## Why
Follow-up to #16379.
`codex-rs/core/src/tools/spec.rs` and the corresponding handlers still
owned several pure tool-definition helpers even though they do not need
`codex-core` runtime state. Keeping that spec-only logic in `codex-core`
keeps the crate boundary blurry and works against the guidance in
`AGENTS.md` to keep shared tooling out of `codex-core` when possible.
This change takes another step toward a dedicated `codex-tools` crate by
moving more metadata and schema-building code behind the `codex-tools`
API while leaving the actual tool execution paths in `codex-core`.
## What Changed
- Added `codex-rs/tools/src/apply_patch_tool.rs` to own
`ApplyPatchToolArgs`, the freeform/json `apply_patch` tool specs, and
the moved `tool_apply_patch.lark` grammar.
- Updated `codex-rs/tools/BUILD.bazel` so Bazel exposes the moved
grammar file to `codex-tools`.
- Moved the `request_user_input` availability and description helpers
into `codex-rs/tools/src/request_user_input_tool.rs`, with the related
unit tests moved alongside that business logic.
- Moved `request_permissions_tool_description()` into
`codex-rs/tools/src/local_tool.rs`.
- Rewired `codex-rs/core/src/tools/spec.rs`,
`codex-rs/core/src/tools/handlers/apply_patch.rs`, and
`codex-rs/core/src/tools/handlers/request_user_input.rs` to consume the
new `codex-tools` exports instead of local helper code.
- Removed the now-redundant helper implementations and tests from
`codex-core`, plus a couple of stale `client_common` re-exports that
became unused after the move.
## Testing
- `cargo test -p codex-tools`
- `cargo test -p codex-core tools::spec::tests`
- `cargo test -p codex-core tools::handlers::apply_patch::tests`
## 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
