fix: preserve exports on close and support themed PDF without export quotas

backend/app/contracts.py

@@ -1426,7 +1426,18 @@ class ExportSource(Contract):
         return self
 
 
+class ExportPalette(Contract):
+    page: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+    surface: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+    text: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+    muted: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+    code: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+    border: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+    accent: str = Field(pattern=r'^#[0-9a-fA-F]{6}$')
+
+
 class ExportOptions(Contract):
+    palette: ExportPalette | None = None
     theme_id: str = "light"
     include_title: bool = True
     include_metadata: bool = False
@@ -1437,16 +1448,23 @@ class ExportOptions(Contract):
 class ExportAsset(Contract):
     kind: Literal['mermaid', 'math_block', 'math_inline', 'image']
     source_hash: str = Field(pattern=r'^[a-f0-9]{64}$')
-    png_base64: str = Field(max_length=2800000)
+    png_base64: str
 
 
 class ExportRequest(Contract):
-    assets: list[ExportAsset] = Field(default_factory=list, max_length=64)
+    assets: list[ExportAsset] = Field(default_factory=list)
     title: str = Field(default="", max_length=200)
     source: ExportSource
     format: ExportFormat
     options: ExportOptions = Field(default_factory=ExportOptions)
 
+    @model_validator(mode="after")
+    def _asset_limits(self) -> "ExportRequest":
+        if self.format != ExportFormat.pdf:
+            if len(self.assets) > 64 or any(len(asset.png_base64) > 2800000 for asset in self.assets):
+                raise ValueError("export asset count or size limit exceeded")
+        return self
+
 
 class ExportProgress(Contract):
     phase: str

backend/app/export/assets.py

@@ -1,4 +1,4 @@
-"""Bounded raster-only resource boundary. No URLs, XML or filesystem paths accepted."""
+"""Raster-only resources; PDF bypasses export quotas but retains path/format validation."""
 import base64
 import hashlib
 import threading
@@ -8,12 +8,14 @@ from app.errors import ApiError
 
 _math_lock = threading.Lock()
 
-def enrich_document(document, file_path=None):
-    """Embed local vault images and bounded MathText. Unsupported TeX stays explicit."""
+def enrich_document(document, file_path=None, unlimited=False, options=None):
+    """Embed Vault images and MathText, with format-specific quotas and palette."""
     from app.config import get_settings
     from urllib.parse import unquote, urlsplit
     vault = get_settings().vault_path.resolve()
     base = (vault / (file_path or '')).parent if file_path else vault
+    from app.export.themes import pdf_palette
+    palette = pdf_palette(options, []) if unlimited and options else None
     warnings = []
     count = total = pixels = 0
     def visit(node):
@@ -21,14 +23,14 @@ def enrich_document(document, file_path=None):
         if node.type in {'image','math_block','math_inline'} or node.attributes.get('static_png'):
             count += 1
             try:
-                if count > 64: raise ValueError('resource count')
+                if not unlimited and count > 64: raise ValueError('resource count')
                 if node.attributes.get('static_png'):
                     raw = node.attributes['static_png']
                 elif node.type == 'image':
                     src = str(node.attributes.get('src',''))
                     if urlsplit(src).scheme or src.startswith('//'): raise ValueError('remote image')
                     path = (base / unquote(src)).resolve()
-                    if not path.is_relative_to(vault) or path.suffix.lower() not in {'.png','.jpg','.jpeg','.webp'} or path.stat().st_size > 2_000_000:
+                    if not path.is_relative_to(vault) or path.suffix.lower() not in {'.png','.jpg','.jpeg','.webp'} or (not unlimited and path.stat().st_size > 2_000_000):
                         raise ValueError('image path or budget')
                     raw = path.read_bytes()
                 else:
@@ -36,23 +38,24 @@ def enrich_document(document, file_path=None):
                     depth = 0
                     for char in source:
                         depth += (char == '{') - (char == '}')
-                        if depth > 20: raise ValueError('math depth')
-                    if len(source) > 512 or depth != 0: raise ValueError('math budget')
+                        if not unlimited and depth > 20: raise ValueError('math depth')
+                    if (not unlimited and len(source) > 512) or depth != 0: raise ValueError('math budget')
                     from matplotlib.mathtext import math_to_image
-                    with _math_lock:
+                    from matplotlib import rc_context
+                    with _math_lock, rc_context({'savefig.transparent': bool(palette)}):
                         out = BytesIO()
-                        math_to_image('$'+source+'$', out, dpi=180, format='png', color='black')
+                        math_to_image('$'+source+'$', out, dpi=180, format='png', color=palette['text'] if palette else 'black')
                         raw = out.getvalue()
                 with Image.open(BytesIO(raw)) as image:
                     pixels += image.width * image.height
-                    if pixels > 16_000_000: raise ValueError('document pixels')
-                    if image.width * image.height > 4_000_000: raise ValueError('image dimensions')
+                    if not unlimited and pixels > 16_000_000: raise ValueError('document pixels')
+                    if not unlimited and image.width * image.height > 4_000_000: raise ValueError('image dimensions')
                     out = BytesIO()
-                    # Flatten alpha on white for portable print/Word output.
-                    rgba=image.convert('RGBA'); background=Image.new('RGBA',rgba.size,'white')
+                    # Composite transparency over the PDF theme or the print/Word white surface.
+                    rgba=image.convert('RGBA'); background=Image.new('RGBA',rgba.size,palette['surface'] if palette else 'white')
                     background.alpha_composite(rgba); background.convert('RGB').save(out,'PNG')
                     png=out.getvalue();total += len(png)
-                    if total > 8_000_000: raise ValueError('resource bytes')
+                    if not unlimited and total > 8_000_000: raise ValueError('resource bytes')
                     node.attributes['static_png']=png
             except Exception:
                 node.attributes.pop('static_png', None)
@@ -66,26 +69,26 @@ def enrich_document(document, file_path=None):
 def source_hash(source):
     return hashlib.sha256(source.strip().encode()).hexdigest()
 
