diff --git a/selfhost/cmd/ww/main.combined.ww b/selfhost/cmd/ww/main.combined.ww
index 1f759d17..cdb8a180 100644
--- a/selfhost/cmd/ww/main.combined.ww
+++ b/selfhost/cmd/ww/main.combined.ww
@@ -3143,45 +3143,17 @@ fn locateimport(dirs: *u8, name: *u8, namelen: u64,
 // build leaves them in the source tree; they parse-error when
 // re-included). Returns true to keep.
 fn dirfilekeep(name: *u8, nlen: u64) bool = {
+	// nlen<=3 guard kept: a bare ".ww" (len 3) is rejected here but
+	// would pass strings.hassuffix(".ww"); preserves cstage parity.
 	if (nlen <= 3u64) { return false; };
-	if (name[nlen - 3u64] != 46u8) { return false; };	// '.'
-	if (name[nlen - 2u64] != 119u8) { return false; };	// 'w'
-	if (name[nlen - 1u64] != 119u8) { return false; };	// 'w'
-	if (nlen >= 7u64) {
-		if (name[nlen - 7u64] == 116u8) {	// 't'
-			if (name[nlen - 6u64] == 101u8) {	// 'e'
-				if (name[nlen - 5u64] == 115u8) {	// 's'
-					if (name[nlen - 4u64] == 116u8) {	// 't'
-						return false;
-					};
-				};
-			};
-		};
-	};
-	if (nlen >= 12u64) {
-		// ".combined.ww" — full 12-char match mirrors cstage
-		// cmd/ww/main.c enumerate_dir_ww strcmp (rule 10); the
-		// trailing .ww is pre-guaranteed by the early-out above.
-		if (name[nlen - 12u64] == 46u8) {	// '.'
-			if (name[nlen - 11u64] == 99u8) {	// 'c'
-				if (name[nlen - 10u64] == 111u8) {	// 'o'
-					if (name[nlen - 9u64] == 109u8) {	// 'm'
-						if (name[nlen - 8u64] == 98u8) {	// 'b'
-							if (name[nlen - 7u64] == 105u8) {	// 'i'
-								if (name[nlen - 6u64] == 110u8) {	// 'n'
-									if (name[nlen - 5u64] == 101u8) {	// 'e'
-										if (name[nlen - 4u64] == 100u8) {	// 'd'
-											return false;
-										};
-									};
-								};
-							};
-						};
-					};
-				};
-			};
-		};
-	};
+	let s: str;
+	s.ptr = name;
+	s.len = nlen: i32;
+	if (!strings.hassuffix(s, ".ww")) { return false; };
+	if (strings.hassuffix(s, "test.ww")) { return false; };
+	// ".combined.ww" — full 12-char match mirrors cstage
+	// cmd/ww/main.c enumerate_dir_ww strcmp (rule 10).
+	if (strings.hassuffix(s, ".combined.ww")) { return false; };
 	return true;
 };
 
@@ -3311,13 +3283,13 @@ fn scanuse(src: *u8, len: u64) (*u8, u64) = {
 		if (src[i] != 32u8) { if (src[i] != 9u8) { break; }; };
 		i += 1u64;
 	};
+	// i+7>len guard kept: hasprefix("import") covers the 6 spell-out
+	// bytes, but the sep read at src[i+6] still needs i+6 < len.
 	if (i + 7u64 > len) { return nil, 0u64; };
-	if (src[i] != 105u8) { return nil, 0u64; };	// 'i'
-	if (src[i + 1u64] != 109u8) { return nil, 0u64; };	// 'm'
-	if (src[i + 2u64] != 112u8) { return nil, 0u64; };	// 'p'
-	if (src[i + 3u64] != 111u8) { return nil, 0u64; };	// 'o'
-	if (src[i + 4u64] != 114u8) { return nil, 0u64; };	// 'r'
-	if (src[i + 5u64] != 116u8) { return nil, 0u64; };	// 't'
+	let rest: str;
+	rest.ptr = src + i;
+	rest.len = (len - i): i32;
+	if (!strings.hasprefix(rest, "import")) { return nil, 0u64; };
 	let sep: u8 = src[i + 6u64];
 	if (sep != 32u8) { if (sep != 9u8) { return nil, 0u64; }; };
 	i += 7u64;
@@ -3411,22 +3383,18 @@ fn peekpackage(pathcs: *u8) *u8 = {
 			s += 1u64;
 		};
 		if (s < q) {
-			if (s + 1u64 < q) {
-				if (buf[s] == 47u8) {
-					if (buf[s + 1u64] == 47u8) {
-						p = q + 1u64;
-						continue;
-					};
-				};
+			let line: str;
+			line.ptr = buf.ptr + s;
+			line.len = (q - s): i32;
+			// hasprefix("//") subsumes the old s+1<q guard.
