fix(sdk-client): address ds-review-bot findings

- api: resolve a relative workspace cwd to absolute before the handshake —
  the child spawns relative to the parent cwd, but the wire cwd is resolved
  again inside the child, so a relative value double-resolved
  (worker -> worker/worker).
- api: make the documented handshake retry real — HarnessClient.close() is
  permanent, so a failed initialize now reaps the runtime and swaps in a
  fresh client; DeepSeekHarness.close() is terminal and stops the respawns.
- api: validate session.event envelopes, assistant/message content, and
  session.finished reasons at the wire boundary — a malformed runtime
  surfaces as SdkProtocolError instead of type-invalid TurnResult data or a
  TypeError out of finalResponse.
- client: a throwing subscribe() filter fails and detaches only its own
  subscription (normalized to Error); sibling fan-out and the transport read
  loop are undisturbed.
- client: NotificationSubscription.close() drops its queued notifications,
  matching its documented contract; runtime-death fail() still leaves
  already-delivered items drainable.
- client: subscribe() after close()/runtime death returns a born-failed
  subscription so next() rejects instead of parking forever.
- client/transport: bounded requests abandon via AbortSignal — the transport
  drops the pending entry at timeout, so repeated bounded calls against a
  hung method retain no per-call state.

One test per finding; per-file coverage stays 100% on both packages.

packages/sdk/sdk-protocol/tests/transport.spec.ts

@@ -60,6 +60,29 @@ describe('JsonRpcLineTransport', () => {
     b.close()
   })
 
+  it('rejects immediately on a pre-aborted signal without registering pending state', async () => {
+    const { b } = transportPair()
+    b.start()
+    const controller = new AbortController()
+    controller.abort(new Error('already gone'))
+    await expect(b.request('never-sent', {}, controller.signal)).rejects.toThrow('already gone')
+    expect((b as unknown as { pending: Map<string, unknown> }).pending.size).toBe(0)
+    b.close()
+  })
+
+  it('abandons a pending request on abort, stringifying a non-Error reason', async () => {
+    const { b } = transportPair()
+    b.start()
+    const controller = new AbortController()
+    const pending = b.request('never-answered', {}, controller.signal)
+    controller.abort('plain-string-reason')
+    await expect(pending).rejects.toThrow('JSON-RPC request aborted: plain-string-reason')
+    // The abandonment removed the pending entry — nothing is retained for a
+    // response that may never come.
+    expect((b as unknown as { pending: Map<string, unknown> }).pending.size).toBe(0)
+    b.close()
+  })
+
   it('preserves structured error data from an error response frame', async () => {
     const { aToB, bToA, b } = transportPair()
     b.start()