-def validate_assets(assets):
+def validate_assets(assets, unlimited=False):
     result = {}
     total = pixels = 0
     for asset in assets:
         try:
             raw = base64.b64decode(asset.png_base64, validate=True)
             total += len(raw)
-            if total > 8 * 1024 * 1024:
+            if not unlimited and total > 8 * 1024 * 1024:
                 raise ValueError('asset budget')
             with Image.open(BytesIO(raw)) as image:
                 pixels += image.width * image.height
-                if pixels > 16_000_000: raise ValueError('document pixel budget')
-                if image.format != 'PNG' or image.width * image.height > 4_000_000:
+                if not unlimited and pixels > 16_000_000: raise ValueError('document pixel budget')
+                if image.format != 'PNG' or (not unlimited and image.width * image.height > 4_000_000):
                     raise ValueError('image budget')
                 image.load()
                 out = BytesIO()
                 rgba = image.convert('RGBA')
                 background = Image.new('RGBA', rgba.size, 'white')
                 background.alpha_composite(rgba)
-                background.convert('RGB').save(out, 'PNG')
+                (rgba if unlimited else background.convert('RGB')).save(out, 'PNG')
                 key = (asset.kind, asset.source_hash)
                 if key in result:
                     raise ValueError('duplicate asset')

backend/app/export/exporters/_common.py

@@ -1,7 +1,6 @@
 """导出器共享工具：URL 协议校验、函数图像预算与占位 warning 文案。
 
-html / pdf / docx 三个导出器共用同一套安全规则与函数图像资源预算，避免各写一份
-导致行为漂移。
+导出器共享 URL 规则；HTML / DOCX 使用文档资源预算，PDF 不使用这些预算。
 """
 
 from __future__ import annotations
@@ -27,7 +26,7 @@ MAX_TOTAL_PLOT_NODES = 8000
 class FunctionPlotBudget:
     """函数图像文档级资源预算：数量上限 + 累计 AST 节点上限。
 
