feat(providers): add Claude Opus 4.8 model support

Register `claude-opus-4-8` in the Anthropic capability table. Opus 4.8
shares Opus 4.7's request/response surface exactly — adaptive-thinking
only (`budget_tokens` rejected), sampling params removed, the
low/medium/high/xhigh/max effort levels, `thinking.display` defaulting to
omitted, 1M context, and 128K output — so the entry is a verbatim copy of
the 4.7 row. `_lookup_capabilities` longest-prefix matching then resolves
date-suffixed ids (e.g. `claude-opus-4-8-20260601`) without colliding
with the 4.7 key.

No provider code paths change: the existing 4.7 handling already covers
all of 4.8's behavior. Models are selected via config.toml / the admin
ConfigStore UI, so there is no catalog or dropdown to update.

- _anthropic.py: new claude-opus-4-8 capability entry + effort comment
- tests/test_providers.py: opus 4.8 bare + dated capability tests
- turnstone.example.toml: bump the showcased model example to 4.8

tests/test_providers.py

@@ -1265,6 +1265,33 @@ class TestAnthropicHelpers:
         assert caps.token_param == "max_tokens"
         assert caps.thinking_mode == "adaptive"
 
+    def test_capabilities_opus_4_8(self) -> None:
+        from turnstone.core.providers._anthropic import AnthropicProvider
+
+        provider = AnthropicProvider()
+        caps = provider.get_capabilities("claude-opus-4-8")
+        assert caps.context_window == 1000000
+        assert caps.max_output_tokens == 128000
+        assert caps.thinking_mode == "adaptive"
+        assert caps.supports_effort is True
+        assert "xhigh" in caps.effort_levels
+        assert "max" in caps.effort_levels
+        assert caps.supports_temperature is False
+        assert caps.thinking_display == "summarized"
+        assert caps.supports_web_search is True
+        assert caps.supports_tool_search is True
+        assert caps.supports_vision is True
+        assert caps.supports_reasoning_replay is True
+
+    def test_capabilities_opus_4_8_dated(self) -> None:
+        from turnstone.core.providers._anthropic import AnthropicProvider
+
+        provider = AnthropicProvider()
+        caps = provider.get_capabilities("claude-opus-4-8-20260601")
+        assert caps.context_window == 1000000
+        assert caps.supports_temperature is False
+        assert caps.thinking_display == "summarized"
+
     def test_capabilities_opus_4_7(self) -> None:
         from turnstone.core.providers._anthropic import AnthropicProvider
 

turnstone.example.toml

@@ -54,7 +54,7 @@
 # supports_web_search = false
 #
 # [models.claude]
-# name = "claude-opus-4-7"
+# name = "claude-opus-4-8"
 # provider = "anthropic"
 
 # --- Database (turnstone, node, console) ---

turnstone/core/providers/_anthropic.py

@@ -85,6 +85,20 @@ _ANTHROPIC_DEFAULT = ModelCapabilities(
 )
 
 _ANTHROPIC_CAPABILITIES: dict[str, ModelCapabilities] = {
+    "claude-opus-4-8": ModelCapabilities(
+        context_window=1000000,
+        max_output_tokens=128000,
+        token_param="max_tokens",
+        thinking_mode="adaptive",
+        supports_effort=True,
+        effort_levels=("low", "medium", "high", "xhigh", "max"),
+        supports_web_search=True,
+        supports_tool_search=True,
+        supports_vision=True,
+        supports_temperature=False,
+        thinking_display="summarized",
+        supports_reasoning_replay=True,
+    ),
     "claude-opus-4-7": ModelCapabilities(
         context_window=1000000,
         max_output_tokens=128000,
@@ -311,7 +325,7 @@ class AnthropicProvider:
             kwargs["tools"] = anthropic_tools
         kwargs.update(thinking_params)
 
-        # Effort param for models that support it (Opus 4.7, Opus 4.6, Sonnet 4.6, Opus 4.5)
+        # Effort param for models that support it (Opus 4.8, Opus 4.7, Opus 4.6, Sonnet 4.6, Opus 4.5)
         if caps.supports_effort and reasoning_effort:
             effort = _map_reasoning_to_effort(reasoning_effort, caps.effort_levels)
             if effort: