Remove deprecated SEA backend

.bot/prompts/engineer/system.md

@@ -106,13 +106,11 @@ up whatever it needs.
 == HOW TO WORK (bug-fix flow) ==
 
 0. **Pick the BACKEND the bug is on — reproduce on that one.** The connector has
-   three backends and a bug on one won't reproduce on another. Choose from the
+   two backends and a bug on one won't reproduce on another. Choose from the
    issue:
    - **kernel** (`use_kernel=True`) — only if the issue is specifically about the
      Rust kernel / `use_kernel`. Repro in `tests/e2e/test_kernel_backend.py` and run
      it alone (it needs the real wheel; see the `-m "not realkernel"` note above).
-   - **SEA** (`use_sea=True`) — if the issue implicates SEA, or the area is
-     backend-parametrized (add the `{"use_sea": True}` param case).
    - **Thrift** (the default, no kwarg) — everything else; this is the common case.
    See CONTRIBUTING.md → "Backends and test tiers" for the full matrix (selection
    kwarg + where each backend's tests live).

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Release History
 
 # Unreleased
+- **Breaking:** Remove the deprecated pure-Python SEA backend and its options; use Thrift (default) or `use_kernel=True`.
+- **Breaking:** Kernel IDs now use `BackendType.KERNEL`, `SessionId.from_kernel_session_id`, and `CommandId.from_kernel_statement_id`. Remove `BackendType.SEA`, the `from_sea_*` / `to_sea_*` helpers, `CommandState.from_sea_state`, and `DatabricksClientType.SEA`.
+- Warn when removed SEA options are passed. On kernel ≥ 1.1.0, use `_pool_maxsize` for the kernel HTTP pool; it does not configure the Thrift query transport.
 
 # 4.9.0 (2026-11-04)
 - Upgrade Databricks SQL Kernel to 1.4.0, which keeps Lakehouse Real-Time session affinity and flushes shared telemetry only after the final session closes.

CONNECTION_PARAMETERS.md

@@ -19,11 +19,6 @@ but ignored (or rejected) on the other is called out in the **Note** column.
 > does **not** splat `**kwargs`. Options implemented in the shared Python driver
 > layer can still apply to both backends; unforwarded backend-specific options
 > are ignored or rejected on the kernel path.
->
-> A separate pure-Python **SEA** backend (`use_sea=True`) also exists but is
-> being deprecated. Its selector and SEA-only hybrid-disposition option are
-> listed for completeness, but this reference does not provide a third SEA
-> support column.
 
 ## Legend
 
@@ -60,10 +55,7 @@ to change without notice.
 
 | Option                   | Type   | Thrift | Kernel | Default Value | Note                                                                                               |
 | ------------------------ | ------ | :----: | :----: | ------------- | -------------------------------------------------------------------------------------------------- |
-| `use_kernel`             | `bool` |   —    |   —    | `False`       | Routing selector: `False` selects Thrift; `True` selects Kernel. Mutually exclusive with `use_sea`. |
-| `use_sea`                | `bool` |   —    |   —    | `False`       | Select the deprecated pure-Python SEA backend. Mutually exclusive with `use_kernel`.               |
-| `use_hybrid_disposition` | `bool` |   ❌   |   ❌   | `False`       | SEA-only result-disposition option; ignored by Thrift and Kernel.                                  |
-| `max_connections`        | `int`  |   ❌   |   ❌   | `10`          | Internal SEA-only HTTP-pool limit; ignored by Thrift and Kernel.                                   |
+| `use_kernel`             | `bool` | —      | —      | `False`       | Routing selector: `False` selects Thrift; `True` selects Kernel.                                   |
 
 ---
 

CONTRIBUTING.md

@@ -146,14 +146,13 @@ The suites marked `[not documented]` require additional configuration which will
 
 #### Backends and test tiers
 
-The connector has **three execution backends**, selected per connection. When you
+The connector has **two execution backends**, selected per connection. When you
 reproduce or fix a bug, use the backend the bug is actually on — a Thrift bug won't
-reproduce on a SEA or kernel connection, and vice versa:
+reproduce on a kernel connection, and vice versa:
 
 | Backend | Select via (connect kwarg / `extra_params`) | Where its tests live |
 | --- | --- | --- |
-| **Thrift** (default) | *(nothing — the default path)* | the general `tests/e2e` suite (the `{}` parametrize case) and mocked `tests/unit` |
-| **SEA** (Statement Execution API) *(deprecated — use Kernel for SEA-native connections)* | `use_sea=True` | the general `tests/e2e` suite (the `{"use_sea": True}` parametrize case, e.g. `tests/e2e/test_driver.py`) and mocked `tests/unit` |
+| **Thrift** (default) | *(nothing — the default path)* | the general `tests/e2e` suite (the default connection) and mocked `tests/unit` |
 | **Kernel** (Rust, optional) | `use_kernel=True` | the dedicated `tests/e2e/test_kernel_backend.py` / `test_kernel_tls.py`, plus the offline routing test `tests/unit/test_session.py -m realkernel` |
 
 Notes that matter when running the suite: