feat(v1.1.3-modules): shared types, migrations, engine + resolver scaffold

Lays down the v1.1.3 plumbing:

- `ScriptKind` enum in `picloud-shared` ('endpoint' | 'module').
- `ModuleSource` trait + `ModuleScript` DTO + `NoopModuleSource` in
  `picloud-shared`. Resolver lives in `executor-core`; Postgres impl
  in `manager-core` (`PostgresModuleSource`).
- `Services::new` grows a fifth `modules: Arc<dyn ModuleSource>` arg.
- `ScriptValidator` returns `ValidatedScript { imports }` so the
  manager can populate the dep-graph table on save. New
  `validate_module` method on the trait gates module-shape rules.
- `Engine::execute_ast(&Arc<rhai::AST>, req)` lets the orchestrator's
  script cache reuse compiled ASTs. `Engine::execute(&str, req)` is
  preserved as a convenience that compiles inline. `Engine::compile`
  exposes the AST for callers that want to cache.
- `PicloudModuleResolver` replaces `DummyModuleResolver` per-call.
  Bridges Rhai's sync `ModuleResolver::resolve` to async
  `ModuleSource::lookup` via `Handle::block_on`. Enforces:
  - cross-app isolation (resolver captures `Arc<SdkCallCx>`),
  - circular import detection (in-progress stack on the resolver),
  - import depth limit (default 8 via
    `Limits::module_import_depth_max`).
- Module-shape validation walks `ast.statements()` via `rhai/internals`
  and accepts only `Var { CONSTANT }`, `Import`, and `Noop`. The
  manager admin endpoint runs `validate_module` at save (primary
  gate); resolver re-runs it at load (defense in depth).
- LRU cache `(AppId, name) -> (updated_at, Arc<Module>)` owned by
  `Engine`. Size from `PICLOUD_MODULE_CACHE_SIZE` (default 512).
- Migration `0015_scripts_kind.sql` adds `scripts.kind` + composite
  index + module-name shape CHECK.
- Migration `0016_script_imports.sql` adds the dep-graph table with
  FK CASCADE on both columns.
- Repo: `kind` threaded through SELECT/INSERT/UPDATE. New
  `count_routes_for_script` / `count_triggers_for_script` /
  `list_imports` methods. `create`/`update` open a transaction and
  call `replace_imports_tx` to populate the dep-graph.
- Admin endpoint: accepts `kind`; rejects reserved module names;
  rejects `endpoint → module` transitions when routes / triggers
  exist.
- SDK_VERSION 1.3 → 1.4.

Workspace builds; full test suite (~440 tests) green.

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

crates/shared/src/modules.rs

@@ -0,0 +1,75 @@
+//! `ModuleSource` — the v1.1.3 Rhai module-loading contract.
+//!
+//! The executor-core `PicloudModuleResolver` calls into this trait to
+//! load `kind = 'module'` scripts referenced by `import "<name>" as <alias>;`
+//! statements. The Postgres impl in `manager-core` reads from the
+//! `scripts` table; tests pin in-memory fakes.
+//!
+//! Implementations MUST derive `app_id` from `cx.app_id` and pass it
+//! to every backend query. The `name` argument carries only the
+//! script's name (the literal between the import quotes); the trait
+//! has no way to express a cross-app lookup. That asymmetry is the
+//! load-bearing cross-app isolation boundary — see `docs/sdk-shape.md`.
+
+use async_trait::async_trait;
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+
+use crate::{AppId, ScriptId, SdkCallCx};
+
+/// A module script as returned by `ModuleSource::lookup`. Carries only
+/// the fields the resolver needs: the id (for diagnostics), the source
+/// (to compile), and `updated_at` (the cache-staleness comparator).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ModuleScript {
+    pub script_id: ScriptId,
+    pub app_id: AppId,
+    pub name: String,
+    pub source: String,
+    pub updated_at: DateTime<Utc>,
+}
+
+/// Lookup contract used by `PicloudModuleResolver`. `lookup` MUST
+/// scope by `cx.app_id`; cross-app reads must be unreachable.
+#[async_trait]
+pub trait ModuleSource: Send + Sync {
+    /// Resolve a module script by `(cx.app_id, name)`. Returns `None`
+    /// when no row exists, or when a row exists but its `kind` is
+    /// `'endpoint'` (endpoints are never importable). The resolver
+    /// surfaces `None` as `ErrorModuleNotFound` to Rhai.
+    async fn lookup(
+        &self,
+        cx: &SdkCallCx,
+        name: &str,
+    ) -> Result<Option<ModuleScript>, ModuleSourceError>;
+}
+
+/// Failure modes surfaced from `ModuleSource::lookup`. "Not found" is
+/// not exceptional — it's `Ok(None)`.
+#[derive(Debug, Error)]
+pub enum ModuleSourceError {
+    /// Backend (Postgres, network, etc.) unavailable or returned an
+    /// error. The string is safe to surface to a script (Rhai wraps
+    /// it in `ErrorModuleNotFound` with the module name + reason).
+    #[error("module backend error: {0}")]
+    Backend(String),
+}
+
+/// Stub used by the executor-core test harness so engine integration
+/// tests don't need a real DB-backed source. Every lookup returns
+/// `Ok(None)` — `import "x"` always errors as "module not found"
+/// under this impl.
+#[derive(Debug, Default, Clone, Copy)]
+pub struct NoopModuleSource;
+
+#[async_trait]
+impl ModuleSource for NoopModuleSource {
+    async fn lookup(
+        &self,
+        _cx: &SdkCallCx,
+        _name: &str,
+    ) -> Result<Option<ModuleScript>, ModuleSourceError> {
+        Ok(None)
+    }
+}