GitHub Actions workflow not triggering on push or PR

GitHub Actions workflow file exists in .github/workflows/ but does not run on push, pull request, or other expected events. No errors shown — it simply does not appear in the Actions tab.

Common causes: (1) Wrong branch in on.push.branches — check if it matches your branch name exactly. (2) Workflow file has YAML syntax errors — validate with yamllint. (3) File not on the default branch — new workflows must be merged to main/master first before they trigger on other branches. (4) paths filter too restrictive — changes to files outside the paths list will not trigger it. (5) Workflow is disabled — check Actions tab for disabled workflows. (6) File must have .yml or .yaml extension. Debug: check the Actions tab for any error banners, and verify the file parses correctly.

GitHub only reads workflow definitions from the default branch for new workflows. YAML parsing failures are silently ignored. Branch and path filters are exact matches.