-    HTML 与 PDF 导出器在渲染每个 function-plot 图块前先问预算，超限即回退源码占位，
+    HTML 与 DOCX 导出器在渲染每个 function-plot 图块前先问预算，超限即回退源码占位，
     不解析不采样，避免多图块组合复杂度耗尽内存/CPU。
     """
 

backend/app/export/exporters/pdf.py

@@ -20,7 +20,7 @@ from reportlab.pdfbase.cidfonts import UnicodeCIDFont
 from reportlab.platypus import (
     Paragraph,
     Indenter,
-    Preformatted,
+    XPreformatted,
     SimpleDocTemplate,
     Spacer,
     Table,
@@ -29,12 +29,11 @@ from reportlab.platypus import (
 from reportlab.platypus.flowables import HRFlowable
 
 from app.contracts import ExportOptions
-from app.export.themes import CALLOUTS, print_theme_warning
+from app.export.themes import CALLOUTS, pdf_palette
 from app.export.document import Document, DocumentNode, ExportResult
 from app.export.exporters._common import (
     MERMAID_WARNING,
     RAW_HTML_WARNING,
-    FunctionPlotBudget,
     format_meta_value,
     format_plot_diagnostic,
     safe_url,
@@ -54,10 +53,11 @@ _HEADING_SIZES = {1: 20, 2: 16, 3: 14, 4: 12, 5: 11, 6: 10.5}
 _QUOTE_COLOR = "#57606a"
 
 
-def _make_styles() -> dict[str, ParagraphStyle]:
+def _make_styles(palette) -> dict[str, ParagraphStyle]:
     body = ParagraphStyle(
         "pdf-body",
         fontName=_FONT,
+        textColor=palette["text"],
         fontSize=10.5,
         leading=16,
         spaceAfter=6,
@@ -67,7 +67,7 @@ def _make_styles() -> dict[str, ParagraphStyle]:
         "pdf-quote",
         parent=body,
         leftIndent=14,
-        textColor="#57606a",
+        textColor=palette["muted"],
         spaceBefore=4,
         spaceAfter=6,
     )
@@ -78,8 +78,8 @@ def _make_styles() -> dict[str, ParagraphStyle]:
         leading=12,
         leftIndent=6,
         rightIndent=6,
-        backColor="#f6f8fa",
-        borderColor="#d0d7de",
+        backColor=palette["code"],
+        borderColor=palette["border"],
         borderWidth=0.5,
         borderPadding=6,
         spaceBefore=4,
@@ -88,9 +88,9 @@ def _make_styles() -> dict[str, ParagraphStyle]:
     math = ParagraphStyle("pdf-math", parent=body, alignment=TA_CENTER, spaceBefore=6)
     cell = ParagraphStyle("pdf-cell", parent=body, fontSize=10, leading=14, spaceAfter=0)
     cell_head = ParagraphStyle(
-        "pdf-cell-head", parent=cell, textColor="#1f2328", fontSize=10
+        "pdf-cell-head", parent=cell, textColor=palette["text"], fontSize=10
     )
-    meta = ParagraphStyle("pdf-meta", parent=body, fontSize=8.5, leading=13, textColor="#57606a")
+    meta = ParagraphStyle("pdf-meta", parent=body, fontSize=8.5, leading=13, textColor=palette["muted"])
     styles: dict[str, ParagraphStyle] = {
         "body": body,
         "title": title,
@@ -109,6 +109,7 @@ def _make_styles() -> dict[str, ParagraphStyle]:
             leading=size * 1.4,
             spaceBefore=14 if level <= 2 else 10,
             spaceAfter=6,
+            keepWithNext=True,
         )
     return styles
 
@@ -118,17 +119,17 @@ class PdfExporter:
 
     def render(self, document: Document, options: ExportOptions) -> ExportResult:
         """同步渲染；CPU 密集，调用方应放入线程执行，避免阻塞事件循环。"""
-        self._styles = _make_styles()
         warnings: list[str] = []
-        print_theme_warning(options, warnings, "PDF")
+        self._palette = pdf_palette(options, warnings)
+        self._styles = _make_styles(self._palette)
         if _FONT == "STSong-Light": warnings.append("PDF 使用 CID 字体，阅读器需提供中文字体；可配置 APP_EXPORT_FONT 嵌入 TrueType 字体")
 
         page = _PAGE_SIZES.get((options.page_size or "A4").lower(), A4)
         self._options = options
-        self._plot_budget = FunctionPlotBudget()
         self._plot_renderer = FunctionPlotStaticRenderer()
         # 内容区宽度（左右各 20mm 边距），供函数图像缩放适配页面
-        self._plot_width = page[0] - 40 * mm
+        self._plot_width = page[0] - 40 * mm - 12
+        self._plot_height = page[1] - 36 * mm - 12
         buf = BytesIO()
         doc = SimpleDocTemplate(
             buf,
@@ -144,7 +145,14 @@ class PdfExporter:
         self._render_header(document, options, story)
         self._render_children(document.children, story, warnings)
 
