fix(audit): keep coverage unknown for an unread unclassified member

A packaged member with no format of its own, such as a PyInstaller
payload.bin, recorded only a skipped text member when its read failed
before the header. Member coverage then stayed complete, though the
member could be a native image or carry a nested package. Leave
coverage unknown and say which member could not be read, as an unread
native member already does.

src/artifacts/ReleaseExposureReader.test.ts

@@ -2482,6 +2482,30 @@ describe("ReleaseExposureReader unexpanded package PE reads", () => {
     }
   });
 
+  it("leaves member coverage unknown when an unclassified packaged member cannot be read", async () => {
+    const root = await bundled([
+      { path: "payload.bin", bytes: Buffer.from([0x7f, 0x45, 0x4c, 0x46]) },
+    ]);
+    createdReaders.wrap = (reader, path) => {
+      if (!path.endsWith("app.dll")) return reader;
+      const open = reader.open.bind(reader);
+      reader.open = (entry, signal) =>
+        entry.path.endsWith("payload.bin")
+          ? Promise.reject(new Error("member read failed"))
+          : open(entry, signal);
+      return reader;
+    };
+    try {
+      const scanned = await inspect(root);
+      expect(scanned.coverage).toBe("unknown");
+      expect(scanned.limitations).toContain(
+        `Could not read ${join(root, "app.dll", "payload.bin")} to rule out a native image or package.`,
+      );
+    } finally {
+      createdReaders.wrap = undefined;
+    }
+  });
+
   it("leaves member coverage unknown when a package cannot be listed", async () => {
     const root = await bundled([{ path: "app.js", bytes: Buffer.from("1") }]);
     createdReaders.wrap = (reader, path) => {

src/artifacts/ReleaseExposureReader.ts

@@ -1011,9 +1011,10 @@ const noteUnreadMember = (state: ScanState, member: MemberView): void => {
 /**
  * A member whose bytes were not read. A native one may carry a package that
  * nothing here can clear, so member coverage stays unknown, as it does for a
- * packaged image the embedded-package probe could not read. A caller that
- * counts the failed read itself passes `countUnreadable: false`, so the member
- * is counted once.
+ * packaged image the embedded-package probe could not read. An unclassified
+ * one whose header was never read may be such an image too, so it leaves
+ * coverage unknown as well. A caller that counts the failed read itself passes
+ * `countUnreadable: false`, so the member is counted once.
  */
 const noteUnreadBinary = (
   state: ScanState,
@@ -1029,7 +1030,14 @@ const noteUnreadBinary = (
       state,
       `Did not probe ${member.location} for an embedded package.`,
     );
-  } else state.skippedText += 1;
+  } else {
+    state.skippedText += 1;
+    state.coverageUnknown = true;
+    pushLimitation(
+      state,
+      `Could not read ${member.location} to rule out a native image or package.`,
+    );
+  }
   if (native === "pe" || PE_MEMBER_NAME.test(member.logical))
     notePeNotExamined(state, member.location);
 };