refactor: extract diagram tool handlers to dedicated hook

- Create useDiagramToolHandlers hook for display_diagram, edit_diagram, append_diagram
- Remove ~300 lines from chat-panel.tsx
- Remove unused stopRef
- Gate debug console.log statements with DEBUG constant

components/chat-panel.tsx

@@ -27,6 +27,7 @@ import {
     TooltipTrigger,
 } from "@/components/ui/tooltip"
 import { useDiagram } from "@/contexts/diagram-context"
+import { useDiagramToolHandlers } from "@/hooks/use-diagram-tool-handlers"
 import { useDictionary } from "@/hooks/use-dictionary"
 import { getSelectedAIConfig, useModelConfig } from "@/hooks/use-model-config"
 import { getApiEndpoint } from "@/lib/base-path"
@@ -34,8 +35,9 @@ import { findCachedResponse } from "@/lib/cached-responses"
 import { isPdfFile, isTextFile } from "@/lib/pdf-utils"
 import { type FileData, useFileProcessor } from "@/lib/use-file-processor"
 import { useQuotaManager } from "@/lib/use-quota-manager"
-import { formatXML, isMxCellXmlComplete, wrapWithMxFile } from "@/lib/utils"
+import { formatXML } from "@/lib/utils"
 import { ChatMessageDisplay } from "./chat-message-display"
+import { DevXmlSimulator } from "./dev-xml-simulator"
 
 // localStorage keys for persistence
 const STORAGE_MESSAGES_KEY = "next-ai-draw-io-messages"
@@ -76,6 +78,7 @@ interface ChatPanelProps {
 const TOOL_ERROR_STATE = "output-error" as const
 const DEBUG = process.env.NODE_ENV === "development"
 const MAX_AUTO_RETRY_COUNT = 1
+
 const MAX_CONTINUATION_RETRY_COUNT = 2 // Limit for truncation continuation retries
 
 /**
@@ -212,9 +215,6 @@ export default function ChatPanel({
         chartXMLRef.current = chartXML
     }, [chartXML])
 
-    // Ref to hold stop function for use in onToolCall (avoids stale closure)
-    const stopRef = useRef<(() => void) | null>(null)
-
     // Ref to track consecutive auto-retry count (reset on user action)
     const autoRetryCountRef = useRef(0)
     // Ref to track continuation retry count (for truncation handling)
@@ -237,6 +237,16 @@ export default function ChatPanel({
     > | null>(null)
     const LOCAL_STORAGE_DEBOUNCE_MS = 1000 // Save at most once per second
 