-        doc.build(story)
+        def paint_page(canvas, template):
+            canvas.saveState()
+            canvas.setFillColor(self._palette['page'])
+            canvas.rect(0, 0, page[0], page[1], fill=1, stroke=0)
+            canvas.setFillColor(self._palette['surface'])
+            canvas.roundRect(12*mm, 10*mm, page[0]-24*mm, page[1]-20*mm, 5*mm, fill=1, stroke=0)
+            canvas.restoreState()
+        doc.build(story, onFirstPage=paint_page, onLaterPages=paint_page)
         return ExportResult(content=buf.getvalue(), mime_type=_MIME, warnings=warnings)
 
     async def export(self, document: Document, options: ExportOptions) -> ExportResult:
@@ -172,7 +180,7 @@ class PdfExporter:
         if node.attributes.get('static_png'):
             from reportlab.platypus import Image
             image = Image(BytesIO(node.attributes['static_png']))
-            scale = min(1, self._plot_width / image.imageWidth, 600 / image.imageHeight)
+            scale = min(1, self._plot_width / image.imageWidth, self._plot_height / image.imageHeight)
             image.drawWidth = image.imageWidth * scale
             image.drawHeight = image.imageHeight * scale
             story.append(image)
@@ -194,9 +202,13 @@ class PdfExporter:
     def _block_callout(self, node, story, warnings):
         kind = node.attributes['kind']
         icon, color = CALLOUTS[kind]
+        from reportlab.lib.colors import HexColor
+        background = HexColor(self._palette['code'])
+        if .2126*background.red + .7152*background.green + .0722*background.blue < .5:
+            color = {'#0969da':'#a5d6ff','#7041a0':'#d2a8ff','#176f41':'#7ee787','#805400':'#f2cc60','#b42318':'#ffa198','#57606a':self._palette['muted']}[color]
         title = self._render_inline(node.children[0].children,warnings)
         style = ParagraphStyle('callout-'+kind,parent=self._styles['body'],textColor=color,
-            backColor='#f6f8fa',borderColor=color,borderWidth=1,borderPadding=6,spaceBefore=8,spaceAfter=8)
+            backColor=self._palette['code'],borderColor=color,borderWidth=1,borderPadding=6,spaceBefore=8,spaceAfter=8)
         story.append(Paragraph(_html.escape(icon)+' '+title,style))
         self._render_children(node.children[1:],story,warnings)
 
@@ -209,7 +221,7 @@ class PdfExporter:
                     Paragraph(self._render_inline(child.children, warnings), self._styles["quote"])
                 )
             elif child.type == "list":
-                self._block_list(child, story, warnings, indent=14, color=_QUOTE_COLOR)
+                self._block_list(child, story, warnings, indent=14, color=self._palette['muted'])
             else:
                 self._render_block(child, story, warnings)
 
@@ -301,7 +313,7 @@ class PdfExporter:
             data.append(cells)
         table = Table(data, repeatRows=head_row_count)
         commands = [
-            ("GRID", (0, 0), (-1, -1), 0.5, "#d0d7de"),
+            ("GRID", (0, 0), (-1, -1), 0.5, self._palette["border"]),
             ("VALIGN", (0, 0), (-1, -1), "TOP"),
             ("LEFTPADDING", (0, 0), (-1, -1), 6),
             ("RIGHTPADDING", (0, 0), (-1, -1), 6),
@@ -309,53 +321,42 @@ class PdfExporter:
             ("BOTTOMPADDING", (0, 0), (-1, -1), 4),
         ]
         if head_row_count:
-            commands.append(("BACKGROUND", (0, 0), (-1, head_row_count - 1), "#f6f8fa"))
+            commands.append(("BACKGROUND", (0, 0), (-1, head_row_count - 1), self._palette["code"]))
         table.setStyle(TableStyle(commands))
         story.append(table)
 
