feat: add tool execution idempotency cache

For tools that declare `is_idempotent() == true`, successful results are
cached per-job so repeated identical calls (common during self-repair
recovery, stuck job retries, or chat-mode retry loops) return instantly
without re-executing. Cache uses SHA-256 content hashing with TTL and
LRU eviction, scoped per job_id.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

benchmarks/src/runner.rs

@@ -385,6 +385,9 @@ async fn run_task_isolated(params: TaskRunParams<'_>) -> TaskResult {
         ironclaw::agent::cost_guard::CostGuardConfig::default(),
     ));
 
+    let idempotency_cache = Arc::new(ironclaw::tools::ToolIdempotencyCache::new(
+        ironclaw::tools::IdempotencyCacheConfig::default(),
+    ));
     let deps = AgentDeps {
         store: None,
         llm: instrumented.clone() as Arc<dyn LlmProvider>,
@@ -397,6 +400,7 @@ async fn run_task_isolated(params: TaskRunParams<'_>) -> TaskResult {
         skills_config: ironclaw::config::SkillsConfig::default(),
         hooks: Arc::new(ironclaw::hooks::HookRegistry::new()),
         cost_guard,
+        idempotency_cache,
     };
 
     let mut channels = ChannelManager::new();