fix(xai-sanitize): deepcopy tools_for_api before in-place mutation (#27907)

The xAI tool-schema sanitizers (strip_slash_enum, strip_pattern_and_format)
mutate their input in place — that's their documented contract. The two
call sites (chat_completion_helpers.build_api_kwargs and the auxiliary
client) were passing agent.tools straight through, so the first xAI
request would permanently strip slash-containing enum constraints and
pattern/format keywords from the per-agent tool registry.

Effect: any subsequent non-xAI call from the same agent (auxiliary task
routed to Anthropic, OpenRouter fallback, mid-session model switch) saw
the already-stripped schema with no way for the user to notice from
their config.

Fix: deepcopy tools_for_api before sanitizing at both call sites.

The slash-enum bug itself (xAI 400ing on enums with '/') was fixed
earlier by #32443 (Nami4D) — that PR landed the strip but used the
sanitizers directly without copying. This salvages #27907's correctness
contribution (the deepcopy) while skipping its redundant parallel
sanitizer (strip_xai_incompatible_enum_values is functionally
equivalent to the existing strip_slash_enum) and its preflight-
neutrality argument (we chose model-gated preflight in #32443).

3 new tests in tests/run_agent/test_run_agent_codex_responses.py:

- strips_slash_enum_from_outgoing_request — outgoing kwargs has no
  slash-containing enum values (functional contract preserved).
- does_not_mutate_agent_tools — headline #27907 regression. Snapshot
  agent.tools before build_api_kwargs, assert it survives intact
  after. Pre-fix this assertion would have caught the mutation.
- is_idempotent_across_repeated_calls — three xAI requests in a row
  each strip cleanly AND don't progressively erode the source schema.

344/344 across tests/agent/test_auxiliary_client.py,
tests/agent/transports/test_codex_transport.py,
tests/run_agent/test_run_agent_codex_responses.py, and
tests/tools/test_schema_sanitizer.py.

Co-authored-by: Gabor Barany <barany.gabor@gmail.com>

scripts/release.py

@@ -263,6 +263,7 @@ AUTHOR_MAP = {
     "harryykyle1@gmail.com": "hharry11",
     "wysie@users.noreply.github.com": "wysie",
     "ronhi@buildabear1.localdomain": "RonHillDev",  # PR #29523 salvage (machine-local commit email)
+    "barany.gabor@gmail.com": "gbarany",  # PR #27907 salvage (xAI sanitizer deepcopy)
     "hello@nami4d.tech": "Nami4D",  # PR #28490 salvage
     "jkausel@gmail.com": "jkausel-ai",
     "e.silacandmr@gmail.com": "Es1la",