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feat(meai): map mid-conversation system messages for Opus 4.8
The MEAI IChatClient mapping previously hoisted every ChatRole.System message into the top-level `system` property regardless of position, so the Opus 4.8 mid-conversation system message feature was unreachable. A ChatRole.System message is now emitted as a `{"role":"system"}` message at its position when the placement is valid (immediately follows a user turn and either ends the array or precedes an assistant turn) and the resolved model supports it (claude-opus-4-8). Leading system messages, invalid positions, and unsupported models fall back to the top-level `system` property, preserving prior behavior. Consecutive system messages are merged into one, per the API constraint. Applied to both the stable and beta IChatClient mappings, with shared tests covering valid placement, mid-list placement, hoist on unsupported model, hoist after an assistant turn, consecutive-merge, leading-only, and cache control. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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‎src/Anthropic.Tests/AnthropicClientExtensionsTestsBase.cs‎

Lines changed: 386 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2060,6 +2060,392 @@ public async Task GetResponseAsync_WithMultipleSystemMessages()
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Assert.NotNull(response);
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}
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[Fact]
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public async Task GetResponseAsync_MidConversationSystemMessage_TrailingAfterUser_OnOpus48()
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{
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VerbatimHttpHandler handler = new(
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expectedRequest: """
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{
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"model": "claude-opus-4-8",
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"messages": [
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Review the process function." }]
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},
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{
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"role": "assistant",
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"content": [{ "type": "text", "text": "Looks fine for small inputs." }]
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},
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Now review the caller." }]
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},
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{
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"role": "system",
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"content": [{ "type": "text", "text": "From now on, require type annotations." }]
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}
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],
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"max_tokens": 1024,
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"system": [{ "type": "text", "text": "You are a code reviewer." }]
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}
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""",
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actualResponse: """
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{
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"id": "msg_mid_conv_01",
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"type": "message",
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"role": "assistant",
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"model": "claude-opus-4-8",
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"content": [{ "type": "text", "text": "Reviewing..." }],
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"stop_reason": "end_turn",
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"usage": { "input_tokens": 30, "output_tokens": 10 }
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}
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"""
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);
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IChatClient chatClient = CreateChatClient(handler, "claude-opus-4-8");
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List<ChatMessage> messages =
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[
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new(ChatRole.System, "You are a code reviewer."),
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new(ChatRole.User, "Review the process function."),
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new(ChatRole.Assistant, "Looks fine for small inputs."),
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new(ChatRole.User, "Now review the caller."),
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new(ChatRole.System, "From now on, require type annotations."),
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];
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ChatResponse response = await chatClient.GetResponseAsync(
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messages,
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new(),
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TestContext.Current.CancellationToken
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);
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Assert.NotNull(response);
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}
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[Fact]
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public async Task GetResponseAsync_MidConversationSystemMessage_BetweenUserAndAssistant_OnOpus48()
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{
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VerbatimHttpHandler handler = new(
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expectedRequest: """
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{
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"model": "claude-opus-4-8",
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"messages": [
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Review this." }]
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},
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{
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"role": "system",
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"content": [{ "type": "text", "text": "Be concise." }]
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},
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{
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"role": "assistant",
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"content": [{ "type": "text", "text": "Looks good." }]
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}
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],
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"max_tokens": 1024
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}
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""",
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actualResponse: """
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{
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"id": "msg_mid_conv_02",
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"type": "message",
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"role": "assistant",
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"model": "claude-opus-4-8",
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"content": [{ "type": "text", "text": "Done." }],
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"stop_reason": "end_turn",
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"usage": { "input_tokens": 15, "output_tokens": 5 }
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}
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"""
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);
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IChatClient chatClient = CreateChatClient(handler, "claude-opus-4-8");
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List<ChatMessage> messages =
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[
