Make output assertions more explicit (#4784)

Match using precise regexes.

codex-rs/core/tests/common/Cargo.toml

@@ -10,6 +10,7 @@ path = "lib.rs"
 anyhow = { workspace = true }
 assert_cmd = { workspace = true }
 codex-core = { workspace = true }
+regex-lite = { workspace = true }
 serde_json = { workspace = true }
 tempfile = { workspace = true }
 tokio = { workspace = true, features = ["time"] }

codex-rs/core/tests/common/lib.rs

@@ -6,6 +6,7 @@ use codex_core::CodexConversation;
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
 use codex_core::config::ConfigToml;
+use regex_lite::Regex;
 
 #[cfg(target_os = "linux")]
 use assert_cmd::cargo::cargo_bin;
@@ -14,6 +15,16 @@ pub mod responses;
 pub mod test_codex;
 pub mod test_codex_exec;
 
+#[track_caller]
+pub fn assert_regex_match<'s>(pattern: &str, actual: &'s str) -> regex_lite::Captures<'s> {
+    let regex = Regex::new(pattern).unwrap_or_else(|err| {
+        panic!("failed to compile regex {pattern:?}: {err}");
+    });
+    regex
+        .captures(actual)
+        .unwrap_or_else(|| panic!("regex {pattern:?} did not match {actual:?}"))
+}
+
 /// Returns a default `Config` whose on-disk state is confined to the provided
 /// temporary directory. Using a per-test directory keeps tests hermetic and
 /// avoids clobbering a developer’s real `~/.codex`.