feat(scripts): self/child/parent attribute and script accessors

Phases 1+2 of the design at
docs/plans/2026-05-12-script-scope-access-design.md.

Adds ergonomic scope-aware accessors to compiled scripts. A script
on a composed TempSensor reads its own attribute via
Attributes["Temperature"]; reaches up to the parent via
Parent.Attributes["SpeedRPM"]; invokes a child script via
Children["TempSensor"].CallScript("Sample"). All resolve to the
existing flat Instance.GetAttribute / SetAttribute / CallScript
delegates by prepending the script's canonical path prefix.

Runtime types (SiteRuntime.Scripts.ScopeAccessors):
  AttributeAccessor   sync indexer + GetAsync / SetAsync
  CompositionAccessor Attributes + CallScript
  ChildrenAccessor    Children["name"] => CompositionAccessor

ScriptGlobals gains Scope, Attributes, Children, Parent properties.
Sync indexer blocks on the Instance Actor Ask; explicit GetAsync /
SetAsync are also available for callers that want to await.

Plumbing:
  - Commons.Types.Scripts.ScriptScope record (SelfPath / ParentPath).
  - ResolvedScript.Scope (defaults to ScriptScope.Root for back-compat).
  - FlatteningService emits new ScriptScope(prefix, "") for each
    composed script so a script defined on TempSensor composed under
    a parent gets SelfPath = "TempSensor".
  - ScriptActor reads the Scope from its ResolvedScript and forwards
    it through ScriptExecutionActor into ScriptGlobals on each call.

RevisionHashService not touched: the per-script canonical name
already encodes the composition path, so any structural change
already flips the hash.

10 new unit tests on the path arithmetic. Site/Template engine
suites stay green (129 + 199).

Editor surface (Phase 3: metadata fetch, Phase 4: completion +
SCADA006 / SCADA007 diagnostics) follows in the next commits.

src/ScadaLink.SiteRuntime/Actors/ScriptActor.cs

@@ -38,6 +38,7 @@ public class ScriptActor : ReceiveActor, IWithTimers
     private TimeSpan? _minTimeBetweenRuns;
     private DateTimeOffset _lastExecutionTime = DateTimeOffset.MinValue;
     private int _executionCounter;
+    private readonly Commons.Types.Scripts.ScriptScope _scope;
 
     public ITimerScheduler Timers { get; set; } = null!;
 
@@ -63,6 +64,7 @@ public class ScriptActor : ReceiveActor, IWithTimers
         _healthCollector = healthCollector;
         _serviceProvider = serviceProvider;
         _minTimeBetweenRuns = scriptConfig.MinTimeBetweenRuns;
+        _scope = scriptConfig.Scope;
 
         // Parse trigger configuration
         _triggerConfig = ParseTriggerConfig(scriptConfig.TriggerType, scriptConfig.TriggerConfiguration);
@@ -215,6 +217,7 @@ public class ScriptActor : ReceiveActor, IWithTimers
             replyTo,
             correlationId,
             _logger,
+            _scope,
             _healthCollector,
             _serviceProvider));
 

src/ScadaLink.SiteRuntime/Actors/ScriptExecutionActor.cs

@@ -33,6 +33,7 @@ public class ScriptExecutionActor : ReceiveActor
         IActorRef replyTo,
         string correlationId,
         ILogger logger,
+        Commons.Types.Scripts.ScriptScope scope,
         ISiteHealthCollector? healthCollector = null,
         IServiceProvider? serviceProvider = null)
     {
@@ -43,7 +44,7 @@ public class ScriptExecutionActor : ReceiveActor
         ExecuteScript(
             scriptName, instanceName, compiledScript, parameters, callDepth,
             instanceActor, sharedScriptLibrary, options, replyTo, correlationId,
-            self, parent, logger, healthCollector, serviceProvider);
+            self, parent, logger, scope, healthCollector, serviceProvider);
     }
 
     private static void ExecuteScript(
@@ -60,6 +61,7 @@ public class ScriptExecutionActor : ReceiveActor
         IActorRef self,
         IActorRef parent,
         ILogger logger,
+        Commons.Types.Scripts.ScriptScope scope,
         ISiteHealthCollector? healthCollector,
         IServiceProvider? serviceProvider)
     {
@@ -102,7 +104,8 @@ public class ScriptExecutionActor : ReceiveActor
                 {
                     Instance = context,
                     Parameters = new ScriptParameters(parameters ?? new Dictionary<string, object?>()),
-                    CancellationToken = cts.Token
+                    CancellationToken = cts.Token,
+                    Scope = scope
                 };
 
                 var state = await compiledScript.RunAsync(globals, cts.Token);