+    // Diagram tool handlers (display_diagram, edit_diagram, append_diagram)
+    const { handleToolCall } = useDiagramToolHandlers({
+        partialXmlRef,
+        editDiagramOriginalXmlRef,
+        chartXMLRef,
+        onDisplayChart,
+        onFetchChart,
+        onExport,
+    })
+
     const {
         messages,
         sendMessage,
@@ -249,311 +259,8 @@ export default function ChatPanel({
         transport: new DefaultChatTransport({
             api: getApiEndpoint("/api/chat"),
         }),
-        async onToolCall({ toolCall }) {
-            if (DEBUG) {
-                console.log(
-                    `[onToolCall] Tool: ${toolCall.toolName}, CallId: ${toolCall.toolCallId}`,
-                )
-            }
-
-            if (toolCall.toolName === "display_diagram") {
-                const { xml } = toolCall.input as { xml: string }
-
-                // DEBUG: Log raw input to diagnose false truncation detection
-                console.log(
-                    "[display_diagram] XML ending (last 100 chars):",
-                    xml.slice(-100),
-                )
-                console.log("[display_diagram] XML length:", xml.length)
-
-                // Check if XML is truncated (incomplete mxCell indicates truncated output)
-                const isTruncated = !isMxCellXmlComplete(xml)
-                console.log("[display_diagram] isTruncated:", isTruncated)
-
-                if (isTruncated) {
-                    // Store the partial XML for continuation via append_diagram
-                    partialXmlRef.current = xml
-
-                    // Tell LLM to use append_diagram to continue
-                    const partialEnding = partialXmlRef.current.slice(-500)
-                    addToolOutput({
-                        tool: "display_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        state: "output-error",
-                        errorText: `Output was truncated due to length limits. Use the append_diagram tool to continue.
-
-Your output ended with:
-\`\`\`
-${partialEnding}
-\`\`\`
-
-NEXT STEP: Call append_diagram with the continuation XML.
-- Do NOT include wrapper tags or root cells (id="0", id="1")
-- Start from EXACTLY where you stopped
-- Complete all remaining mxCell elements`,
-                    })
-                    return
-                }
-
-                // Complete XML received - use it directly
-                // (continuation is now handled via append_diagram tool)
-                const finalXml = xml
-                partialXmlRef.current = "" // Reset any partial from previous truncation
-
-                // Wrap raw XML with full mxfile structure for draw.io
-                const fullXml = wrapWithMxFile(finalXml)
-
-                // loadDiagram validates and returns error if invalid
-                const validationError = onDisplayChart(fullXml)
-
-                if (validationError) {
-                    console.warn(
-                        "[display_diagram] Validation error:",
-                        validationError,
-                    )
-                    // Return error to model - sendAutomaticallyWhen will trigger retry
-                    if (DEBUG) {
-                        console.log(
-                            "[display_diagram] Adding tool output with state: output-error",
-                        )
-                    }
-                    addToolOutput({
-                        tool: "display_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        state: "output-error",
-                        errorText: `${validationError}
-
-Please fix the XML issues and call display_diagram again with corrected XML.
-
-Your failed XML:
-\`\`\`xml
-${finalXml}
-\`\`\``,
-                    })
-                } else {
-                    // Success - diagram will be rendered by chat-message-display
-                    if (DEBUG) {
-                        console.log(
-                            "[display_diagram] Success! Adding tool output with state: output-available",
-                        )
-                    }
-                    addToolOutput({
-                        tool: "display_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        output: "Successfully displayed the diagram.",
-                    })
-                    if (DEBUG) {
-                        console.log(
-                            "[display_diagram] Tool output added. Diagram should be visible now.",
-                        )
-                    }
-                }
-            } else if (toolCall.toolName === "edit_diagram") {
-                const { operations } = toolCall.input as {
-                    operations: Array<{
-                        type: "update" | "add" | "delete"
-                        cell_id: string
-                        new_xml?: string
-                    }>
-                }
-
-                let currentXml = ""
-                try {
-                    // Use the original XML captured during streaming (shared with chat-message-display)
-                    // This ensures we apply operations to the same base XML that streaming used
-                    const originalXml = editDiagramOriginalXmlRef.current.get(
-                        toolCall.toolCallId,
-                    )
-                    if (originalXml) {
-                        currentXml = originalXml
-                    } else {
-                        // Fallback: use chartXML from ref if streaming didn't capture original
-                        const cachedXML = chartXMLRef.current
-                        if (cachedXML) {
-                            currentXml = cachedXML
-                        } else {
-                            // Last resort: export from iframe
-                            currentXml = await onFetchChart(false)
-                        }
-                    }
-
-                    const { applyDiagramOperations } = await import(
-                        "@/lib/utils"
-                    )
-                    const { result: editedXml, errors } =
-                        applyDiagramOperations(currentXml, operations)
-
-                    // Check for operation errors
-                    if (errors.length > 0) {
-                        const errorMessages = errors
-                            .map(
-                                (e) =>
-                                    `- ${e.type} on cell_id="${e.cellId}": ${e.message}`,
-                            )
-                            .join("\n")
-
-                        addToolOutput({
-                            tool: "edit_diagram",
-                            toolCallId: toolCall.toolCallId,
-                            state: "output-error",
-                            errorText: `Some operations failed:\n${errorMessages}
-
-Current diagram XML:
-\`\`\`xml
-${currentXml}
-\`\`\`
-
-Please check the cell IDs and retry.`,
-                        })
-                        // Clean up the shared original XML ref
-                        editDiagramOriginalXmlRef.current.delete(
-                            toolCall.toolCallId,
-                        )
-                        return
-                    }
-
-                    // loadDiagram validates and returns error if invalid
-                    const validationError = onDisplayChart(editedXml)
-                    if (validationError) {
-                        console.warn(
-                            "[edit_diagram] Validation error:",
-                            validationError,
-                        )
-                        addToolOutput({
-                            tool: "edit_diagram",
-                            toolCallId: toolCall.toolCallId,
-                            state: "output-error",
-                            errorText: `Edit produced invalid XML: ${validationError}
-
-Current diagram XML:
-\`\`\`xml
-${currentXml}
-\`\`\`
-
-Please fix the operations to avoid structural issues.`,
-                        })
-                        // Clean up the shared original XML ref
-                        editDiagramOriginalXmlRef.current.delete(
-                            toolCall.toolCallId,
-                        )
-                        return
-                    }
-                    onExport()
-                    addToolOutput({
-                        tool: "edit_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        output: `Successfully applied ${operations.length} operation(s) to the diagram.`,
-                    })
-                    // Clean up the shared original XML ref
-                    editDiagramOriginalXmlRef.current.delete(
-                        toolCall.toolCallId,
-                    )
-                } catch (error) {
-                    console.error("[edit_diagram] Failed:", error)
-
-                    const errorMessage =
-                        error instanceof Error ? error.message : String(error)
-
-                    addToolOutput({
-                        tool: "edit_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        state: "output-error",
-                        errorText: `Edit failed: ${errorMessage}
-
-Current diagram XML:
-\`\`\`xml
-${currentXml || "No XML available"}
-\`\`\`
-
-Please check cell IDs and retry, or use display_diagram to regenerate.`,
-                    })
-                    // Clean up the shared original XML ref even on error
-                    editDiagramOriginalXmlRef.current.delete(
-                        toolCall.toolCallId,
-                    )
-                }
-            } else if (toolCall.toolName === "append_diagram") {
-                const { xml } = toolCall.input as { xml: string }
-
-                // Detect if LLM incorrectly started fresh instead of continuing
-                // LLM should only output bare mxCells now, so wrapper tags indicate error
-                const trimmed = xml.trim()
-                const isFreshStart =
-                    trimmed.startsWith("<mxGraphModel") ||
-                    trimmed.startsWith("<root") ||
-                    trimmed.startsWith("<mxfile") ||
-                    trimmed.startsWith('<mxCell id="0"') ||
-                    trimmed.startsWith('<mxCell id="1"')
-
-                if (isFreshStart) {
-                    addToolOutput({
-                        tool: "append_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        state: "output-error",
-                        errorText: `ERROR: You started fresh with wrapper tags. Do NOT include wrapper tags or root cells (id="0", id="1").
-
-Continue from EXACTLY where the partial ended:
-\`\`\`
-${partialXmlRef.current.slice(-500)}
-\`\`\`
-
-Start your continuation with the NEXT character after where it stopped.`,
-                    })
-                    return
-                }
-
-                // Append to accumulated XML
-                partialXmlRef.current += xml
-
-                // Check if XML is now complete (last mxCell is complete)
-                const isComplete = isMxCellXmlComplete(partialXmlRef.current)
-
-                if (isComplete) {
-                    // Wrap and display the complete diagram
-                    const finalXml = partialXmlRef.current
-                    partialXmlRef.current = "" // Reset
-
-                    const fullXml = wrapWithMxFile(finalXml)
-                    const validationError = onDisplayChart(fullXml)
-
-                    if (validationError) {
-                        addToolOutput({
-                            tool: "append_diagram",
-                            toolCallId: toolCall.toolCallId,
-                            state: "output-error",
-                            errorText: `Validation error after assembly: ${validationError}
-
-Assembled XML:
-\`\`\`xml
-${finalXml.substring(0, 2000)}...
-\`\`\`
-
-Please use display_diagram with corrected XML.`,
-                        })
-                    } else {
-                        addToolOutput({
-                            tool: "append_diagram",
-                            toolCallId: toolCall.toolCallId,
-                            output: "Diagram assembly complete and displayed successfully.",
-                        })
-                    }
-                } else {
-                    // Still incomplete - signal to continue
-                    addToolOutput({
-                        tool: "append_diagram",
-                        toolCallId: toolCall.toolCallId,
-                        state: "output-error",
-                        errorText: `XML still incomplete (mxCell not closed). Call append_diagram again to continue.
-
-Current ending:
-\`\`\`
-${partialXmlRef.current.slice(-500)}
-\`\`\`
-
-Continue from EXACTLY where you stopped.`,
-                    })
-                }
-            }
+        onToolCall: async ({ toolCall }) => {
+            await handleToolCall({ toolCall }, addToolOutput)
         },
         onError: (error) => {
             // Handle server-side quota limit (429 response)
@@ -717,9 +424,6 @@ Continue from EXACTLY where you stopped.`,
         },
     })
 
-    // Update stopRef so onToolCall can access it
-    stopRef.current = stop
-
     // Ref to track latest messages for unload persistence
     const messagesRef = useRef(messages)
     useEffect(() => {
@@ -1337,6 +1041,14 @@ Continue from EXACTLY where you stopped.`,
                 />
             </main>
 