+			if (strings.hasprefix(line, "//")) {
+				p = q + 1u64;
+				continue;
 			};
+			// s+8<=q guard kept: hasprefix("package") needs only 7
+			// bytes, but the sep read at buf[s+7] needs s+7 < q.
 			if (s + 8u64 <= q) {
-				if (buf[s] == 112u8) {	// 'p'
-				if (buf[s + 1u64] == 97u8) {	// 'a'
-				if (buf[s + 2u64] == 99u8) {	// 'c'
-				if (buf[s + 3u64] == 107u8) {	// 'k'
-				if (buf[s + 4u64] == 97u8) {	// 'a'
-				if (buf[s + 5u64] == 103u8) {	// 'g'
-				if (buf[s + 6u64] == 101u8) {	// 'e'
+				if (strings.hasprefix(line, "package")) {
 					let sep: u8 = buf[s + 7u64];
 					if (sep == 32u8) { }
 					else { if (sep != 9u8) { return nil; }; };
@@ -3455,7 +3423,7 @@ fn peekpackage(pathcs: *u8) *u8 = {
 					for (k < plen) { r[k] = buf[start + k]; k += 1u64; };
 					r[plen] = 0u8;
 					return r.ptr;
-				}; }; }; }; }; }; };
+				};
 			};
 			return nil;
 		};
diff --git a/selfhost/cmd/ww/main.ww b/selfhost/cmd/ww/main.ww
index 1904f3c4..d7658e4e 100644
--- a/selfhost/cmd/ww/main.ww
+++ b/selfhost/cmd/ww/main.ww
@@ -309,45 +309,17 @@ fn locateimport(dirs: *u8, name: *u8, namelen: u64,
 // build leaves them in the source tree; they parse-error when
 // re-included). Returns true to keep.
 fn dirfilekeep(name: *u8, nlen: u64) bool = {
+	// nlen<=3 guard kept: a bare ".ww" (len 3) is rejected here but
+	// would pass strings.hassuffix(".ww"); preserves cstage parity.
 	if (nlen <= 3u64) { return false; };
-	if (name[nlen - 3u64] != 46u8) { return false; };	// '.'
-	if (name[nlen - 2u64] != 119u8) { return false; };	// 'w'
-	if (name[nlen - 1u64] != 119u8) { return false; };	// 'w'
-	if (nlen >= 7u64) {
-		if (name[nlen - 7u64] == 116u8) {	// 't'
-			if (name[nlen - 6u64] == 101u8) {	// 'e'
-				if (name[nlen - 5u64] == 115u8) {	// 's'
-					if (name[nlen - 4u64] == 116u8) {	// 't'
-						return false;
-					};
-				};
-			};
-		};
-	};
-	if (nlen >= 12u64) {
-		// ".combined.ww" — full 12-char match mirrors cstage
-		// cmd/ww/main.c enumerate_dir_ww strcmp (rule 10); the
-		// trailing .ww is pre-guaranteed by the early-out above.
-		if (name[nlen - 12u64] == 46u8) {	// '.'
