diff --git a/coderd/chatd/integration_test.go b/coderd/chatd/integration_test.go
new file mode 100644
index 0000000000..be65ded0f9
--- /dev/null
+++ b/coderd/chatd/integration_test.go
@@ -0,0 +1,278 @@
+package chatd_test
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/coderd/coderdtest"
+	"github.com/coder/coder/v2/coderd/util/ptr"
+	"github.com/coder/coder/v2/codersdk"
+	"github.com/coder/coder/v2/testutil"
+)
+
+// TestAnthropicWebSearchRoundTrip is an integration test that verifies
+// provider-executed tool results (web_search) survive the full
+// persist → reconstruct → re-send cycle. It sends a query that
+// triggers Anthropic's web_search server tool, waits for completion,
+// then sends a follow-up message. If the PE tool result was lost or
+// corrupted during persistence, Anthropic rejects the second request:
+//
+//	web_search tool use with id srvtoolu_... was found without a
+//	corresponding web_search_tool_result block
+//
+// The test requires ANTHROPIC_API_KEY to be set.
+func TestAnthropicWebSearchRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	apiKey := os.Getenv("ANTHROPIC_API_KEY")
+	if apiKey == "" {
+		t.Skip("ANTHROPIC_API_KEY not set; skipping Anthropic integration test")
+	}
+	baseURL := os.Getenv("ANTHROPIC_BASE_URL")
+
+	ctx := testutil.Context(t, testutil.WaitSuperLong)
+
+	// Stand up a full coderd with the agents experiment.
+	deploymentValues := coderdtest.DeploymentValues(t)
+	deploymentValues.Experiments = []string{string(codersdk.ExperimentAgents)}
+	client := coderdtest.New(t, &coderdtest.Options{
+		DeploymentValues: deploymentValues,
+	})
+	_ = coderdtest.CreateFirstUser(t, client)
+
+	// Configure an Anthropic provider with the real API key.
+	_, err := client.CreateChatProvider(ctx, codersdk.CreateChatProviderConfigRequest{
+		Provider: "anthropic",
+		APIKey:   apiKey,
+		BaseURL:  baseURL,
+	})
+	require.NoError(t, err)
+
+	// Create a model config that enables web_search.
+	contextLimit := int64(200000)
+	isDefault := true
+	_, err = client.CreateChatModelConfig(ctx, codersdk.CreateChatModelConfigRequest{
+		Provider:     "anthropic",
+		Model:        "claude-sonnet-4-20250514",
+		ContextLimit: &contextLimit,
+		IsDefault:    &isDefault,
+		ModelConfig: &codersdk.ChatModelCallConfig{
+			ProviderOptions: &codersdk.ChatModelProviderOptions{
+				Anthropic: &codersdk.ChatModelAnthropicProviderOptions{
+					WebSearchEnabled: ptr.Ref(true),
+				},
+			},
+		},
+	})
+	require.NoError(t, err)
+
+	// --- Step 1: Send a message that triggers web_search ---
+	t.Log("Creating chat with web search query...")
+	chat, err := client.CreateChat(ctx, codersdk.CreateChatRequest{
+		Content: []codersdk.ChatInputPart{
+			{
+				Type: codersdk.ChatInputPartTypeText,
+				Text: "What is the current weather in San Francisco right now? Use web search to find out.",
+			},
+		},
+	})
+	require.NoError(t, err)
+	t.Logf("Chat created: %s (status=%s)", chat.ID, chat.Status)
+
+	// Stream events until the chat reaches a terminal status.
+	events, closer, err := client.StreamChat(ctx, chat.ID, nil)
+	require.NoError(t, err)
+	defer closer.Close()
+
+	waitForChatDone(ctx, t, events, "step 1")
+
+	// Verify the chat completed and messages were persisted.
+	chatData, err := client.GetChat(ctx, chat.ID)
+	require.NoError(t, err)
+	t.Logf("Chat status after step 1: %s, messages: %d",
+		chatData.Chat.Status, len(chatData.Messages))
+	logMessages(t, chatData.Messages)
+
+	require.Equal(t, codersdk.ChatStatusWaiting, chatData.Chat.Status,
+		"chat should be in waiting status after step 1")
+
+	// Find the first assistant message and verify it has the
+	// content parts the UI needs to render web search results:
+	// tool-call(PE), source, tool-result(PE), and text.
