bazel: run sharded rust integration tests (#21057)

## Why

Bazel CI was not actually exercising some sharded Rust integration-test
targets on macOS. The `rules_rust` sharding wrapper expects a symlink
runfiles tree, but this repo runs Bazel with `--noenable_runfiles`. In
that configuration the wrapper could fail to find the generated test
binary, produce an empty test list, and exit successfully. That made
targets such as `//codex-rs/core:core-all-test` look green even when
Cargo CI could still catch failures in the same Rust tests.

The coverage gap appears to have been introduced by
[#18082](https://github.com/openai/codex/pull/18082), which enabled
rules_rust native sharding on `//codex-rs/core:core-all-test` and the
other large Rust test labels. The manifest-runfiles setup itself
predates that change in
[#10098](https://github.com/openai/codex/pull/10098), but #18082 is
where the affected integration tests started running through the
incompatible rules_rust sharding wrapper.
[#18913](https://github.com/openai/codex/pull/18913) fixed the same
class of issue for wrapped unit-test shards, but integration-test shards
were still going through the rules_rust wrapper until this PR.

We still do not have the V8/code-mode pieces stable under the Bazel CI
cross-compile setup, so this keeps those tests out of Bazel while
restoring coverage for the rest of the sharded Rust integration suites.
Cargo CI remains responsible for V8/code-mode coverage for now.

This change did uncover a real failing core test on `main`:
`approved_folder_write_request_permissions_unblocks_later_apply_patch`.
That fix is split into
[#21060](https://github.com/openai/codex/pull/21060), which enables the
`apply_patch` tool in the test, teaches the aggregate core test binary
to dispatch the sandboxed filesystem helper, canonicalizes the macOS
temp patch target, and isolates the core test harness from managed
local/enterprise config. Keeping that fix separate lets this PR stay
focused on restoring Bazel coverage while documenting the first failure
it exposed.

## What changed

- Build sharded Rust integration tests as manual `*-bin` binaries and
run them through the existing manifest-aware `workspace_root_test`
launcher.
- Keep Bazel sharding on the launcher target so Rust test cases are
still distributed by stable test-name hashing.
- Configure Bazel CI to skip Rust tests whose names contain
`suite::code_mode::`.
- Exclude the standalone `codex-rs/code-mode` and `codex-rs/v8-poc`
unit-test targets from `bazel.yml`.

## Verification

- `bazel query --output=build //codex-rs/core:core-all-test` now shows
`workspace_root_test` wrapping `//codex-rs/core:core-all-test-bin`.
- `bazel test --test_output=all --nocache_test_results
--test_sharding_strategy=disabled //codex-rs/core:core-all-test
--test_filter=suite::request_permissions_tool::approved_folder_write_request_permissions_unblocks_later_apply_patch`
runs the actual Rust test body and passes.
- `bazel test --test_output=errors --nocache_test_results
--test_env=CODEX_BAZEL_TEST_SKIP_FILTERS=suite::code_mode::
//codex-rs/core:core-all-test` runs the sharded target with code-mode
skipped and passes overall locally, with one flaky attempt retried by
the existing `flaky = True` setting.

.bazelrc

@@ -79,6 +79,10 @@ common:ci --disk_cache=
 # Shared config for the main Bazel CI workflow.
 common:ci-bazel --config=ci
 common:ci-bazel --build_metadata=TAG_workflow=bazel
+# Bazel CI cross-compiles in several legs, and the V8-backed code-mode tests
+# are not stable in that setup yet. Keep running the rest of the Rust
+# integration suites through the workspace-root launcher.
+common:ci-bazel --test_env=CODEX_BAZEL_TEST_SKIP_FILTERS=suite::code_mode::
 
 # Shared config for Bazel-backed Rust linting.
 build:clippy --aspects=@rules_rust//rust:defs.bzl%rust_clippy_aspect
@@ -164,9 +168,9 @@ common:ci-windows-cross --strategy=remote
 common:ci-windows-cross --strategy=TestRunner=local
 common:ci-windows-cross --local_test_jobs=4
 common:ci-windows-cross --test_env=RUST_TEST_THREADS=1
-# Native Windows CI still covers these tests. The cross-built gnullvm binaries
-# currently crash in V8-backed code-mode tests and hang in PowerShell AST parser
-# tests when those binaries are run on the Windows runner.
+# Native Windows CI still covers the PowerShell tests. The cross-built gnullvm
+# binaries currently hang in PowerShell AST parser tests when those binaries are
+# run on the Windows runner.
 common:ci-windows-cross --test_env=CODEX_BAZEL_TEST_SKIP_FILTERS=suite::code_mode::,powershell
 common:ci-windows-cross --platforms=//:windows_x86_64_gnullvm
 common:ci-windows-cross --extra_execution_platforms=//:rbe,//:windows_x86_64_msvc