Phase 23: refine routing inspection, signal-flow layout and atomic wire insertion

docs/GUI.md

@@ -77,8 +77,9 @@ to connect. Click a node or wire to select it (yellow outline/wire), then press
 Delete/Backspace or **Delete selection**. Deleting a node deletes its incident
 wires. Escape cancels a drag preview. Canvas scrollbars pan the view; positions
 are retained across edits/reconnect but not across application restart. There
-is no graph zoom, multiselection, undo or external routing UI yet.
-The editor supports 64 nodes on a fixed 2000x4000 canvas.
+is no graph zoom, multiselection or external hardware routing UI. Semantic
+graph edits participate in project undo/redo; layout does not. The default
+project supports 64 nodes; auto-layout can grow the scrollable canvas.
 
 Every semantic action becomes a C graph command. The window owns a C project containing the graph
 handle and publishes the C-created candidate through the backend. Cycle,
@@ -202,3 +203,12 @@ acknowledgement and deactivates JACK. Recording Stop, Home, fault handling and
 project installation retain immediate semantics. See
 [AUDIO_QUALITY.md](AUDIO_QUALITY.md) for timing, overload/denormal behavior, latency
 limits, test commands and the pending human-listening checklist.
+
+## Phase 23 routing refinement
+
+Graph selection now reports edge counts, output reachability and external-input
+fallback. Direction arrows, role colors, incident-wire highlighting and no-output
+badges help inspect routes. View / Arrange graph by signal flow (L) is a layout
+command; Edit / Insert unity gain in selected wire (I) is one undoable graph edit.
+Left/Right selects nodes; Tab retains ordinary focus navigation. See [ROUTING.md](ROUTING.md) for summing, stereo-lane,
+cycle, live publication and deferred grouping/template semantics.