bazel: fix snapshot parity for tests/*.rs rust_test targets (#11893)

## Summary
- make `rust_test` targets generated from `tests/*.rs` use Cargo-style
crate names (file stem) so snapshot names match Cargo (`all__...`
instead of Bazel-derived names)
- split lib vs `tests/*.rs` test env wiring in `codex_rust_crate` to
keep existing lib snapshot behavior while applying Bazel
runfiles-compatible workspace root for `tests/*.rs`
- compute the `tests/*.rs` snapshot workspace root from package depth so
`insta` resolves committed snapshots under Bazel `--noenable_runfiles`

## Validation
- `bazelisk test //codex-rs/core:core-all-test
--test_arg=suite::compact:: --cache_test_results=no`
- `bazelisk test //codex-rs/core:core-all-test
--test_arg=suite::compact_remote:: --cache_test_results=no`

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

@@ -26,6 +26,26 @@ fn enable_deterministic_unified_exec_process_ids_for_tests() {
     codex_core::test_support::set_deterministic_process_ids(true);
 }
 
+#[ctor]
+fn configure_insta_workspace_root_for_snapshot_tests() {
+    if std::env::var_os("INSTA_WORKSPACE_ROOT").is_some() {
+        return;
+    }
+
+    let workspace_root = codex_utils_cargo_bin::repo_root()
+        .ok()
+        .map(|root| root.join("codex-rs"));
+
+    if let Some(workspace_root) = workspace_root
+        && let Ok(workspace_root) = workspace_root.canonicalize()
+    {
+        // Safety: this ctor runs at process startup before test threads begin.
+        unsafe {
+            std::env::set_var("INSTA_WORKSPACE_ROOT", workspace_root);
+        }
+    }
+}
+
 #[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| {

defs.bzl

@@ -170,20 +170,28 @@ def codex_rust_crate(
         cargo_env["CARGO_BIN_EXE_" + binary] = "$(rlocationpath %s)" % binary_label
 
     for test in native.glob(["tests/*.rs"], allow_empty = True):
-        test_name = name + "-" + test.removeprefix("tests/").removesuffix(".rs").replace("/", "-")
+        test_file_stem = test.removeprefix("tests/").removesuffix(".rs")
+        test_crate_name = test_file_stem.replace("-", "_")
+        test_name = name + "-" + test_file_stem.replace("/", "-")
         if not test_name.endswith("-test"):
             test_name += "-test"
 
         rust_test(
             name = test_name,
+            crate_name = test_crate_name,
             crate_root = test,
             srcs = [test],
             data = native.glob(["tests/**"], allow_empty = True) + sanitized_binaries + test_data_extra,
             compile_data = native.glob(["tests/**"], allow_empty = True) + integration_compile_data_extra,
             deps = maybe_lib + deps + dev_deps + integration_deps_extra,
             proc_macro_deps = proc_macro_deps + proc_macro_dev_deps,
-            rustc_flags = rustc_flags_extra,
+            # Keep `file!()` paths Cargo-like (`core/tests/...`) instead of
+            # Bazel workspace-prefixed (`codex-rs/core/tests/...`) for snapshot parity.
+            rustc_flags = rustc_flags_extra + ["--remap-path-prefix=codex-rs="],
             rustc_env = rustc_env,
-            env = test_env | cargo_env,
+            # Important: do not merge `test_env` here. Its unit-test-only
+            # `INSTA_WORKSPACE_ROOT="."` can point integration tests at the
+            # runfiles cwd and cause false `.snap.new` churn on Linux.
+            env = cargo_env,
             tags = test_tags,
         )