fix(newos4): never overwrite a directory node; ls honours a path after its flags

MAINT-010 and MAINT-016, the two high items the review left open. Both were re-probed
before the change and the new test is red on HEAD (5 passed, 7 FAILED).

- virtual-fs.js rename()/copy(): they assigned dst.dir.content[dst.name] with no destination
  type check, so `mv file /docs` replaced the /docs node and every child vanished while the
  command printed "Moved: …". Refuse when the destination is a real directory node (the
  virtual /sys entry is exempt). rename() also erased the file on `mv a a`, because assigning
  and then deleting the same key removes it; that path is now an explicit no-op.
- module-fs.js mv/cp: a refusal used to surface as "No such file or directory", which sent
  the operator looking for a missing source. The destination is now inspected first and the
  message says "is a directory — refusing to overwrite it".
- module-fs.js ls: the path was only read from argv[0], so `ls -l /work` listed the cwd.
  The first non-flag argument is now the target; the path-first form is unchanged.

Tests: modules/test/test-fs-mv-cp-guard.js (12 asserts) — RED on HEAD (A1-A3, B1, B2, C2, E1),
GREEN now; maintain --fix reports "node tests 7/7 pass". Browser on v4.6.104:
"mv: /vtest: is a directory — refusing to overwrite it", child and source intact,
"ls -l /vtest" lists /vtest (keep.txt), not the cwd.

1 files changed, 17 insertions, 4 deletions

diff --git a/modules/core/module-fs.js b/modules/core/module-fs.js
index f2b215a..583cfda 100644
--- a/modules/core/module-fs.js
+++ b/modules/core/module-fs.js
@@ -44,8 +44,11 @@ class FileSystemModule {
     registerCommands() {
         const self = this;
         this.commands['ls'] = (args) => {
-            const target = args && args.length > 0 && !args[0].startsWith('-') ? args[0] : undefined;
-            const flags = (args || []).filter(a => a.startsWith('-'));
+            const argv = args || [];
+            // v4.6.104: the path may follow the flags — `ls -l /work` used to list the cwd
+            // because only argv[0] was considered (MAINT-016).
+            const flags = argv.filter(a => a.startsWith('-'));
+            const target = argv.find(a => !a.startsWith('-'));
             const showLong = flags.some(f => f.includes('l'));
             const showHidden = flags.some(f => f.includes('a'));
             const files = this.terminal.fs.ls(target);
@@ -180,14 +183,24 @@ class FileSystemModule {
         };
         this.commands['mv'] = (args) => {
             if(!args[0] || !args[1]) return this.terminal.print('Usage: mv <source> <dest>', 'warning');
-            if (this.terminal.fs.mv(args[0], args[1]))
+            const fs = this.terminal.fs;
+            const d = fs._resolvePath(args[1]);
+            const dn = d && d.name ? d.dir.content[d.name] : null;
+            if (dn && dn.type === 'dir' && !dn._virtual)
+                return this.terminal.print('mv: ' + args[1] + ': is a directory — refusing to overwrite it', 'error');
+            if (fs.mv(args[0], args[1]))
                 this.terminal.print('Moved: ' + args[0] + ' to ' + args[1], 'success');
             else
                 this.terminal.print('mv: ' + args[0] + ': No such file or directory', 'error');
         };
         this.commands['cp'] = (args) => {
             if(!args[0] || !args[1]) return this.terminal.print('Usage: cp <source> <dest>', 'warning');
-            if (this.terminal.fs.cp(args[0], args[1]))
+            const fs = this.terminal.fs;
+            const d = fs._resolvePath(args[1]);
+            const dn = d && d.name ? d.dir.content[d.name] : null;
+            if (dn && dn.type === 'dir' && !dn._virtual)
+                return this.terminal.print('cp: ' + args[1] + ': is a directory — refusing to overwrite it', 'error');
+            if (fs.cp(args[0], args[1]))
                 this.terminal.print('Copied: ' + args[0] + ' to ' + args[1], 'success');
             else
                 this.terminal.print('cp: ' + args[0] + ': No such file or directory', 'error');