Python and FastAPI: fix cards and security baseline

Build the signed-in user in a dependency (current_user) from the authenticated session and the users table, never from request data, and put the same scope in every query's WHERE clause: same tenant, and the caller's own rows unless they are a billing admin.

Refuse backslashes and control characters, then split next with urlsplit: accept a path that starts with exactly one slash, or an https URL whose hostname is in an exact allowlist, with no port and no @.

Resolve both paths and compare whole components before building the FileResponse: base = Path(base_dir).resolve(), target = (base / name).resolve(), and serve target only if target.is_relative_to(base). resolve() collapses ../ and follows symlinks, and the check also catches absolute names, which replace base in the / operator.

Attach the policy to the connection, not the URL string or its Pydantic type.

Use argon2-cffi's PasswordHasher with explicit parameters at or above OWASP's minimum, PasswordHasher(time_cost=2, memory_cost=19456, parallelism=1), and store ph.hash(password) from a plain def path operation.

Never evaluate user input as code. Parse the expression with ast.parse and walk the tree, allowing only numeric literals, the supplied variables and arithmetic operators; refuse everything else.

Pass values as bound parameters: text("... WHERE c.name = :customer") with session.execute(sql, {"customer": customer}), or build the query with select() and column comparisons.

Bound every resource the client controls. Cap the request body while you read it -- count the stream and return 413 as soon as it exceeds the limit, never trusting Content-Length -- and bound pagination with Query(limit, ge=1, le=100) so an out-of-range page size is a 422.

Decide the type from the bytes and never let the client pick the name.

Put verification in one dependency that every protected route declares: HTTPBearer() reads the token, then jwt.decode(token, key, algorithms=["RS256"], issuer=..., audience=..., leeway=30, options={"require": ["exp", "iss", "aud", "sub"]}) with the key from configuration, and any PyJWTError becomes 401.

Put an authentication dependency on every protected path operation.

Do not rebuild objects from client data. Parse the token as JSON with a Pydantic model (Profile.model_validate_json(raw)), which keeps only declared fields of declared types; pickle.loads runs code chosen by the bytes.

Give each write route its own Pydantic body model that declares only the fields that caller may change (here displayName and bio), never the model that describes the whole stored user, and copy model_dump(exclude_none=True) onto the record. extra="forbid" turns any other key into a 422.