Add --check flag for CI exit code on breaking changes

.github/workflows/ci.yml

@@ -40,4 +40,4 @@ jobs:
           BASE_REF="origin/${{ github.base_ref }}"
           HEAD_REF="HEAD"
           echo "Comparing API surface: $BASE_REF..$HEAD_REF"
-          node dist/cli.js "$BASE_REF..$HEAD_REF" --entrypoint src/index.ts || true
+          node dist/cli.js "$BASE_REF..$HEAD_REF" --entrypoint src/index.ts --check

README.md

@@ -33,6 +33,9 @@ npx sigdiff --entrypoint src/index.ts
 
 # JSON output
 npx sigdiff --json
+
+# Exit with code 1 if breaking changes are detected (useful for CI)
+npx sigdiff --check
 ```
 
 ## Example output
@@ -67,6 +70,18 @@ Changes are classified as `major`, `minor`, or `patch` per semver rules.
 | Config required       | None            | Yes                     | Yes                  | Yes             |
 | Git ref comparison    | Any ref         | N/A                     | N/A                  | Baseline file   |
 
+## CI integration
+
+Use `--check` to fail your pipeline when breaking changes are introduced:
+
+```yaml
+# .github/workflows/ci.yml
+- name: API surface check
+  run: npx sigdiff origin/main..HEAD --entrypoint src/index.ts --check
+```
+
+Without `--check`, sigdiff always exits 0 and just prints the diff. With `--check`, it exits 1 if any breaking changes are detected, making it easy to gate PRs.
+
 ## Programmatic API
 
 ```typescript

src/cli.ts

@@ -14,7 +14,9 @@ cli
   .command('[range]', 'Diff the public API surface between two git refs')
   .option('--entrypoint <path>', 'Scope to a specific file')
   .option('--json', 'Output as JSON instead of markdown')
-  .action((range: string | undefined, options: { entrypoint?: string; json?: boolean }) => {
+  .option('--check', 'Exit with code 1 if breaking changes are detected')
+  .action(
+    (range: string | undefined, options: { entrypoint?: string; json?: boolean; check?: boolean }) => {
     try {
       assertGitRepo();
 
@@ -28,14 +30,19 @@ cli
       const output = format(result, { json: options.json });
 
       process.stdout.write(output);
+
+      if (options.check && result.breaking.length > 0) {
+        process.exit(1);
+      }
     } catch (err) {
       if (err instanceof SigdiffException) {
         process.stderr.write(`Error: ${err.error.message}\n`);
         process.exit(1);
       }
       throw err;
     }
-  });
+  },
+);
 
 cli.help();
 cli.version(pkgVersion);