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new(ChatRole.User, "Review this."),
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new(ChatRole.System, "Be concise."),
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new(ChatRole.Assistant, "Looks good."),
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];
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ChatResponse response = await chatClient.GetResponseAsync(
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messages,
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new(),
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TestContext.Current.CancellationToken
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);
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Assert.NotNull(response);
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}
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[Fact]
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public async Task GetResponseAsync_MidConversationSystemMessage_OnUnsupportedModel_HoistsToTopLevel()
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{
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VerbatimHttpHandler handler = new(
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expectedRequest: """
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{
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"model": "claude-haiku-4-5",
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"messages": [
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Review the process function." }]
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},
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{
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"role": "assistant",
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"content": [{ "type": "text", "text": "Looks fine for small inputs." }]
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},
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Now review the caller." }]
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}
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],
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"max_tokens": 1024,
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"system": [
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{ "type": "text", "text": "You are a code reviewer." },
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{ "type": "text", "text": "From now on, require type annotations." }
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]
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}
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""",
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actualResponse: """
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{
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"id": "msg_mid_conv_03",
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"type": "message",
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"role": "assistant",
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"model": "claude-haiku-4-5",
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"content": [{ "type": "text", "text": "Reviewing..." }],
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"stop_reason": "end_turn",
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"usage": { "input_tokens": 30, "output_tokens": 10 }
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}
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"""
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);
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IChatClient chatClient = CreateChatClient(handler, "claude-haiku-4-5");
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List<ChatMessage> messages =
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[
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new(ChatRole.System, "You are a code reviewer."),
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new(ChatRole.User, "Review the process function."),
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new(ChatRole.Assistant, "Looks fine for small inputs."),
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new(ChatRole.User, "Now review the caller."),
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new(ChatRole.System, "From now on, require type annotations."),
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];
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ChatResponse response = await chatClient.GetResponseAsync(
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messages,
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new(),
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TestContext.Current.CancellationToken
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);
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Assert.NotNull(response);
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}
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[Fact]
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public async Task GetResponseAsync_SystemMessageAfterAssistant_OnOpus48_IsHoisted()
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{
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// A system message that follows an assistant turn is an invalid mid-conversation
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// position, so it is hoisted to the top-level `system` property even on Opus 4.8.
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VerbatimHttpHandler handler = new(
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expectedRequest: """
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{
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"model": "claude-opus-4-8",
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"messages": [
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Hello" }]
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},
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{
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"role": "assistant",
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"content": [{ "type": "text", "text": "Hi!" }]
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},
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Tell me about AI" }]
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}
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],
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"max_tokens": 1024,
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"system": [{ "type": "text", "text": "Be concise." }]
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}
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""",
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actualResponse: """
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{
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"id": "msg_mid_conv_04",
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"type": "message",
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"role": "assistant",
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"model": "claude-opus-4-8",
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"content": [{ "type": "text", "text": "AI is..." }],
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"stop_reason": "end_turn",
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"usage": { "input_tokens": 20, "output_tokens": 10 }
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}
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"""
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);
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IChatClient chatClient = CreateChatClient(handler, "claude-opus-4-8");
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List<ChatMessage> messages =
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[
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new(ChatRole.User, "Hello"),
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new(ChatRole.Assistant, "Hi!"),
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new(ChatRole.System, "Be concise."),
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new(ChatRole.User, "Tell me about AI"),
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];
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ChatResponse response = await chatClient.GetResponseAsync(
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messages,
