[codex] Align implicit skill reads with parser (#27926)

## Summary
- reuse the shared shell read parser for implicit skill doc invocation
detection
- add regression coverage for `nl -ba .../SKILL.md`

## Why
Desktop could render `Read User Context skill` for reads recognized by
the shared command parser, while implicit `skill_invocation` analytics
used a separate reader allowlist and missed cases such as `nl`.

## Validation
- `HOME=/private/tmp/codex-core-skills-home-pr
PATH=/Users/alexsong/.cache/cargo-home/bin:$PATH
CARGO_HOME=/Users/alexsong/.cache/cargo-home just test -p
codex-core-skills`
- `git diff --cached --check`
- `just fmt` attempted; Rust formatting completed, but the Python
formatters could not download uncached Ruff wheels because
`files.pythonhosted.org` is blocked in this sandbox.
- `bazel mod deps --lockfile_mode=update/error
--repo_env=ASPECT_TOOLS_TELEMETRY= --repo_env=DO_NOT_TRACK=1` evaluated
the module graph and produced no `MODULE.bazel.lock` diff, but Bazel
crashed on sandboxed `sysctl` during exit.

codex-rs/Cargo.lock

@@ -2782,6 +2782,7 @@ dependencies = [
  "codex-model-provider",
  "codex-otel",
  "codex-protocol",
+ "codex-shell-command",
  "codex-skills",
  "codex-utils-absolute-path",
  "codex-utils-output-truncation",

codex-rs/core-skills/Cargo.toml

@@ -23,6 +23,7 @@ codex-login = { workspace = true }
 codex-model-provider = { workspace = true }
 codex-otel = { workspace = true }
 codex-protocol = { workspace = true }
+codex-shell-command = { workspace = true }
 codex-skills = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
 codex-utils-output-truncation = { workspace = true }

codex-rs/core-skills/src/invocation_utils.rs

@@ -3,6 +3,8 @@ use std::path::Path;
 
 use crate::SkillLoadOutcome;
 use crate::SkillMetadata;
+use codex_protocol::parse_command::ParsedCommand;
+use codex_shell_command::parse_command::parse_command_impl;
 use codex_utils_absolute_path::AbsolutePathBuf;
 
 pub(crate) fn build_implicit_skill_path_indexes(
@@ -101,33 +103,18 @@ fn detect_skill_doc_read(
     tokens: &[String],
     workdir: &AbsolutePathBuf,
 ) -> Option<SkillMetadata> {
-    if !command_reads_file(tokens) {
-        return None;
-    }
-
-    for token in tokens.iter().skip(1) {
-        if token.starts_with('-') {
-            continue;
-        }
-        let path = Path::new(token);
-        let candidate_path = canonicalize_if_exists(&workdir.join(path));
-        if let Some(candidate) = outcome.implicit_skills_by_doc_path.get(&candidate_path) {
-            return Some(candidate.clone());
+    for command in parse_command_impl(tokens) {
+        if let ParsedCommand::Read { path, .. } = command {
+            let candidate_path = canonicalize_if_exists(&workdir.join(path.as_path()));
+            if let Some(candidate) = outcome.implicit_skills_by_doc_path.get(&candidate_path) {
+                return Some(candidate.clone());
+            }
         }
     }
 
     None
 }
 
-fn command_reads_file(tokens: &[String]) -> bool {
-    const READERS: [&str; 8] = ["cat", "sed", "head", "tail", "less", "more", "bat", "awk"];
-    let Some(program) = tokens.first() else {
-        return false;
-    };
-    let program = command_basename(program).to_ascii_lowercase();
-    READERS.contains(&program.as_str())
-}
-
 fn command_basename(command: &str) -> String {
     Path::new(command)
         .file_name()

codex-rs/core-skills/src/invocation_utils_tests.rs

@@ -76,6 +76,30 @@ fn skill_doc_read_detection_matches_absolute_path() {
     );
 }
 
+#[test]
+fn skill_doc_read_detection_matches_shared_read_parser() {
+    let skill_doc_path = test_path_buf("/tmp/skill-test/SKILL.md").abs();
+    let normalized_skill_doc_path = canonicalize_if_exists(&skill_doc_path);
+    let skill = test_skill_metadata(skill_doc_path);
+    let outcome = SkillLoadOutcome {
+        implicit_skills_by_scripts_dir: Arc::new(HashMap::new()),
+        implicit_skills_by_doc_path: Arc::new(HashMap::from([(normalized_skill_doc_path, skill)])),
+        ..Default::default()
+    };
+
+    let tokens = vec![
+        "nl".to_string(),
+        "-ba".to_string(),
+        test_path_display("/tmp/skill-test/SKILL.md"),
+    ];
+    let found = detect_skill_doc_read(&outcome, &tokens, &test_path_buf("/tmp").abs());
+
+    assert_eq!(
+        found.map(|value| value.name),
+        Some("test-skill".to_string())
+    );
+}
+
 #[test]
 fn skill_script_run_detection_matches_relative_path_from_skill_root() {
     let skill_doc_path = test_path_buf("/tmp/skill-test/SKILL.md").abs();