## Why
Some tool providers, especially MCP servers and dynamic tool sources,
can supply schema nodes that omit `type` and have no recognized JSON
Schema shape hints. Previously, `sanitize_json_schema` filled those
unknown nodes in as `string`, which made the schema parseable but
invented a scalar constraint that the provider did not specify. For
description-only fields, that could incorrectly steer tool arguments
away from the provider's actual accepted shape.
The Responses API accepts permissive empty schemas such as `{}` at
nested property positions, so Codex should preserve that permissive
meaning instead of coercing unknown schema nodes into a misleading
scalar type.
## What Changed
- Changed the no-hints fallback in `codex-rs/tools/src/json_schema.rs`
to clear unrecognized object schema nodes to `{}`.
- Empty schemas now remain `{}` rather than becoming `type: "string"`.
- Description-only or otherwise metadata-only nested property schemas
now become `{}` while surrounding object/array/string/number inference
still applies when recognized hints are present.
- Updated `codex-tools` and `codex-core` tests to cover top-level empty
schemas, nested empty schemas, metadata-only malformed schemas, dynamic
tools, and MCP tool specs.
## Verification
- `cargo test -p codex-tools`
- `cargo test -p codex-core
test_mcp_tool_property_missing_type_defaults_to_empty_schema`
- Manually verified the real Responses API behavior for both
empty-schema positions:
- Top-level function `parameters: {}` is accepted and echoed back as
`{"type":"object","properties":{}}`; when forced to call the tool,
Responses emitted empty object arguments: `"arguments": "{}"`.
- Nested property schema `{}` is accepted and preserved as `{}`; when
forced to call a tool with `metadata.extra`, Responses emitted
`"arguments": "{\"metadata\":{\"extra\":\"codex schema sanitizer
behavior\"}}"`.
## Why
`parse_tool_input_schema` and the supporting `JsonSchema` model were
living in `core/src/tools/spec.rs`, but they already serve callers
outside `codex-core`.
Keeping that shared schema parsing logic inside `codex-core` makes the
crate boundary harder to reason about and works against the guidance in
`AGENTS.md` to avoid growing `codex-core` when reusable code can live
elsewhere.
This change takes the first extraction step by moving the schema parsing
primitive into its own crate while keeping the rest of the tool-spec
assembly in `codex-core`.
## What changed
- added a new `codex-tools` crate under `codex-rs/tools`
- moved the shared tool input schema model and sanitizer/parser into
`tools/src/json_schema.rs`
- kept `tools/src/lib.rs` exports-only, with the module-level unit tests
split into `json_schema_tests.rs`
- updated `codex-core` to use `codex-tools::JsonSchema` and re-export
`parse_tool_input_schema`
- updated `codex-app-server` dynamic tool validation to depend on
`codex-tools` directly instead of reaching through `codex-core`
- wired the new crate into the Cargo workspace and Bazel build graph
Celia Chen