     def _block_code_block(self, node: DocumentNode, story: list, warnings: list[str]) -> None:
-        story.append(Preformatted(node.text, self._styles["code"]))
+        story.append(XPreformatted(_html.escape(node.text), self._styles["code"]))
 
     def _block_thematic_break(self, node: DocumentNode, story: list, warnings: list[str]) -> None:
         story.append(Spacer(1, 4))
-        story.append(HRFlowable(width="100%", color="#d0d7de", thickness=0.5))
+        story.append(HRFlowable(width="100%", color=self._palette["border"], thickness=0.5))
         story.append(Spacer(1, 6))
 
     def _block_mermaid(self, node: DocumentNode, story: list, warnings: list[str]) -> None:
         warnings.append(MERMAID_WARNING)
-        story.append(Preformatted(node.text, self._styles["code"]))
+        story.append(XPreformatted(_html.escape(node.text), self._styles["code"]))
 
     def _block_function_plot(self, node: DocumentNode, story: list, warnings: list[str]) -> None:
-        # 文档级数量上限：超出部分直接回退占位，不解析不采样，防止海量图像耗尽资源
-        over = self._plot_budget.check_count()
-        if over is not None:
-            warnings.append(over)
-            story.append(Preformatted(node.text, self._styles["code"]))
-            return
         # 解析与渲染共同纳入局部异常回退：单个图像失败只回退占位 + warning，
         # 绝不阻断整篇导出（含复杂表达式触发的 RecursionError 等异常）。
         try:
             request = StaticRenderRequest(
                 kind="function_plot", source=node.text, theme=self._options.theme_id
             )
-            parsed = self._plot_renderer.parse(request)
+            from app.plot.parser import parse_source
+            parsed = parse_source(request.source, unlimited=True)
             for diag in parsed.diagnostics:
                 warnings.append(format_plot_diagnostic(diag))
             if parsed.plot is None:
-                story.append(Preformatted(node.text, self._styles["code"]))
-                return
-            # 文档级累计复杂度预算：超出后回退占位，不再采样求值
-            over = self._plot_budget.check_nodes(parsed.plot.node_count)
-            if over is not None:
-                warnings.append(over)
-                story.append(Preformatted(node.text, self._styles["code"]))
+                story.append(XPreformatted(_html.escape(node.text), self._styles["code"]))
                 return
             # Drawing 本身即 Flowable，缩放后追加到 story，与 HTML 视觉一致
-            drawing = render_drawing(parsed.plot, width=self._plot_width)
+            drawing = render_drawing(parsed.plot, width=self._plot_width, palette=self._palette, unlimited=True, max_height=self._plot_height)
             story.append(drawing)
         except Exception as exc:
             warnings.append(f"函数图像：解析或渲染失败，已回退占位（{exc}）")
-            story.append(Preformatted(node.text, self._styles["code"]))
+            story.append(XPreformatted(_html.escape(node.text), self._styles["code"]))
 
     def _block_math_block(self, node: DocumentNode, story: list, warnings: list[str]) -> None:
         story.append(Paragraph(f"$${_html.escape(node.text)}$$", self._styles["math"]))
@@ -393,7 +394,7 @@ class PdfExporter:
             if safe_href is None:
                 warnings.append(f"链接协议不安全，已降级为纯文本：{href!r}")
                 return inner
-            return f'<a href="{_html.escape(safe_href)}">{inner}</a>'
+            return f'<a href="{_html.escape(safe_href)}" color="{self._palette["accent"]}">{inner}</a>'
         if t == "image":
             src = str(node.attributes.get("src") or "")
             alt = str(node.attributes.get("alt") or "")

