docs: fix mermaid parse error in happy-path diagram

Mermaid treats ';' as a statement separator, so the label
'lastPos (== start; re-sync)' terminated mid-line and the parser then
expected an arrow (the 'Parse error on line 59' the preview showed).
Removed the semicolon and, defensively, replaced 'Iterable<Point>' with
plain text so the angle brackets aren't interpreted as an HTML tag in the
rendered label.

docs/execution-happy-path.md

@@ -48,7 +48,7 @@ sequenceDiagram
     Sim->>Exec: executePath(strategy, ctx, dev, log, config)
 
     Exec->>Strat: path(ctx)
-    Strat-->>Exec: Iterable<Point>
+    Strat-->>Exec: iterable of Points
 
     loop for each target point (clean run)
         Exec->>Exec: resolveTarget(bounds, target) → point
@@ -66,7 +66,7 @@ sequenceDiagram
     Sim-->>Keeper: (done)
 
     Keeper->>Dev: getPosition()
-    Dev-->>Keeper: lastPos (== start; re-sync)
+    Dev-->>Keeper: lastPos (equals start, re-synced)
     Note over Keeper: lastActivity = now<br/>loop continues
 ```