+	assistantMsg := findAssistantWithText(t, chatData.Messages)
+	require.NotNil(t, assistantMsg,
+		"expected an assistant message with text content after step 1")
+
+	partTypes := partTypeSet(assistantMsg.Content)
+	require.Contains(t, partTypes, codersdk.ChatMessagePartTypeToolCall,
+		"assistant message should contain a PE tool-call part")
+	require.Contains(t, partTypes, codersdk.ChatMessagePartTypeSource,
+		"assistant message should contain source parts for UI citations")
+	require.Contains(t, partTypes, codersdk.ChatMessagePartTypeToolResult,
+		"assistant message should contain a PE tool-result part")
+	require.Contains(t, partTypes, codersdk.ChatMessagePartTypeText,
+		"assistant message should contain a text part")
+
+	// Verify the PE tool-call is marked as provider-executed.
+	for _, part := range assistantMsg.Content {
+		if part.Type == codersdk.ChatMessagePartTypeToolCall {
+			require.True(t, part.ProviderExecuted,
+				"web_search tool-call should be provider-executed")
+			break
+		}
+	}
+
+	// --- Step 2: Send a follow-up message ---
+	// This is the critical test: if PE tool results were lost during
+	// persistence, the reconstructed conversation will be rejected
+	// by Anthropic because server_tool_use has no matching
+	// web_search_tool_result.
+	t.Log("Sending follow-up message...")
+	_, err = client.CreateChatMessage(ctx, chat.ID,
+		codersdk.CreateChatMessageRequest{
+			Content: []codersdk.ChatInputPart{
+				{
+					Type: codersdk.ChatInputPartTypeText,
+					Text: "Thanks! What about New York?",
+				},
+			},
+		})
+	require.NoError(t, err)
+
+	// Stream the follow-up response.
+	events2, closer2, err := client.StreamChat(ctx, chat.ID, nil)
+	require.NoError(t, err)
+	defer closer2.Close()
+
+	waitForChatDone(ctx, t, events2, "step 2")
+
+	// Verify the follow-up completed and produced content.
+	chatData2, err := client.GetChat(ctx, chat.ID)
+	require.NoError(t, err)
+	t.Logf("Chat status after step 2: %s, messages: %d",
+		chatData2.Chat.Status, len(chatData2.Messages))
+	logMessages(t, chatData2.Messages)
+
+	require.Equal(t, codersdk.ChatStatusWaiting, chatData2.Chat.Status,
+		"chat should be in waiting status after step 2")
+	require.Greater(t, len(chatData2.Messages), len(chatData.Messages),
+		"follow-up should have added more messages")
+
+	// The last assistant message should have text.
+	lastAssistant := findLastAssistantWithText(t, chatData2.Messages)
+	require.NotNil(t, lastAssistant,
+		"expected an assistant message with text in the follow-up")
+
+	t.Log("Anthropic web_search round-trip test passed.")
+}
+
+// waitForChatDone drains the event stream until the chat reaches
+// a terminal status (waiting, completed, or error).
+func waitForChatDone(
+	ctx context.Context,
+	t *testing.T,
+	events <-chan codersdk.ChatStreamEvent,
+	label string,
+) {
+	t.Helper()
+	for {
+		select {
+		case <-ctx.Done():
+			require.FailNow(t, "timed out waiting for "+label+" completion")
+		case event, ok := <-events:
+			if !ok {
+				return
+			}
+			switch event.Type {
+			case codersdk.ChatStreamEventTypeError:
+				if event.Error != nil {
+					t.Logf("[%s] stream error: %s", label, event.Error.Message)
+				}
+			case codersdk.ChatStreamEventTypeStatus:
+				if event.Status != nil {
+					t.Logf("[%s] status → %s", label, event.Status.Status)
+					switch event.Status.Status {
+					case codersdk.ChatStatusWaiting,
+						codersdk.ChatStatusCompleted:
+						return
+					case codersdk.ChatStatusError:
+						require.FailNow(t, label+" ended with error status")
+					}
+				}
+			case codersdk.ChatStreamEventTypeMessage:
+				if event.Message != nil {
+					t.Logf("[%s] persisted message: role=%s parts=%d",
+						label, event.Message.Role, len(event.Message.Content))
+				}
+			case codersdk.ChatStreamEventTypeMessagePart:
+				// Streaming delta — just note it.
+				if event.MessagePart != nil {
+					t.Logf("[%s] part: type=%s",
+						label, event.MessagePart.Part.Type)
+				}
+			}
+		}
+	}
+}
+
+// findAssistantWithText returns the first assistant message that
+// contains a non-empty text part.
+func findAssistantWithText(t *testing.T, msgs []codersdk.ChatMessage) *codersdk.ChatMessage {
+	t.Helper()
+	for i := range msgs {
+		if msgs[i].Role != "assistant" {
+			continue
+		}
+		for _, part := range msgs[i].Content {
+			if part.Type == codersdk.ChatMessagePartTypeText && part.Text != "" {
+				return &msgs[i]
+			}
+		}
+	}
+	return nil
+}
+
+// findLastAssistantWithText returns the last assistant message that
+// contains a non-empty text part.
