authoring-github-workflows

This error usually means the workflow file is valid YAML but invalid for GitHub Actions. The most common cause is a `#` inside an unquoted `${{ }}` expression being parsed as a YAML comment, truncating the value into an unterminated expression. Quote the scalar and validate with actionlint.

Run actionlint against your workflow files, for example `actionlint -shellcheck= -pyflakes= .github/workflows/*.yml`. It understands the Actions schema and expression grammar, catching errors that yaml.safe_load and yamllint miss. A clean exit code 0 means the workflows are structurally valid.

Quote the entire scalar when the value contains a `${{ }}` expression plus a literal `#`, a colon followed by a space, or a leading special character like `*`, `&`, `!`, or `@`. Prefer double quotes when the inner expression uses single quotes, and never escape the `${{ }}` braces.

No. YAML-only linters like yamllint and yaml.safe_load accept the truncated-comment form where `#` silently cuts off an expression, so the bug passes validation but GitHub Actions refuses to run the file. Only actionlint (or pushing and watching Actions parse it) validates the Actions layer.

No. It covers only syntactic and structural correctness of workflow YAML — quoting, parsing, and actionlint-level validity. For semantic and functional workflow design, including agentic-workflow behavior, it defers to the complementary agentic-workflows agent guidance.