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mesh_identity

tit.mesh_identity

Content identity for replaying recorded placements on their original head mesh.

sha256_file 

sha256_file(path: Path) -> str

Hash a file incrementally without holding a head mesh in memory.

Source code in tit/mesh_identity.py 
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def sha256_file(path: Path) -> str:
    """Hash a file incrementally without holding a head mesh in memory."""
    digest = hashlib.sha256()
    with path.open("rb") as stream:
        for chunk in iter(lambda: stream.read(1024 * 1024), b""):
            digest.update(chunk)
    return digest.hexdigest()

verify_subject_mesh 

verify_subject_mesh(pm, subject: str, expected_sha256: str) -> Path

Require the selected subject's confined mesh to match recorded bytes.

The saved source path is provenance only, never an input to file access.

Source code in tit/mesh_identity.py 
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def verify_subject_mesh(pm, subject: str, expected_sha256: str) -> Path:
    """Require the selected subject's confined mesh to match recorded bytes.

    The saved source path is provenance only, never an input to file access.
    """
    if not isinstance(expected_sha256, str) or not re.fullmatch(
        r"[0-9a-f]{64}", expected_sha256
    ):
        raise ValueError("Recorded head mesh SHA-256 is invalid.")
    try:
        path = Path(
            resolve_within(
                pm.project_dir, str(Path(pm.m2m(subject)) / f"{subject}.msh")
            )
        )
    except ValueError as exc:
        raise ValueError("Replay head mesh escapes the selected project.") from exc
    if not path.is_file():
        raise ValueError("The recorded candidate's subject head mesh is missing.")
    if sha256_file(path) != expected_sha256:
        raise ValueError(
            "The subject head mesh has changed since candidate recording; replay is refused."
        )
    return path