Add argument-comment Dylint runner (#14651)

tools/argument-comment-lint/README.md

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+# argument-comment-lint
+
+Isolated [Dylint](https://github.com/trailofbits/dylint) library for enforcing
+Rust argument comments in the exact `/*param*/` shape.
+
+Prefer self-documenting APIs over comment-heavy call sites when possible. If a
+call site would otherwise read like `foo(false)` or `bar(None)`, consider an
+enum, named helper, newtype, or another idiomatic Rust API shape first, and
+use an argument comment only when a smaller compatibility-preserving change is
+more appropriate.
+
+It provides two lints:
+
+- `argument_comment_mismatch` (`warn` by default): validates that a present
+  `/*param*/` comment matches the resolved callee parameter name.
+- `uncommented_anonymous_literal_argument` (`allow` by default): flags
+  anonymous literal-like arguments such as `None`, `true`, `false`, and numeric
+  literals when they do not have a preceding `/*param*/` comment.
+
+String and char literals are exempt because they are often already
+self-descriptive at the callsite.
+
+## Behavior
+
+Given:
+
+```rust
+fn create_openai_url(base_url: Option<String>, retry_count: usize) -> String {
+    let _ = (base_url, retry_count);
+    String::new()
+}
+```
+
+This is accepted:
+
+```rust
+create_openai_url(/*base_url*/ None, /*retry_count*/ 3);
+```
+
+This is warned on by `argument_comment_mismatch`:
+
+```rust
+create_openai_url(/*api_base*/ None, 3);
+```
+
+This is only warned on when `uncommented_anonymous_literal_argument` is enabled:
+
+```rust
+create_openai_url(None, 3);
+```
+
+## Development
+
+Install the required tooling once:
+
+```bash
+cargo install cargo-dylint dylint-link
+rustup toolchain install nightly-2025-09-18 \
+  --component llvm-tools-preview \
+  --component rustc-dev \
+  --component rust-src
+```
+
+Run the lint crate tests:
+
+```bash
+cd tools/argument-comment-lint
+cargo test
+```
+
+Run the lint against `codex-rs` from the repo root:
+
+```bash
+./tools/argument-comment-lint/run.sh -p codex-core
+just argument-comment-lint -p codex-core
+```
+
+If no package selection is provided, `run.sh` defaults to checking the
+`codex-rs` workspace with `--workspace --no-deps`.
+
+Repo runs also promote `uncommented_anonymous_literal_argument` to an error by
+default:
+
+```bash
+./tools/argument-comment-lint/run.sh -p codex-core
+```
+
+The wrapper does that by setting `DYLINT_RUSTFLAGS`, and it leaves an explicit
+existing setting alone. It also defaults `CARGO_INCREMENTAL=0` unless you have
+already set it, because the current nightly Dylint flow can otherwise hit a
+rustc incremental compilation ICE locally. To override that behavior for an ad
+hoc run:
+
+```bash
+DYLINT_RUSTFLAGS="-A uncommented_anonymous_literal_argument" \
+CARGO_INCREMENTAL=1 \
+  ./tools/argument-comment-lint/run.sh -p codex-core
+```
+
+To expand target coverage for an ad hoc run:
+
+```bash
+./tools/argument-comment-lint/run.sh -p codex-core -- --all-targets
+```