feat(tools): live dispatch lifecycle + native-contract parallel sub-calls in Code Mode

The bridge replaces its serialization queue with a pool that reuses the
native concurrency contract: submissions classify through
registry.executionMode (fail-closed isConcurrencySafe), start strictly in
submission order, overlap up to the validated maxParallelSubCalls config
(default 10; 1 restores serial), and exclusive calls drain the pool, run
alone, and bar later calls. Each started sub-call logs a
tool/code-dispatch-start event at pool entry; the existing
tool/code-dispatch settles the pair (started ⇔ settles exactly once;
abandoned queued calls log neither). SDK prompt guidance now states the
true Promise.all contract — re-recorded across every code/both-mode
snapshot (plus the stale cordis-dynamic-toolchain fixture gaining the
required description arg).

Client: CodeSubCall widens to RunningToolCall | ToolResultNode — starts
land the running shape (rows wear the native running ring), settles
replace in place preserving start order, callTime pairs to the start
time. Fixture emits start/settle pairs; jsdom pins the running sub-row;
runtime specs pin in-place settlement and out-of-order completion.

packages/client/runtime/tests/event-script.ts

@@ -26,6 +26,11 @@ export const ev = {
     at(seq, { type: 'tool/call', data: { turn, step, callId, name, arguments: args } }),
   toolResult: (seq: number, turn: number, callId: string, body: string, step = 0): SessionEvent =>
     at(seq, { type: 'tool/result', surfaceOp: 'append', data: { turn, step, callId, content: text(body), isError: false } }),
+  codeDispatchStart: (seq: number, parentCallId: string, n: number, name: string, args: unknown): SessionEvent =>
+    at(seq, {
+      type: 'tool/code-dispatch-start',
+      data: { parentCallId, subCallId: `${parentCallId}:code:${n}`, name, arguments: args },
+    }),
   codeDispatch: (seq: number, parentCallId: string, n: number, name: string, args: unknown, body: string, isError = false): SessionEvent =>
     at(seq, {
       type: 'tool/code-dispatch',