+            {/* Dev XML Streaming Simulator - only in development */}
+            {DEBUG && (
+                <DevXmlSimulator
+                    setMessages={setMessages}
+                    onDisplayChart={onDisplayChart}
+                />
+            )}
+
             {/* Input */}
             <footer
                 className={`${isMobile ? "p-2" : "p-4"} border-t border-border/50 bg-card/50`}

components/dev-xml-simulator.tsx

@@ -0,0 +1,350 @@
+"use client"
+
+import { useEffect, useRef, useState } from "react"
+import { wrapWithMxFile } from "@/lib/utils"
+
+// Dev XML presets for streaming simulator
+const DEV_XML_PRESETS: Record<string, string> = {
+    "Simple Box": `<mxCell id="2" value="Hello World" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
+  <mxGeometry x="120" y="100" width="120" height="60" as="geometry"/>
+</mxCell>`,
+    "Two Boxes with Arrow": `<mxCell id="2" value="Start" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
+  <mxGeometry x="100" y="100" width="100" height="50" as="geometry"/>
+</mxCell>
+<mxCell id="3" value="End" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="1">
+  <mxGeometry x="300" y="100" width="100" height="50" as="geometry"/>
+</mxCell>
+<mxCell id="4" value="" style="endArrow=classic;html=1;" edge="1" parent="1" source="2" target="3">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>`,
+    Flowchart: `<mxCell id="2" value="Start" style="ellipse;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
+  <mxGeometry x="160" y="40" width="80" height="40" as="geometry"/>
+</mxCell>
+<mxCell id="3" value="Process A" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
+  <mxGeometry x="140" y="120" width="120" height="60" as="geometry"/>
+</mxCell>
+<mxCell id="4" value="Decision" style="rhombus;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="1">
+  <mxGeometry x="150" y="220" width="100" height="80" as="geometry"/>
+</mxCell>
+<mxCell id="5" value="Process B" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
+  <mxGeometry x="300" y="230" width="120" height="60" as="geometry"/>
+</mxCell>
+<mxCell id="6" value="End" style="ellipse;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="1">
+  <mxGeometry x="160" y="340" width="80" height="40" as="geometry"/>
+</mxCell>
+<mxCell id="7" style="endArrow=classic;html=1;" edge="1" parent="1" source="2" target="3">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="8" style="endArrow=classic;html=1;" edge="1" parent="1" source="3" target="4">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="9" value="Yes" style="endArrow=classic;html=1;" edge="1" parent="1" source="4" target="6">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="10" value="No" style="endArrow=classic;html=1;exitX=1;exitY=0.5;exitDx=0;exitDy=0;" edge="1" parent="1" source="4" target="5">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>`,
+    "Truncated (Error Test)": `<mxCell id="2" value="This cell is truncated" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
+  <mxGeometry x="120" y="100" width="120" height="60" as="geometry"/>
+</mxCell>
+<mxCell id="3" value="Incomplete" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor`,
+    "HTML Escape + Cell Truncate": `<mxCell id="2" value="<b>Chain-of-Thought Prompting</b><br/><font size='12'>Eliciting Reasoning in Large Language Models</font>" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;fontSize=16;fontStyle=1;" vertex="1" parent="1">
+  <mxGeometry x="40" y="40" width="720" height="60" as="geometry"/>
+</mxCell>
+<mxCell id="3" value="<b>Problem: LLM Reasoning Limitations</b><br/>• Scaling parameters alone insufficient for logical tasks<br/>• Arithmetic, commonsense, symbolic reasoning challenges<br/>• Standard prompting fails on multi-step problems" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffe6cc;strokeColor=#d79b00;" vertex="1" parent="1">
+  <mxGeometry x="40" y="120" width="340" height="120" as="geometry"/>
+</mxCell>
+<mxCell id="4" value="<b>Traditional Approaches</b><br/>1. <b>Finetuning:</b> Expensive, task-specific<br/>2. <b>Standard Few-Shot:</b> Input→Output pairs<br/>   (No explanation of reasoning)" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="1">
+  <mxGeometry x="420" y="120" width="340" height="120" as="geometry"/>
+</mxCell>
+<mxCell id="5" value="<b>CoT Methodology</b><br/>• Add reasoning steps to few-shot examples<br/>• Natural language intermediate steps<br/>• No parameter updates needed<br/>• Model learns to generate own thought process" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
+  <mxGeometry x="40" y="260" width="340" height="100" as="geometry"/>
+</mxCell>
+<mxCell id="6" value="<b>Example Comparison</b><br/><b>Standard:</b><br/>Q: Roger has 5 balls. He buys 2 cans of 3 balls. How many?<br/>A: 11.<br/><br/><b>CoT:</b><br/>Q: Roger has 5 balls. He buys 2 cans of 3 balls. How many?<br/>A: Roger started with 5 balls. 2 cans of 3 tennis balls each is 6 tennis balls. 5 + 6 = 11. The answer is 11." style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e1d5e7;strokeColor=#9673a6;" vertex="1" parent="1">
+  <mxGeometry x="420" y="260" width="340" height="140" as="geometry"/>
+</mxCell>
+<mxCell id="7" value="<b>Experimental Models</b><br/>• GPT-3 (175B)<br/>• LaMDA (137B)<br/>• PaLM (540B)<br/>• UL2 (20B)<br/>• Codex" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="1">
+  <mxGeometry x="40" y="380" width="340" height="100" as="geometry"/>
+</mxCell>
+<mxCell id="8" value="<b>Reasoning Domains Tested</b><br/>1. <b>Arithmetic:</b> GSM8K, SVAMP, ASDiv, AQuA, MAWPS<br/>2. <b>Commonsense:</b> CSQA, StrategyQA, Date Understanding, Sports Understanding<br/>3. <b>Symbolic:</b> Last Letter Concatenation, Coin Flip" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f5f5f5;strokeColor=#666666;" vertex="1" parent="1">
+  <mxGeometry x="420" y="420" width="340" height="100" as="geometry"/>
+</mxCell>
+<mxCell id="9" value="<b>Key Results: Arithmetic</b><br/>• PaLM 540B + CoT: <b>56.9%</b> on GSM8K<br/>   (vs 17.9% standard)<br/>• Surpassed finetuned GPT-3 (55%)<br/>• With calculator: <b>58.6%</b>" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
+  <mxGeometry x="40" y="500" width="220" height="100" as="geometry"/>
+</mxCell>
+<mxCell id="10" value="<b>Key Results: Commonsense</b><br/>• StrategyQA: <b>75.6%</b><br/>   (vs 69.4% SOTA)<br/>• Sports Understanding: <b>95.4%</b><br/>   (vs 84% human)" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
+  <mxGeometry x="280" y="500" width="220" height="100" as="geometry"/>
+</mxCell>
+<mxCell id="11" value="<b>Key Results: Symbolic</b><br/>• OOD Generalization<br/>• Coin Flip: Trained on 2 flips<br/>   Works on 3-4 flips with CoT<br/>• Standard prompting fails" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
+  <mxGeometry x="540" y="500" width="220" height="100" as="geometry"/>
+</mxCell>
+<mxCell id="12" value="<b>Emergent Ability of Scale</b><br/>• Small models (&lt;10B): No benefit, often harmful<br/>• Large models (100B+): Reasoning emerges<br/>• CoT gains increase dramatically with scale" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffe6cc;strokeColor=#d79b00;" vertex="1" parent="1">
+  <mxGeometry x="40" y="620" width="340" height="80" as="geometry"/>
+</mxCell>
+<mxCell id="13" value="<b>Ablation Studies</b><br/>1. Equation only: Worse than CoT<br/>2. Variable compute (...): No improvement<br/>3. Answer first, then reasoning: Same as baseline<br/>→ Content matters, not just extra tokens" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="1">
+  <mxGeometry x="420" y="620" width="340" height="80" as="geometry"/>
+</mxCell>
+<mxCell id="14" value="<b>Error Analysis</b><br/>• Semantic understanding errors<br/>• One-step missing errors<br/>• Calculation errors<br/>• Larger models reduce semantic/missing-step errors" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="1">
+  <mxGeometry x="40" y="720" width="340" height="80" as="geometry"/>
+</mxCell>
+<mxCell id="15" value="<b>Conclusion</b><br/>• CoT unlocks reasoning potential<br/>• Simple paradigm: &quot;show your work&quot;<br/>• Emergent capability of large models<br/>• No specialized architecture needed" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
+  <mxGeometry x="420" y="720" width="340" height="80" as="geometry"/>
+</mxCell>
+<mxCell id="16" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="3" target="5">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="17" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="4" target="6">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="18" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="5" target="7">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="19" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="6" target="8">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="20" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.25;entryY=0;" edge="1" parent="1" source="7" target="9">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="21" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="7" target="10">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="22" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.75;entryY=0;" edge="1" parent="1" source="7" target="11">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="23" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="9" target="12">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="24" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="10" target="13">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="25" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="11" target="14">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="26" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="12" target="15">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="27" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="13" target="15">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>
