fix: set the allocator purge delay before the launched entry loads native code

The `sqb` launcher hands off to `sqlbuild.cli.entry.main.launched`, which
imported `LAUNCH_RECORD_OPTION` from `sqlbuild._native` at module import.
That loaded the extension, and its mimalloc allocator, before
`entry.main` defaulted `MIMALLOC_PURGE_DELAY`, so mimalloc kept its
default purge delay and returned far less freed memory to the OS. Dense
10000-model compiles peaked about 200-400 MiB higher.

Default the purge delay in the launched entry before importing the
native constant, and extend the fresh-process allocator entry test to
cover the launched entry.

Author: kvlonge

src/sqlbuild/cli/entry/main/launched.py

@@ -1,13 +1,22 @@
 """Python CLI entrypoint the native `sqb` executable hands every invocation it does not serve."""
 
+import os
 import sys
 
-from sqlbuild._native import LAUNCH_RECORD_OPTION
+from sqlbuild.cli.entry.constants import (
+    NATIVE_ALLOCATOR_PURGE_DELAY_MILLISECONDS,
+    NATIVE_ALLOCATOR_PURGE_DELAY_VARIABLE,
+)
 from sqlbuild.cli.entry.main.entry import main as run_cli
 
 
 def main() -> int:
-    """Run the CLI with the arguments `sqb` received; the CLI reads a leading launch record."""
+    """Run the CLI with the `sqb` arguments, setting the allocator purge delay first."""
+
+    os.environ.setdefault(
+        NATIVE_ALLOCATOR_PURGE_DELAY_VARIABLE, NATIVE_ALLOCATOR_PURGE_DELAY_MILLISECONDS
+    )
+    from sqlbuild._native import LAUNCH_RECORD_OPTION
 
     arguments: list[str] = sys.argv[1:]
     offered: bool = bool(arguments) and arguments[0].startswith(LAUNCH_RECORD_OPTION)

tests/integration/src/sqlbuild/cli/commands/main/_test_types.py

@@ -928,6 +928,7 @@ class DiscoveryWorkTestCase:
 @dataclass(frozen=True)
 class NativeAllocatorEntryTestCase:
     description: str
+    entry_module: str
     inherited_environment: tuple[tuple[str, str], ...]
     expected_purge_delay: str
 

tests/integration/src/sqlbuild/cli/commands/main/test_native_allocator_entry.py

@@ -14,14 +14,18 @@
 )
 
 _PURGE_DELAY_VARIABLE: str = "MIMALLOC_PURGE_DELAY"
+_ENTRY_MODULE: str = "sqlbuild.cli.entry.main.entry"
+_LAUNCHED_MODULE: str = "sqlbuild.cli.entry.main.launched"
 _SCRIPT: str = """
+import importlib
 import json
 import os
 import sys
-from sqlbuild.cli.entry.main.entry import main
 
+entry = importlib.import_module(sys.argv[1])
 loaded_at_import = "sqlbuild._native" in sys.modules
-exit_code = main(["--version"])
+sys.argv = ["sqlbuild-python", "--version"]
+exit_code = entry.main() if entry.__name__.endswith(".launched") else entry.main(["--version"])
 loaded_by_version = "sqlbuild._native" in sys.modules
 import sqlbuild._native
 print(json.dumps({
@@ -38,11 +42,25 @@
     [
         NativeAllocatorEntryTestCase(
             description="unset purge delay defaults to ten milliseconds",
+            entry_module=_ENTRY_MODULE,
             inherited_environment=(),
             expected_purge_delay="10",
         ),
         NativeAllocatorEntryTestCase(
             description="user purge delay is preserved",
+            entry_module=_ENTRY_MODULE,
+            inherited_environment=((_PURGE_DELAY_VARIABLE, "250"),),
+            expected_purge_delay="250",
+        ),
+        NativeAllocatorEntryTestCase(
+            description="launched entry defaults the purge delay before native load",
+            entry_module=_LAUNCHED_MODULE,
+            inherited_environment=(),
+            expected_purge_delay="10",
+        ),
+        NativeAllocatorEntryTestCase(
+            description="launched entry preserves a user purge delay",
+            entry_module=_LAUNCHED_MODULE,
             inherited_environment=((_PURGE_DELAY_VARIABLE, "250"),),
             expected_purge_delay="250",
         ),
@@ -57,7 +75,7 @@ def test_given_fresh_process_when_running_cli_entry_then_purge_delay_is_set_befo
     environment.update(test_case.inherited_environment)
 
     result: subprocess.CompletedProcess[str] = subprocess.run(
-        [sys.executable, "-c", _SCRIPT],
+        [sys.executable, "-c", _SCRIPT, test_case.entry_module],
         check=True,
         capture_output=True,
         env=environment,