feat(code_runner): rename module, fix __del__ + kernel name, expand tests

- Rename `wrenn.code_interpreter` → `wrenn.code_runner` (canonical).
  Keep old path as deprecation alias that emits a FutureWarning on
  import, mirroring the existing `Sandbox` → `Capsule` pattern.
  Submodule shims `code_interpreter/{capsule,async_capsule,models}.py`
  keep direct-submodule imports working.

- Fix sync/async ctor-failure-safe `__del__`: initialise `_kernel_id`,
  `_kernel_name`, `_proxy_client` before calling `super().__init__` so
  a failed creation no longer crashes the destructor with
  AttributeError.

- Send the kernel name to Jupyter. Previously `POST /api/kernels` had
  no body, so the server picked an arbitrary default kernelspec. Now
  sends `{"name": "wrenn"}` (override via `Capsule(kernel=...)`) and
  reuses an existing kernel only when its `name` matches.

- Preserve Jupyter `text/plain` verbatim in `Result.from_bundle`.
  The previous outer-quote strip was lossy (the string `'2'` became
  indistinguishable from the int `2`, and strings containing escaped
  quotes were mangled). `text` is now the `repr()` Jupyter sends.
  Updated the stale `test_capsule_features` quote-strip test.

- Validate `run_code(language=...)`. Anything other than `"python"`
  now raises `ValueError` instead of being silently ignored.

- Async `__del__` no longer touches the event loop; users must call
  `await close()` or use `async with`.

- New unit suite `tests/test_code_runner_unit.py` (46 tests): MIME
  unpacking, deprecation alias + warning, default template + kernel,
  custom kernel override, ctor-failure-safe __del__, kernel
  create/reuse/cache, retry on 5xx, 4xx propagation, request shape,
  run_code stream/result/error/foreign-parent/idle/unsupported-language,
  async variants.

- New e2e suite `tests/test_code_runner_e2e.py` (44 tests, integration
  marker): template == `code-runner-beta`, kernel == `wrenn`, stdout
  /stderr capture, state/import/function/class persistence, exceptions
  (Value/Name/Syntax), callbacks, multi-line, `text` repr preservation,
  filesystem round-trip, isolation between capsules, deprecated import
  path. MIME-type class covers html, markdown, json, latex, svg,
  javascript, png (matplotlib + seaborn), jpeg, multi-format bundles,
  and text-round-trip via numpy + requests.

- `make test-code-runner` runs unit + e2e together. `make test`
  extended to include the unit file.

- README: "Code Interpreter" section renamed to "Code Runner", all
  imports updated, `kernel=` documented, removed the incorrect
  "quotes stripped automatically" claim, replaced with the actual
  `text/plain` semantics.

- CLAUDE.md: appended a "Code Runner Module" section covering module
  path, defaults, kernel-reuse semantics, lifecycle invariant, and
  the new test files + make target.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -169,3 +169,39 @@ Fall back to Grep/Glob/Read **only** when the graph doesn't cover what you need.
 2. Use `detect_changes` for code review.
 3. Use `get_affected_flows` to understand impact.
 4. Use `query_graph` pattern="tests_for" to check coverage.
+
+## Code Runner Module
+
+`wrenn.code_runner` — stateful code execution capsule via persistent
+Jupyter kernel.
+
+- **Module path:** `wrenn.code_runner` (canonical). The old path
+  `wrenn.code_interpreter` is a deprecation alias that emits a
+  `FutureWarning` on import; do not introduce new uses.
+- **Defaults:** template `code-runner-beta`, kernelspec `wrenn`.
+  Both overridable via `Capsule(template=..., kernel=...)`.
+- **Kernel reuse:** `_ensure_kernel` lists `/api/kernels`, reuses the
+  first kernel whose `name` matches the configured kernelspec, else
+  POSTs `{"name": <kernel>}` to create one. Matching by name (not just
+  "any kernel") is intentional — multiple kernelspecs may coexist on
+  the same Jupyter.
+- **Lifecycle invariant:** the constructor sets `_kernel_id`,
+  `_kernel_name`, `_proxy_client` to safe defaults *before* calling
+  `super().__init__`. `__del__` must never assume construction
+  completed. Async `__del__` only drops the reference — the proxy
+  `httpx.AsyncClient` must be closed via `await close()` or
+  `async with`.
+
+### Tests
+
+- `tests/test_code_runner_unit.py` — pure unit tests (respx + mocked
+  WebSocket). Covers `Result.from_bundle`, MIME unpacking,
+  quote-stripping, `Execution.text`, kernel reuse vs create, retry on
+  5xx, 4xx propagation, ctor-failure-safe `__del__`, deprecation
+  alias.
+- `tests/test_code_runner_e2e.py` — live integration tests (marked
+  `integration`, skipped without `WRENN_API_KEY`). Covers stateful
+  execution, exceptions, callbacks, rich outputs (HTML, matplotlib,
+  pandas), async variant, isolation between capsules, and the
+  deprecated `code_interpreter` import path.
+- Run both: `make test-code-runner`.