fix(client): a successful root op must never blank the operator's table

`ops.update_root` and `remove_root` returned `[]` when the group context had
no live RootSet, and `group-page.js` accepted it: `if (msg.roots)` is true for
an empty array. An op that succeeded would have emptied the shared-directories
table, and "the node says this group has no directories" is not something the
client can tell from "the node could not say". Both ends now refuse it — the
node builds from config rather than answering empty, and the client requires a
non-empty array.

Found while adding `test_spa_imports.py`, which is the other half of this: it
resolves every named import across the SPA against what the target actually
exports. That failure has a shape nothing else here catches — no build step to
fail, so the browser resolves the graph at load, finds a missing binding, and
the page renders blank or the component just does not appear. `node --check`
parses one file at a time and the source-reading guards look inside a file
rather than between two. The settings split moved two shared components into a
new module and rewired eight files to import them, which is exactly the change
where a rename lands in one file and not the other.

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

3 files changed, 104 insertions, 3 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/group-page.js b/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
index 747cb74..e762fc8 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
@@ -374,7 +374,11 @@ function GroupPage({ groupId, group, token, username, userId, userPrefs,
         transport.onMusicbrainzEnabled = (enabled) =>
           setMusicbrainzConfig((prev) => ({ ...(prev || {}), enabled }));
         transport.onRootsChanged = (msg) => {
-          if (msg.roots) {
+          // `msg.roots &&` would accept `[]`, and an empty array is truthy —
+          // so a node that could not describe its roots would blank the
+          // operator's table on an op that actually succeeded. A group always
+          // has at least one root, so nothing legitimate is dropped here.
+          if (Array.isArray(msg.roots) && msg.roots.length) {
             setNodeRoots(msg.roots);
           }
         };
diff --git a/packages/meshbay-hub/tests/test_spa_imports.py b/packages/meshbay-hub/tests/test_spa_imports.py
new file mode 100644
index 0000000..230f33f
--- /dev/null
+++ b/packages/meshbay-hub/tests/test_spa_imports.py
@@ -0,0 +1,87 @@
+"""
+Every import in the SPA points at a file that exports what it names.
+
+The failure this catches has a distinctive shape: nothing errors at build time,
+because there is no build; the browser resolves the module graph at load, finds
+a binding that is not there, and the page renders blank or the component simply
+does not appear. `node --check` cannot see it — it parses one file at a time —
+and neither can the source-reading guards, which look inside a file rather than
+between two.
+
+Written after the settings-page split, which moved two shared components into a
+new module and rewired eight files to import them from there. That is exactly
+the change where a rename lands in one file and not the other.
+
+It is a static check, not a load: it says the name is exported, not that the
+value is what the caller expects. `test_spa_syntax` covers parsing;
+`test_hook_ordering` covers the ordering fault that also presents as a missing
+component.
+"""
+
+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")
+
+# `import { a, b as c } from './x.js';` / `import * as p from ...` / default.
+IMPORT = re.compile(
+    r"^import\s+(?:\{([^}]*)\}|(\*\s+as\s+\w+)|(\w+))\s+from\s+'([^']+)';", re.M)
+EXPORT_BLOCK = re.compile(r"^export\s+\{([^}]*)\};", re.M)
+EXPORT_DECL = re.compile(
+    r"^export\s+(?:default\s+)?(?:async\s+)?(?:function|const|class|let|var)\s+(\w+)",
+    re.M)
+
+
+def _exported(source: str) -> set[str]:
+    names = set(EXPORT_DECL.findall(source))
+    for block in EXPORT_BLOCK.findall(source):
+        for raw in block.split(","):
+            name = raw.strip().split(" as ")[-1].strip()
+            if name:
+                names.add(name)
+    return names
+
+
+def test_every_named_import_resolves():
+    problems: list[str] = []
+    for path in sorted(STATIC.glob("*.js")):
+        source = path.read_text(encoding="utf-8")
+        for names, star, default, spec in IMPORT.findall(source):
+            # vendor/ is third-party, bundled, and does not use a form this
+            # reads. Its exports are covered by the app failing to start.
+            if not spec.startswith("./") or "vendor/" in spec:
+                continue
+            target = (path.parent / spec[2:]).resolve()
+            if not target.exists():
+                problems.append(f"{path.name}: imports {spec} — no such file")
+                continue
+            if star or default or not names.strip():
+                continue
+            available = _exported(target.read_text(encoding="utf-8"))
+            for raw in names.split(","):
+                name = raw.strip().split(" as ")[0].strip()
+                if name and name not in available:
+                    problems.append(
+                        f"{path.name}: imports {{{name}}} from {spec}, "
+                        f"which does not export it")
+
+    assert not problems, "unresolved imports:\n" + "\n".join(problems)
+
+
+def test_the_check_can_see_a_real_module():
+    """
+    Guard against the parser quietly matching nothing — a regex that stopped
+    finding imports would make the test above pass over an empty set, which
+    looks exactly like success.
+    """
+    source = (STATIC / "apps.js").read_text(encoding="utf-8")
+    found = IMPORT.findall(source)
+    assert len(found) >= 5, (
+        "the import pattern no longer matches apps.js — this test is then "
+        "checking nothing")
+    assert "configurableApps" in _exported(source)
diff --git a/packages/meshbay-node/src/meshbay_node/ops.py b/packages/meshbay-node/src/meshbay_node/ops.py
index f7f6190..11694c3 100644
--- a/packages/meshbay-node/src/meshbay_node/ops.py
+++ b/packages/meshbay-node/src/meshbay_node/ops.py
@@ -728,7 +728,12 @@ async def remove_root(state: dict, group_id: str, root_name: str) -> dict:
         live_roots.roots = [
             r for r in live_roots.roots if fold(r.name) != target]
 
-    result_roots = live_roots.describe() if live_roots else []
+    # Built from config when there is no live set, never returned empty: an
+    # empty list is a *valid answer* meaning "this group has no directories",
+    # and the client cannot tell it from "the node could not say". It would
+    # blank the operator's table on an op that succeeded.
+    result_roots = (live_roots.describe() if live_roots
+                    else RootSet.build([asdict(r) for r in cfg.roots]).describe())
 
     log.info("Root removed: %s from group %s", root_name, group_id[:8])
     return {"status": "removed", "name": root_name, "group_id": group_id,
@@ -788,7 +793,12 @@ async def update_root(state: dict, group_id: str, root_name: str, *,
                     lr.removable = removable
                 break
 
-    result_roots = live_roots.describe() if live_roots else []
+    # Built from config when there is no live set, never returned empty: an
+    # empty list is a *valid answer* meaning "this group has no directories",
+    # and the client cannot tell it from "the node could not say". It would
+    # blank the operator's table on an op that succeeded.
+    result_roots = (live_roots.describe() if live_roots
+                    else RootSet.build([asdict(r) for r in cfg.roots]).describe())
 
     log.info("Root updated: %s (writable=%s, removable=%s) in group %s",
              root_name, match.writable, match.removable, group_id[:8])