Safer YAML parsing and structured JSON errors

This update makes YAML parsing stricter to ensure files always deploy the values you write. It also returns a clear JSON error if a JSON request is malformed.

Stricter YAML parsing

This release introduces a breaking change. The YAML parser now rejects unsafe input instead of changing it without notice. As a result, three patterns that previously worked will now fail:

• A value that starts with a colon, like :draft. Remove the colon to fix this.
• A tag declaration, such as !ruby/object:Foo. Remove the tag to resolve this.
• An alias without a matching anchor, like *missing. Add the anchor it refers to.

Files with these patterns may have deployed values different from what you wrote. Check your YAML files before upgrading.

What still works

Standard YAML features are not affected. Anchors, aliases, merges, and dates still work as they did before.

Structured JSON errors

If you send a request with Content-Type: application/json and the body is malformed, you now get a structured JSON error like {"status":400,"error":"There was a problem in the JSON you submitted: ..."} instead of plain text. Other content types still get a text response, now with a clear Content-Type: text/plain header.

Read the full YAML Parsing release notes.