Error marker highlights colon instead of invalid value

[ellanan]

Description

When a value fails schema validation (e.g., an invalid type value), the diagnostic from/to positions point to the colon (:) after the property key, rather than the actual invalid value.

Reproduction

Schema:

{
  "type": "object",
  "properties": {
    "type": {
      "anyOf": [
        { "enum": ["object", "array", "string", "number", "integer", "boolean", "null"] },
        { "type": "array", "items": { "enum": ["object", "array", "string", "number", "integer", "boolean", "null"] } }
      ]
    }
  }
}

Document being validated:

{"type": "objectd"}

Expected

The error marker should highlight "objectd" (positions 12–21).

Actual

The diagnostic reports from: 10, to: 11, which is the : character after "type".

{"type": "objectd"}
          ^
          position 10-11 (colon highlighted)

Console output from forEachDiagnostic:

{
  message: 'Value `objectd` at `type` does not match any schema...',
  severity: 'error',
  from: 10,
  to: 11,
  source: 'json-schema'
}

Analysis

In validation.js, the positioning logic uses pointer.valueFrom / pointer.valueTo for non-positional errors (line 137-138). The pointer values appear to be off by one — landing on the separator rather than the value.

Environment

• codemirror-json-schema: 0.8.1 (latest)
• @uiw/react-codemirror wrapper

Related: #158 (also about incorrect error marker positions)