fix(hub): a downloaded file opens in a tab only under a type that runs nothing

Open is offered for PDFs, raster images, audio, video and plain text, typed
from the name; HTML, SVG and the rest are not opened in the hub's origin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 55 insertions, 4 deletions

diff --git a/packages/meshbay-hub/tests/test_downloads.py b/packages/meshbay-hub/tests/test_downloads.py
index c8c68a9..3716f4c 100644
--- a/packages/meshbay-hub/tests/test_downloads.py
+++ b/packages/meshbay-hub/tests/test_downloads.py
@@ -101,13 +101,44 @@ def test_the_open_action_reads_the_file_back(tmp_path):
     """
     "Open" is the browser being handed the bytes, not a desktop application
     being started — no web page can do the second, and none can show a file
-    manager either. It is only offered for a file written into a granted folder,
-    since that is the one a page can read back.
+    manager either. A file written into a granted folder is read back from it.
     """
     src = DOWNLOADS.read_text(encoding="utf-8")
     target = src[src.index("export async function openTarget"):]
-    assert "getFile()" in target and "window.open(" in target
-    assert "revokeObjectURL" in target, "the blob URL must not be leaked"
+    assert "openInTab(await handle.getFile(), name)" in target
+    opener = src[src.index("export function openInTab"):]
+    opener = opener[:opener.index("\n}\n")]
+    assert "window.open(" in opener
+    assert "revokeObjectURL" in opener, "the blob URL must not be leaked"
+
+
+def test_a_tab_is_opened_only_for_a_type_that_runs_nothing(tmp_path):
+    """
+    A tab on a `blob:` URL is a document of the hub's origin, with its session
+    and its keys. Measured in Chrome and Firefox: HTML typed `text/html` runs
+    there, the same bytes typed `text/plain` do not. So the type is chosen from
+    the name, never guessed from the bytes, and what could run is not opened.
+    """
+    result = _run("""
+const opened = [];
+globalThis.window = { open: (url) => opened.push(url) };
+globalThis.URL.createObjectURL = (blob) => `blob:${blob.type}`;
+globalThis.URL.revokeObjectURL = () => {};
+globalThis.setTimeout = () => 0;   // the revoke a minute later; node would wait for it
+const bytes = new Blob(['<script>alert(1)</script>'], { type: 'text/html' });
+for (const name of ['page.html', 'page.HTM', 'logo.svg', 'feed.xml', 'x.xhtml',
+                    'tool.js', 'noext', 'notes.txt', 'film.MP4', 'scan.pdf', 'pic.jpeg']) {
+  say([name, M.openInTab(bytes, name)]);
+}
+say(opened);
+""", tmp_path)
+    *verdicts, opened = result
+    refused = {name for name, ok in verdicts if not ok}
+    assert refused == {"page.html", "page.HTM", "logo.svg", "feed.xml", "x.xhtml",
+                       "tool.js", "noext"}
+    assert opened == ["blob:text/plain;charset=utf-8", "blob:video/mp4",
+                      "blob:application/pdf", "blob:image/jpeg"], \
+        "a tab must get the type chosen from the name, not the blob's own"
 
 
 # ── Streaming to disk without the File System Access API ────────────────────
diff --git a/packages/meshbay-hub/tests/test_transfers.py b/packages/meshbay-hub/tests/test_transfers.py
index 1d0c0f0..c7a9dc5 100644
--- a/packages/meshbay-hub/tests/test_transfers.py
+++ b/packages/meshbay-hub/tests/test_transfers.py
@@ -918,3 +918,23 @@ def test_the_reason_is_translated_everywhere():
     `transfers.not_pausable` in a tooltip rather than a sentence."""
     for path in sorted((STATIC / "locales").glob("*.js")):
         assert "'transfers.not_pausable'" in path.read_text(encoding="utf-8"), path.name
+
+
+def test_open_is_offered_only_when_the_target_says_it_can_be(tmp_path):
+    """A row whose file cannot be opened (a type that could run in the hub's
+    origin, an archive, a stream the page cannot read back) has no Open button,
+    rather than one that does nothing."""
+    result = _run("""
+const store = new TransferStore();
+const done = (openable) => store.start({
+  kind: 'download', name: 'f', total: 1,
+  prepare: async () => (openable === undefined ? {} : { openable }),
+  open: () => {},
+  run: async ({ onProgress }) => { onProgress(1, 1); },
+});
+done(false); done(true); done(undefined);
+await new Promise(r => setTimeout(r, 30));
+say(...store.list().map(it => [it.status, it.canOpen]));
+""", tmp_path)
+    assert sorted(map(tuple, result)) == sorted([
+        ("done", False), ("done", True), ("done", True)])