feat(modules): lexical import resolver — seal imports to defining node (Phase 4b C3)

Make `import` resolution lexical (§5.5): an inherited group script's
imports resolve against the module set at its OWN defining node, walking
up from there — a leaf app can't shadow them, and a group script behaves
identically under every inheriting app.

Mechanism — Rhai's `_source` carries the importing AST's origin tag:
- The entry script has no source tag → resolve from `default_origin` (its
  defining node, threaded in via C2).
- Each resolved module's AST source is set to `encode(module.owner())`
  before `eval_ast_as_new`, so its nested `import`s carry the module's own
  node as `_source` and resolve from there — lexical chaining.
- `encode_origin`/`decode_origin` map a `ScriptOwner` to/from `app:<uuid>`
  / `group:<uuid>`.

Cache rekeyed from `(app_id, name)` to the resolved `ScriptId`: a compiled
module is lexically self-contained, so its body is a pure function of
`(script_id, updated_at)` — this also dedupes a shared group module across
inheriting apps and keeps same-named cross-app modules distinct.

Adds two executor-core unit tests (origin-keyed fake) proving the trust
boundary: a group module's import binds the group's module even when an
app-owned module of the same name exists; `ScriptOwner` gains `Hash`.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/executor-core/tests/modules.rs

@@ -16,9 +16,9 @@ use async_trait::async_trait;
 use chrono::{DateTime, Utc};
 use picloud_executor_core::{Engine, ExecRequest, InvocationType, Limits};
 use picloud_shared::{
-    AppId, ExecutionId, ModuleScript, ModuleSource, ModuleSourceError, NoopDeadLetterService,
-    NoopDocsService, NoopEventEmitter, NoopHttpService, NoopKvService, RequestId, ScriptId,
-    ScriptOwner, ScriptSandbox, Services,
+    AppId, ExecutionId, GroupId, ModuleScript, ModuleSource, ModuleSourceError,
+    NoopDeadLetterService, NoopDocsService, NoopEventEmitter, NoopHttpService, NoopKvService,
+    RequestId, ScriptId, ScriptOwner, ScriptSandbox, Services,
 };
 use tokio::sync::Mutex;
 
@@ -609,3 +609,130 @@ fn validate_endpoint_skips_dynamic_imports_in_imports_list() {
         v.imports
     );
 }
+
+// ---------------------------------------------------------------------------
+// Phase 4b — lexical (origin-aware) resolution.
+//
+// `LexicalModuleSource` keys modules by their *exact* defining node, with no
+// chain walk. That's enough to prove the resolver passes the RIGHT origin:
+// `default_origin` for the entry AST, and each module's own owner (decoded
+// from Rhai's `_source`) for its nested imports. The chain-walk + group-tree
+// semantics are covered end-to-end by the CLI journey tests against Postgres.
+// ---------------------------------------------------------------------------
+
+#[derive(Default)]
+struct LexicalModuleSource {
+    table: Mutex<HashMap<(ScriptOwner, String), ModuleScript>>,
+}
+
+impl LexicalModuleSource {
+    fn new() -> Arc<Self> {
+        Arc::new(Self::default())
+    }
+
+    async fn put(self: &Arc<Self>, owner: ScriptOwner, name: &str, source: &str) {
+        let (app_id, group_id) = match owner {
+            ScriptOwner::App(a) => (Some(a), None),
+            ScriptOwner::Group(g) => (None, Some(g)),
+        };
+        self.table.lock().await.insert(
+            (owner, name.to_string()),
+            ModuleScript {
+                script_id: ScriptId::new(),
+                app_id,
+                group_id,
+                name: name.to_string(),
+                source: source.to_string(),
+                updated_at: Utc::now(),
+            },
+        );
+    }
+}
+
+#[async_trait]
+impl ModuleSource for LexicalModuleSource {
+    async fn resolve(
+        &self,
+        origin: ScriptOwner,
+        name: &str,
+    ) -> Result<Option<ModuleScript>, ModuleSourceError> {
+        Ok(self
+            .table
+            .lock()
+            .await
+            .get(&(origin, name.to_string()))
+            .cloned())
+    }
+}
+
+fn req_with_owner(app_id: AppId, owner: ScriptOwner) -> ExecRequest {
+    let mut r = req(app_id);
+    r.script_owner = Some(owner);
+    r
+}
+
+/// A group module's `import` resolves from the GROUP (its own defining
+/// node), not the inheriting app — even when an app-owned module of the
+/// same name exists. This is the §5.5 trust boundary: a leaf can't shadow
+/// a module an inherited group script depends on.
+#[tokio::test(flavor = "multi_thread")]
+async fn lexical_nested_import_seals_to_module_owner() {
+    let source = LexicalModuleSource::new();
+    let app = AppId::new();
+    let group = GroupId::new();
+
+    // Two "inner" modules: the group's (real) and the app's (a trap).
+    source
+        .put(ScriptOwner::Group(group), "inner", "fn v() { 42 }")
+        .await;
+    source
+        .put(ScriptOwner::App(app), "inner", "fn v() { 999 }")
+        .await;
+    // The group's "outer" imports "inner" — must bind the group's inner.
+    source
+        .put(
+            ScriptOwner::Group(group),
+            "outer",
+            r#"import "inner" as i; fn val() { i::v() }"#,
+        )
+        .await;
+
+    let engine = engine_with(source.clone());
+    // Entry script runs as the inherited GROUP script (default_origin = group).
+    let resp = engine
+        .execute(
+            r#"import "outer" as o; o::val()"#,
+            req_with_owner(app, ScriptOwner::Group(group)),
+        )
+        .expect("should execute");
+    assert_eq!(
+        resp.body,
+        serde_json::json!(42),
+        "group module's import must seal to the group's `inner`, not the app's trap"
+    );
+}
+
+/// The same registry, entered as an APP-owned script, reaches the app's
+/// module — proving the fake distinguishes origins and the entry uses
+/// `default_origin`.
+#[tokio::test(flavor = "multi_thread")]
+async fn lexical_entry_origin_selects_app_module() {
+    let source = LexicalModuleSource::new();
+    let app = AppId::new();
+    let group = GroupId::new();
+    source
+        .put(ScriptOwner::Group(group), "inner", "fn v() { 42 }")
+        .await;
+    source
+        .put(ScriptOwner::App(app), "inner", "fn v() { 999 }")
+        .await;
+
+    let engine = engine_with(source.clone());
+    let resp = engine
+        .execute(
+            r#"import "inner" as i; i::v()"#,
+            req_with_owner(app, ScriptOwner::App(app)),
+        )
+        .expect("should execute");
+    assert_eq!(resp.body, serde_json::json!(999));
+}