fix(core): resolve JSON Pointer array indexes in $ref paths

[hsusul]

Summary

`resolve_ref()` treated every JSON Pointer hop as a dict lookup. A valid pointer such as `#/allOf/0` therefore crashed with `AssertionError: encountered non-dictionary entry` because `allOf` is an array.

JSON Pointer (RFC 6901) uses decimal array indexes. OpenAPI and MCP schemas commonly `$ref` into `allOf` / `anyOf` / `prefixItems` members. Default `FunctionTool` construction (`strict_json_schema=True`) and MCP `convert_schemas_to_strict=True` run this path, so those tools fail at setup.

Reproduction

from agents.tool import FunctionTool

schema = {
    \"type\": \"object\",
    \"properties\": {
        \"value\": {\"\$ref\": \"#/allOf/0\", \"description\": \"first member\"},
    },
    \"allOf\": [
        {\"type\": \"object\", \"properties\": {\"a\": {\"type\": \"string\"}}, \"required\": [\"a\"], \"additionalProperties\": False},
        {\"type\": \"object\", \"properties\": {\"b\": {\"type\": \"integer\"}}, \"required\": [\"b\"], \"additionalProperties\": False},
    ],
}

FunctionTool(name=\"t\", description=\"d\", params_json_schema=schema, on_invoke_tool=lambda ctx, s: s)
# Before: AssertionError
# After: schema is inlined as a strict object

Solution

Walk dict keys and RFC 6901 array indexes. Reject non-integer tokens, leading zeros, and out-of-range indexes with `ValueError`. Nested `$id` resource checks still apply only to dict nodes.

Test plan

• Direct `resolve_ref("#/allOf/0")` and `#/allOf/1`
• Invalid array token raises `ValueError`
• `ensure_strict_json_schema` inlines a sibling `$ref` into an `allOf` member
• `uv run pytest tests/test_strict_schema.py` (75 passed)
• `ruff` / `pyright` on the changed files

Issue number

N/A

Checks

• I've added new tests, if relevant
• I've run format, lint, typecheck, and targeted tests
• If using Codex, I've run `/review` before submitting this PR

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[seratch]

The array-index support is needed, but str.isdigit() accepts non-ASCII numerals such as Arabic-Indic and full-width digits. Those are not valid JSON Pointer array-index tokens and can cause a malformed third-party schema to resolve to a different array member instead of being rejected.

Please restrict the token to the ASCII array-index grammar, preserving the existing leading-zero and bounds checks, and add cases for Arabic-Indic, full-width, and mixed digit strings.

[hsusul]

Addressed in 6b4ee86.

_json_pointer_child now validates array-index tokens with ASCII 0-9 only, instead of str.isdigit(). Leading-zero and out-of-range checks are unchanged.

Added regression coverage for Arabic-Indic (\u0660, \u0661), full-width (\uff10, \uff11), and mixed ASCII/non-ASCII digit strings.

[seratch]

Thanks, the resolver now follows RFC 6901's ASCII array-index grammar, and I do not see a remaining defect in the implementation itself. Before merge, please strengthen the regression coverage at the supported boundary.

The current test_ensure_strict_json_schema_inlines_ref_to_allof_member fixture is unsatisfiable: the root permits only value, while the two allOf branches respectively require and permit only a or b. It therefore proves traversal, but not that a usable strict schema is produced. Please replace it with a satisfiable valid JSON Schema and exercise FunctionTool construction or an equivalent public conversion boundary. Also add leading-zero and out-of-range cases, since regressions in those branches could accept or select the wrong array location.

With those focused tests and green CI, this should be ready.