feat(scripts): add Python check-prerequisites PoC (#3302)

* feat(scripts): add Python check-prerequisites PoC

* fix(scripts): address check-prerequisites parity feedback

* test(scripts): label PowerShell prerequisite parity cases

---------

Co-authored-by: root <kinsonnee@gmail.com>

Author: WOLIKIMCHENG

scripts/python/check_prerequisites.py

@@ -0,0 +1,207 @@
+#!/usr/bin/env python3
+"""Consolidated prerequisite checking script."""
+
+from __future__ import annotations
+
+import json
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+
+try:
+    from common import FeaturePaths, format_speckit_command, get_feature_paths
+except ImportError:  # pragma: no cover - direct execution from unusual cwd
+    sys.path.insert(0, str(Path(__file__).resolve().parent))
+    from common import FeaturePaths, format_speckit_command, get_feature_paths
+
+
+def _json_line(payload: object) -> str:
+    return json.dumps(payload, ensure_ascii=False, separators=(",", ":")) + "\n"
+
+
+HELP_TEXT = """Usage: check_prerequisites.py [OPTIONS]
+
+Consolidated prerequisite checking for Spec-Driven Development workflow.
+
+OPTIONS:
+  --json              Output in JSON format
+  --require-tasks     Require tasks.md to exist (for implementation phase)
+  --include-tasks     Include tasks.md in AVAILABLE_DOCS list
+  --paths-only        Only output path variables (no prerequisite validation)
+  --help, -h          Show this help message
+
+EXAMPLES:
+  # Check task prerequisites (plan.md required)
+  ./check_prerequisites.py --json
+
+  # Check implementation prerequisites (plan.md + tasks.md required)
+  ./check_prerequisites.py --json --require-tasks --include-tasks
+
+  # Get feature paths only (no validation)
+  ./check_prerequisites.py --paths-only
+
+"""
+
+
+@dataclass(frozen=True)
+class Args:
+    json_mode: bool = False
+    require_tasks: bool = False
+    include_tasks: bool = False
+    paths_only: bool = False
+
+
+def _parse_args(argv: list[str]) -> Args:
+    json_mode = False
+    require_tasks = False
+    include_tasks = False
+    paths_only = False
+
+    for arg in argv:
+        if arg == "--json":
+            json_mode = True
+        elif arg == "--require-tasks":
+            require_tasks = True
+        elif arg == "--include-tasks":
+            include_tasks = True
+        elif arg == "--paths-only":
+            paths_only = True
+        elif arg in {"--help", "-h"}:
+            sys.stdout.write(HELP_TEXT)
+            raise SystemExit(0)
+        else:
+            print(
+                f"ERROR: Unknown option '{arg}'. Use --help for usage information.",
+                file=sys.stderr,
+            )
+            raise SystemExit(1)
+
+    return Args(
+        json_mode=json_mode,
+        require_tasks=require_tasks,
+        include_tasks=include_tasks,
+        paths_only=paths_only,
+    )
+
+
+def _dir_has_entries(path: Path) -> bool:
+    try:
+        return path.is_dir() and any(path.iterdir())
+    except OSError:
+        return False
+
+
+def _available_docs(paths: FeaturePaths, include_tasks: bool) -> list[str]:
+    docs: list[str] = []
+    if paths.research.is_file():
+        docs.append("research.md")
+    if paths.data_model.is_file():
+        docs.append("data-model.md")
+    if _dir_has_entries(paths.contracts_dir):
+        docs.append("contracts/")
+    if paths.quickstart.is_file():
+        docs.append("quickstart.md")
+    if include_tasks and paths.tasks.is_file():
+        docs.append("tasks.md")
+    return docs
+
+
+def _print_paths_only(paths: FeaturePaths, json_mode: bool) -> None:
+    if json_mode:
+        sys.stdout.write(
+            _json_line(
+                {
+                    "REPO_ROOT": str(paths.repo_root),
+                    "BRANCH": paths.current_branch,
+                    "FEATURE_DIR": str(paths.feature_dir),
+                    "FEATURE_SPEC": str(paths.feature_spec),
+                    "IMPL_PLAN": str(paths.impl_plan),
+                    "TASKS": str(paths.tasks),
+                }
+            )
+        )
+        return
+
+    print(f"REPO_ROOT: {paths.repo_root}")
+    print(f"BRANCH: {paths.current_branch}")
+    print(f"FEATURE_DIR: {paths.feature_dir}")
+    print(f"FEATURE_SPEC: {paths.feature_spec}")
+    print(f"IMPL_PLAN: {paths.impl_plan}")
+    print(f"TASKS: {paths.tasks}")
+
+
+def _check_file(path: Path, description: str) -> None:
+    marker = "✓" if path.is_file() else "✗"
+    print(f"  {marker} {description}")
+
+
+def _check_dir(path: Path, description: str) -> None:
+    marker = "✓" if _dir_has_entries(path) else "✗"
+    print(f"  {marker} {description}")
+
+
+def _print_text_results(paths: FeaturePaths, include_tasks: bool) -> None:
+    print(f"FEATURE_DIR:{paths.feature_dir}")
+    print("AVAILABLE_DOCS:")
+    _check_file(paths.research, "research.md")
+    _check_file(paths.data_model, "data-model.md")
+    _check_dir(paths.contracts_dir, "contracts/")
+    _check_file(paths.quickstart, "quickstart.md")
+    if include_tasks:
+        _check_file(paths.tasks, "tasks.md")
+
+
+def main(argv: list[str] | None = None) -> int:
+    args = _parse_args(list(argv if argv is not None else sys.argv[1:]))
+
+    try:
+        paths = get_feature_paths(
+            no_persist=args.paths_only,
+            script_file=Path(__file__),
+        )
+    except SystemExit as exc:
+        if exc.code == 0:
+            return 0
+        print("ERROR: Failed to resolve feature paths", file=sys.stderr)
+        return int(exc.code) if isinstance(exc.code, int) else 1
+
+    if args.paths_only:
+        _print_paths_only(paths, args.json_mode)
+        return 0
+
+    if not paths.feature_dir.is_dir():
+        print(f"ERROR: Feature directory not found: {paths.feature_dir}", file=sys.stderr)
+        print(
+            f"Run {format_speckit_command('specify', paths.repo_root)} first to create the feature structure.",
+            file=sys.stderr,
+        )
+        return 1
+
+    if not paths.impl_plan.is_file():
+        print(f"ERROR: plan.md not found in {paths.feature_dir}", file=sys.stderr)
+        print(
+            f"Run {format_speckit_command('plan', paths.repo_root)} first to create the implementation plan.",
+            file=sys.stderr,
+        )
+        return 1
+
+    if args.require_tasks and not paths.tasks.is_file():
+        print(f"ERROR: tasks.md not found in {paths.feature_dir}", file=sys.stderr)
+        print(
+            f"Run {format_speckit_command('tasks', paths.repo_root)} first to create the task list.",
+            file=sys.stderr,
+        )
+        return 1
+
+    docs = _available_docs(paths, args.include_tasks)
+    if args.json_mode:
+        sys.stdout.write(
+            _json_line({"FEATURE_DIR": str(paths.feature_dir), "AVAILABLE_DOCS": docs})
+        )
+    else:
+        _print_text_results(paths, args.include_tasks)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())