content collection does not satisfy its schema or slug contract

Verniz could not turn an authored Markdown, JSON, TOML, or YAML file into the metadata struct declared by content.collection. The diagnostic points to the collection expression and names the content file and field that failed.

For example, this collection requires every post to have a string title, a valid ISO date, and an optional draft flag:

use std::content

struct PostMeta {
  title: str,
  date: content.Date,
  draft: bool = false,
}

const posts = comptime content.collection(
  "posts",
  "content/posts/**/*.md",
  PostMeta,
)

Fix the named frontmatter field, remove fields that are not present in the struct, or give each document a unique portable slug. Dates accept YYYY-MM-DD or a complete RFC 3339 timestamp. Static production builds also reject documents marked draft: true; development keeps them visible for authoring.

Collection paths use the same two anchors as client entries: ./content/** starts beside the declaring Zolo file, while content/** starts at the project root. Backslashes, absolute paths, and paths that escape the project are not portable and are rejected.

Markdown is sanitized during compilation. Raw authored HTML is removed, and unsafe link/image schemes are reported as TE775 instead of reaching the output.

YAML frontmatter is strict YAML. Escape an apostrophe inside a single-quoted scalar by doubling it ('Zolo''s strings'); the compiler does not accept or rewrite permissive YAML-like legacy syntax.

When a collection uses content.ContentTransform, TE775 also rejects a route callback that does not return a portable root-relative route, malformed alias maps, fallback entries without a resolved route, and relative .md links that do not exist in the current or fallback collection. Fix the authored link, add an explicit portable alias, or provide a transformed base-locale collection as fallback.

See also: the Content collections section of the Verniz Sites specification.