What's broken on master

action is an ambient strict-mode keyword in Ember (registered in STRICT_MODE_KEYWORDS at @ember/template-compiler/lib/plugins/index.ts), so {{action this.x}} works in .gjs/.gts templates without an import. The rule correctly flags the ambient keyword in both modes, but it doesn't account for users who legitimately shadow action with a JS binding or a template block param:

import action from './my-action-helper';
<template>{{action this.handleClick}}</template>   // false-positive on master

<template>
  {{#each items as |action|}}
    {{action this.x}}    {/* false-positive on master — `action` is the iterator */}
  {{/each}}
</template>

Fix

Add the JS-scope-walk + block-param tracking pattern already established in template-no-log, template-no-unbound, template-no-restricted-invocations, etc.:

• Walk sourceCode.getScope().variables to detect JS bindings named action.
• Push/pop GlimmerBlockStatement.program.blockParams and GlimmerElementNode.blockParams to track template-side block params.
• Skip the report when action resolves to a local binding (either source).

The existing @action and this.action head-type guards are unchanged (those are JS-side namespaces, not the template keyword).

Test plan

22 tests pass on the branch (was 8). New cases:

• 5 valid GJS/GTS cases covering JS-scope shadowing (import, const, mustache/sub-expression/modifier positions, both extensions)
• 4 valid cases covering template block-param shadowing ({{#each as |action|}}, {{#let as |action|}}, modifier inside block, element-level <Foo as |action|>)
• 3 invalid GJS/GTS cases confirming the ambient keyword is still flagged when not shadowed
• 1 invalid case confirming that an unrelated JS import (import handler from './handler') does NOT mask the rule
• 1 invalid case confirming that ambient action outside a block-param scope is still flagged even when a sibling block legitimately shadows it

Cowritten by claude