harness: attachments named by real m.filename, not the caption; mimetype-derived extension fallback

src/matrix.zig

@@ -339,6 +339,8 @@ pub const Event = struct {
     url: ?[]u8 = null, // allocated; caller frees
     mimetype: []u8 = "", // allocated; caller frees
     size: i64 = 0,
+    /// Original attachment filename (distinct from body, which is the caption).
+    filename: []u8 = &.{}, // allocated; caller frees
 };
 
 /// One sync poll. Returns message events + next `since` token. Caller frees.
@@ -438,6 +440,11 @@ pub fn sync(alloc: std.mem.Allocator, io: Io, token: []const u8, since: []const
 
             // Attachment fields (m.file / m.image / m.audio / m.video).
             var url_copy: ?[]u8 = null;
+            var fname_copy: []u8 = "";
+            if (content.get("filename")) |f| switch (f) {
+                .string => |v| fname_copy = alloc.dupe(u8, v) catch "",
+                else => {},
+            };
             if (content.get("url")) |u| switch (u) {
                 .string => |v| url_copy = alloc.dupe(u8, v) catch null,
                 else => {},
@@ -463,7 +470,7 @@ pub fn sync(alloc: std.mem.Allocator, io: Io, token: []const u8, since: []const
                 alloc.free(sender_copy);
                 continue;
             };
-            events.append(alloc, .{ .sender = sender_copy, .body = body_copy, .ts = ts, .url = url_copy, .mimetype = mime, .size = size }) catch {
+            events.append(alloc, .{ .sender = sender_copy, .body = body_copy, .ts = ts, .url = url_copy, .filename = fname_copy, .mimetype = mime, .size = size }) catch {
                 alloc.free(sender_copy);
                 alloc.free(body_copy);
             };

src/matrix_harness.zig

@@ -247,6 +247,7 @@ pub fn main(init: std.process.Init) !void {
         for (first.events) |ev| {
             defer alloc.free(ev.sender);
             defer alloc.free(ev.body);
+            defer if (ev.filename.len > 0) alloc.free(ev.filename);
             defer if (ev.url) |u| alloc.free(u);
             defer if (ev.mimetype.len > 0) alloc.free(ev.mimetype);
             if (ev.ts > new_max) new_max = ev.ts;
@@ -303,6 +304,7 @@ pub fn main(init: std.process.Init) !void {
         for (result.events) |ev| {
             defer alloc.free(ev.sender);
             defer alloc.free(ev.body);
+            defer if (ev.filename.len > 0) alloc.free(ev.filename);
             defer if (ev.url) |u| alloc.free(u);
             defer if (ev.mimetype.len > 0) alloc.free(ev.mimetype);
             defer if (ev.ts > 0) saveSeenTs(io, ev.ts);
@@ -321,7 +323,30 @@ pub fn main(init: std.process.Init) !void {
 
             // Attachment: download locally and forward the path to the agent.
             if (ev.url) |mxc| {
-                const local = saveAttachment(alloc, io, session.token, ev.ts, ev.body, mxc) catch |e| blk: {
+                // Use the attachment's REAL filename; the event body is just
+                // the caption ("This us?" is not a filename). Fall back to
+                // body, and ensure an extension via mimetype.
+                const fname_src = if (ev.filename.len > 0) ev.filename else ev.body;
+                var fname_buf: std.ArrayListUnmanaged(u8) = .empty;
+                var fname: []const u8 = fname_src;
+                if (std.mem.lastIndexOfScalar(u8, fname_src, '.') == null and ev.mimetype.len > 0) {
+                    const ext_map = [_]struct{ m: []const u8, e: []const u8 }{
+                        .{ .m = "image/jpeg", .e = ".jpg" },  .{ .m = "image/png", .e = ".png" },
+                        .{ .m = "image/webp", .e = ".webp" }, .{ .m = "application/pdf", .e = ".pdf" },
+                        .{ .m = "application/gzip", .e = ".gz" }, .{ .m = "application/zip", .e = ".zip" },
+                        .{ .m = "text/plain", .e = ".txt" },
+                    };
+                    for (ext_map) |pair| {
+                        if (std.mem.eql(u8, ev.mimetype, pair.m)) {
+                            fname_buf.appendSlice(alloc, fname_src) catch {};
+                            fname_buf.appendSlice(alloc, pair.e) catch {};
+                            fname = fname_buf.items;
+                            break;
+                        }
+                    }
+                }
+                defer fname_buf.deinit(alloc);
+                const local = saveAttachment(alloc, io, session.token, ev.ts, fname, mxc) catch |e| blk: {
                     std.debug.print("matrix_harness: attachment download failed: {s}\n", .{@errorName(e)});
                     break :blk null;
                 };