fix(tools): wrap bare scalars in single-element list for array-typed args#19717
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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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Open-weight models (DeepSeek, Qwen, GLM) sometimes emit
{"urls": "https://a.com"}where the schema expectstype: array. The call was JSON-valid but semantically wrong — the tool then failed with a confusing type error.coerce_tool_argsnow wraps non-list, non-null values into a single-element list.Changes
model_tools.coerce_tool_args: +24 LOC — new array-wrap branch that runs strings through_coerce_valuefirst (so JSON-encoded arrays and nullable"null"still work), then falls back to[value]wrap for bare scalars.Nonepreserved.tests/run_agent/test_tool_arg_coercion.pycovering bare string / int / dict / JSON-encoded / list-passthrough / None / existing-test-updated.Validation
{"urls": "https://a.com"}on array field["https://a.com"]{"urls": '["a","b"]'}["a","b"]["a","b"](unchanged){"stages": "null"}nullable arrayNoneNone(unchanged){"items": None}NoneNone(unchanged — we don't second-guess deliberate nulls)tests/run_agent/Relation to #19652
Salvaged from #19652 by @NikolayGusev-astra. The broader validate-then-repair layer in that PR had several problems: it duplicated the existing
coerce_tool_argspath for string→array, mis-classifiedold_stringas a path field (would silently corruptpatchcalls), hardcodedoffset=1 / limit=500defaults that only fitread_file, and prepended a[validate-then-repair: ...]prefix to every tool result — breaking any downstream consumer that JSON-parses tool output. The genuinely new capability was bare-scalar-as-array wrapping, which this PR implements directly inside the existing coercion path in ~24 LOC.Co-authored-by: Nikolay Gusev ngusev@astralinux.ru