Clean up: fix stale comment, stronger test assertions, import order

- on.ts comment: "this.*" → "path read" since binding applies to all
  paths now
- fn-test.ts: assert seenThis has expected property (arg1 === 'foo')
  instead of just non-null, matching reviewer feedback
- expressions.ts: alphabetize imports

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: NullVoxPopuli

packages/@glimmer-workspace/integration-tests/test/helpers/fn-test.ts

@@ -181,18 +181,25 @@ class FnTest extends RenderTest {
   'this context is available within the callback'(assert: Assert) {
     let seenThis: unknown;
 
-    this.render(`<Stash @stashedFn={{fn this.myFunc this.arg1}}/>`, {
+    let context = {
       myFunc() {
         assert.step('calling stashed function');
         seenThis = this;
       },
 
       arg1: 'foo',
-    });
+    };
+
+    this.render(`<Stash @stashedFn={{fn this.myFunc this.arg1}}/>`, context);
 
     this.stashedFn?.();
     assert.verifySteps(['calling stashed function']);
-    assert.ok(seenThis !== null && seenThis !== undefined, 'this is bound to the context');
+    assert.ok(seenThis !== null && seenThis !== undefined, 'this is not null/undefined');
+    assert.strictEqual(
+      (seenThis as Record<string, unknown>)['arg1'],
+      'foo',
+      'this is bound to the object myFunc is defined on'
+    );
   }
 
   @test

packages/@glimmer/runtime/lib/compiled/opcodes/expressions.ts

@@ -45,8 +45,8 @@ import type { Reference } from '@glimmer/reference';
 import {
   childRefFor,
   createComputeRef,
-  setBindingParentRef,
   FALSE_REFERENCE,
+  setBindingParentRef,
   TRUE_REFERENCE,
   UNDEFINED_REFERENCE,
   valueForRef,

packages/@glimmer/runtime/lib/modifiers/on.ts

@@ -183,9 +183,9 @@ export class OnModifierState {
     if (shouldUpdate) {
       let callback = userProvidedCallback;
 
-      // If the callback ref was created by VM_GET_PROPERTY_BOUND_OP (i.e. a
-      // `this.*` path read), bind the callback to the parent object so that
-      // class methods preserve their `this` context.
+      // If the callback ref was created by VM_GET_PROPERTY_BOUND_OP (a path
+      // read like `this.foo`, `o.method`, etc.), bind the callback to the
+      // parent object so that methods preserve their `this` context.
       let bindingParentRef = arg1 ? getBindingParentRef(arg1) : undefined;
       if (bindingParentRef) {
         let parentValue = valueForRef(bindingParentRef);