## Why
`ToolName::display()` made it too easy to flatten tool identity and
accidentally compare rendered strings. Tool identity should stay
structural until a legacy string boundary actually requires the
flattened spelling.
## What
- Removes `ToolName::display()` and relies on the existing `Display`
impl for messages and errors.
- Adds structural ordering for `ToolName` and uses it for
sorting/deduping deferred tools.
- Carries `ToolName` through tool/sandbox plumbing, flattening only at
legacy boundaries such as hook payloads, telemetry tags, and Responses
tool names.
- Updates MCP normalization tests to assert `ToolName` structure instead
of rendered strings.
## Testing
- `cargo test -p codex-mcp test_normalize_tools`
- `cargo test -p codex-core unavailable_tool`
- `just fix -p codex-protocol`
- `just fix -p codex-mcp`
- `just fix -p codex-core`
stacked on #17402.
MCP tools returned by `tool_search` (deferred tools) get registered in
our `ToolRegistry` with a different format than directly available
tools. this leads to two different ways of accessing MCP tools from our
tool catalog, only one of which works for each. fix this by registering
all MCP tools with the namespace format, since this info is already
available.
also, direct MCP tools are registered to responsesapi without a
namespace, while deferred MCP tools have a namespace. this means we can
receive MCP `FunctionCall`s in both formats from namespaces. fix this by
always registering MCP tools with namespace, regardless of deferral
status.
make code mode track `ToolName` provenance of tools so it can map the
literal JS function name string to the correct `ToolName` for
invocation, rather than supporting both in core.
this lets us unify to a single canonical `ToolName` representation for
each MCP tool and force everywhere to use that one, without supporting
fallbacks.