backend/app/export/service.py

@@ -146,7 +146,7 @@ def _evict_terminal() -> bool:
     return True
 
 
-async def _resolve_source(source: ExportSource) -> tuple[str, str, dict | None]:
+async def _resolve_source(source: ExportSource, unlimited: bool = False) -> tuple[str, str, dict | None]:
     """把导出源解析为 (markdown, title, metadata)；metadata 仅 note 源提供。"""
     if source.type == ExportSourceType.note:
         note = await note_service.get_note(source.note_id)
@@ -157,7 +157,7 @@ async def _resolve_source(source: ExportSource) -> tuple[str, str, dict | None]:
                 "note not found",
                 {"note_id": source.note_id},
             )
-        if len(note.markdown) > MAX_MARKDOWN_CHARS:
+        if not unlimited and len(note.markdown) > MAX_MARKDOWN_CHARS:
             raise ApiError(
                 400,
                 "EXPORT_OPTIONS_INVALID",
@@ -175,7 +175,7 @@ async def _resolve_source(source: ExportSource) -> tuple[str, str, dict | None]:
     markdown = source.markdown or ""
     if not markdown.strip():
         raise ApiError(400, "EXPORT_OPTIONS_INVALID", "markdown source must not be empty")
-    if len(markdown) > MAX_MARKDOWN_CHARS:
+    if not unlimited and len(markdown) > MAX_MARKDOWN_CHARS:
         raise ApiError(
             400,
             "EXPORT_OPTIONS_INVALID",
@@ -187,10 +187,10 @@ async def _resolve_source(source: ExportSource) -> tuple[str, str, dict | None]:
 
 async def create_export(request: ExportRequest) -> ExportJob:
     """创建导出任务，立即返回 queued 的 ExportJob，由后台 Task 渲染。"""
-    markdown, title, metadata = await _resolve_source(request.source)
+    markdown, title, metadata = await _resolve_source(request.source, request.format == ExportFormat.pdf)
     title = request.title or title
     from app.export.assets import validate_assets
-    assets = await asyncio.to_thread(validate_assets, request.assets)
+    assets = await asyncio.to_thread(validate_assets, request.assets, request.format == ExportFormat.pdf)
 
     if not _evict_terminal():
         raise ApiError(
@@ -283,12 +283,12 @@ async def _execute(
             document.attributes["metadata"] = metadata
 
         from app.export.assets import enrich_document
-        resource_warnings = await asyncio.to_thread(enrich_document, document, (metadata or {}).get('file_path'))
+        resource_warnings = await asyncio.to_thread(enrich_document, document, (metadata or {}).get('file_path'), format == ExportFormat.pdf, options)
         result = await asyncio.to_thread(_render_document, document, options, format)
         result.warnings[:0] = resource_warnings
         if cancel_event.is_set():
             raise ExportCancelled()
-        if len(result.content) > MAX_EXPORT_BYTES:
+        if format != ExportFormat.pdf and len(result.content) > MAX_EXPORT_BYTES:
             raise ExportTooLarge()
 
         ext = _extension_for(format)

backend/app/export/themes.py

@@ -32,3 +32,13 @@ ALIASES = {'summary':'abstract','tldr':'abstract','hint':'tip',
            'check':'success','done':'success','help':'question','faq':'question',
            'caution':'warning','attention':'warning','fail':'failure','missing':'failure',
            'error':'danger','cite':'quote'}
+
+
+def pdf_palette(options, warnings):
+    if options.palette is not None:
+        return options.palette.model_dump()
+    theme_id = options.theme_id
+    if theme_id not in PALETTES:
+        warnings.append(f'PDF 不支持主题 {theme_id}，已使用 light 导出配色')
+        theme_id = 'light'
+    return dict(zip(('page','surface','text','muted','code','border','accent'), PALETTES[theme_id]))

backend/app/plot/parser.py

@@ -143,7 +143,7 @@ def _preprocess(expr: str) -> str:
     return _insert_implicit_multiplication(expr.replace("^", "**"))
 
 
-def _check_node(node: ast.AST, depth: int = 0, counter: list[int] | None = None) -> None:
+def _check_node(node: ast.AST, depth: int = 0, counter: list[int] | None = None, unlimited: bool = False) -> None:
     """白名单校验：任何越界节点都抛 FUNCTION_PLOT_EXPRESSION_UNSAFE。
 
