Channels: live variable-name hint in code editor updates with sources

When sources are added, removed, or changed in the derived channel editor,
the code group now shows a live "Variables: A0 = x[0]  ·  encoder = x[1]"
hint above the code editor so users know the exact names to use in scripts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/ui/windows/channels_window.py b/ui/windows/channels_window.py
index ecc7cbc..3730b12 100644
--- a/ui/windows/channels_window.py
+++ b/ui/windows/channels_window.py
@@ -743,6 +743,10 @@ class DerivedBlock(QFrame):
         # Code editor (shown for all kinds — read-only for built-ins)
         self._code_grp = QGroupBox("Code")
         code_lay = QVBoxLayout(self._code_grp); code_lay.setContentsMargins(6, 4, 6, 4)
+        # Live variable-name hint — updated whenever sources change
+        self._vars_lbl = QLabel("")
+        self._vars_lbl.setObjectName("traceSource"); self._vars_lbl.setWordWrap(True)
+        code_lay.addWidget(self._vars_lbl)
         _mono = QFont("IBM Plex Mono, Consolas, Monospace"); _mono.setStyleHint(QFont.StyleHint.Monospace)
         self._code = QTextEdit(); self._code.setObjectName("codeEditor")
         self._code.setMinimumHeight(90); self._code.setMaximumHeight(180)
@@ -776,6 +780,7 @@ class DerivedBlock(QFrame):
         body.setVisible(False)
         outer.addWidget(body)
         self._body = body
+        self._update_vars_hint()
         self._update_visibility()
 
     def _toggle(self):
@@ -792,11 +797,13 @@ class DerivedBlock(QFrame):
             for i in range(cb.count()):
                 if cb.itemData(i) == src:
                     cb.setCurrentIndex(i); break
+        cb.currentIndexChanged.connect(lambda _: self._update_vars_hint())
         rm = QToolButton(); rm.setText("✕"); rm.setObjectName("traceRemoveBtn")
         rm.setFixedSize(22, 22); rm.clicked.connect(lambda: self._rm_src(row, cb))
         row.addWidget(cb, 1); row.addWidget(rm)
         self._src_vlay.addLayout(row)
         self._src_combos.append(cb)
+        self._update_vars_hint()
 
     def _rm_src(self, row, cb):
         if cb in self._src_combos:
@@ -804,6 +811,20 @@ class DerivedBlock(QFrame):
         while row.count():
             it = row.takeAt(0)
             if it.widget(): it.widget().deleteLater()
+        self._update_vars_hint()
+
+    def _update_vars_hint(self):
+        """Refresh the variable-name hint above the code editor."""
+        if not hasattr(self, "_vars_lbl"):
+            return
+        from core.signal_processor import _make_src_names
+        sources = [cb.currentData() for cb in self._src_combos if cb.currentData()]
+        if not sources:
+            self._vars_lbl.setText("No sources — add sources above to use named variables")
+            return
+        names = _make_src_names(sources)
+        parts = [f"{name} = x[{i}]" for i, name in enumerate(names)]
+        self._vars_lbl.setText("Variables:  " + "  ·  ".join(parts))
 
     def _on_kind(self, idx: int):
         from ui.code_templates import BUILTIN_TEMPLATES
@@ -815,6 +836,7 @@ class DerivedBlock(QFrame):
         if k in _BUILTIN:
             # Show the template as a read-only preview
             self._code.setPlainText(BUILTIN_TEMPLATES.get(k, ""))
+        self._update_vars_hint()
         self._update_visibility()
 
     def _on_wrt_changed(self, idx: int):