## TL;DR
Point the link at the public re-export, make the item public, or mark it doc(hidden) and stop linking to it. Rustdoc refuses to link to items that are not part of the public API.

## Error
```text
error: unresolved link to `mylib::secret value :Helper`
```

## Steps
1. Check the item's visibility: if it is private and should stay private, the docs must not link to it. Expected: a decision on whether the item is public API.
2. If it is meant to be public, add `pub` (possibly `pub(crate)` will not help; docs need real public visibility or a public re-export). Expected: the item is reachable from the crate root.
3. If the item is public but reached through a private module path, link via the public re-export path instead (e.g. `mylib::Helper` rather than `mylib::secret value :Helper`). Expected: the link uses the public path.
4. Re-run `cargo doc`. Expected: the intra-doc link resolves with no error.

## When to use
- rustdoc errors on an intra-doc link to a private item
- A refactor made a module private but docs still link the old path
- A docs agent linked internal helpers

## When not to use
- The link target does not exist at all (create it or remove the link)
- You want the item documented but private (use doc(hidden) and drop the link)
- The error is a warning, not an error (treat warnings the same way before they become errors)

## Tool compatibility
Rust 1.70+; intra-doc link errors became deny-by-default in recent editions. Same behavior on docs.rs.

### Variant phrasings
### intra-doc link to a pub(crate) item
pub(crate) is still private to rustdoc. Re-export publicly or remove the link.

### link worked before a visibility refactor
Update the link to the new public path; refactors that privatize modules break doc links silently until the next doc build.

## Why it happens
Rustdoc resolves intra-doc links against the public API surface. Private items are intentionally excluded, so links to them are errors, not warnings. Visibility refactors are the usual trigger.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_zL8Y34LakaL-uOgKECnsSA