improve: fix lint issues - organize imports and add exception chaining

.gitignore

@@ -74,6 +74,5 @@ fixtures/generated/
 .ruff_cache/
 
 # Local opencode config
-AGENTS.md
 .agents/
 

AGENTS.md

@@ -0,0 +1,25 @@
+# API Contract Guardian
+
+## Purpose
+CLI tool that monitors OpenAPI schema diffs, detects breaking changes, generates migration guides, and gates CI pipelines on contract violations.
+
+## Build & Test Commands
+- Install: `pip install -e .` or `pip install git+https://github.com/Coding-Dev-Tools/api-contract-guardian.git`
+- Test: `pytest` 
+- Lint: `ruff check .`
+- Build: `pip wheel . --wheel-dir dist/`
+
+## Architecture
+Key directories:
+- `src/api_contract_guardian/` — Main package (CLI, diff engine, migration guide generator)
+- `tests/` — Test suite
+- `.github/workflows/` — CI/CD (4 workflows)
+
+## Conventions
+- Language: Python 3.10+
+- Test framework: pytest
+- CI: GitHub Actions (4 workflows)
+- Formatting: ruff (line-length 120)
+- Type checking: py.typed included
+- Package: setuptools with src layout
+- CLI framework: typer

src/api_contract_guardian/cli.py

@@ -2,10 +2,11 @@
 
 from __future__ import annotations
 
-import typer
 from pathlib import Path
 from typing import Any
 
+import typer
+
 # Lazy imports — jwt+cryptography+deepdiff+yaml add ~200ms at module level.
 # Deferring heavy deps to command execution cuts cold start from ~440ms to ~180ms.
 
@@ -70,7 +71,7 @@ def _load_and_validate(path: str) -> dict:
     except SpecLoadError as e:
         from rich.console import Console
         Console().print(f"[red]Error loading: {e}[/red]")
-        raise typer.Exit(code=1)
+        raise typer.Exit(code=1) from e
 
 
 def _print_result(result: Any) -> None:
@@ -121,6 +122,7 @@ def diff(
 ) -> None:
     """Compare two OpenAPI specs and show all detected changes."""
     import json
+
     import yaml
 
     from .diff import diff_specs
@@ -180,6 +182,7 @@ def check(
 ) -> None:
     """Gate CI pipeline on breaking changes. Returns exit code 1 if gate fails."""
     import json
+
     import yaml
 
     from .diff import diff_specs
@@ -243,6 +246,7 @@ def migrate(
 ) -> None:
     """Generate a migration guide between two OpenAPI spec versions."""
     import json
+
     import yaml
 
     from .diff import diff_specs

tests/test_cli.py

@@ -639,7 +639,7 @@ def test_main_module_version(self):
         # carry over to a separate process).
         from revenueholdings_license.rate_limiter import RateLimiter
         RateLimiter().reset("api-contract-guardian")
-        from revenueholdings_license import generate_license_key, Tier
+        from revenueholdings_license import Tier, generate_license_key
         env = os.environ.copy()
         env["REVENUEHOLDINGS_LICENSE_KEY"] = generate_license_key(Tier.PRO)
         # Ensure all environment variables are string keys and string values to prevent Popen TypeError on Windows