fix: cap filename tokens at the full 200-char limit, not 80

renderRaw (and the attachment-template renderer) sanitised each {token}
with sanitizePart's default 80-char cap, so a single long token such as
{subject} was truncated to 80 — well before the documented 200-char
filename limit, which was therefore unreachable per token. Introduce a
FILENAME_MAX_LEN (200) constant and use it for the per-token cap so the
overall limit governs. Adds tests.

lib/__tests__/download-filename.test.ts

@@ -41,11 +41,11 @@ describe('emailExportFilename', () => {
     expect(emailExportFilename(makeEmail({}), '{unknown_token}')).toBe('email.eml');
   });
 
-  it('CHARACTERISATION: per-token sanitise caps each value at 80 chars', () => {
-    // sanitizePart defaults to maxLen=80, applied per {token} during render —
-    // so a single long {subject} is truncated to 80 well before the 200 cap.
+  it('lets a single long token reach the 200-char filename cap', () => {
+    // Each {token} is now capped at FILENAME_MAX_LEN (200), so the overall
+    // filename limit governs instead of an earlier 80-char per-token cap.
     const out = emailExportFilename(makeEmail({ subject: 'a'.repeat(300) }), '{subject}');
-    expect(out).toBe('a'.repeat(80) + '.eml');
+    expect(out).toBe('a'.repeat(200) + '.eml');
   });
 });
 

lib/download-filename.ts

@@ -64,6 +64,11 @@ export const BUNDLE_TOKENS: { token: string; description: string }[] = [
   { token: "day", description: "2-digit day" },
 ];
 
+// Overall cap for a generated filename stem. Also used as the per-token cap so
+// a single long token (e.g. {subject}) isn't truncated earlier than the final
+// filename would be.
+const FILENAME_MAX_LEN = 200;
+
 function sanitizePart(input: string, maxLen = 80): string {
   const cleaned = input
     .replace(SAFE_CHARS, "_")
@@ -173,7 +178,7 @@ function renderRaw(template: string, vars: Record<string, string>): string {
   return template.replace(/\{(\w+)\}/g, (_, key: string) => {
     const value = vars[key];
     if (value === undefined) return "";
-    return sanitizePart(value);
+    return sanitizePart(value, FILENAME_MAX_LEN);
   });
 }
 
@@ -184,9 +189,9 @@ export function emailExportFilename(
   const opts = typeof options === "string" ? { template: options } : options;
   const template = opts.template ?? DEFAULT_EMAIL_TEMPLATE;
   const rendered = renderRaw(template, emailVars(email));
-  const cleaned = sanitizePart(rendered, 200);
+  const cleaned = sanitizePart(rendered, FILENAME_MAX_LEN);
   const transformed = applyTransforms(cleaned, opts);
-  const stem = transformed.slice(0, 200) || "email";
+  const stem = transformed.slice(0, FILENAME_MAX_LEN) || "email";
   return `${stem}.eml`;
 }
 
@@ -199,7 +204,7 @@ export function attachmentDownloadFilename(
   const template = opts.template ?? DEFAULT_ATTACHMENT_TEMPLATE;
   if (!email) {
     const filename = (attachment.name || "attachment").trim();
-    const cleaned = sanitizePart(filename, 200) || "attachment";
+    const cleaned = sanitizePart(filename, FILENAME_MAX_LEN) || "attachment";
     return applyTransforms(cleaned, opts) || cleaned;
   }
   const vars = attachmentVars(email, attachment);
@@ -208,10 +213,10 @@ export function attachmentDownloadFilename(
     if (value === undefined) return "";
     // Preserve dots in {filename} so the original extension survives the
     // sanitiser (it strips trailing dots otherwise).
-    return key === "filename" ? value.replace(SAFE_CHARS, "_") : sanitizePart(value);
+    return key === "filename" ? value.replace(SAFE_CHARS, "_") : sanitizePart(value, FILENAME_MAX_LEN);
   });
   const templateMentionsExt = /\{(ext|filename)\}/.test(template);
-  const cleaned = sanitizePart(rendered, 200) || "attachment";
+  const cleaned = sanitizePart(rendered, FILENAME_MAX_LEN) || "attachment";
   if (templateMentionsExt) {
     return applyTransforms(cleaned, opts) || cleaned;
   }
@@ -235,9 +240,9 @@ export function bundleExportFilename(
   const opts = typeof options === "string" ? { template: options } : options;
   const template = opts.template ?? DEFAULT_BUNDLE_TEMPLATE;
   const rendered = renderRaw(template, bundleVars(count, iso));
-  const cleaned = sanitizePart(rendered, 200);
+  const cleaned = sanitizePart(rendered, FILENAME_MAX_LEN);
   const transformed = applyTransforms(cleaned, opts);
-  const stem = transformed.slice(0, 200) || "emails";
+  const stem = transformed.slice(0, FILENAME_MAX_LEN) || "emails";
   return `${stem}.zip`;
 }