Path rules and trap paths match the path decoded once too (closes #85)

A path rule matched only the path as the client sent it, so /%2eenv got
past the default env-file rule while an app that decodes the path
serves /.env. A path rule now matches the path as sent or decoded once,
as a uri rule already did, and so does a path in SWWAF_TRAP_PATHS:
/%77p-login.php matches /wp-login.php. The query is cut off before the
path is decoded, and the path is decoded only once, so /%252eenv is not
/.env. A ban's notes keep the path as sent. SPEC.md and README.md say
so.

Model: opus-5-5

internal/proxy/trappaths_test.go

@@ -32,10 +32,9 @@ func TestTrapPathBansAsABanRuleDoes(t *testing.T) {
 	})
 	start := clk.Now()
 
-	// Only the path itself, as the client sent it, is a trap path.
-	for _, path := range []string{
-		"/wp-login.php/", "/WP-LOGIN.PHP", "/blog/xmlrpc.php", "/%77p-login.php",
-	} {
+	// Only the path itself, the whole of it in the same case, is a trap
+	// path.
+	for _, path := range []string{"/wp-login.php/", "/WP-LOGIN.PHP", "/blog/xmlrpc.php"} {
 		s.request(otherClient, path, http.StatusOK, requestlog.ActionForward)
 	}
 
@@ -84,6 +83,22 @@ func TestTrapPathBansAsABanRuleDoes(t *testing.T) {
 	}
 }
 
+func TestTrapPathMatchesThePathDecodedOnce(t *testing.T) {
+	t.Parallel()
+
+	s, _, server := startWithClock(t, "", map[string]string{trapPaths: trapPathList})
+
+	// %2577 decodes once to %77, not to w.
+	s.request(otherClient, "/%2577p-login.php", http.StatusOK, requestlog.ActionForward)
+	s.request(client, "/%77p-login.php", http.StatusForbidden, requestlog.ActionBanned)
+
+	// The ban's notes give the path as the client sent it.
+	got := server.Ledger.Bans(netip.MustParsePrefix(client + "/32"))
+	if len(got) != 1 || got[0].Notes.TrapPath != "/%77p-login.php" {
+		t.Fatalf("bans %+v, want one whose notes give the trap path /%%77p-login.php", got)
+	}
+}
+
 func TestTrapPathsNeedNoRuleFiles(t *testing.T) {
 	t.Parallel()