refactor: read measurements from the local tree

The site compiles the index and the SQLite files from measurements/
instead of a pinned clone. The pin, the sync script, the CI clone steps,
the freshness area and its refresh handler are gone. core_probe --record
writes into measurements/ of the checkout by default, and a test fails
when a line or data file HEAD holds changed or vanished.

scripts/core_probe.py

@@ -10,10 +10,10 @@ Three modes share one runner:
 
 Each repetition runs in its own process, under strace when it is installed,
 so the files a core opened are read from the kernel rather than guessed.
-`--record DIR` appends one record per invocation to a clone of the
-measurements repository, carrying what is needed to reproduce it (core build,
-frontend commit, host, inputs by hash). measurement_records.py splits it into
-a slim line and a gzip sidecar.
+`--record` appends one record per invocation to measurements/ of this
+repository, carrying what is needed to reproduce it (core build, frontend
+commit, host, inputs by hash). measurement_records.py splits it into a slim
+line and a gzip sidecar.
 """
 
 from __future__ import annotations
@@ -39,7 +39,6 @@ from dataclasses import dataclass, field
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parent.parent
-MEASUREMENTS_CLONE = ROOT / ".cache" / "measurements"
 MIN_BENCH_REPETITIONS = 5
 DEFAULT_WORK_DIR = ROOT / "tmp" / "core_probe"
 BASE_OBSERVABLES = ("frame_sha1", "video_sha1", "audio_sha1", "state_sha1")
@@ -771,10 +770,10 @@ def build_parser() -> argparse.ArgumentParser:
     common.add_argument("--core-repo", help="source repository URL of the core build")
     common.add_argument("--core-commit", help="commit the core was built from")
     common.add_argument("--build-command", help="command and flags that built the core")
-    common.add_argument("--record", metavar="DIR",
-                        help="append the record to the measurements clone DIR "
-                             f"(records/<emulator>.jsonl and data/<emulator>/), "
-                             f"for example {MEASUREMENTS_CLONE.relative_to(ROOT)}")
+    common.add_argument("--record", metavar="DIR", nargs="?", const=str(ROOT),
+                        help="append the record to measurements/<emulator>.jsonl and write "
+                             "its data file in measurements/data/<emulator>/ of the checkout "
+                             "DIR (default: this one)")
     common.add_argument("--emulator", help="profile the record is filed under (default: the "
                                            "profile whose cores: names the .so, else the "
                                            "core's library name)")
@@ -823,7 +822,6 @@ def validate_args(args: argparse.Namespace) -> list[str]:
     if args.png_dir and not args.frame_hash_every:
         problems.append("--png-dir needs --frame-hash-every")
     if args.record:
-        problems.extend(record_target_problems(Path(args.record)))
         if not args.emulator and Path(args.core).is_file():
             try:
                 default_emulator(Path(args.core), None)
@@ -907,32 +905,6 @@ def check_result(variants: list[dict], observable: str) -> dict:
     }
 
 
-def record_target_problems(directory: Path) -> list[str]:
-    """Why records may not be written under ``directory``.
-
-    Records live in their own repository. A directory inside this one's
-    tracked tree would put them in its history, megabytes per campaign;
-    an ignored directory (tmp/, the clone under .cache/) is fine.
-    """
-    target = directory.resolve()
-    if target != ROOT and ROOT not in target.parents:
-        return []
-    try:
-        ignored = subprocess.run(["git", "check-ignore", "-q", str(target)], cwd=ROOT,
-                                 capture_output=True, check=False).returncode
-    except OSError as exc:
-        return [f"--record {directory}: cannot ask git whether it is tracked ({exc})"]
-    if ignored == 0:
-        return []
-    if ignored != 1:
-        # 128: not a git checkout, nothing to keep records out of.
-        return []
-    return [f"--record {directory}: inside the tracked tree of this repository. Records go "
-            f"to the measurements repository: clone it with "
-            f"`python scripts/sync_measurements.py --fetch` and pass "
-            f"--record {MEASUREMENTS_CLONE.relative_to(ROOT)}"]
-
-
 def default_emulator(core_file: Path, library_name: str | None) -> str:
     """The profile whose cores: names the .so, else the library name as a slug."""
     stem = core_file.name.split(".")[0].removesuffix("_libretro")