BLOCK #1 — anchor drag couldn't return to start. `apply_cursor_move`
only called `set_path_anchor_position` when the cursor doc-point
differed from `start_doc`, so dragging away and then BACK onto the
original point silently skipped the final write — release committed
history with the anchor stuck at the last off-start frame.
Fix: always write the cursor position during an active drag; use
the start-doc comparison only to flip `moved` (which gates history
push). Regression test `anchor_drag_back_to_start_lands_at_start`
simulates the round-trip and asserts the anchor follows the cursor
all the way home.
BLOCK #2 — MCP tool registry dropped the request id. `McpTool::call`
only received `&BTreeMap<String, String>`, forcing tools to invent
response ids (test double used `RequestId::Num(0)`). JSON-RPC + MCP
require every response to echo the originating request id. Fix:
change the trait signature to `call(&self, request: &ToolCall) ->
ToolResponse` and have `dispatch` forward the whole call. EchoTool
updated to read `request.id`; the registry test now asserts the
id round-trips.
BLOCK #3 — opening a native saved file leaked variables across
documents. `apply_payload` reset pages + history + selection but
never touched `doc.var_table` or `doc.components` (both added in
recent commits). Open a variable-bearing canonical `.op`, then
open a plain saved `.pen` — codegen would still emit the stale
canonical variables. Fix: `apply_payload` now reassigns both to
`Default::default()` after the page/UI reset block.
Tests: 206 shell-core + 20 shell-native (+1 anchor return) + 8 desktop.
Wasm32 build clean.
883bd70a65