refactor(client): name the compile face in every client test filename

A test file under packages/client now says which face it covers:
`*.client.spec.{ts,tsx}` and its `*.client.{ts,tsx}` helpers belong to the
Client aggregate, `*.host.spec.ts` to the host aggregate. The carrier's four
node-half specs take the Host suffix.

The two suffixes are mutually exclusive, so each aggregate excludes the
other's and both keep one broad test glob: `exclude` wins over `include`, and
`packages/client/**` no longer has to be excluded wholesale from the host
program with per-file `files` entries carved back out of it. A Host-face spec
that reaches only Host source therefore needs no cross-face project
reference, which the split-project rule rejects.

vitest still discovers every file through `**/*.spec.{ts,tsx}`.

packages/client/connection/tests/api-helpers.client.spec.ts

@@ -0,0 +1,21 @@
+/**
+ * Contract-layer helpers: transport-error folding and response unwrapping.
+ * (The assistant block classifier half of the legacy spec lives in
+ * runtime/tests — the classifier moved there.)
+ */
+
+import { describe, expect, it } from 'vitest'
+import { RpcId, resultOf, transportError } from '../src/client/api.ts'
+
+describe('transportError', () => {
+  it('folds an Error to internal keeping the message, and stringifies non-Errors', () => {
+    expect(transportError(new Error('线断了'))).toEqual({ ok: false, error: { code: 'internal', message: '线断了', details: {} } })
+    expect(transportError('raw string')).toMatchObject({ ok: false, error: { message: 'raw string' } })
+  })
+})
+
+describe('resultOf', () => {
+  it('unwraps the result slot', () => {
+    expect(resultOf({ rpcId: RpcId('r'), result: { ok: true, value: 7 } })).toEqual({ ok: true, value: 7 })
+  })
+})