refactor(executor-core): extract sdk/ module + move json↔dynamic bridge

Hoist the json_to_dynamic / dynamic_to_json helpers out of engine.rs
into a new sdk/bridge.rs so the v1.1.x service modules (KV, docs, …)
can use them without engine.rs being the sole owner. No behavioural
change — the sdk_contract round-trip test pins the observable JSON
fidelity.

Also lands the structural shape that subsequent v1.1.x PRs hook into:

  - sdk::register_all(engine, services, cx) — single per-call hook
    every stateful service registers through. Body is a no-op for
    v1.1.0; SdkCallCx construction inside Engine::execute lands in
    the next commit alongside the new ExecRequest fields it reads.
  - sdk::cx re-exports picloud_shared::SdkCallCx so SDK callers don't
    cross-import shared for one type.

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

crates/executor-core/src/engine.rs

@@ -8,6 +8,7 @@ use rhai::{Dynamic, Engine as RhaiEngine, EvalAltResult, Map, Module, Scope};
 use serde_json::Value as Json;
 
 use crate::sandbox::Limits;
+use crate::sdk::bridge::{dynamic_to_json, json_to_dynamic};
 use crate::types::{
     ExecError, ExecRequest, ExecResponse, ExecStats, InvocationType, LogEntry, LogLevel,
 };
@@ -265,69 +266,6 @@ fn parse_structured_response(map: Map) -> Result<(u16, BTreeMap<String, String>,
     Ok((status_code, headers, body))
 }
 
-// ----------------------------------------------------------------------------
-// Rhai ↔ serde_json bridges
-// ----------------------------------------------------------------------------
-
-fn json_to_dynamic(value: Json) -> Dynamic {
-    match value {
-        Json::Null => Dynamic::UNIT,
-        Json::Bool(b) => b.into(),
-        Json::Number(n) => {
-            if let Some(i) = n.as_i64() {
-                i.into()
-            } else if let Some(f) = n.as_f64() {
-                f.into()
-            } else {
-                n.to_string().into()
-            }
-        }
-        Json::String(s) => s.into(),
-        Json::Array(arr) => arr
-            .into_iter()
-            .map(json_to_dynamic)
-            .collect::<Vec<Dynamic>>()
-            .into(),
-        Json::Object(obj) => {
-            let mut m = Map::new();
-            for (k, v) in obj {
-                m.insert(k.into(), json_to_dynamic(v));
-            }
-            Dynamic::from(m)
-        }
-    }
-}
-
-fn dynamic_to_json(value: &Dynamic) -> Json {
-    if value.is_unit() {
-        return Json::Null;
-    }
-    if let Ok(b) = value.as_bool() {
-        return Json::Bool(b);
-    }
-    if let Ok(i) = value.as_int() {
-        return Json::Number(i.into());
-    }
-    if let Ok(f) = value.as_float() {
-        return serde_json::Number::from_f64(f).map_or(Json::Null, Json::Number);
-    }
-    if value.is_string() {
-        return Json::String(value.clone().into_string().unwrap_or_default());
-    }
-    if let Some(arr) = value.clone().try_cast::<rhai::Array>() {
-        return Json::Array(arr.iter().map(dynamic_to_json).collect());
-    }
-    if let Some(map) = value.clone().try_cast::<Map>() {
-        let mut out = serde_json::Map::new();
-        for (k, v) in map {
-            out.insert(k.to_string(), dynamic_to_json(&v));
-        }
-        return Json::Object(out);
-    }
-    // Anything else (timestamps, custom types) — best-effort string form.
-    Json::String(value.to_string())
-}
-
 // ----------------------------------------------------------------------------
 // Error mapping
 // ----------------------------------------------------------------------------