     同时限制 AST 深度与节点总数，避免超长/超深表达式在递归校验或求值时触发
@@ -151,10 +151,10 @@ def _check_node(node: ast.AST, depth: int = 0, counter: list[int] | None = None)
     """
     if counter is None:
         counter = [0]
-    if depth > _MAX_AST_DEPTH:
+    if not unlimited and depth > _MAX_AST_DEPTH:
         _unsafe(f"表达式嵌套过深（超过 {_MAX_AST_DEPTH} 层）")
     counter[0] += 1
-    if counter[0] > _MAX_AST_NODES:
+    if not unlimited and counter[0] > _MAX_AST_NODES:
         _unsafe(f"表达式过于复杂（节点数超过 {_MAX_AST_NODES}）")
     if isinstance(node, ast.Constant):
         if isinstance(node.value, bool) or not isinstance(node.value, (int, float)):
@@ -167,13 +167,13 @@ def _check_node(node: ast.AST, depth: int = 0, counter: list[int] | None = None)
     if isinstance(node, ast.BinOp):
         if not isinstance(node.op, _ALLOWED_BINOPS):
             _unsafe(f"不支持的运算符 {type(node.op).__name__}")
-        _check_node(node.left, depth + 1, counter)
-        _check_node(node.right, depth + 1, counter)
+        _check_node(node.left, depth + 1, counter, unlimited)
+        _check_node(node.right, depth + 1, counter, unlimited)
         return
     if isinstance(node, ast.UnaryOp):
         if not isinstance(node.op, _ALLOWED_UNARY):
             _unsafe(f"不支持的运算符 {type(node.op).__name__}")
-        _check_node(node.operand, depth + 1, counter)
+        _check_node(node.operand, depth + 1, counter, unlimited)
         return
     if isinstance(node, ast.Call):
         if not isinstance(node.func, ast.Name) or node.func.id not in _FUNCTIONS:
@@ -184,12 +184,12 @@ def _check_node(node: ast.AST, depth: int = 0, counter: list[int] | None = None)
         if len(node.args) != 1:
             _unsafe(f"{node.func.id} 需要 1 个参数，实际 {len(node.args)} 个")
         for arg in node.args:
-            _check_node(arg, depth + 1, counter)
+            _check_node(arg, depth + 1, counter, unlimited)
         return
     _unsafe(f"不支持的语法 {type(node).__name__}")
 
 
-def parse_expression(expr: str) -> ast.Expression:
+def parse_expression(expr: str, unlimited: bool = False) -> ast.Expression:
     """把数学表达式解析为已通过白名单校验的 AST（可直接交给 evaluate）。"""
     preprocessed = _preprocess(expr)
     try:
@@ -211,7 +211,7 @@ def parse_expression(expr: str) -> ast.Expression:
                 message="表达式嵌套过深，无法解析",
             )
         ) from exc
-    _check_node(tree.body)
+    _check_node(tree.body, unlimited=unlimited)
     return tree
 
 
@@ -279,7 +279,7 @@ def _parse_directive(line: str) -> tuple[str, str] | None:
     return key, value.strip()
 
 
-def parse_source(source: str) -> FunctionPlotParseResult:
+def parse_source(source: str, unlimited: bool = False) -> FunctionPlotParseResult:
     """把 function-plot fenced block 源码解析为 FunctionPlot + 诊断。"""
     diagnostics: list[PlotDiagnostic] = []
     expressions: list[FunctionPlotExpression] = []
@@ -371,7 +371,7 @@ def parse_source(source: str) -> FunctionPlotParseResult:
             continue
 
         try:
-            tree = parse_expression(expr_text)
+            tree = parse_expression(expr_text, unlimited=unlimited)
         except PlotParseError as exc:
             exc.diagnostic.line = lineno
             diagnostics.append(exc.diagnostic)
@@ -380,7 +380,7 @@ def parse_source(source: str) -> FunctionPlotParseResult:
         total_nodes += _count_nodes(tree.body)
         expressions.append(FunctionPlotExpression(expression=expr_text))
         # 表达式数量超限：整块回退并提前终止，避免对海量表达式做采样求值
-        if len(expressions) > _MAX_EXPRESSIONS:
+        if not unlimited and len(expressions) > _MAX_EXPRESSIONS:
             diagnostics.append(
                 PlotDiagnostic(
                     severity="error",

