Merge PR #1028: add document API with atomic edits

Add the typed document facade and plugin IPC adapter. Prepare bulk edits
before mutation, preserve undo and dirty state, keep profile elevations,
validate numeric inputs and session bindings, and generate Python constructors
with typed results.

Reuse existing entity transforms and profile conversion. Compute mass
properties and closed-surface bounds in cadkernel; pin its main revision
6a5e6fc2822f6af6b2611cd605b44437b35158f0. Keep plugin API metadata at version 6.

Validation: 646 native application tests, 597 kernel tests, 12 document API
tests, 91 plugin API tests, 3 Python tests, default/IPC feature builds and
wasm32 check passed.

crates/ocs_plugin_api/src/ipc/protocol.rs

@@ -138,6 +138,12 @@ pub enum PluginRequest {
     GetTabId,
     /// V5: ask the host for the filesystem path of the document in `tab_id`.
     DocumentPath { tab_id: u64 },
+    /// DocApi v2 (`ocs_doc_api`): carry one bincode-serialized `DocApiEnvelope`
+    /// (one write op OR a read-only query batch). Appended at the end to keep
+    /// existing discriminants stable. The host routes this to the DocApi executor.
+    /// `serde_bytes` keeps the payload a single length-prefixed bulk copy (the
+    /// outer frame would otherwise walk it byte-by-byte).
+    DocApiRequest { tab_id: u64, #[serde(with = "serde_bytes")] bytes: Vec<u8> },
 }
 
 /// Responses the host sends back for `PluginRequest`.
@@ -164,6 +170,10 @@ pub enum PluginResponse {
     TabId(u64),
     /// V5: filesystem path of the document in the requested tab, if any.
     DocumentPath(Option<std::ffi::OsString>),
+    /// DocApi v2 (`ocs_doc_api`): the bincode-serialized `Result<Receipt, ApiError>` answering a
+    /// `PluginRequest::DocApiRequest`. Appended at the end (discriminant stability).
+    /// `serde_bytes` keeps the payload a single length-prefixed bulk copy.
+    DocApiResponse { #[serde(with = "serde_bytes")] bytes: Vec<u8> },
 }
 
 /// Messages sent from the host to the plugin runner.