codex-tools: extract collaboration tool specs (#16141)

## Why

The recent `codex-tools` migration steps have moved shared tool models
and low-coupling spec helpers out of `codex-core`, but
`core/src/tools/spec.rs` still owned a large block of pure
collaboration-tool spec construction. Those builders do not need session
state or runtime behavior; they only need a small amount of core-owned
configuration injected at the seam.

Moving that cohesive slice into `codex-tools` makes the crate boundary
more honest and removes a substantial amount of passive tool-spec logic
from `codex-core` without trying to move the runtime-coupled multi-agent
handlers at the same time.

## What changed

- added `agent_tool.rs`, `request_user_input_tool.rs`, and
`agent_job_tool.rs` to `codex-tools`, with sibling `*_tests.rs` coverage
and an exports-only `lib.rs`
- moved the pure `ToolSpec` builders for:
- collaboration tools such as `spawn_agent`, `send_input`,
`send_message`, `assign_task`, `resume_agent`, `wait_agent`,
`list_agents`, and `close_agent`
  - `request_user_input`
  - agent-job specs `spawn_agents_on_csv` and `report_agent_job_result`
- rewired `core/src/tools/spec.rs` to call the extracted builders while
still supplying the core-owned inputs, such as spawn-agent role
descriptions and wait timeout bounds
- updated the `core/src/tools/spec.rs` seam tests to build expected
collaboration specs through `codex-tools`
- updated `codex-rs/tools/README.md` so the crate documentation reflects
the broader collaboration-tool boundary

## Test plan

- `CARGO_TARGET_DIR=/tmp/codex-tools-collab-specs cargo test -p
codex-tools`
- `CARGO_TARGET_DIR=/tmp/codex-core-collab-specs cargo test -p
codex-core --lib tools::spec::`
- `just fix -p codex-tools -p codex-core`
- `just argument-comment-lint`

## References

- #15923
- #15928
- #15944
- #15953
- #16031
- #16047
- #16129
- #16132
- #16138

codex-rs/tools/src/request_user_input_tool.rs

@@ -0,0 +1,94 @@
+use crate::JsonSchema;
+use crate::ResponsesApiTool;
+use crate::ToolSpec;
+use std::collections::BTreeMap;
+
+pub fn create_request_user_input_tool(description: String) -> ToolSpec {
+    let option_props = BTreeMap::from([
+        (
+            "label".to_string(),
+            JsonSchema::String {
+                description: Some("User-facing label (1-5 words).".to_string()),
+            },
+        ),
+        (
+            "description".to_string(),
+            JsonSchema::String {
+                description: Some(
+                    "One short sentence explaining impact/tradeoff if selected.".to_string(),
+                ),
+            },
+        ),
+    ]);
+
+    let options_schema = JsonSchema::Array {
+        description: Some(
+            "Provide 2-3 mutually exclusive choices. Put the recommended option first and suffix its label with \"(Recommended)\". Do not include an \"Other\" option in this list; the client will add a free-form \"Other\" option automatically."
+                .to_string(),
+        ),
+        items: Box::new(JsonSchema::Object {
+            properties: option_props,
+            required: Some(vec!["label".to_string(), "description".to_string()]),
+            additional_properties: Some(false.into()),
+        }),
+    };
+
+    let question_props = BTreeMap::from([
+        (
+            "id".to_string(),
+            JsonSchema::String {
+                description: Some(
+                    "Stable identifier for mapping answers (snake_case).".to_string(),
+                ),
+            },
+        ),
+        (
+            "header".to_string(),
+            JsonSchema::String {
+                description: Some(
+                    "Short header label shown in the UI (12 or fewer chars).".to_string(),
+                ),
+            },
+        ),
+        (
+            "question".to_string(),
+            JsonSchema::String {
+                description: Some("Single-sentence prompt shown to the user.".to_string()),
+            },
+        ),
+        ("options".to_string(), options_schema),
+    ]);
+
+    let questions_schema = JsonSchema::Array {
+        description: Some("Questions to show the user. Prefer 1 and do not exceed 3".to_string()),
+        items: Box::new(JsonSchema::Object {
+            properties: question_props,
+            required: Some(vec![
+                "id".to_string(),
+                "header".to_string(),
+                "question".to_string(),
+                "options".to_string(),
+            ]),
+            additional_properties: Some(false.into()),
+        }),
+    };
+
+    let properties = BTreeMap::from([("questions".to_string(), questions_schema)]);
+
+    ToolSpec::Function(ResponsesApiTool {
+        name: "request_user_input".to_string(),
+        description,
+        strict: false,
+        defer_loading: None,
+        parameters: JsonSchema::Object {
+            properties,
+            required: Some(vec!["questions".to_string()]),
+            additional_properties: Some(false.into()),
+        },
+        output_schema: None,
+    })
+}
+
+#[cfg(test)]
+#[path = "request_user_input_tool_tests.rs"]
+mod tests;