feat(todo): per-conversation task list tool + surface

New standard tool extension with a single todo_write tool (opencode
todowrite pattern: full-list replace, returns JSON, no business-rule
enforcement — the description guides the model). Per-conversation in-memory
state + per-conversation surface (rendererId: todo, scope: conversation)
via subscriber-notify (message-queue pattern).

Wave 0 (kernel contract): added conversationId?: string to ToolExecuteContext
(additive, backward-compatible). Wired in dispatch.ts — the kernel already
had it but wasn't passing it through to tools.

Wave 1 (todo extension): pure core (validateTodos — shape only; getTodos/
setTodos/clearTodos; buildTodoSpec; formatTodoResult). Shell:
createTodoWriteTool + surface provider. Tool description matches opencode's
todowrite.txt depth (when-to-use, examples, task states). Priority field
removed (bloats the tool with little value). 25 tests.

Wave 2 (host-bin): registered todo in CORE_EXTENSIONS + dep + root tsconfig ref.

Verified: tsc EXIT 0, 1123 vitest, biome clean (314 files). Boot smoke clean.
FE handoff: frontend-todo-handoff.md.

1 files changed, 24 insertions, 0 deletions

diff --git a/packages/todo/src/index.ts b/packages/todo/src/index.ts
new file mode 100644
index 0000000..320b674
--- /dev/null
+++ b/packages/todo/src/index.ts
@@ -0,0 +1,24 @@
+/**
+ * @dispatch/todo — the per-conversation task list. Owns the list state + a
+ * per-conversation `custom` surface; the model maintains the list via the
+ * `todo_write` tool (full-list replace, opencode pattern). The list is
+ * transient (in-memory, per-conversation); the surface is the ONLY way the
+ * frontend reads todo state.
+ */
+
+export { extension, manifest } from "./extension.js";
+export {
+	buildTodoSpec,
+	clearTodos,
+	formatTodoResult,
+	getTodos,
+	setTodos,
+	TODO_RENDERER_ID,
+	TODO_SURFACE_ID,
+	type TodoItem,
+	type TodoState,
+	type TodoStatus,
+	type ValidationResult,
+	validateTodos,
+} from "./pure.js";
+export { createTodoWriteTool, type TodoWriteToolDeps } from "./tool.js";