docs(spec): the guardOf docblock and its test title state the has() rule that holds now

packages/spec/src/automation/flow-value-slot-template.test.ts

@@ -198,7 +198,7 @@ describe('a head CEL claims is read through `vars`, the route a `$`-named head t
     expect(refusalOf('{record.true}')).not.toContain('the guarded form');
   });
 
-  it('an index anywhere in the path leaves it unguarded — `has()` refuses one at run time', () => {
+  it('an index in the path leaves it unguarded — a step-at-a-time guard would end a `has()` on it, which `has()` refuses at run time', () => {
     expect(refusalOf('{rows.0.name}')).toContain("source: 'rows[0].name' }");
     expect(refusalOf('{rows.0.name}')).not.toContain('the guarded form');
   });

packages/spec/src/automation/flow-value-slot-template.ts

@@ -315,10 +315,12 @@ type Write = (source: string) => string;
 
 /**
  * A `has()` guard for a path of keys — the absent-variable and absent-key
- * remedy. `has()` takes a field selection over names alone: an index anywhere
- * in its argument (`has(a[0].b)`, `has(vars["$x"].y)`) is refused when it
- * runs, so a path with a numeric segment, a `$`-named head or a keyword
- * segment gets no guard.
+ * remedy. `has()` refuses an index as the last step of its argument
+ * (`has(a[0])`, `has(vars["$x"])`) when it runs; an index before the last
+ * step is a presence test like any other (`has(a[0].b)`). The guard tests
+ * every step of the path, and a numeric segment, a `$`-named head or a keyword
+ * segment is read by index, so one of its tests would end on that index: such
+ * a path gets no guard.
  *
  * The guard tests one step at a time, from `vars`, which holds only the
  * variables the run has bound: `has(vars.source) && has(vars.source.id) ?