Apply confirmed code-review fixes to integrations/vercel-ai/typescript:

- Make createZepMiddleware context-injection only. Inject the Context Block
  as a system message ONLY on a genuine new user turn (last prompt message
  role is 'user'), skipping tool-loop continuation steps. This stops the
  per-step wrapGenerate persistence that fragmented a turn across multiple
  thread.addMessages calls (writing intermediate tool-call preamble as a real
  assistant message) and re-fetched the Context Block once per step. Remove
  wrapGenerate and the `persist` option entirely.
- Add createZepOnFinish({ client, threadId, userId?, user?, ... }): an AI SDK
  onFinish callback that persists the whole turn exactly once (user input +
  final assistant text from the event) via persistZepTurn. Fires once per turn
  for both generateText and streamText.
- zepRemember graph.add path: add GRAPH_MAX_CHARS (10,000-char Zep limit) and
  truncate-with-warning, mirroring the 4,096-char thread path. Never silently
  drops; logs lengths only.
- ensureZepUserAndThread: gate "already exists" tolerance on the typed SDK
  signal (Zep.ConflictError / statusCode === 409) instead of a loose message
  regex; surface other errors (401/network/5xx) as real warnings.
- toRoleType: optional debug log (role NAME only, no content) when coercing an
  unknown role to 'norole'.
- Update both examples (generate-text, stream-text) to inject-via-middleware +
  persist-via-onFinish. Update README/SETUP/CHANGELOG and index.ts JSDoc to
  describe the new pattern, fix the createZepTools `binding` wrapper in JSDoc,
  remove the false "persisted automatically once per turn" claims, and align
  the zod requirement to 3 or 4.
- Tests: add a multi-step tool-loop middleware test (context injected only on
  the new-user-turn step, fetched exactly once per turn) and createZepOnFinish
  tests (turn persisted once with the final text, no preamble); add graph.add
  truncation and toRoleType debug-log tests; convert ensureZepUserAndThread
  tests to the typed ConflictError signal.

Validation: tsc --noEmit clean, eslint clean, 59 tests pass (1 live skipped),
tsup build succeeds.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>