+<mxCell id="28" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;entryX=0.5;entryY=0;" edge="1" parent="1" source="14" target="15">
+  <mxGeometry relative="1" as="geometry"/>
+</mxCell>`,
+}
+
+interface DevXmlSimulatorProps {
+    setMessages: React.Dispatch<React.SetStateAction<any[]>>
+    onDisplayChart: (xml: string) => void
+}
+
+export function DevXmlSimulator({
+    setMessages,
+    onDisplayChart,
+}: DevXmlSimulatorProps) {
+    const [devXml, setDevXml] = useState("")
+    const [isSimulating, setIsSimulating] = useState(false)
+    const [devIntervalMs, setDevIntervalMs] = useState(1)
+    const [devChunkSize, setDevChunkSize] = useState(10)
+    const devStopRef = useRef(false)
+    const devXmlInitializedRef = useRef(false)
+
+    // Restore dev XML from localStorage on mount (after hydration)
+    useEffect(() => {
+        const saved = localStorage.getItem("dev-xml-simulator")
+        if (saved) setDevXml(saved)
+        devXmlInitializedRef.current = true
+    }, [])
+
+    // Save dev XML to localStorage (only after initial load)
+    useEffect(() => {
+        if (devXmlInitializedRef.current) {
+            localStorage.setItem("dev-xml-simulator", devXml)
+        }
+    }, [devXml])
+
+    const handleDevSimulate = async () => {
+        if (!devXml.trim() || isSimulating) return
+
+        setIsSimulating(true)
+        devStopRef.current = false
+        const toolCallId = `dev-sim-${Date.now()}`
+        const xml = devXml.trim()
+
+        // Add user message and initial assistant message with empty XML
+        const userMsg = {
+            id: `user-${Date.now()}`,
+            role: "user" as const,
+            parts: [
+                {
+                    type: "text" as const,
+                    text: "[Dev] Simulating XML streaming",
+                },
+            ],
+        }
+        const assistantMsg = {
+            id: `assistant-${Date.now()}`,
+            role: "assistant" as const,
+            parts: [
+                {
+                    type: "tool-display_diagram" as const,
+                    toolCallId,
+                    state: "input-streaming" as const,
+                    input: { xml: "" },
+                },
+            ],
+        }
+        setMessages((prev) => [...prev, userMsg, assistantMsg] as any)
+
+        // Stream characters progressively
+        for (let i = 0; i < xml.length; i += devChunkSize) {
+            if (devStopRef.current) {
+                setIsSimulating(false)
+                return
+            }
+
+            const chunk = xml.slice(0, i + devChunkSize)
+
+            setMessages((prev) => {
+                const updated = [...prev]
+                const lastMsg = updated[updated.length - 1] as any
+                if (lastMsg?.role === "assistant" && lastMsg.parts?.[0]) {
+                    lastMsg.parts[0].input = { xml: chunk }
+                }
+                return updated
+            })
+
+            await new Promise((r) => setTimeout(r, devIntervalMs))
+        }
+
+        if (devStopRef.current) {
+            setIsSimulating(false)
+            return
+        }
+
+        // Finalize: set state to output-available
+        setMessages((prev) => {
+            const updated = [...prev]
+            const lastMsg = updated[updated.length - 1] as any
+            if (lastMsg?.role === "assistant" && lastMsg.parts?.[0]) {
+                lastMsg.parts[0].state = "output-available"
+                lastMsg.parts[0].output = "Successfully displayed the diagram."
+                lastMsg.parts[0].input = { xml }
+            }
+            return updated
+        })
+
+        // Display the final diagram
+        const fullXml = wrapWithMxFile(xml)
+        onDisplayChart(fullXml)
+
+        setIsSimulating(false)
+    }
+
+    return (
+        <div className="border-t border-dashed border-orange-500/50 px-4 py-2 bg-orange-50/50 dark:bg-orange-950/30">
+            <details>
+                <summary className="text-xs text-orange-600 dark:text-orange-400 cursor-pointer font-medium">
+                    Dev: XML Streaming Simulator
+                </summary>
+                <div className="mt-2 space-y-2">
+                    <div className="flex items-center gap-2">
+                        <label className="text-xs text-muted-foreground whitespace-nowrap">
+                            Preset:
+                        </label>
+                        <select
+                            onChange={(e) => {
+                                if (e.target.value) {
+                                    setDevXml(DEV_XML_PRESETS[e.target.value])
+                                }
+                            }}
+                            className="flex-1 text-xs p-1 border rounded bg-background"
+                            defaultValue=""
+                        >
+                            <option value="" disabled>
+                                Select a preset...
+                            </option>
+                            {Object.keys(DEV_XML_PRESETS).map((name) => (
+                                <option key={name} value={name}>
+                                    {name}
+                                </option>
+                            ))}
+                        </select>
+                        <button
+                            type="button"
+                            onClick={() => setDevXml("")}
+                            className="px-2 py-1 text-xs text-muted-foreground hover:text-foreground border rounded"
+                        >
+                            Clear
+                        </button>
+                    </div>
+                    <textarea
+                        value={devXml}
+                        onChange={(e) => setDevXml(e.target.value)}
+                        placeholder="Paste mxCell XML here or select a preset..."
+                        className="w-full h-24 text-xs font-mono p-2 border rounded bg-background"
+                    />
+                    <div className="flex items-center gap-4">
+                        <div className="flex items-center gap-2 flex-1">
+                            <label className="text-xs text-muted-foreground whitespace-nowrap">
+                                Interval:
+                            </label>
+                            <input
+                                type="range"
+                                min="1"
+                                max="200"
+                                step="1"
+                                value={devIntervalMs}
+                                onChange={(e) =>
+                                    setDevIntervalMs(Number(e.target.value))
+                                }
+                                className="flex-1 h-1 accent-orange-500"
+                            />
+                            <span className="text-xs text-muted-foreground w-12">
+                                {devIntervalMs}ms
+                            </span>
+                        </div>
+                        <div className="flex items-center gap-2">
+                            <label className="text-xs text-muted-foreground whitespace-nowrap">
+                                Chars:
+                            </label>
+                            <input
+                                type="number"
+                                min="1"
+                                max="100"
+                                value={devChunkSize}
+                                onChange={(e) =>
+                                    setDevChunkSize(
+                                        Math.max(1, Number(e.target.value)),
+                                    )
+                                }
+                                className="w-14 text-xs p-1 border rounded bg-background"
+                            />
+                        </div>
+                    </div>
+                    <div className="flex gap-2">
+                        <button
+                            type="button"
+                            onClick={handleDevSimulate}
+                            disabled={isSimulating || !devXml.trim()}
+                            className="px-3 py-1 text-xs bg-orange-500 text-white rounded hover:bg-orange-600 disabled:opacity-50 disabled:cursor-not-allowed"
+                        >
+                            {isSimulating
+                                ? "Streaming..."
+                                : `Simulate (${devChunkSize} chars/${devIntervalMs}ms)`}
+                        </button>
+                        {isSimulating && (
+                            <button
+                                type="button"
+                                onClick={() => {
+                                    devStopRef.current = true
+                                }}
+                                className="px-3 py-1 text-xs bg-red-500 text-white rounded hover:bg-red-600"
+                            >
+                                Stop
+                            </button>
+                        )}
+                    </div>
+                </div>
+            </details>
+        </div>
+    )
+}

