fix: omit temperature for Opus 4.7+ on native Anthropic path (#3117)

Anthropic removed the sampling parameters (temperature, top_p, top_k)
starting with Claude Opus 4.7 — sending temperature at all, even 0.0,
returns HTTP 400. _build_anthropic_payload sent it unconditionally, so
every native-Anthropic request to Opus 4.7/4.8 failed: the research probe
(ResearchHandler._probe_endpoint, temperature=0) aborted runs before they
started, and all DeepResearcher._llm calls 400'd.

Add _anthropic_rejects_temperature (version-gates opus-N-M >= (4,7)) and
omit temperature in the Anthropic builder for those models. Older Claude
models (Opus 4.6 and below, Sonnet/Haiku) keep temperature and the
existing [0,1] clamp.

The version gate is hardened against real-world model id shapes:
- a word-boundary anchor so a substring like `octopus-4-8` is not read
  as Opus and stripped of temperature;
- a 1-2 digit minor cap so a dated id such as `claude-opus-4-20250514`
  (Opus 4.0, listed in ANTHROPIC_MODELS) parses as major-only and keeps
  temperature, while dated 4.7+ snapshots still match;
- a non-string guard so a non-string model can't raise AttributeError
  (the previous builder never called .lower() on it).

Adds regression tests covering 4.7/4.8 omission, older/dated/legacy
retention, the substring overmatch, and non-string inputs.

Fixes #3065

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_llm_core_anthropic_temp_omit.py

@@ -0,0 +1,94 @@
+"""Regression guard: Opus 4.7+ rejects the temperature field entirely.
+
+Anthropic removed the sampling parameters (temperature, top_p, top_k) starting
+with Claude Opus 4.7 — sending `temperature` at all, even 0.0, returns HTTP 400.
+This broke every native-Anthropic call to Opus 4.7/4.8, including the research
+endpoint probe (temperature=0) and all DeepResearcher LLM calls, because
+_build_anthropic_payload sent `temperature` unconditionally.
+
+Earlier Claude models (Opus 4.6 and below, every Sonnet/Haiku) still accept
+temperature in [0.0, 1.0], so the omission is version-gated — the clamp-to-[0,1]
+behavior for those models (test_llm_core_anthropic_temp_clamp.py) is unchanged.
+"""
+import os
+
+os.environ.setdefault("DATABASE_URL", "sqlite:///:memory:")
+
+import pytest
+
+from src.llm_core import _anthropic_rejects_temperature, _build_anthropic_payload
+
+
+@pytest.mark.parametrize(
+    "model",
+    [
+        "claude-opus-4-7",
+        "claude-opus-4-8",
+        "claude-opus-4-8-20260101",  # tolerate a dated snapshot suffix
+        "claude-opus-4-7-20260201",  # dated 4.7 snapshot — explicit minor, still >= 4.7
+        "anthropic/claude-opus-4-7",  # tolerate a provider-prefixed id
+        "claude-opus-4-10",  # future minor still >= 4.7
+        "claude-opus-5-0",  # future major
+    ],
+)
+def test_opus_47_plus_rejects_temperature(model):
+    assert _anthropic_rejects_temperature(model) is True
+
+
+@pytest.mark.parametrize(
+    "model",
+    [
+        "claude-opus-4-6",
+        "claude-opus-4-5",
+        "claude-opus-4-1",
+        "claude-opus-4-0",
+        "claude-opus-4",  # bare major (no minor) — kept
+        "claude-opus-4-20250514",  # Opus 4.0 dated id — the date must NOT read as a 4.7+ minor
+        "claude-opus-4-1-20250805",  # Opus 4.1 dated id — explicit minor before the date
+        "claude-opus-4-6-20251201",  # dated 4.6 snapshot — older, still keeps temperature
+        "claude-sonnet-4-6",
+        "claude-3-5-sonnet",
+        "claude-3-opus-20240229",  # legacy Claude 3 Opus — no opus-N-M pattern, kept
+        "claude-haiku-4-5",
+        "claude-x",
+        "octopus-4-8",  # "opus" only as a substring of another word — must not match
+        "myproxy/octopus-4-8",  # same, behind a provider prefix
+        "",
+        None,
+    ],
+)
+def test_older_claude_models_keep_temperature(model):
+    assert _anthropic_rejects_temperature(model) is False
+
+
+@pytest.mark.parametrize("model", [123, 1.5, ["claude-opus-4-8"], {"a": 1}, object()])
+def test_non_string_model_is_handled_without_crashing(model):
+    # Defensive: the gate must not raise on a non-string model (the old builder
+    # never called .lower() on it). Truthy non-strings should classify as False.
+    assert _anthropic_rejects_temperature(model) is False
+
+
+def _payload(model, temperature=0.0):
+    return _build_anthropic_payload(
+        model, [{"role": "user", "content": "hi"}], temperature, 100
+    )
+
+
+def test_payload_omits_temperature_for_opus_47_plus():
+    # The endpoint probe sends temperature=0; on Opus 4.7+ that field must be gone.
+    payload = _payload("claude-opus-4-8", 0.0)
+    assert "temperature" not in payload
+
+
+def test_payload_keeps_temperature_for_older_models():
+    payload = _payload("claude-opus-4-6", 0.3)
+    assert payload["temperature"] == 0.3
+    # Older models retain the [0,1] clamp (Nietzsche preset at 1.2 -> 1.0).
+    assert _payload("claude-3-5-sonnet", 1.2)["temperature"] == 1.0
+
+
+def test_payload_keeps_temperature_for_dated_opus_4_0():
+    # Anthropic's dated id for Opus 4.0 (claude-opus-4-20250514) is in this repo's
+    # ANTHROPIC_MODELS list. The date must not be misread as a >= 4.7 minor, or the
+    # user's temperature would be silently dropped on a model that accepts it.
+    assert _payload("claude-opus-4-20250514", 0.5)["temperature"] == 0.5