vcs: stop both vcs and vcs.jt4 from moving cursor on EmuHalt

src/ide/ui.ts

@@ -2641,11 +2641,14 @@ export function getSaveState() {
 export function emulationHalted(err: EmuHalt) {
   var msg = (err && err.message) || msg;
   showExceptionAsError(err, msg);
-  projectWindows.refresh(false); // don't mess with cursor
+  // passive refresh: show the PC gutter arrow but don't move the cursor or
+  // repaint the current line, since the user may be typing
+  projectWindows.refresh(false);
   if (platform.saveState) {
-    const state = platform.saveState()
+    const state = platform.saveState();
     showDebugInfo(state);
-    openRelevantListing(state);
+    // don't do this because it'll mess with user selected window!
+    //openRelevantListing(state);
   }
 }
 

src/ide/views/editors.ts

@@ -624,8 +624,11 @@ export class SourceEditor implements ProjectView {
       this.editor.dispatch({
         effects: [
           currentPcMarker.set.of(line.line),
-          currentPc.effect.of(line.line),
-          // Follow the execution point when stepping/hitting breakpoints.
+          // Follow the execution point when stepping/hitting breakpoints. A
+          // passive halt (e.g. the program ends while the user is typing) only
+          // shows the gutter arrow, so it doesn't repaint/highlight the line
+          // out from under the user's cursor.
+          currentPc.effect.of(moveCursor ? line.line : null),
           ...(moveCursor ? [EditorView.scrollIntoView(this.editor.state.doc.line(line.line).from, { y: "center" })] : []),
         ]
       });

src/platform/vcs.ts

@@ -97,9 +97,13 @@ class VCSPlatform extends BasePlatform {
       self.probe.logNewFrame();
       this.oldClockPulse();
       // look for KIL instruction
-      if (Javatari.room.console.getCPUState().o == 0x02 && Javatari.room.console.onBreakpointHit != null) {
-        Javatari.room.console.onBreakpointHit(Javatari.room.console.saveState());
-        //throw new EmuHalt("CPU STOPPED"); // TODO: requires browser reload
+      // Halt passively, like vcs.jt4, instead of stopping as a breakpoint would
+      // (which moves the cursor). Throw outside Javatari's clock, since it
+      // can't recover from an exception.
+      if (Javatari.room.console.getCPUState().o == 0x02 && self.isRunning()) {
+        self.pause();
+        const pc = (Javatari.room.console.saveState().c.PC - 1) & 0xffff;
+        setTimeout(() => { throw new EmuHalt(`CPU halted at $${pc.toString(16)}`); }, 0);
       }
     }
     // intercept TIA end of line