feat(v1.1.1-kv): Rhai kv:: SDK module + ctx.event wiring

Wires the KV store into Rhai scripts via the handle pattern:

    let widgets = kv::collection("widgets");
    widgets.set("k", #{ n: 1 });
    let v = widgets.get("k");          // value or () if absent
    widgets.has("k") / widgets.delete("k")
    let page = widgets.list();          // cursor-style pagination

`KvHandle` is a custom Rhai type holding `Arc<dyn KvService>` + the
per-call `Arc<SdkCallCx>`. Methods route async service calls through
`tokio::Handle::current().block_on(...)` — works because
`LocalExecutorClient` runs the script under `spawn_blocking` so a
runtime is reachable. The bridge surfaces `app_id` exclusively
through `cx.app_id`; no public-facing argument can spoof an app.

`TriggerEvent` lands in `picloud-shared` as the wire shape the
dispatcher will emit (KV + DeadLetter variants — KV exercised now,
DL hooks up with the dispatcher in commit 5/8). `SdkCallCx` and
`ExecRequest` grow `is_dead_letter_handler: bool` and
`event: Option<TriggerEvent>`. `engine.rs::build_ctx_map` flattens
the event into `ctx.event` for triggered handlers; direct ingress
leaves the key absent so scripts can `if "event" in ctx`.

Tests:
- 7 `sdk_kv.rs` integration tests covering the full Rhai surface
  (round-trip, missing-key unit, has bool, delete was-present,
  empty-collection rejection, cursor pagination, cross-app
  isolation through the bridge).
- 3 new `engine.rs` tests pinning `ctx.event` shape per
  design notes §4 (KV insert with value, delete with unit value,
  direct invocations have no `event` key).

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

crates/shared/src/trigger_event.rs

@@ -0,0 +1,105 @@
+//! `TriggerEvent` — the description of the event that fired a script.
+//!
+//! Built by the dispatcher (in `manager-core`) from the outbox row and
+//! attached to the `ExecRequest` that's handed to `executor-core`. The
+//! Rhai bridge in `executor-core::engine::build_ctx_map` flattens this
+//! into `ctx.event` for the script.
+//!
+//! Living in `picloud-shared` so the dispatcher and the executor agree
+//! on the wire shape. Serializable so cluster mode (v1.3+) can ship
+//! ExecRequests over HTTP without rewriting this type.
+
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+
+use crate::{DeadLetterId, ScriptId, TriggerId};
+
+/// Operations a KV trigger can fire on. Stored as a lowercase string
+/// in `kv_trigger_details.ops` (Postgres `text[]`).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum KvEventOp {
+    Insert,
+    Update,
+    Delete,
+}
+
+impl KvEventOp {
+    #[must_use]
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::Insert => "insert",
+            Self::Update => "update",
+            Self::Delete => "delete",
+        }
+    }
+
+    #[must_use]
+    pub fn from_wire(s: &str) -> Option<Self> {
+        match s {
+            "insert" => Some(Self::Insert),
+            "update" => Some(Self::Update),
+            "delete" => Some(Self::Delete),
+            _ => None,
+        }
+    }
+}
+
+/// Discriminated description of a triggering event. Lifted from the
+/// outbox row's payload at dispatch time. Each variant carries the
+/// fields the corresponding `ctx.event` shape exposes to the script.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "source", rename_all = "snake_case")]
+pub enum TriggerEvent {
+    /// A KV insert / update / delete fired this handler.
+    Kv {
+        op: KvEventOp,
+        collection: String,
+        key: String,
+        /// Present on `insert` and `update`. Absent on `delete`.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        value: Option<serde_json::Value>,
+    },
+
+    /// A dead-letter row fired this handler. The original event is
+    /// nested verbatim plus the dead-letter metadata the design notes
+    /// §4 require.
+    DeadLetter {
+        dead_letter_id: DeadLetterId,
+        original: Box<TriggerEvent>,
+        attempts: u32,
+        last_error: String,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        trigger_id: Option<TriggerId>,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        script_id: Option<ScriptId>,
+        first_attempt_at: DateTime<Utc>,
+        last_attempt_at: DateTime<Utc>,
+    },
+}
+
+impl TriggerEvent {
+    /// The `source` discriminant the script sees on `ctx.event.source`.
+    #[must_use]
+    pub const fn source(&self) -> &'static str {
+        match self {
+            Self::Kv { .. } => "kv",
+            Self::DeadLetter { .. } => "dead_letter",
+        }
+    }
+}
+
+/// Convenience accessor on the dead-letter variant for places that
+/// already know they're handling a DL event. Pulled out so the
+/// dispatcher and the dashboard don't have to repeat the match.
+#[derive(Debug, Clone)]
+pub struct DeadLetterEventDetail {
+    pub dead_letter_id: DeadLetterId,
+    pub original: TriggerEvent,
+    pub attempts: u32,
+    pub last_error: String,
+    pub trigger_id: Option<TriggerId>,
+    pub script_id: Option<ScriptId>,
+    pub first_attempt_at: DateTime<Utc>,
+    pub last_attempt_at: DateTime<Utc>,
+}