Edit the graph during play and watch values and flow run through it

The graph was only locked by five edit-mode guards in GraphCanvas. The
running game reads the graph by reference each frame, so a new node, edge,
changed value, disconnect or undo takes effect from the next frame. Stop
discards these edits like everything else changed in play. A new On start
node does not fire for a behavior that has already started.

During play every data output shows the value it last produced, in the
highlight colour and refreshed ten times a second. Values are kept per
graph, because node ids are only unique within one; with several
instances the most recent value wins. The Variables node reads the live
variable bag, so only its own outputs are kept, as a snapshot.

Each time an exec edge fires, a bead runs along it in 0.3 s, at most one
every 0.15 s per edge, following the same curve the edge is drawn with.
Beads run on game time and freeze while paused; the game logic is
unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -313,7 +313,14 @@ shown on the node and editable in the inspector.
   falls back to another one – the picker is how you switch on purpose.
 - **Live view**: Play always switches to the Game tab; switch to Graph while playing and
   the exec edges and nodes that just ran light up – the same canvas draws editor and game, so
-  this costs nothing extra.
+  this costs nothing extra. Each fire of an exec edge also sends a bead along it (0.3 s, at most
+  one per 0.15 s and edge): a key press is a single bead, `On update` an even chain. Beads run
+  on game time, so a paused game holds them where they are. Every data output shows, in the same colour, the value it last
+  carried (`0.017  dt`, `Pause box  object`), refreshed ten times a second. With several objects
+  running the same behavior it is the one that produced last; in a loop, the last round. An
+  output nothing has asked for yet shows nothing. The graph stays editable meanwhile: the interpreter reads the runtime
+  copy's graph on every pulse, so an edit takes effect on the next frame and is discarded with
+  the run. A new `On start` node does not fire for a behavior that has already started.
 - **Runtime**: `BehaviorSystem` creates one `GraphInterpreter` per behavior entity; graphs only
   touch world entities. A runaway pulse throws (see *Loops* for the two limits) and stops play
   with a notice.
@@ -670,7 +677,7 @@ npm run check        # typecheck + lint + format:check + tests, what CI would ru
                      #   code is lost (tail's is reported), so a red run reads as green
 npm run build        # writes dist/ and regenerates index.html
 export GM_REMOTE=user@host                                    # optional: run the browser elsewhere; see below
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 578 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 588 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 – a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result