-			if (name[nlen - 11u64] == 99u8) {	// 'c'
-				if (name[nlen - 10u64] == 111u8) {	// 'o'
-					if (name[nlen - 9u64] == 109u8) {	// 'm'
-						if (name[nlen - 8u64] == 98u8) {	// 'b'
-							if (name[nlen - 7u64] == 105u8) {	// 'i'
-								if (name[nlen - 6u64] == 110u8) {	// 'n'
-									if (name[nlen - 5u64] == 101u8) {	// 'e'
-										if (name[nlen - 4u64] == 100u8) {	// 'd'
-											return false;
-										};
-									};
-								};
-							};
-						};
-					};
-				};
-			};
-		};
-	};
+	let s: str;
+	s.ptr = name;
+	s.len = nlen: i32;
+	if (!strings.hassuffix(s, ".ww")) { return false; };
+	if (strings.hassuffix(s, "test.ww")) { return false; };
+	// ".combined.ww" — full 12-char match mirrors cstage
+	// cmd/ww/main.c enumerate_dir_ww strcmp (rule 10).
+	if (strings.hassuffix(s, ".combined.ww")) { return false; };
 	return true;
 };
 
@@ -477,13 +449,13 @@ fn scanuse(src: *u8, len: u64) (*u8, u64) = {
 		if (src[i] != 32u8) { if (src[i] != 9u8) { break; }; };
 		i += 1u64;
 	};
+	// i+7>len guard kept: hasprefix("import") covers the 6 spell-out
+	// bytes, but the sep read at src[i+6] still needs i+6 < len.
 	if (i + 7u64 > len) { return nil, 0u64; };
-	if (src[i] != 105u8) { return nil, 0u64; };	// 'i'
-	if (src[i + 1u64] != 109u8) { return nil, 0u64; };	// 'm'
-	if (src[i + 2u64] != 112u8) { return nil, 0u64; };	// 'p'
-	if (src[i + 3u64] != 111u8) { return nil, 0u64; };	// 'o'
-	if (src[i + 4u64] != 114u8) { return nil, 0u64; };	// 'r'
-	if (src[i + 5u64] != 116u8) { return nil, 0u64; };	// 't'
+	let rest: str;
+	rest.ptr = src + i;
+	rest.len = (len - i): i32;
+	if (!strings.hasprefix(rest, "import")) { return nil, 0u64; };
 	let sep: u8 = src[i + 6u64];
 	if (sep != 32u8) { if (sep != 9u8) { return nil, 0u64; }; };
 	i += 7u64;
@@ -577,22 +549,18 @@ fn peekpackage(pathcs: *u8) *u8 = {
 			s += 1u64;
 		};
 		if (s < q) {
-			if (s + 1u64 < q) {
-				if (buf[s] == 47u8) {
-					if (buf[s + 1u64] == 47u8) {
-						p = q + 1u64;
-						continue;
-					};
-				};
+			let line: str;
+			line.ptr = buf.ptr + s;
+			line.len = (q - s): i32;
+			// hasprefix("//") subsumes the old s+1<q guard.
+			if (strings.hasprefix(line, "//")) {
+				p = q + 1u64;
+				continue;
 			};
+			// s+8<=q guard kept: hasprefix("package") needs only 7
+			// bytes, but the sep read at buf[s+7] needs s+7 < q.
 			if (s + 8u64 <= q) {
-				if (buf[s] == 112u8) {	// 'p'
-				if (buf[s + 1u64] == 97u8) {	// 'a'
-				if (buf[s + 2u64] == 99u8) {	// 'c'
-				if (buf[s + 3u64] == 107u8) {	// 'k'
-				if (buf[s + 4u64] == 97u8) {	// 'a'
-				if (buf[s + 5u64] == 103u8) {	// 'g'
-				if (buf[s + 6u64] == 101u8) {	// 'e'
+				if (strings.hasprefix(line, "package")) {
 					let sep: u8 = buf[s + 7u64];
 					if (sep == 32u8) { }
 					else { if (sep != 9u8) { return nil; }; };
@@ -621,7 +589,7 @@ fn peekpackage(pathcs: *u8) *u8 = {
 					for (k < plen) { r[k] = buf[start + k]; k += 1u64; };
 					r[plen] = 0u8;
 					return r.ptr;
-				}; }; }; }; }; }; };
+				};
 			};
 			return nil;
 		};