fix(client): New folder did nothing — prompt() throws in the desktop client

The same `static/` tree is the web page and the application, and Electron does
not implement `window.prompt`: Chromium leaves it to the embedder and Electron
declines. It does not return null — it **throws**. The call sat above its own
try, so clicking produced no folder, no error and nothing on screen to react
to. A dead button, which is exactly how it was reported.

Measured against this repo's own Electron 44 rather than assumed, because the
first two diagnoses this session were reasoned and wrong:

    prompt('name?')  ->  Error: prompt() is not supported.
    confirm('sure?') ->  opens a real modal
    alert('hi')      ->  opens a real modal

So `confirm` and `alert` stay — a dozen call sites depend on them — and only
`prompt` is banned. `test_no_prompt_in_the_spa.py` holds the whole tree to it,
with the near-misses it must not flag (`mkdir_prompt`, `promptForName`).

The name now comes from a field in the toolbar, which works in both clients and
can show the node's refusal beside the input instead of after a dialog has
closed. Navigating away drops a half-typed name: it would otherwise create the
folder somewhere the person is no longer looking.

The rest of the chain was verified end to end and was sound: `dir_create`
{dir,name} → the node's handler → `dir_create_ack`, and `list_dirs` walks the
filesystem rather than the index, so a folder with nothing in it appears on the
very fetch that follows. The field itself was then driven inside a real
Electron window — typing, Enter, the click, and the icon rendering.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pvMdvLBG92jyhvD5pD6us

2 files changed, 102 insertions, 5 deletions

diff --git a/packages/meshbay-hub/tests/test_no_prompt_in_the_spa.py b/packages/meshbay-hub/tests/test_no_prompt_in_the_spa.py
new file mode 100644
index 0000000..d126a05
--- /dev/null
+++ b/packages/meshbay-hub/tests/test_no_prompt_in_the_spa.py
@@ -0,0 +1,90 @@
+"""
+`window.prompt` does not exist in the desktop client.
+
+The same `static/` tree is the web page and the application (CLAUDE.md's "one
+UI source"), and Electron does not implement `prompt` — Chromium leaves it to
+the embedder and Electron declines. It does not return null: it **throws**,
+`Error: prompt() is not supported.`
+
+That made the Files toolbar's New folder button do nothing whatsoever. The call
+sat above its own try, so the click produced no folder, no error, and nothing
+on screen to react to — the failure looks exactly like a dead button, which is
+what it was reported as.
+
+Measured rather than assumed, against this repo's own Electron 44:
+
+    prompt('name?')  ->  Error: prompt() is not supported.
+    confirm('sure?') ->  opens a real modal
+    alert('hi')      ->  opens a real modal
+
+So `confirm` and `alert` stay allowed and are used in a dozen places; only
+`prompt` is banned. Anything that needs typed input needs a field.
+"""
+
+import re
+from pathlib import Path
+
+import pytest
+
+STATIC = Path(__file__).resolve().parents[1] / "src" / "meshbay_hub" / "static"
+
+pytestmark = pytest.mark.skipif(not STATIC.exists(),
+                                reason="SPA sources unavailable")
+
+# `prompt(` as a call, not `window.prompt` inside a comment or a longer
+# identifier like `mkdir_prompt` / `promptForName`.
+CALL = re.compile(r"(?<![\w.$])(?:window\.)?prompt\s*\(")
+
+
+def _code_only(source: str) -> str:
+    source = re.sub(r"/\*.*?\*/", "", source, flags=re.S)
+    return re.sub(r"^\s*//.*$", "", source, flags=re.M)
+
+
+def test_nothing_calls_prompt():
+    offenders = []
+    for path in sorted(STATIC.glob("*.js")):
+        if path.name == "sw.js":
+            continue
+        for i, line in enumerate(_code_only(
+                path.read_text(encoding="utf-8")).splitlines(), 1):
+            if CALL.search(line):
+                offenders.append(f"{path.name}:{i}: {line.strip()}")
+
+    assert not offenders, (
+        "prompt() throws in the desktop client, and the click that reaches it "
+        "does nothing at all:\n  " + "\n  ".join(offenders))
+
+
+def test_the_pattern_would_catch_a_real_call():
+    """
+    A guard that matches nothing passes over an empty set, which looks exactly
+    like success. Both spellings, and the near-misses it must not flag.
+    """
+    assert CALL.search("const n = prompt('x');")
+    assert CALL.search("const n = window.prompt('x');")
+    assert not CALL.search("t('group.mkdir_prompt')")
+    assert not CALL.search("promptForName();")
+    assert not CALL.search("this.prompt(1);")
+
+
+def test_creating_a_folder_uses_a_field():
+    """
+    The control the ban is about. A typed name needs somewhere to type it, and
+    an inline field can show the node's refusal beside the input rather than
+    after a dialog has closed.
+    """
+    source = (STATIC / "files-app.js").read_text(encoding="utf-8")
+    assert "tb-mkdir-input" in source
+    assert "newDirName" in source
+    assert "group.mkdir_prompt" in source, "the field has no label or placeholder"
+
+
+def test_leaving_the_folder_drops_a_half_typed_name():
+    """
+    Otherwise the folder is created where the person is no longer looking —
+    they navigated away, the draft came along, and the name lands in a
+    directory they were not thinking about.
+    """
+    source = (STATIC / "files-app.js").read_text(encoding="utf-8")
+    assert "useEffect(() => { setNewDirName(null); }, [currentPath]);" in source
diff --git a/packages/meshbay-hub/tests/test_upload_controls_hidden.py b/packages/meshbay-hub/tests/test_upload_controls_hidden.py
index a61de1f..bdba373 100644
--- a/packages/meshbay-hub/tests/test_upload_controls_hidden.py
+++ b/packages/meshbay-hub/tests/test_upload_controls_hidden.py
@@ -94,13 +94,20 @@ def test_an_icon_only_button_still_says_what_it_is():
     The name moved into a tooltip to save toolbar width. A `title` is invisible
     to a screen reader on a button with no text, so the label has to be there
     as well — otherwise the control is simply unnamed for anyone not reading
-    with their eyes.
+    with their eyes. The same goes for the field it opens, which has a
+    placeholder and no visible label.
     """
     page = _component(FILES_APP.read_text(encoding="utf-8"), "FilesPanel")
-    block = page[page.index("canCreateDir && html`"):]
-    block = block[:block.index("</button>")]
-    assert "title=" in block and "aria-label=" in block
-    assert "group.mkdir" in block
+    opener = page[page.index("canCreateDir && newDirName === null"):]
+    opener = opener[:opener.index("</button>")]
+    assert "title=" in opener and "aria-label=" in opener
+    assert "group.mkdir" in opener
+
+    field = page[page.index("canCreateDir && newDirName !== null"):]
+    field = field[:field.index("</span>")]
+    assert "aria-label=" in field, (
+        "the name field is labelled by a placeholder alone, which a screen "
+        "reader does not announce as a name")
 
 
 def test_the_chat_composer_hides_its_paperclip():