Open-weight models (DeepSeek, Qwen, GLM) sometimes emit tool calls like
`{"urls": "https://a.com"}` when the tool schema declares
`type: array`. The call was JSON-valid but semantically wrong, and
`coerce_tool_args` would pass the bare string through — the tool then
failed with a confusing type error.
`coerce_tool_args` now wraps non-list, non-null values in a
single-element list when the schema declares `array`. Strings still go
through `_coerce_value` first so JSON-encoded arrays
(`'["a","b"]'`) parse correctly and nullable `"null"` still
becomes `None`. `None` itself is preserved — tools with sensible
defaults already handle it, and we don't want to silently mask a
deliberate null.
Salvaged from #19652 (NikolayGusev-astra) — the broader validate-then-
repair layer had several issues (duplicated existing coercion,
mis-classified `old_string` as a path field, prepended non-JSON
prefixes to tool results that break downstream JSON parsing, hardcoded
offset/limit defaults unsuitable for non-read_file tools). The one
genuinely new capability is wrapping bare scalars, which is implemented
here directly inside the existing coercion path.
Co-authored-by: Nikolay Gusev <ngusev@astralinux.ru>
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