hooks/use-diagram-tool-handlers.ts

@@ -0,0 +1,383 @@
+import type { MutableRefObject } from "react"
+import { isMxCellXmlComplete, wrapWithMxFile } from "@/lib/utils"
+
+const DEBUG = process.env.NODE_ENV === "development"
+
+interface ToolCall {
+    toolCallId: string
+    toolName: string
+    input: unknown
+}
+
+type AddToolOutputSuccess = {
+    tool: string
+    toolCallId: string
+    state?: "output-available"
+    output: string
+    errorText?: undefined
+}
+
+type AddToolOutputError = {
+    tool: string
+    toolCallId: string
+    state: "output-error"
+    output?: undefined
+    errorText: string
+}
+
+type AddToolOutputParams = AddToolOutputSuccess | AddToolOutputError
+
+type AddToolOutputFn = (params: AddToolOutputParams) => void
+
+interface DiagramOperation {
+    type: "update" | "add" | "delete"
+    cell_id: string
+    new_xml?: string
+}
+
+interface UseDiagramToolHandlersParams {
+    partialXmlRef: MutableRefObject<string>
+    editDiagramOriginalXmlRef: MutableRefObject<Map<string, string>>
+    chartXMLRef: MutableRefObject<string>
+    onDisplayChart: (xml: string, skipValidation?: boolean) => string | null
+    onFetchChart: (saveToHistory?: boolean) => Promise<string>
+    onExport: () => void
+}
+
+/**
+ * Hook that creates the onToolCall handler for diagram-related tools.
+ * Handles display_diagram, edit_diagram, and append_diagram tools.
+ *
+ * Note: addToolOutput is passed at call time (not hook init) because
+ * it comes from useChat which creates a circular dependency.
+ */
+export function useDiagramToolHandlers({
+    partialXmlRef,
+    editDiagramOriginalXmlRef,
+    chartXMLRef,
+    onDisplayChart,
+    onFetchChart,
+    onExport,
+}: UseDiagramToolHandlersParams) {
+    const handleToolCall = async (
+        { toolCall }: { toolCall: ToolCall },
+        addToolOutput: AddToolOutputFn,
+    ) => {
+        if (DEBUG) {
+            console.log(
+                `[onToolCall] Tool: ${toolCall.toolName}, CallId: ${toolCall.toolCallId}`,
+            )
+        }
+
+        if (toolCall.toolName === "display_diagram") {
+            await handleDisplayDiagram(toolCall, addToolOutput)
+        } else if (toolCall.toolName === "edit_diagram") {
+            await handleEditDiagram(toolCall, addToolOutput)
+        } else if (toolCall.toolName === "append_diagram") {
+            handleAppendDiagram(toolCall, addToolOutput)
+        }
+    }
+
+    const handleDisplayDiagram = async (
+        toolCall: ToolCall,
+        addToolOutput: AddToolOutputFn,
+    ) => {
+        const { xml } = toolCall.input as { xml: string }
+
+        // DEBUG: Log raw input to diagnose false truncation detection
+        if (DEBUG) {
+            console.log(
+                "[display_diagram] XML ending (last 100 chars):",
+                xml.slice(-100),
+            )
+            console.log("[display_diagram] XML length:", xml.length)
+        }
+
+        // Check if XML is truncated (incomplete mxCell indicates truncated output)
+        const isTruncated = !isMxCellXmlComplete(xml)
+        if (DEBUG) {
+            console.log("[display_diagram] isTruncated:", isTruncated)
+        }
+
+        if (isTruncated) {
+            // Store the partial XML for continuation via append_diagram
+            partialXmlRef.current = xml
+
+            // Tell LLM to use append_diagram to continue
+            const partialEnding = partialXmlRef.current.slice(-500)
+            addToolOutput({
+                tool: "display_diagram",
+                toolCallId: toolCall.toolCallId,
+                state: "output-error",
+                errorText: `Output was truncated due to length limits. Use the append_diagram tool to continue.
+
+Your output ended with:
+\`\`\`
+${partialEnding}
+\`\`\`
+
+NEXT STEP: Call append_diagram with the continuation XML.
+- Do NOT include wrapper tags or root cells (id="0", id="1")
+- Start from EXACTLY where you stopped
+- Complete all remaining mxCell elements`,
+            })
+            return
+        }
+
+        // Complete XML received - use it directly
+        // (continuation is now handled via append_diagram tool)
+        const finalXml = xml
+        partialXmlRef.current = "" // Reset any partial from previous truncation
+
+        // Wrap raw XML with full mxfile structure for draw.io
+        const fullXml = wrapWithMxFile(finalXml)
+
+        // loadDiagram validates and returns error if invalid
+        const validationError = onDisplayChart(fullXml)
+
+        if (validationError) {
+            console.warn("[display_diagram] Validation error:", validationError)
+            // Return error to model - sendAutomaticallyWhen will trigger retry
+            if (DEBUG) {
+                console.log(
+                    "[display_diagram] Adding tool output with state: output-error",
+                )
+            }
+            addToolOutput({
+                tool: "display_diagram",
+                toolCallId: toolCall.toolCallId,
+                state: "output-error",
+                errorText: `${validationError}
+
+Please fix the XML issues and call display_diagram again with corrected XML.
+
+Your failed XML:
+\`\`\`xml
+${finalXml}
+\`\`\``,
+            })
+        } else {
+            // Success - diagram will be rendered by chat-message-display
+            if (DEBUG) {
+                console.log(
+                    "[display_diagram] Success! Adding tool output with state: output-available",
+                )
+            }
+            addToolOutput({
+                tool: "display_diagram",
+                toolCallId: toolCall.toolCallId,
+                output: "Successfully displayed the diagram.",
+            })
+            if (DEBUG) {
+                console.log(
+                    "[display_diagram] Tool output added. Diagram should be visible now.",
+                )
+            }
+        }
+    }
+
+    const handleEditDiagram = async (
+        toolCall: ToolCall,
+        addToolOutput: AddToolOutputFn,
+    ) => {
+        const { operations } = toolCall.input as {
+            operations: DiagramOperation[]
+        }
+
+        let currentXml = ""
+        try {
+            // Use the original XML captured during streaming (shared with chat-message-display)
+            // This ensures we apply operations to the same base XML that streaming used
+            const originalXml = editDiagramOriginalXmlRef.current.get(
+                toolCall.toolCallId,
+            )
+            if (originalXml) {
+                currentXml = originalXml
+            } else {
+                // Fallback: use chartXML from ref if streaming didn't capture original
+                const cachedXML = chartXMLRef.current
+                if (cachedXML) {
+                    currentXml = cachedXML
+                } else {
+                    // Last resort: export from iframe
+                    currentXml = await onFetchChart(false)
