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, 10 insertions, 0 deletions

diff --git a/packages/todo/tsconfig.json b/packages/todo/tsconfig.json
new file mode 100644
index 0000000..102c8f0
--- /dev/null
+++ b/packages/todo/tsconfig.json
@@ -0,0 +1,10 @@
+{
+	"extends": "../../tsconfig.base.json",
+	"compilerOptions": { "rootDir": "src", "outDir": "dist", "composite": true },
+	"include": ["src/**/*.ts"],
+	"references": [
+		{ "path": "../kernel" },
+		{ "path": "../surface-registry" },
+		{ "path": "../ui-contract" }
+	]
+}