+func findLastAssistantWithText(t *testing.T, msgs []codersdk.ChatMessage) *codersdk.ChatMessage {
+	t.Helper()
+	for i := len(msgs) - 1; i >= 0; i-- {
+		if msgs[i].Role != "assistant" {
+			continue
+		}
+		for _, part := range msgs[i].Content {
+			if part.Type == codersdk.ChatMessagePartTypeText && part.Text != "" {
+				return &msgs[i]
+			}
+		}
+	}
+	return nil
+}
+
+// logMessages prints a summary of all messages for debugging.
+func logMessages(t *testing.T, msgs []codersdk.ChatMessage) {
+	t.Helper()
+	for i, msg := range msgs {
+		types := make([]string, 0, len(msg.Content))
+		for _, part := range msg.Content {
+			s := string(part.Type)
+			if part.ProviderExecuted {
+				s += "(PE)"
+			}
+			types = append(types, s)
+		}
+		t.Logf("  msg[%d] role=%s parts=%v", i, msg.Role, types)
+	}
+}
+
+// partTypeSet returns the set of part types present in a message.
+func partTypeSet(parts []codersdk.ChatMessagePart) map[codersdk.ChatMessagePartType]struct{} {
+	set := make(map[codersdk.ChatMessagePartType]struct{}, len(parts))
+	for _, p := range parts {
+		set[p.Type] = struct{}{}
+	}
+	return set
+}
diff --git a/go.mod b/go.mod
index fb6e0a7b88..84b1784c3b 100644
--- a/go.mod
+++ b/go.mod
@@ -76,7 +76,7 @@ replace github.com/spf13/afero => github.com/aslilac/afero v0.0.0-20250403163713
 // 1) Adds thinking effort to Anthropic provider
 // 2) Downgraded to Go 1.25 due to issue with Windows CI
 // https://github.com/kylecarbs/fantasy/compare/main...kylecarbs:fantasy:cj/go1.25
-replace charm.land/fantasy => github.com/kylecarbs/fantasy v0.0.0-20260311152049-8eff3573caec
+replace charm.land/fantasy => github.com/kylecarbs/fantasy v0.0.0-20260312154649-e4bbc7bb3054
 
 replace github.com/charmbracelet/anthropic-sdk-go => github.com/kylecarbs/anthropic-sdk-go v0.0.0-20260223140439-63879b0b8dab
 
diff --git a/go.sum b/go.sum
index 16fc5c4d77..8a82ba436b 100644
--- a/go.sum
+++ b/go.sum
@@ -797,8 +797,8 @@ github.com/kylecarbs/anthropic-sdk-go v0.0.0-20260223140439-63879b0b8dab h1:5UMY
 github.com/kylecarbs/anthropic-sdk-go v0.0.0-20260223140439-63879b0b8dab/go.mod h1:hqlYqR7uPKOKfnNeicUbZp0Ps0GeYFlKYtwh5HGDCx8=
 github.com/kylecarbs/chroma/v2 v2.0.0-20240401211003-9e036e0631f3 h1:Z9/bo5PSeMutpdiKYNt/TTSfGM1Ll0naj3QzYX9VxTc=
 github.com/kylecarbs/chroma/v2 v2.0.0-20240401211003-9e036e0631f3/go.mod h1:BUGjjsD+ndS6eX37YgTchSEG+Jg9Jv1GiZs9sqPqztk=
-github.com/kylecarbs/fantasy v0.0.0-20260311152049-8eff3573caec h1:JBaAQYkOre8gAaQZ6SKiQZ2g+em35WxzHTWtTtFDX5M=
-github.com/kylecarbs/fantasy v0.0.0-20260311152049-8eff3573caec/go.mod h1:p6cYJVG8D8AC51MgejAKCMu0myRyQ+vKLuoJQ3biaXo=
+github.com/kylecarbs/fantasy v0.0.0-20260312154649-e4bbc7bb3054 h1:PlN4sfr5xfHsw5HnHEHEu6TqMZr1icbwt1I1QeqitmI=
+github.com/kylecarbs/fantasy v0.0.0-20260312154649-e4bbc7bb3054/go.mod h1:p6cYJVG8D8AC51MgejAKCMu0myRyQ+vKLuoJQ3biaXo=
 github.com/kylecarbs/spinner v1.18.2-0.20220329160715-20702b5af89e h1:OP0ZMFeZkUnOzTFRfpuK3m7Kp4fNvC6qN+exwj7aI4M=
 github.com/kylecarbs/spinner v1.18.2-0.20220329160715-20702b5af89e/go.mod h1:mQak9GHqbspjC/5iUx3qMlIho8xBS/ppAL/hX5SmPJU=
 github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=