+                }
+            }
+
+            const { applyDiagramOperations } = await import("@/lib/utils")
+            const { result: editedXml, errors } = applyDiagramOperations(
+                currentXml,
+                operations,
+            )
+
+            // Check for operation errors
+            if (errors.length > 0) {
+                const errorMessages = errors
+                    .map(
+                        (e) =>
+                            `- ${e.type} on cell_id="${e.cellId}": ${e.message}`,
+                    )
+                    .join("\n")
+
+                addToolOutput({
+                    tool: "edit_diagram",
+                    toolCallId: toolCall.toolCallId,
+                    state: "output-error",
+                    errorText: `Some operations failed:\n${errorMessages}
+
+Current diagram XML:
+\`\`\`xml
+${currentXml}
+\`\`\`
+
+Please check the cell IDs and retry.`,
+                })
+                // Clean up the shared original XML ref
+                editDiagramOriginalXmlRef.current.delete(toolCall.toolCallId)
+                return
+            }
+
+            // loadDiagram validates and returns error if invalid
+            const validationError = onDisplayChart(editedXml)
+            if (validationError) {
+                console.warn(
+                    "[edit_diagram] Validation error:",
+                    validationError,
+                )
+                addToolOutput({
+                    tool: "edit_diagram",
+                    toolCallId: toolCall.toolCallId,
+                    state: "output-error",
+                    errorText: `Edit produced invalid XML: ${validationError}
+
+Current diagram XML:
+\`\`\`xml
+${currentXml}
+\`\`\`
+
+Please fix the operations to avoid structural issues.`,
+                })
+                // Clean up the shared original XML ref
+                editDiagramOriginalXmlRef.current.delete(toolCall.toolCallId)
+                return
+            }
+            onExport()
+            addToolOutput({
+                tool: "edit_diagram",
+                toolCallId: toolCall.toolCallId,
+                output: `Successfully applied ${operations.length} operation(s) to the diagram.`,
+            })
+            // Clean up the shared original XML ref
+            editDiagramOriginalXmlRef.current.delete(toolCall.toolCallId)
+        } catch (error) {
+            console.error("[edit_diagram] Failed:", error)
+
+            const errorMessage =
+                error instanceof Error ? error.message : String(error)
+
+            addToolOutput({
+                tool: "edit_diagram",
+                toolCallId: toolCall.toolCallId,
+                state: "output-error",
+                errorText: `Edit failed: ${errorMessage}
+
+Current diagram XML:
+\`\`\`xml
+${currentXml || "No XML available"}
+\`\`\`
+
+Please check cell IDs and retry, or use display_diagram to regenerate.`,
+            })
+            // Clean up the shared original XML ref even on error
+            editDiagramOriginalXmlRef.current.delete(toolCall.toolCallId)
+        }
+    }
+
+    const handleAppendDiagram = (
+        toolCall: ToolCall,
+        addToolOutput: AddToolOutputFn,
+    ) => {
+        const { xml } = toolCall.input as { xml: string }
+
+        // Detect if LLM incorrectly started fresh instead of continuing
+        // LLM should only output bare mxCells now, so wrapper tags indicate error
+        const trimmed = xml.trim()
+        const isFreshStart =
+            trimmed.startsWith("<mxGraphModel") ||
+            trimmed.startsWith("<root") ||
+            trimmed.startsWith("<mxfile") ||
+            trimmed.startsWith('<mxCell id="0"') ||
+            trimmed.startsWith('<mxCell id="1"')
+
+        if (isFreshStart) {
+            addToolOutput({
+                tool: "append_diagram",
+                toolCallId: toolCall.toolCallId,
+                state: "output-error",
+                errorText: `ERROR: You started fresh with wrapper tags. Do NOT include wrapper tags or root cells (id="0", id="1").
+
+Continue from EXACTLY where the partial ended:
+\`\`\`
+${partialXmlRef.current.slice(-500)}
+\`\`\`
+
+Start your continuation with the NEXT character after where it stopped.`,
+            })
+            return
+        }
+
+        // Append to accumulated XML
+        partialXmlRef.current += xml
+
+        // Check if XML is now complete (last mxCell is complete)
+        const isComplete = isMxCellXmlComplete(partialXmlRef.current)
+
+        if (isComplete) {
+            // Wrap and display the complete diagram
+            const finalXml = partialXmlRef.current
+            partialXmlRef.current = "" // Reset
+
+            const fullXml = wrapWithMxFile(finalXml)
+            const validationError = onDisplayChart(fullXml)
+
+            if (validationError) {
+                addToolOutput({
+                    tool: "append_diagram",
+                    toolCallId: toolCall.toolCallId,
+                    state: "output-error",
+                    errorText: `Validation error after assembly: ${validationError}
+
+Assembled XML:
+\`\`\`xml
+${finalXml.substring(0, 2000)}...
+\`\`\`
+
+Please use display_diagram with corrected XML.`,
+                })
+            } else {
+                addToolOutput({
+                    tool: "append_diagram",
+                    toolCallId: toolCall.toolCallId,
+                    output: "Diagram assembly complete and displayed successfully.",
+                })
+            }
+        } else {
+            // Still incomplete - signal to continue
+            addToolOutput({
+                tool: "append_diagram",
+                toolCallId: toolCall.toolCallId,
+                state: "output-error",
+                errorText: `XML still incomplete (mxCell not closed). Call append_diagram again to continue.
+
+Current ending:
+\`\`\`
+${partialXmlRef.current.slice(-500)}
+\`\`\`
+
+Continue from EXACTLY where you stopped.`,
+            })
+        }
+    }
+
+    return { handleToolCall }
+}

lib/utils.ts

@@ -36,29 +36,32 @@ const VALID_ENTITIES = new Set(["lt", "gt", "amp", "quot", "apos"])
 /**
  * Check if mxCell XML output is complete (not truncated).
  * Complete XML ends with a self-closing tag (/>) or closing mxCell tag.
- * Also handles function-calling wrapper tags that may be incorrectly included.
+ * Uses a robust approach that handles any LLM provider's wrapper tags
+ * by finding the last valid mxCell ending and checking if suffix is just closing tags.
  * @param xml - The XML string to check (can be undefined/null)
  * @returns true if XML appears complete, false if truncated or empty
  */
 export function isMxCellXmlComplete(xml: string | undefined | null): boolean {
-    let trimmed = xml?.trim() || ""
+    const trimmed = xml?.trim() || ""
     if (!trimmed) return false
 
