refactor(memory): S3-generic store on boto3; RustFS is the tested server (no MinIO naming)

The plane's memory store no longer names one vendor. `MinioStore`/`SdkClient`/
`minio_settings`/`MINIO_KEYS` become `S3Store`/`S3Client`/`s3_settings`/`S3_KEYS`;
the URL scheme is `s3://<bucket>[/<prefix>]` (`s3://` alone uses `S3_BUCKET`); the
settings are `S3_ENDPOINT` (a full URL), `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`,
optional `AWS_SESSION_TOKEN` and `S3_REGION`. The client is boto3 (extra `s3`,
imported lazily): SigV4, path-style addressing, SDK checksum trailers off, paginated
listing, versions and delete markers listed and deleted by version (`purge`, used by
the contract tests' teardown so the bucket keeps nothing of a run).

Behaviour is unchanged: the store never configures its bucket and verifies
versioning, the `runs/` expiry rule, S3 Select and tag reads at startup; no local
fallback; every row carries every queryable field with "" placeholders. The admin
hints read `--endpoint-url "$S3_ENDPOINT"`. The fake client still reproduces RustFS's
two Select failures (unbound leading-row field, null-typed column).

Docs: rustfs.md stays the tested server's setup page (policy JSON unchanged, env
names updated, any S3-compatible store with versioning, lifecycle, tags and Select
works); memory.md, ops/ax/README.md, README.md, steering and the two current spec
designs use the S3 naming. Retired specs and committed measurements are untouched.

Real server (RustFS, OUSAST_MEMORY_TEST_S3=1): test_plane_memory + test_learn_compile
75 passed, 1 skipped. Store copy of the live local store to a temporary prefix: every
count matched (776 row objects, 2982 rows, 22 facts, 788 excerpts, 2601 responses,
2 programs, 1793 index entries), 4190 versions purged afterwards.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

tests/test_learn_compile.py

@@ -11,7 +11,7 @@ from pathlib import Path
 
 import pytest
 from learn_fixtures import ScriptedChat, by_id, corpus, default_answer, example
-from test_plane_memory import FakeObjects, _real_minio
+from test_plane_memory import FakeObjects, _real_s3
 
 from openultrasast.learn import compile as compile_module
 from openultrasast.learn.compile import (
@@ -34,7 +34,7 @@ from openultrasast.learn.examples import Example
 from openultrasast.learn.folds import Fold, FoldError
 from openultrasast.learn.program import Caller, Demo
 from openultrasast.plane.budget import MeteredClient
-from openultrasast.plane.memory import FileStore, MemoryStore, MinioStore
+from openultrasast.plane.memory import FileStore, MemoryStore, S3Store
 
 PRICES = {"cache_hit_per_m": 0.014, "input_per_m": 0.44, "output_per_m": 1.32}
 MEMORY = corpus(groups=24, per_group=4)
@@ -58,14 +58,14 @@ def answer(messages: Sequence[Mapping[str, object]], temperature: float | None)
     return json.dumps(data)
 
 
-@pytest.fixture(params=["file", "fake-minio", "minio"])
+@pytest.fixture(params=["file", "fake-s3-select", "s3"])
 def store(request: pytest.FixtureRequest, tmp_path: Path) -> Iterator[MemoryStore]:
     if request.param == "file":
         yield FileStore(tmp_path / "memory")
-    elif request.param == "minio":
-        yield from _real_minio()
+    elif request.param == "s3":
+        yield from _real_s3()
     else:
-        yield MinioStore(FakeObjects("works"), "bucket", "p")
+        yield S3Store(FakeObjects("works"), "bucket", "p")
 
 
 def _caller(chat: ScriptedChat, store: MemoryStore | None = None, **budget: object) -> Caller: