fix(wrap): emit bare dotted keys for Codex --config overrides (#2383)

## Description

`headroom wrap codex` with a custom provider emits `--config` overrides
whose dotted key quotes **every** segment
(`"model_providers"."litellm_prod"."base_url"=…`). Codex's override
parser matches dotted segments literally and silently ignores quoted
ones, so the overrides are dropped, the session keeps the provider's
real `base_url`, and traffic **bypasses Headroom entirely** — the exact
silent-bypass reported in #2358 on Codex 0.144.5.

I reproduced the parser behavior differentially on a local Codex
**0.144.1** (see Real Behavior Proof): a bare key is parsed (Codex
errors on the injected value), the same key quoted produces no error at
all — the override is silently discarded.

Fix: `_codex_dotted_key()` now emits segments **bare** whenever they are
valid bare keys (`[A-Za-z0-9_-]+`, which covers `model_providers`, every
normal provider id, and hyphenated header names like
`X-Headroom-Base-Url`), and quotes only segments where bare emission
would corrupt the dotted path (e.g. a provider id containing a dot).

Fixes #2358.

## Type of Change

- [x] Bug fix (silent proxy bypass for custom-provider Codex wraps)

## Changes Made

- `headroom/cli/wrap.py`: `_codex_dotted_key()` quotes only non-bare-key
segments; docstring explains the observed Codex parser behavior. The
default `openai` path (`openai_base_url=…`, already bare) is unchanged.
- `tests/test_cli/test_wrap_codex.py`: the custom-provider launch test
now pins the bare form for all three overrides (`base_url`,
`supports_websockets`, `env_http_headers.X-Headroom-Base-Url`), plus 2
direct unit tests (bare-when-safe incl. hyphens, quote-only-unsafe).

## Testing

- [x] Unit tests pass (`pytest`)
- [x] Linting passes (`ruff` + `mypy`, CI-pinned settings)
- [x] Reproduced the parser behavior on a real Codex CLI first, then
fixed

### Test Output

```text
$ .venv/bin/python -m pytest tests/test_cli/test_wrap_codex.py -q
93 passed

# Before the fix the updated assertions fail (generated args still fully quoted):
#   FAILED ...::test_codex_session_launch_settings_preserve_custom_provider_identity
#   FAILED ...::test_codex_dotted_key_emits_bare_segments_when_safe
#   FAILED ...::test_codex_dotted_key_quotes_only_unsafe_segments

$ ruff check headroom/cli/wrap.py tests/test_cli/test_wrap_codex.py   # All checks passed!
$ ruff format --check <both>                                          # formatted
$ mypy headroom/cli/wrap.py --ignore-missing-imports                  # Success: no issues
```

## Real Behavior Proof

- Environment: macOS (Darwin), Codex CLI **0.144.1**
(`/opt/homebrew/bin/codex`), empty temp `CODEX_HOME` (no auth, no
network side effects), branch `fix/codex-config-bare-keys` off `main`
(`56c7d4a5`).
- Exact command / steps: differential probe of the override parser —
`codex exec --skip-git-repo-check -c 'profile="__nope__"' 'hi'` (bare
key) vs `codex exec --skip-git-repo-check -c '"profile"="__nope__"'
'hi'` (quoted key), each run once against a fresh empty `CODEX_HOME`.
- Observed result: bare key → Codex **parsed the override** and failed
fast on it (`Error: legacy profile = "__nope__" config is no longer
supported…`); quoted key → **no error referencing the override at all**,
Codex proceeded to start a session (banner printed) — the quoted
override was silently discarded. That is precisely the #2358 bypass
mechanism: every generated custom-provider override was quoted, hence
dropped, hence traffic went straight to the real upstream.
- Not tested: an end-to-end wrapped session against a live LiteLLM
upstream on Codex 0.144.5 (the reporter's exact version); the parser
behavior above is version-adjacent (0.144.1) and the argv shape is
pinned by unit tests.

## Review Readiness

- [x] I have performed a self-review
- [x] This PR is ready for human review

## Checklist

- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation — N/A
(docstring added)
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective
- [x] New and existing unit tests pass locally with my changes
- [ ] I have updated the CHANGELOG.md — N/A

## Additional Notes

- Segments that genuinely need quoting (a provider id with a dot) keep
their quotes: on parsers that ignore quoted segments those overrides
still won't apply, but bare emission would corrupt a *different* key
path, which is strictly worse. Such ids are rare; the common
LiteLLM/custom-provider case is fully bare after this fix.

tests/test_cli/test_wrap_codex.py

@@ -1172,11 +1172,39 @@ def test_codex_session_launch_settings_preserve_custom_provider_identity(
     )
 
     assert "model_provider=headroom" not in " ".join(args)
-    assert '"model_providers"."company"."base_url"="http://127.0.0.1:9898/v1"' in args
+    # Bare dotted keys — Codex (0.144.x) silently ignores quoted segments (#2358).
+    assert 'model_providers.company.base_url="http://127.0.0.1:9898/v1"' in args
+    assert "model_providers.company.supports_websockets=true" in args
+    assert (
+        "model_providers.company.env_http_headers.X-Headroom-Base-Url"
+        '="HEADROOM_CODEX_UPSTREAM_BASE_URL"'
+    ) in args
     assert env[wrap_mod._UPSTREAM_BASE_URL_ENV_VAR] == "https://api.example.test/v1"
     assert config_file.read_text(encoding="utf-8") == original_config
 
 
+def test_codex_dotted_key_emits_bare_segments_when_safe() -> None:
+    """#2358: quoted segments are silently ignored by Codex's --config parser."""
+    assert (
+        wrap_mod._codex_dotted_key("model_providers", "litellm_prod", "base_url")
+        == "model_providers.litellm_prod.base_url"
+    )
+    # Hyphens are valid in bare keys (header names under env_http_headers).
+    assert (
+        wrap_mod._codex_dotted_key("env_http_headers", "X-Headroom-Base-Url")
+        == "env_http_headers.X-Headroom-Base-Url"
+    )
+
+
+def test_codex_dotted_key_quotes_only_unsafe_segments() -> None:
+    # A provider name that would corrupt the dotted path if emitted bare keeps
+    # its quotes; every safe neighbor stays bare.
+    assert (
+        wrap_mod._codex_dotted_key("model_providers", "my.provider", "base_url")
+        == 'model_providers."my.provider".base_url'
+    )
+
+
 def test_wrap_codex_rejects_custom_provider_without_upstream_base_url(
     runner: CliRunner, monkeypatch: pytest.MonkeyPatch, tmp_path: Path
 ) -> None: