Harden LaTeX entrypoint and \input{} resolution in parser

[Copilot]

This change improves parser robustness in LaTeX projects where file layout is non-trivial. It eliminates fragile entrypoint selection and makes \input{} expansion resilient to nested includes and cyclic/self references.

• Entrypoint correctness

  • Parsing a specific .tex file now uses that file as the project entrypoint.
  • Previously, file parsing could be redirected by directory-level main-file detection, producing inconsistent results.

• Deterministic nested \input{} expansion

  • \input{} resolution is now recursive across subdirectories.
  • Substitutions are handled through regex replacement callbacks, avoiding global str.replace() side effects when the same directive appears multiple times.

• Cycle-safe include handling

  • Added path-tracking during recursion to detect include cycles.
  • Cyclic includes are cut off safely (replaced with empty expansion) instead of re-entering recursion.

• I/O fault tolerance

  • Main-file detection and include expansion now tolerate unreadable files without crashing.
  • On read failure, unresolved include directives are preserved unless the path is part of an active cycle.

def _resolve_inputs(self, directory: Path, tex_content: str, visited_paths: Optional[Set[Path]] = None) -> str:
    if visited_paths is None:
        visited_paths = set()

    pattern = re.compile(r"\\input\{([^}]+)\}")

    def _replace(match: re.Match) -> str:
        input_path = (directory / match.group(1)).with_suffix(".tex") if not (directory / match.group(1)).suffix else (directory / match.group(1))
        input_path = input_path.resolve()

        if input_path in visited_paths:
            return ""  # cycle protection

        ...