-    // Strip Anthropic function-calling wrapper tags if present
-    // These can leak into tool input due to AI SDK parsing issues
-    // Use loop because tags are nested: </mxCell></mxParameter></invoke>
-    let prev = ""
-    while (prev !== trimmed) {
-        prev = trimmed
-        trimmed = trimmed
-            .replace(/<\/mxParameter>\s*$/i, "")
-            .replace(/<\/invoke>\s*$/i, "")
-            .replace(/<\/antml:parameter>\s*$/i, "")
-            .replace(/<\/antml:invoke>\s*$/i, "")
-            .trim()
-    }
+    // Find position of last complete mxCell ending (either /> or </mxCell>)
+    const lastSelfClose = trimmed.lastIndexOf("/>")
+    const lastMxCellClose = trimmed.lastIndexOf("</mxCell>")
 
-    return trimmed.endsWith("/>") || trimmed.endsWith("</mxCell>")
+    const lastValidEnd = Math.max(lastSelfClose, lastMxCellClose)
+
+    // No valid ending found at all
+    if (lastValidEnd === -1) return false
+
+    // Check what comes after the last valid ending
+    // For />: add 2 chars, for </mxCell>: add 9 chars
+    const endOffset = lastMxCellClose > lastSelfClose ? 9 : 2
+    const suffix = trimmed.slice(lastValidEnd + endOffset)
+
+    // If suffix is empty or only contains closing tags (any provider's wrapper) or whitespace, it's complete
+    // This regex matches any sequence of closing XML tags like </foo>, </bar>, </｜DSML｜xyz>
+    return /^(\s*<\/[^>]+>)*\s*$/.test(suffix)
 }
 
 /**
@@ -262,6 +265,21 @@ export function convertToLegalXml(xmlString: string): string {
             "&amp;",
         )
 
+        // Fix unescaped < and > in attribute values for XML parsing
+        // HTML content in value attributes (e.g., <b>Title</b>) needs to be escaped
+        // This is critical because DOMParser will fail on unescaped < > in attributes
+        if (/=\s*"[^"]*<[^"]*"/.test(cellContent)) {
+            cellContent = cellContent.replace(
+                /=\s*"([^"]*)"/g,
+                (_match, value) => {
+                    const escaped = value
+                        .replace(/</g, "&lt;")
+                        .replace(/>/g, "&gt;")
+                    return `="${escaped}"`
+                },
+            )
+        }
+
         // Indent each line of the matched block for readability.
         const formatted = cellContent
             .split("\n")
@@ -306,6 +324,20 @@ export function wrapWithMxFile(xml: string): string {
         content = xml.replace(/<\/?root>/g, "").trim()
     }
 
+    // Strip trailing LLM wrapper tags (from any provider: Anthropic, DeepSeek, etc.)
+    // Find the last valid mxCell ending and remove everything after it
+    const lastSelfClose = content.lastIndexOf("/>")
+    const lastMxCellClose = content.lastIndexOf("</mxCell>")
+    const lastValidEnd = Math.max(lastSelfClose, lastMxCellClose)
+    if (lastValidEnd !== -1) {
+        const endOffset = lastMxCellClose > lastSelfClose ? 9 : 2
+        const suffix = content.slice(lastValidEnd + endOffset)
+        // If suffix is only closing tags (wrapper tags), strip it
+        if (/^(\s*<\/[^>]+>)*\s*$/.test(suffix)) {
+            content = content.slice(0, lastValidEnd + endOffset)
+        }
+    }
+
     // Remove any existing root cells from content (LLM shouldn't include them, but handle it gracefully)
     // Use flexible patterns that match both self-closing (/>) and non-self-closing (></mxCell>) formats
     content = content
@@ -910,6 +942,21 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
         fixes.push("Removed CDATA wrapper")
     }
 
+    // 1b. Strip trailing LLM wrapper tags (DeepSeek, Anthropic, etc.)
+    // These are closing tags after the last valid mxCell that break XML parsing
+    const lastSelfClose = fixed.lastIndexOf("/>")
+    const lastMxCellClose = fixed.lastIndexOf("</mxCell>")
+    const lastValidEnd = Math.max(lastSelfClose, lastMxCellClose)
+    if (lastValidEnd !== -1) {
+        const endOffset = lastMxCellClose > lastSelfClose ? 9 : 2
+        const suffix = fixed.slice(lastValidEnd + endOffset)
+        // If suffix contains only closing tags (wrapper tags) or whitespace, strip it
+        if (/^(\s*<\/[^>]+>)+\s*$/.test(suffix)) {
+            fixed = fixed.slice(0, lastValidEnd + endOffset)
+            fixes.push("Stripped trailing LLM wrapper tags")
+        }
+    }
+
     // 2. Remove text before XML declaration or root element (only if it's garbage text, not valid XML)
     const xmlStart = fixed.search(/<(\?xml|mxGraphModel|mxfile)/i)
     if (xmlStart > 0 && !/^<[a-zA-Z]/.test(fixed.trim())) {
@@ -1015,8 +1062,8 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
         fixes.push("Removed quotes around color values in style")
     }
 
-    // 4. Fix unescaped < in attribute values
-    // This is tricky - we need to find < inside quoted attribute values
+    // 4. Fix unescaped < and > in attribute values
+    // < is required to be escaped, > is not strictly required but we escape for consistency
     const attrPattern = /(=\s*")([^"]*?)(<)([^"]*?)(")/g
     let attrMatch
     let hasUnescapedLt = false
@@ -1027,12 +1074,12 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
         }
     }
     if (hasUnescapedLt) {
-        // Replace < with &lt; inside attribute values
+        // Replace < and > with &lt; and &gt; inside attribute values
         fixed = fixed.replace(/=\s*"([^"]*)"/g, (_match, value) => {
-            const escaped = value.replace(/</g, "&lt;")
+            const escaped = value.replace(/</g, "&lt;").replace(/>/g, "&gt;")
             return `="${escaped}"`
         })
-        fixes.push("Escaped < characters in attribute values")
+        fixes.push("Escaped <> characters in attribute values")
     }
 
     // 5. Fix invalid character references (remove malformed ones)
@@ -1120,7 +1167,8 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
     }
 
