fix(executor-core): F-P-004 cache AST across invoke() re-entry (per-Engine cache)

Two paths bypassed the AST cache: LocalExecutorClient::execute (tests +
fallback) and the synchronous invoke() re-entry in the executor SDK.
The latter is the hot one — composed workflows multiplied parse cost
by depth, so a 4-deep invoke chain on a 200-line script paid the parse
budget × 4 per call.

Add a per-Engine HashMap<ScriptId, (updated_at, Arc<AST>)> + a
`compile_for_identity(script_id, updated_at, source)` helper that
behaves like LocalExecutorClient::get_or_compile but lives on the
Engine. Update the SDK invoke synchronous re-entry to:
  resolved → compile_for_identity → execute_ast

The orchestrator-core LocalExecutorClient cache (HTTP-path dispatch)
is left untouched — it caches a different access pattern at a
different boundary.

AUDIT.md anchor: F-P-004.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/executor-core/src/sdk/invoke.rs

@@ -187,10 +187,21 @@ fn invoke_blocking(
         event: None,
     };
 
-    // Synchronous re-entry — same engine instance, same Services,
-    // fresh SdkCallCx built inside Engine::execute_ast.
+    // F-P-004: synchronous re-entry — route through the per-Engine
+    // AST cache so each callee parses once per (script_id, updated_at),
+    // not once per invoke. Composed workflows multiply parse cost by
+    // depth; the cache cuts that to constant compile + N executions.
+    let ast = self_engine
+        .compile_for_identity(resolved.script_id, resolved.updated_at, &resolved.source)
+        .map_err(|e| -> Box<EvalAltResult> {
+            EvalAltResult::ErrorRuntime(
+                format!("invoke({target_label}): {e}").into(),
+                rhai::Position::NONE,
+            )
+            .into()
+        })?;
     let resp = self_engine
-        .execute(&resolved.source, req)
+        .execute_ast(&ast, req)
         .map_err(|e| -> Box<EvalAltResult> {
             EvalAltResult::ErrorRuntime(
                 format!("invoke({target_label}): {e}").into(),