src/ScadaLink.SiteRuntime/Scripts/ScopeAccessors.cs

@@ -0,0 +1,105 @@
+namespace ScadaLink.SiteRuntime.Scripts;
+
+/// <summary>
+/// Scope-aware view onto the instance's attributes, anchored at a path prefix.
+/// <c>Attributes["X"]</c> on the root scope resolves to canonical name "X";
+/// on a composition with prefix "TempSensor" it resolves to "TempSensor.X".
+/// Reads block on the actor Ask; async variants are provided for callers
+/// that prefer to await explicitly.
+/// </summary>
+public class AttributeAccessor
+{
+    private readonly ScriptRuntimeContext _ctx;
+
+    /// <summary>Canonical-name prefix, e.g. "" for root or "TempSensor" for a composition.</summary>
+    public string ScopePrefix { get; }
+
+    public AttributeAccessor(ScriptRuntimeContext ctx, string prefix)
+    {
+        _ctx = ctx;
+        ScopePrefix = prefix;
+    }
+
+    public string Resolve(string key) =>
+        ScopePrefix.Length == 0 ? key : ScopePrefix + "." + key;
+
+    public object? this[string key]
+    {
+        get => _ctx.GetAttribute(Resolve(key)).GetAwaiter().GetResult();
+        set => _ctx.SetAttribute(Resolve(key), value?.ToString() ?? string.Empty);
+    }
+
+    public Task<object?> GetAsync(string key) => _ctx.GetAttribute(Resolve(key));
+
+    public Task SetAsync(string key, object? value)
+    {
+        _ctx.SetAttribute(Resolve(key), value?.ToString() ?? string.Empty);
+        return Task.CompletedTask;
+    }
+}
+
+/// <summary>
+/// A view of one composition at a path. Exposes its attributes via
+/// <see cref="AttributeAccessor"/> and an invokable <c>CallScript</c>.
+/// </summary>
+public class CompositionAccessor
+{
+    private readonly ScriptRuntimeContext _ctx;
+
+    /// <summary>Canonical-name path this composition is rooted at.</summary>
+    public string Path { get; }
+
+    public AttributeAccessor Attributes { get; }
+
+    public CompositionAccessor(ScriptRuntimeContext ctx, string path)
+    {
+        _ctx = ctx;
+        Path = path;
+        Attributes = new AttributeAccessor(ctx, path);
+    }
+
+    public string ResolveScript(string scriptName) =>
+        Path.Length == 0 ? scriptName : Path + "." + scriptName;
+
+    public Task<object?> CallScript(string scriptName, IReadOnlyDictionary<string, object?>? parameters = null)
+        => _ctx.CallScript(ResolveScript(scriptName), parameters);
+}
+
+/// <summary>
+/// Dictionary-style accessor for the script's child compositions. Indexing
+/// returns a <see cref="CompositionAccessor"/> rooted at the child's path.
+/// </summary>
+public class ChildrenAccessor
+{
+    private readonly ScriptRuntimeContext _ctx;
+    private readonly string _selfPath;
+
+    public ChildrenAccessor(ScriptRuntimeContext ctx, string selfPath)
+    {
+        _ctx = ctx;
+        _selfPath = selfPath;
+    }
+
+    public CompositionAccessor this[string compositionName]
+    {
+        get
+        {
+            var path = _selfPath.Length == 0
+                ? compositionName
+                : _selfPath + "." + compositionName;
+            return new CompositionAccessor(_ctx, path);
+        }
+    }
+}
+
+internal static class ScopeAccessorFactory
+{
+    public static AttributeAccessor AttributesFor(ScriptRuntimeContext ctx, string selfPath)
+        => new(ctx, selfPath);
+
+    public static ChildrenAccessor ChildrenFor(ScriptRuntimeContext ctx, string selfPath)
+        => new(ctx, selfPath);
+
+    public static CompositionAccessor? ParentFor(ScriptRuntimeContext ctx, string? parentPath)
+        => parentPath == null ? null : new CompositionAccessor(ctx, parentPath);
+}

src/ScadaLink.SiteRuntime/Scripts/ScriptCompilationService.cs

@@ -181,6 +181,14 @@ public class ScriptGlobals
     public ScriptParameters Parameters { get; set; } = new ScriptParameters();
     public CancellationToken CancellationToken { get; set; }
 
+    /// <summary>
+    /// Where this script sits in the composition tree. Defaults to root for
+    /// scripts on top-level templates; a flattened composed script gets
+    /// SelfPath = "TempSensor" (etc.) and a ParentPath set to one level up.
+    /// </summary>
+    public Commons.Types.Scripts.ScriptScope Scope { get; set; } =
+        Commons.Types.Scripts.ScriptScope.Root;
+
     /// <summary>
     /// Top-level ExternalSystem access for scripts (delegates to Instance.ExternalSystem).
     /// Usage: ExternalSystem.Call("systemName", "methodName", params)
@@ -204,4 +212,27 @@ public class ScriptGlobals
     /// Usage: Scripts.CallShared("scriptName", params)
     /// </summary>
     public ScriptRuntimeContext.ScriptCallHelper Scripts => Instance.Scripts;
+
+    /// <summary>
+    /// Read/write the current template's attributes by name. Resolves to the
+    /// canonical name for the script's scope, so a script on a composed
+    /// TempSensor reads its own Temperature via <c>Attributes["Temperature"]</c>.
+    /// </summary>
+    public AttributeAccessor Attributes => new(Instance, Scope.SelfPath);
+
+    /// <summary>
+    /// Indexed access to child compositions.
+    /// <c>Children["TempSensor"].Attributes["Temperature"]</c> reads the
+    /// composed child's attribute. <c>Children["TempSensor"].CallScript("Sample")</c>
+    /// invokes a script on the child.
+    /// </summary>
+    public ChildrenAccessor Children => new(Instance, Scope.SelfPath);
+
+    /// <summary>
+    /// Parent composition (null when this script is on a root-level template).
+    /// <c>Parent.Attributes["SpeedRPM"]</c> reaches the parent's attribute;
+    /// <c>Parent.CallScript("Trip")</c> invokes a parent script.
+    /// </summary>
+    public CompositionAccessor? Parent =>
+        Scope.ParentPath == null ? null : new CompositionAccessor(Instance, Scope.ParentPath);
 }