feat: add friendly error for cross-hook property access (#8813)

When accessing one hook's struct properties from within another
hook's begin/end block, show a helpful error suggesting sharedVec3
or sharedFloat instead of the cryptic undefined TypeError.

Author: BHARATH0153

src/strands/strands_api.js

@@ -795,6 +795,50 @@ export function createShaderHooksFunctions(strandsContext, fn, shader) {
     hook.set = function(result) {
       hook._result = result;
     };
+    hook._active = false;
+
+    const numStructArgs = hookType.parameters.filter(
+      param => param.type && param.type.properties
+    ).length;
+    let argIdx = -1;
+    if (numStructArgs === 1) {
+      argIdx = hookType.parameters.findIndex(
+        param => param.type && param.type.properties
+      );
+    }
+    if (argIdx >= 0) {
+      const structParam = hookType.parameters[argIdx];
+      if (structParam.type.properties) {
+        for (const prop of structParam.type.properties) {
+          const key = prop.name;
+          Object.defineProperty(hook, key, {
+            get() {
+              if (!this._active) {
+                FES.userError(
+                  'scope error',
+                  `It looks like you're trying to access "${hookType.name}.${key}" outside of its begin()/end() block.\n\n` +
+                  `Properties of ${hookType.name} are only available between ` +
+                  `${hookType.name}.begin() and ${hookType.name}.end().\n\n` +
+                  `To share data between hooks, use sharedVec3() or sharedFloat() ` +
+                  `to pass values between them.`
+                );
+              }
+              return this._args[this._argIdx][key];
+            },
+            set(val) {
+              if (!this._active) {
+                FES.userError(
+                  'scope error',
+                  `It looks like you're trying to set "${hookType.name}.${key}" outside of its begin()/end() block.`
+                );
+              }
+              this._args[this._argIdx][key] = val;
+            },
+            enumerable: true,
+          });
+        }
+      }
+    }
 
     let entryBlockID;
     function setupHook() {
@@ -803,25 +847,14 @@ export function createShaderHooksFunctions(strandsContext, fn, shader) {
       CFG.addEdge(cfg, cfg.currentBlock, entryBlockID);
       CFG.pushBlock(cfg, entryBlockID);
       const args = createHookArguments(strandsContext, hookType.parameters);
-      const numStructArgs = hookType.parameters.filter(param => param.type.properties).length;
-      let argIdx = -1;
-      if (numStructArgs === 1) {
-        argIdx = hookType.parameters.findIndex(param => param.type.properties);
-      }
+      hook._active = true;
+      hook._args = args;
+      hook._argIdx = argIdx;
       hook._properties = [];
       for (let i = 0; i < args.length; i++) {
         if (i === argIdx) {
           for (const key of args[argIdx].structProperties || []) {
             hook._properties.push(key);
-            Object.defineProperty(hook, key, {
-              get() {
-                return args[argIdx][key];
-              },
-              set(val) {
-                args[argIdx][key] = val;
-              },
-              enumerable: true,
-            });
           }
           if (hookType.returnType?.typeName === hookType.parameters[argIdx].type.typeName) {
             hook.set(args[argIdx]);
@@ -835,6 +868,7 @@ export function createShaderHooksFunctions(strandsContext, fn, shader) {
     };
 
     function finishHook() {
+      hook._active = false;
       const userReturned = hook._result;
       strandsContext.activeHook = undefined;