fix: prototype pollution and shallow freeze in SkillFollowups.get() (#558)

Adversarial testing for v0.5.14 release found 2 bugs:

1. **Prototype pollution:** `FOLLOWUPS["__proto__"]` traversed
   `Object.prototype` instead of returning `[]`. Fixed with
   `Object.hasOwn()` guard.

2. **Shallow freeze:** `Object.freeze()` on the array didn't freeze
   nested suggestion objects, allowing shared state mutation across
   callers. Fixed with deep copy via `Object.freeze({ ...s })`.

Includes 52 adversarial tests covering injection attacks, boundary
values, immutability, concurrency, and data integrity for
`SkillFollowups`, `Locale.duration`, and `Dispatcher.reset`.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: anandgupta42

packages/opencode/src/skill/followups.ts

@@ -153,9 +153,13 @@ export namespace SkillFollowups {
   const WAREHOUSE_NUDGE =
     "**Tip:** Connect a warehouse to validate against real data. Run `/discover` to auto-detect your connections."
 
+  // altimate_change start — upstream_fix: guard against prototype pollution and deep-freeze suggestions
   export function get(skillName: string): readonly Suggestion[] {
-    return Object.freeze(FOLLOWUPS[skillName] ?? [])
+    if (!Object.hasOwn(FOLLOWUPS, skillName)) return Object.freeze([])
+    const suggestions = FOLLOWUPS[skillName]!
+    return Object.freeze(suggestions.map((s) => Object.freeze({ ...s })))
   }
+  // altimate_change end
 
   export function format(skillName: string): string {
     const suggestions = get(skillName)