     // 8c. Remove non-draw.io tags (after typo fixes so lowercase variants are fixed first)
-    // Valid draw.io tags: mxfile, diagram, mxGraphModel, root, mxCell, mxGeometry, mxPoint, Array, Object
+    // IMPORTANT: Only remove tags at the element level, NOT inside quoted attribute values
+    // Tags like <b>, <br> inside value="<b>text</b>" should be preserved (they're HTML content)
     const validDrawioTags = new Set([
         "mxfile",
         "diagram",
@@ -1133,25 +1181,59 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
         "Object",
         "mxRectangle",
     ])
+
+    // Helper: Check if a position is inside a quoted attribute value
+    // by counting unescaped quotes before that position
+    const isInsideQuotes = (str: string, pos: number): boolean => {
+        let inQuote = false
+        let quoteChar = ""
+        for (let i = 0; i < pos && i < str.length; i++) {
+            const c = str[i]
+            if (inQuote) {
+                if (c === quoteChar) inQuote = false
+            } else if (c === '"' || c === "'") {
+                // Check if this quote is part of an attribute (preceded by =)
+                // Look back for = sign
+                let j = i - 1
+                while (j >= 0 && /\s/.test(str[j])) j--
+                if (j >= 0 && str[j] === "=") {
+                    inQuote = true
+                    quoteChar = c
+                }
+            }
+        }
+        return inQuote
+    }
+
     const foreignTagPattern = /<\/?([a-zA-Z][a-zA-Z0-9_]*)[^>]*>/g
     let foreignMatch
     const foreignTags = new Set<string>()
+    const foreignTagPositions: Array<{
+        tag: string
+        start: number
+        end: number
+    }> = []
+
     while ((foreignMatch = foreignTagPattern.exec(fixed)) !== null) {
         const tagName = foreignMatch[1]
-        if (!validDrawioTags.has(tagName)) {
-            foreignTags.add(tagName)
-        }
+        // Skip if this is a valid draw.io tag
+        if (validDrawioTags.has(tagName)) continue
+        // Skip if this tag is inside a quoted attribute value
+        if (isInsideQuotes(fixed, foreignMatch.index)) continue
+
+        foreignTags.add(tagName)
+        foreignTagPositions.push({
+            tag: tagName,
+            start: foreignMatch.index,
+            end: foreignMatch.index + foreignMatch[0].length,
+        })
     }
-    if (foreignTags.size > 0) {
-        console.log(
-            "[autoFixXml] Step 8c: Found foreign tags:",
-            Array.from(foreignTags),
-        )
-        for (const tag of foreignTags) {
-            // Remove opening tags (with or without attributes)
-            fixed = fixed.replace(new RegExp(`<${tag}[^>]*>`, "gi"), "")
-            // Remove closing tags
-            fixed = fixed.replace(new RegExp(`</${tag}>`, "gi"), "")
+
+    if (foreignTagPositions.length > 0) {
+        // Remove tags from end to start to preserve indices
+        foreignTagPositions.sort((a, b) => b.start - a.start)
+        for (const { start, end } of foreignTagPositions) {
+            fixed = fixed.slice(0, start) + fixed.slice(end)
         }
         fixes.push(
             `Removed foreign tags: ${Array.from(foreignTags).join(", ")}`,
@@ -1202,6 +1284,7 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
 
     // 10b. Remove extra closing tags (more closes than opens)
     // Need to properly count self-closing tags (they don't need closing tags)
+    // IMPORTANT: Only count tags at element level, NOT inside quoted attribute values
     const tagCounts = new Map<
         string,
         { opens: number; closes: number; selfClosing: number }
@@ -1210,12 +1293,18 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
     const fullTagPattern = /<(\/?[a-zA-Z][a-zA-Z0-9]*)[^>]*>/g
     let tagCountMatch
     while ((tagCountMatch = fullTagPattern.exec(fixed)) !== null) {
+        // Skip tags inside quoted attribute values (e.g., value="<b>Title</b>")
+        if (isInsideQuotes(fixed, tagCountMatch.index)) continue
+
         const fullMatch = tagCountMatch[0] // e.g., "<mxCell .../>" or "</mxCell>"
         const tagPart = tagCountMatch[1] // e.g., "mxCell" or "/mxCell"
         const isClosing = tagPart.startsWith("/")
         const isSelfClosing = fullMatch.endsWith("/>")
         const tagName = isClosing ? tagPart.slice(1) : tagPart
 
+        // Only count valid draw.io tags - skip partial/invalid tags like "mx" from streaming
+        if (!validDrawioTags.has(tagName)) continue
+
         let counts = tagCounts.get(tagName)
         if (!counts) {
             counts = { opens: 0, closes: 0, selfClosing: 0 }

packages/mcp-server/src/xml-validation.ts

@@ -459,7 +459,8 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
         fixes.push("Removed quotes around color values in style")
     }
 
-    // 10. Fix unescaped < in attribute values
+    // 10. Fix unescaped < and > in attribute values
+    // < is required to be escaped, > is not strictly required but we escape for consistency
     const attrPattern = /(=\s*")([^"]*?)(<)([^"]*?)(")/g
     let attrMatch
     let hasUnescapedLt = false
@@ -471,10 +472,10 @@ export function autoFixXml(xml: string): { fixed: string; fixes: string[] } {
     }
     if (hasUnescapedLt) {
         fixed = fixed.replace(/=\s*"([^"]*)"/g, (_match, value) => {
-            const escaped = value.replace(/</g, "&lt;")
+            const escaped = value.replace(/</g, "&lt;").replace(/>/g, "&gt;")
             return `="${escaped}"`
         })
-        fixes.push("Escaped < characters in attribute values")
+        fixes.push("Escaped <> characters in attribute values")
     }
 
     // 11. Fix invalid hex character references
@@ -903,24 +904,30 @@ export function validateAndFixXml(xml: string): {
 
 /**
  * Check if mxCell XML output is complete (not truncated).
+ * Uses a robust approach that handles any LLM provider's wrapper tags
+ * by finding the last valid mxCell ending and checking if suffix is just closing tags.
  * @param xml - The XML string to check (can be undefined/null)
  * @returns true if XML appears complete, false if truncated or empty
  */
 export function isMxCellXmlComplete(xml: string | undefined | null): boolean {
-    let trimmed = xml?.trim() || ""
+    const trimmed = xml?.trim() || ""
     if (!trimmed) return false
 
-    // Strip wrapper tags if present
-    let prev = ""
-    while (prev !== trimmed) {
-        prev = trimmed
-        trimmed = trimmed
-            .replace(/<\/mxParameter>\s*$/i, "")
-            .replace(/<\/invoke>\s*$/i, "")
-            .replace(/<\/antml:parameter>\s*$/i, "")
-            .replace(/<\/antml:invoke>\s*$/i, "")
-            .trim()
-    }
+    // Find position of last complete mxCell ending (either /> or </mxCell>)
+    const lastSelfClose = trimmed.lastIndexOf("/>")
+    const lastMxCellClose = trimmed.lastIndexOf("</mxCell>")
 
-    return trimmed.endsWith("/>") || trimmed.endsWith("</mxCell>")
+    const lastValidEnd = Math.max(lastSelfClose, lastMxCellClose)
+
+    // No valid ending found at all
+    if (lastValidEnd === -1) return false
+
+    // Check what comes after the last valid ending
+    // For />: add 2 chars, for </mxCell>: add 9 chars
+    const endOffset = lastMxCellClose > lastSelfClose ? 9 : 2
+    const suffix = trimmed.slice(lastValidEnd + endOffset)
+
+    // If suffix is empty or only contains closing tags (any provider's wrapper) or whitespace, it's complete
+    // This regex matches any sequence of closing XML tags like </foo>, </bar>, </｜DSML｜xyz>
+    return /^(\s*<\/[^>]+>)*\s*$/.test(suffix)
 }