refactor(ai_client): obliterate 5 legacy model-list wrappers (Phase 4)

Phase 4 (5 of 9 cruft sites obliterated):

OBLITERATED wrappers:
1. _reread_file_items (4 callers in _send_gemini + _send_gemini_cli + 2 others)
2. _list_anthropic_models (1 caller in list_models)
3. _list_gemini_models (1 caller in list_models)
4. _extract_gemini_thoughts (1 caller in _send_gemini)
5. _list_minimax_models (2 callers in _set_minimax_provider_result + set_provider)

Migration: each caller now uses the _result sibling directly with .ok check
+ .data extraction. The Result[T] error context (structured ErrorInfo) is now
propagated instead of dropped. _send_gemini gets .data with explicit .ok check.

Updated tests to assert OBLITERATED state (5 sub-track 5 tests inverted from
'_legacy_preserved' to '_legacy_obliterated'):
- tests/test_baseline_result.py: test_phase9_redo_modules_import_cleanly
- tests/tier2/phase10_invariant_test.py: _list_gemini_models removed from list
- tests/tier2/phase10_site1_test.py: _legacy_unchanged -> _legacy_obliterated
- tests/tier2/phase11_invariant_test.py: _extract/_list_minimax moved to obliterated
- tests/tier2/phase11_sites78_test.py: _legacy_preserved -> _legacy_obliterated
- tests/tier2/phase12_invariant_test.py: _list_anthropic moved to obliterated
- tests/tier2/phase12_site4_test.py: _legacy_preserved -> _legacy_obliterated
- tests/test_gemini_thinking_format.py: helper uses _result directly
- tests/test_cruft_removal.py: 5 new obliterated-wrappers invariant tests

Test result: 122/122 pass (31 baseline + 16 heuristic + 9 cruft + 5 thinking + 61 tier2).
Audit gate: src/ai_client.py --strict exits 0 (no new violations introduced).
Wrapper count: 9 -> 3 (Phase 5-6 remaining: rag_engine 1, gui_2 2).

tests/test_gemini_thinking_format.py

@@ -9,10 +9,18 @@ ThinkingSegment.
 from unittest.mock import MagicMock, patch
 from google.genai.types import Part, Content, Candidate, GenerateContentResponse
 
-from src.ai_client import _extract_gemini_thoughts
+from src.ai_client import _extract_gemini_thoughts_result
 from src.thinking_parser import parse_thinking_trace
 
 
+def _call(resp):
+    """Migration helper: _extract_gemini_thoughts wrapper was OBLITERATED (cruft-removal Phase 4).
+    Call _extract_gemini_thoughts_result(...).data directly; on failure return empty string.
+    """
+    result = _extract_gemini_thoughts_result(resp)
+    return result.data if result.ok else ""
+
+
 def test_extract_gemini_thoughts_returns_thinking_only() -> None:
  """The helper must return concatenated thought=True parts and ignore thought=False parts."""
  resp = GenerateContentResponse(
@@ -23,7 +31,7 @@ def test_extract_gemini_thoughts_returns_thinking_only() -> None:
    Part(text="visible text 2"),
   ]))]
  )
- thoughts = _extract_gemini_thoughts(resp)
+ thoughts = _call(resp)
  assert thoughts == "step 1 reasoningstep 2 reasoning"
 
 
@@ -32,7 +40,7 @@ def test_extract_gemini_thoughts_returns_empty_when_no_thoughts() -> None:
  resp = GenerateContentResponse(
   candidates=[Candidate(content=Content(parts=[Part(text="just visible")]))]
  )
- assert _extract_gemini_thoughts(resp) == ""
+ assert _call(resp) == ""
 
 
 def test_extract_gemini_thoughts_handles_missing_attributes() -> None:
@@ -40,9 +48,9 @@ def test_extract_gemini_thoughts_handles_missing_attributes() -> None:
  fake = MagicMock()
  fake.candidates = [MagicMock()]
  fake.candidates[0].content.parts = [MagicMock(thought=True, text="thinking text")]
- assert _extract_gemini_thoughts(fake) == "thinking text"
+ assert _call(fake) == "thinking text"
  fake.candidates = []
- assert _extract_gemini_thoughts(fake) == ""
+ assert _call(fake) == ""
 
 
 def test_gemini_thinking_segment_extractable_after_wrap() -> None:
@@ -53,7 +61,7 @@ def test_gemini_thinking_segment_extractable_after_wrap() -> None:
    Part(text="final answer"),
   ]))]
  )
- thoughts = _extract_gemini_thoughts(resp)
+ thoughts = _call(resp)
  wrapped = f"<thinking>\n{thoughts}\n</thinking>\n\nfinal answer"
  segments, response = parse_thinking_trace(wrapped)
  assert len(segments) == 1
@@ -64,7 +72,7 @@ def test_gemini_thinking_segment_extractable_after_wrap() -> None:
 
 def test_extract_gemini_thoughts_handles_none_resp() -> None:
  """Defensive: must not crash on None response."""
- assert _extract_gemini_thoughts(None) == ""
+ assert _call(None) == ""
 
 
 if __name__ == "__main__":