security: workbook path allowlist + stronger image polyglot validation (#54)

- dispo workbook imports are pinned to DISPO_IMPORT_DIR (default ./imports):
  tRPC input rejects absolute paths and .. segments, runtime reader
  re-validates containment via path.relative. Closes a path-traversal
  class that reached ExcelJS CVEs through admin/compromised tokens.
- image validator now checks the full 8-byte PNG magic, enforces PNG IEND
  and JPEG EOI trailers, scans the decoded buffer for markup polyglot
  markers (<script, <svg, <iframe, javascript:, onerror=, ...), and
  explicitly rejects SVG. Provider-generated covers (DALL-E, Gemini) run
  through the same validator before persistence — an untrusted upstream
  cannot smuggle a stored-XSS payload past us.
- added image-validation.test.ts and tightened documentation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/application/src/__tests__/read-workbook.test.ts

@@ -3,7 +3,7 @@ import { cp, mkdtemp, rm, writeFile } from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
-import { afterEach, describe, expect, it } from "vitest";
+import { afterAll, afterEach, beforeAll, describe, expect, it } from "vitest";
 import {
   MAX_DISPO_WORKBOOK_BYTES,
   MAX_DISPO_WORKBOOK_COLUMNS,
@@ -33,6 +33,20 @@ const itIfSamples = hasSamples ? it : it.skip;
 
 const tempDirectories: string[] = [];
 
+// The dispo reader now enforces DISPO_IMPORT_DIR as an allowlist. Existing
+// tests pass absolute paths from sample fixtures or tmpdirs that live outside
+// any production import dir, so scope the allowlist to the filesystem root
+// for the test suite. New tests below restore a narrow allowlist to exercise
+// the containment check explicitly.
+const originalImportDir = process.env["DISPO_IMPORT_DIR"];
+beforeAll(() => {
+  process.env["DISPO_IMPORT_DIR"] = "/";
+});
+afterAll(() => {
+  if (originalImportDir === undefined) delete process.env["DISPO_IMPORT_DIR"];
+  else process.env["DISPO_IMPORT_DIR"] = originalImportDir;
+});
+
 afterEach(async () => {
   await Promise.all(
     tempDirectories.splice(0).map(async (directory) => {
@@ -136,4 +150,58 @@ describe("readWorksheetMatrix", () => {
       `exceeds the ${MAX_DISPO_WORKBOOK_COLUMNS} column import limit`,
     );
   }, 30000);
+
+  describe("DISPO_IMPORT_DIR allowlist", () => {
+    it("rejects absolute paths that escape the configured import dir", async () => {
+      const allowedDir = await makeTempDirectory();
+      const outsideDir = await makeTempDirectory();
+      const outsidePath = path.join(outsideDir, "outside.xlsx");
+      await writeWorkbook(outsidePath, [["a"]]);
+
+      const previous = process.env["DISPO_IMPORT_DIR"];
+      process.env["DISPO_IMPORT_DIR"] = allowedDir;
+      try {
+        await expect(readWorksheetMatrix(outsidePath, "Sheet1")).rejects.toThrow(
+          "Workbook path must be inside the configured import directory",
+        );
+      } finally {
+        process.env["DISPO_IMPORT_DIR"] = previous;
+      }
+    });
+
+    it("rejects relative paths that traverse out of the configured import dir", async () => {
+      const allowedDir = await makeTempDirectory();
+      const siblingDir = await makeTempDirectory();
+      const siblingPath = path.join(siblingDir, "sibling.xlsx");
+      await writeWorkbook(siblingPath, [["a"]]);
+
+      const relative = path.relative(allowedDir, siblingPath);
+      expect(relative.startsWith("..")).toBe(true);
+
+      const previous = process.env["DISPO_IMPORT_DIR"];
+      process.env["DISPO_IMPORT_DIR"] = allowedDir;
+      try {
+        await expect(readWorksheetMatrix(relative, "Sheet1")).rejects.toThrow(
+          "Workbook path must be inside the configured import directory",
+        );
+      } finally {
+        process.env["DISPO_IMPORT_DIR"] = previous;
+      }
+    });
+
+    it("accepts paths that resolve inside the configured import dir", async () => {
+      const allowedDir = await makeTempDirectory();
+      const insidePath = path.join(allowedDir, "inside.xlsx");
+      await writeWorkbook(insidePath, [["hello"]]);
+
+      const previous = process.env["DISPO_IMPORT_DIR"];
+      process.env["DISPO_IMPORT_DIR"] = allowedDir;
+      try {
+        const rows = await readWorksheetMatrix("inside.xlsx", "Sheet1");
+        expect(rows[0]?.[0]).toBe("hello");
+      } finally {
+        process.env["DISPO_IMPORT_DIR"] = previous;
+      }
+    });
+  });
 });