feat(mcp-server): load .drawio.svg, change summary, XML reference by topic, preview options, truncation message (#982)

* feat(mcp-server): load .drawio.svg (Editable SVG) files with load_diagram

* feat(mcp-server): summarize the user's manual changes per cell in stale rejections and get_diagram

* feat(mcp-server): XML reference for tables, layers and groups via get_drawing_guide topic

* feat(mcp-server): DRAWIO_LANG, DRAWIO_UI and DRAWIO_DARK for the preview page

Three host-config environment variables fix the language, theme and
dark mode of the draw.io editor embedded in the preview page. The new
drawio-themes module holds the theme list and draw.io's locale names
(zh-hant becomes zh-tw); drawioEmbedParams() in http-server.ts builds
the variable tail of the iframe query and getHtmlPage fills the new
{{DRAWIO_PARAMS}} placeholder. Without the variables the page keeps
sending dark=auto as before. Both READMEs document the variables.

* feat(mcp-server): report XML cut off inside a cell and explain drawing in parts

create_new_diagram and add_page now detect bare-cell XML that ends inside an
unfinished mxCell (XML comments stripped first) and return an error with the
last 300 characters of the input, asking the model to resend from that cell or
continue with edit_diagram add operations. isMxCellXmlComplete moves from
lib/utils.ts into packages/mcp-server/src/new-diagram.ts and is re-exported
from lib/utils.ts for the web app. The drawing guide gains a "Large diagrams"
paragraph and the INSTRUCTIONS edit_diagram line mentions drawing in parts.

* fix(mcp-server): review fixes for load .drawio.svg, change summary, XML reference, draw.io embed options, truncation message

* fix(mcp-server): Codex review fixes for .drawio.svg loading, change summary, references, embed options and truncation

- Truncation check: a closing tag such as </mxCell/> that the auto-fix
  repairs is no cut, and input without any cell keeps the validator's
  message
- Guide: a call rejected as cut off drew nothing, so all of its cells are
  sent again; the topic pointer is its own paragraph
- Change summary: decoded labels (no &nbsp; or merged words from <br>),
  a fast path for equal XML, and "the order of the cells changed" as
  the fallback
- DRAWIO_UI in any case, DRAWIO_LANG=zh-Hans maps to draw.io's zh
- load_diagram and export_diagram describe which files load again

lib/utils.ts

@@ -2,8 +2,6 @@ import { type ClassValue, clsx } from "clsx"
 import * as pako from "pako"
 import { twMerge } from "tailwind-merge"
 import { hasCells } from "@/packages/mcp-server/src/pages.ts"
-import { readStyleClasses } from "@/packages/mcp-server/src/style-classes.ts"
-import { repairQuoteBeforeSlash } from "@/packages/mcp-server/src/xml-validation.ts"
 
 export function cn(...inputs: ClassValue[]) {
     return twMerge(clsx(inputs))
@@ -34,55 +32,7 @@ export function isRealDiagram(xml: string | undefined | null): boolean {
 // mxCell XML Helpers
 // ============================================================================
 
-/**
- * Check if mxCell XML output is complete (not truncated).
- * Complete XML ends with a self-closing tag (/>) or closing mxCell tag.
- * 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 {
-    // Named style definitions before the cells are not cells: output cut off
-    // right after them is incomplete. A compact cell whose last quote is
-    // missing is complete; prepareNewDiagram repairs it.
-    const trimmed = repairQuoteBeforeSlash(
-        readStyleClasses(xml || "").xml,
-    ).trim()
-    if (!trimmed) return false
-
-    // Find position of last complete mxCell ending (either /> or </mxCell>)
-    const lastSelfClose = trimmed.lastIndexOf("/>")
-    const lastMxCellClose = trimmed.lastIndexOf("</mxCell>")
-
-    const lastValidEnd = Math.max(lastSelfClose, lastMxCellClose)
-
-    // No valid ending found at all
-    if (lastValidEnd === -1) return false
-
-    // If the last mxCell has no </mxCell> after it, it must be self-closing.
-    // Otherwise the trailing "/>" belongs to a child such as <mxGeometry .../>
-    // and the output was cut off before the cell was closed.
-    const lastCellStart = trimmed.lastIndexOf("<mxCell")
-    if (
-        lastCellStart > lastMxCellClose &&
-        // (quoted values may hold a raw "<", which the auto-fix escapes)
-        !/^<mxCell\b(?:[^<>"']|"[^"]*"|'[^']*')*\/>/.test(
-            trimmed.slice(lastCellStart),
-        )
-    ) {
-        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)
-}
+export { isMxCellXmlComplete } from "@/packages/mcp-server/src/new-diagram.ts"
 
 /**
  * Extract only complete mxCell elements from partial/streaming XML.