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new(),
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TestContext.Current.CancellationToken
2292+
);
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Assert.NotNull(response);
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}
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[Fact]
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public async Task GetResponseAsync_ConsecutiveSystemMessages_AreMerged_OnOpus48()
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{
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VerbatimHttpHandler handler = new(
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expectedRequest: """
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{
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"model": "claude-opus-4-8",
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"messages": [
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{
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"role": "user",
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"content": [{ "type": "text", "text": "Hello" }]
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},
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{
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"role": "system",
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"content": [
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{ "type": "text", "text": "Rule A." },
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{ "type": "text", "text": "Rule B." }
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]
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}
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],
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"max_tokens": 1024
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}
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""",
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actualResponse: """
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{
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"id": "msg_mid_conv_05",
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"type": "message",
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"role": "assistant",
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"model": "claude-opus-4-8",
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"content": [{ "type": "text", "text": "Understood." }],
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"stop_reason": "end_turn",
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"usage": { "input_tokens": 15, "output_tokens": 5 }
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}
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"""
2330+
);
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IChatClient chatClient = CreateChatClient(handler, "claude-opus-4-8");
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List<ChatMessage> messages =
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[
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new(ChatRole.User, "Hello"),
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new(ChatRole.System, "Rule A."),
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new(ChatRole.System, "Rule B."),
2339+
];
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2341+
ChatResponse response = await chatClient.GetResponseAsync(
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messages,
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new(),
2344+
TestContext.Current.CancellationToken
2345+
);
2346+
Assert.NotNull(response);
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}
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[Fact]
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public async Task GetResponseAsync_LeadingSystemMessage_OnOpus48_StaysTopLevel()
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{
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VerbatimHttpHandler handler = new(
2353+
expectedRequest: """
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{
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"model": "claude-opus-4-8",
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"messages": [{
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"role": "user",
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"content": [{ "type": "text", "text": "Tell me about AI" }]
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}],
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"max_tokens": 1024,
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"system": [{ "type": "text", "text": "You are helpful." }]
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}
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""",
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actualResponse: """
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{
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"id": "msg_mid_conv_06",
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"type": "message",
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"role": "assistant",
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"model": "claude-opus-4-8",
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"content": [{ "type": "text", "text": "AI is..." }],
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"stop_reason": "end_turn",
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"usage": { "input_tokens": 20, "output_tokens": 10 }
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}
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"""
2375+
);
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IChatClient chatClient = CreateChatClient(handler, "claude-opus-4-8");
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List<ChatMessage> messages =
2380+
[
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new(ChatRole.System, "You are helpful."),
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new(ChatRole.User, "Tell me about AI"),
2383+
];
2384+
2385+
ChatResponse response = await chatClient.GetResponseAsync(
2386+
messages,
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new(),
2388+
TestContext.Current.CancellationToken
2389+
);
2390+
Assert.NotNull(response);
2391+
}
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[Fact]
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public async Task GetResponseAsync_WithCacheControlOnMidConversationSystemMessage()
2395+
{
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VerbatimHttpHandler handler = new(
2397+
expectedRequest: """
2398+
{
2399+
"model": "claude-opus-4-8",
2400+
"messages": [
2401+
{
2402+
"role": "user",
2403+
"content": [{ "type": "text", "text": "Hello" }]
2404+
},
2405+
{
2406+
"role": "system",
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"content": [{
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"type": "text",
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"text": "Remember the rules.",
2410+
"cache_control": { "type": "ephemeral", "ttl": "1h" }
2411+
}]
2412+
}
2413+
],
2414+
"max_tokens": 1024
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}
2416+
""",
2417+
actualResponse: """
2418+
{
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"id": "msg_mid_conv_07",
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"type": "message",
2421+
"role": "assistant",
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"model": "claude-opus-4-8",
2423+
"content": [{ "type": "text", "text": "Understood." }],
2424+
"stop_reason": "end_turn",
2425+
"usage": { "input_tokens": 15, "output_tokens": 5 }
2426+
}
2427+
"""
2428+
);
2429+
2430+
IChatClient chatClient = CreateChatClient(handler, "claude-opus-4-8");
2431+
2432+
var systemContent = new TextContent("Remember the rules.").WithCacheControl(
2433+
Anthropic.Models.Messages.Ttl.Ttl1h
2434+
);
2435+
2436+
List<ChatMessage> messages =
2437+
[
2438+
new(ChatRole.User, "Hello"),
2439+
new(ChatRole.System, [systemContent]),
2440+
];
2441+
2442+
ChatResponse response = await chatClient.GetResponseAsync(
2443+
messages,
2444+
cancellationToken: TestContext.Current.CancellationToken
2445+
);
2446+
Assert.NotNull(response);
2447+
}
2448+
20632449
[Fact]
20642450
public async Task GetResponseAsync_WithMixedContentTypes()
20652451
{

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