fix(formats): preserve high bits in Windows signature checks

Decode MZ and Windows signature bytes without ASCII high-bit masking. Move malformed signature cases into the shared Go diagnostics fixtures so provider, compiled CLI, and MCP workflows cover NE, LE, LX, and PE lookalikes; remove the superseded provider-only cases.

Validation: runtime build, check:ci, and focused DOS/Go/target/CLI/MCP tests. Windows-only reference-import cases await CI.

src/domain/dosMz.test.ts

@@ -170,18 +170,26 @@ describe("MZ Windows header observations", () => {
     });
   });
 
-  it("keeps a complete non-Windows signature candidate as DOS", () => {
-    const bytes = dosMz(64);
-    const offset = 32;
-    bytes.writeUInt32LE(offset, 60);
-    bytes.write("PEZZ", offset, "ascii");
+  it.each(["PEZZ", "NE", "LE", "LX", "PE"])(
+    "keeps a non-Windows %s signature candidate as DOS",
+    (signature) => {
+      const bytes = dosMz(64);
+      const offset = 32;
+      bytes.writeUInt32LE(offset, 60);
+      const candidate = Buffer.from(
+        [...Buffer.from(signature)].map((byte) =>
+          signature === "PEZZ" ? byte : byte | 0x80,
+        ),
+      );
+      bytes.set(candidate, offset);
 
-    expect(observeMzWindowsHeader(bytes)).toEqual({ state: "absent" });
-    expect(parseExecutableHeader(bytes, "x64")).toMatchObject({
-      ok: true,
-      value: { format: "dos-mz", architecture: "x86" },
-    });
-  });
+      expect(observeMzWindowsHeader(bytes)).toEqual({ state: "absent" });
+      expect(parseExecutableHeader(bytes, "x64")).toMatchObject({
+        ok: true,
+        value: { format: "dos-mz", architecture: "x86" },
+      });
+    },
+  );
 
   it("accepts a short-header candidate only when it points at a Windows signature", () => {
     const stub = dosMz(64);

src/domain/dosMz.ts

@@ -62,7 +62,7 @@ export const observeMzWindowsHeader = (
   const observedPePrefix =
     available !== undefined &&
     available.length >= 2 &&
-    available.toString("ascii", 0, 2) === "PE";
+    available.toString("latin1", 0, 2) === "PE";
   if (fileSize - offset < (observedPePrefix ? 4 : 2))
     return { state: "absent" };
   return { state: "signature-needed", offset };
@@ -72,7 +72,7 @@ const windowsHeaderSignature = (
   bytes: Buffer | undefined,
 ): "PE" | "NE" | "LE" | "LX" | "other" | "unobserved" => {
   if (bytes === undefined || bytes.length < 2) return "unobserved";
-  const prefix = bytes.toString("ascii", 0, 2);
+  const prefix = bytes.toString("latin1", 0, 2);
   if (prefix === "NE" || prefix === "LE" || prefix === "LX") return prefix;
   if (prefix !== "PE") return "other";
   if (bytes.length < 4) return "unobserved";
@@ -91,7 +91,7 @@ export const parseDosMzHeader = (
   fileSize = bytes.length,
   signatureAtOffset?: Buffer,
 ): Result<DosMzHeader, string> => {
-  if (bytes.length < 28 || bytes.toString("ascii", 0, 2) !== "MZ")
+  if (bytes.length < 28 || bytes.toString("latin1", 0, 2) !== "MZ")
     return err("invalid or truncated DOS MZ header");
   if (!Number.isSafeInteger(fileSize) || fileSize < bytes.length)
     return err("invalid DOS MZ file length");

tests/boundary/go/goBinaryProvider.test.ts

@@ -49,20 +49,6 @@ it.each([32, 64] as const)(
   },
 );
 
-it.each([{ signature: [0xce, 0xc5] }, { signature: [0xcc, 0xd8] }])(
-  "rejects high-bit lookalikes of Windows signatures %j",
-  async ({ signature }) => {
-    const root = await createTestTempDirectory("rea-go-pe-signature-");
-    const fixture = createGoBinaryFixture({ format: "pe" });
-    fixture.bytes.set(signature, 128);
-    const path = join(root, "corrupt-signature.exe");
-    await writeFile(path, fixture.bytes);
-    const result = await new GoBinaryProvider().inspect({ path });
-    expect(result.ok).toBe(false);
-    if (!result.ok) expect(result.error).toBeInstanceOf(AnalysisInputError);
-  },
-);
-
 it("preserves the actual build-info byte guard as a resource failure", async () => {
   const fixture = createGoBinaryFixture();
   fixture.bytes.set([0x81, 0x80, 0x40], fixture.headerOffset + 32);

tests/fixtures/go/image.ts

@@ -203,6 +203,14 @@ export const createGoBinaryDiagnosticFixtures = () => {
   }
   const damagedPe = createGoBinaryFixture({ format: "pe" }).bytes;
   damagedPe.write("NO", 128, "ascii");
+  const highBitSignatures = ["NE", "LE", "LX", "PE"].map((signature) => {
+    const bytes = createGoBinaryFixture({ format: "pe" }).bytes;
+    bytes.set(
+      [...Buffer.from(signature)].map((byte) => byte | 0x80),
+      128,
+    );
+    return { name: `high-bit-${signature.toLowerCase()}`, bytes };
+  });
   const absentDirectories = createGoBinaryFixture({ format: "pe" }).bytes;
   absentDirectories.writeUInt32LE(1, 152 + 108);
   const shortOptionalHeaders = [0, 1].map((size) => {
@@ -220,6 +228,7 @@ export const createGoBinaryDiagnosticFixtures = () => {
     })),
     ...[
       { name: "damaged-pe", bytes: damagedPe },
+      ...highBitSignatures,
       { name: "absent-directories", bytes: absentDirectories },
       ...shortOptionalHeaders,
     ].map((fixture) => ({