fix(plugin/event): bind team-idle-wake-hint client methods to SDK Session

The team-mode wiring at `createEventHandler` extracted
`pluginContext.client.session.promptAsync` and `.status` into a fresh
wrapper object. The methods were copied by reference, so the prompt-async
gate's `session.promptAsync.bind(session)` was binding to that plain
wrapper rather than the underlying SDK `Session` instance. The opencode
SDK's `promptAsync` reads `this._client.post(...)`, so production calls
threw `TypeError: undefined is not an object (evaluating 'this._client')`
on the very first dispatch — fingerprinted in /tmp/oh-my-opencode.log as
688 `background-agent-parent-wake`, 47 `model-suggestion-retry`, and 4
`team-idle-wake-hint` failures over the past three days.

Move the wrapper construction into `buildTeamIdleWakeHintClient`, which
preserves the narrow factory contract while binding both methods back to
the SDK `Session` so `_client` survives the dispatch. Cover the contract
with four BDD-style tests including the historical destructure-only
failure mode so any future regression is caught at unit-test time.

src/plugin/build-team-idle-wake-hint-client.ts

@@ -0,0 +1,25 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+
+type SdkSession = PluginInput["client"]["session"]
+type SdkPromptAsync = SdkSession["promptAsync"]
+type SdkStatus = SdkSession["status"]
+
+export type TeamIdleWakeHintNarrowClient = {
+  session: {
+    promptAsync?: SdkPromptAsync
+    status?: SdkStatus
+  }
+}
+
+export function buildTeamIdleWakeHintClient(client: PluginInput["client"]): TeamIdleWakeHintNarrowClient {
+  const session = client.session
+  const promptAsync = typeof session.promptAsync === "function"
+    ? session.promptAsync.bind(session) as SdkPromptAsync
+    : undefined
+  const status = typeof session.status === "function"
+    ? session.status.bind(session) as SdkStatus
+    : undefined
+  return {
+    session: { promptAsync, status },
+  }
+}