist>

Author: josealekhine

internal/audit/raw_time_formats_test.go

@@ -0,0 +1,134 @@
+//   /    ctx:                         https://ctx.ist
+// ,'`./    do you remember?
+// `.,'\
+//   \    Copyright 2026-present Context contributors.
+//                 SPDX-License-Identifier: Apache-2.0
+
+package audit
+
+import (
+	"go/ast"
+	"go/token"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// timeFormatFuncs lists time package methods that take
+// a layout string argument.
+var timeFormatFuncs = map[string]bool{
+	"Parse":        true,
+	"Format":       true,
+	"AppendFormat": true,
+}
+
+// goRefTime matches substrings of Go's reference time
+// (Mon Jan 2 15:04:05 MST 2006) that indicate a raw
+// time layout string.
+var goRefTimeHints = []string{
+	"2006", "01", "02", "15", "04", "05",
+	"Jan", "Mon", "MST",
+}
+
+// TestNoRawTimeFormats ensures raw time layout strings
+// in time.Parse, time.Format, and time.AppendFormat
+// calls use config/time constants instead of inline
+// format strings.
+//
+// Stdlib constants (time.RFC3339, etc.) are exempt
+// because they are already named.
+//
+// The definition site (internal/config/time/) is exempt.
+// Test files are exempt.
+//
+// See specs/ast-audit-tests.md for rationale.
+func TestNoRawTimeFormats(t *testing.T) {
+	pkgs := loadPackages(t)
+	var violations []string
+
+	for _, pkg := range pkgs {
+		if strings.Contains(pkg.PkgPath, "config/time") {
+			continue
+		}
+
+		for _, file := range pkg.Syntax {
+			fpath := pkg.Fset.Position(file.Pos()).Filename
+			if isTestFile(fpath) {
+				continue
+			}
+
+			ast.Inspect(file, func(n ast.Node) bool {
+				call, ok := n.(*ast.CallExpr)
+				if !ok {
+					return true
+				}
+
+				sel, ok := call.Fun.(*ast.SelectorExpr)
+				if !ok {
+					return true
+				}
+
+				if !timeFormatFuncs[sel.Sel.Name] {
+					return true
+				}
+
+				// Find the layout argument: first arg
+				// for Parse, first arg for Format/
+				// AppendFormat (method on time.Time).
+				var layoutArg ast.Expr
+				switch sel.Sel.Name {
+				case "Parse":
+					// time.Parse(layout, value)
+					if len(call.Args) >= 1 {
+						layoutArg = call.Args[0]
+					}
+				case "Format", "AppendFormat":
+					// t.Format(layout)
+					if len(call.Args) >= 1 {
+						layoutArg = call.Args[0]
+					}
+				}
+
+				if layoutArg == nil {
+					return true
+				}
+
+				lit, ok := layoutArg.(*ast.BasicLit)
+				if !ok || lit.Kind != token.STRING {
+					return true
+				}
+
+				s, err := strconv.Unquote(lit.Value)
+				if err != nil {
+					return true
+				}
+
+				if looksLikeTimeLayout(s) {
+					violations = append(violations,
+						posString(pkg.Fset, lit.Pos())+
+							": raw time format "+
+							lit.Value+
+							" — use config/time",
+					)
+				}
+
+				return true
+			})
+		}
+	}
+
+	for _, v := range violations {
+		t.Error(v)
+	}
+}
+
+// looksLikeTimeLayout reports whether s contains
+// Go reference time components.
+func looksLikeTimeLayout(s string) bool {
+	for _, hint := range goRefTimeHints {
+		if strings.Contains(s, hint) {
+			return true
+		}
+	}
+	return false
+}