backend/app/plot/render.py

@@ -339,7 +339,7 @@ def _sample_segments(
     return clipped
 
 
-def compute_geometry(plot: FunctionPlot) -> PlotGeometry:
+def compute_geometry(plot: FunctionPlot, unlimited: bool = False) -> PlotGeometry:
     """解析并计算几何，供 SVG 与 reportlab 后端复用。"""
     warnings: list[str] = []
     xmin, xmax = plot.domain
@@ -351,7 +351,7 @@ def compute_geometry(plot: FunctionPlot) -> PlotGeometry:
     fns: list[tuple[object, object]] = []
     for expr in plot.expressions:
         try:
-            tree = parse_expression(expr.expression)
+            tree = parse_expression(expr.expression, unlimited=unlimited)
         except PlotParseError as exc:
             warnings.append(f"表达式无法渲染，已跳过：{expr.expression}（{exc.diagnostic.message}）")
             continue

backend/app/plot/render_reportlab.py

@@ -26,9 +26,12 @@ _TICK_FONT_SIZE = 10
 _LABEL_FONT_SIZE = 12
 
 
-def _build_drawing(geo: PlotGeometry) -> Drawing:
+def _build_drawing(geo: PlotGeometry, palette=None) -> Drawing:
     """由共享几何构建矢量 Drawing（坐标翻转后仍沿用 SVG 的像素布局）。"""
     drawing = Drawing(geo.width, geo.height)
+    grid_color = HexColor(palette['border']) if palette else _GRID_COLOR
+    axis_color = HexColor(palette['muted']) if palette else _AXIS_COLOR
+    label_color = HexColor(palette['text']) if palette else _LABEL_COLOR
 
     # SVG y-down → reportlab y-up：翻转像素 y
     def sx(x: float) -> float:
@@ -41,19 +44,19 @@ def _build_drawing(geo: PlotGeometry) -> Drawing:
     if geo.grid:
         for x in geo.xticks:
             drawing.add(
-                Line(sx(x), sy(geo.ymin), sx(x), sy(geo.ymax), strokeColor=_GRID_COLOR, strokeWidth=0.5)
+                Line(sx(x), sy(geo.ymin), sx(x), sy(geo.ymax), strokeColor=grid_color, strokeWidth=0.5)
             )
         for y in geo.yticks:
             drawing.add(
-                Line(sx(geo.xmin), sy(y), sx(geo.xmax), sy(y), strokeColor=_GRID_COLOR, strokeWidth=0.5)
+                Line(sx(geo.xmin), sy(y), sx(geo.xmax), sy(y), strokeColor=grid_color, strokeWidth=0.5)
             )
 
     # 坐标轴（过原点画在原点，否则贴边，与 SVG 一致）
     drawing.add(
-        Line(sx(geo.xmin), sy(geo.x_axis_y), sx(geo.xmax), sy(geo.x_axis_y), strokeColor=_AXIS_COLOR, strokeWidth=0.7)
+        Line(sx(geo.xmin), sy(geo.x_axis_y), sx(geo.xmax), sy(geo.x_axis_y), strokeColor=axis_color, strokeWidth=0.7)
     )
     drawing.add(
-        Line(sx(geo.y_axis_x), sy(geo.ymin), sx(geo.y_axis_x), sy(geo.ymax), strokeColor=_AXIS_COLOR, strokeWidth=0.7)
+        Line(sx(geo.y_axis_x), sy(geo.ymin), sx(geo.y_axis_x), sy(geo.ymax), strokeColor=axis_color, strokeWidth=0.7)
     )
 
     # 刻度数字（x 轴下方、y 轴左侧）
@@ -61,14 +64,14 @@ def _build_drawing(geo: PlotGeometry) -> Drawing:
         drawing.add(
             String(
                 sx(x), sy(geo.x_axis_y) - 14, _fmt_num(x),
-                fontName=_FONT, fontSize=_TICK_FONT_SIZE, fillColor=_AXIS_COLOR, textAnchor="middle",
+                fontName=_FONT, fontSize=_TICK_FONT_SIZE, fillColor=axis_color, textAnchor="middle",
             )
         )
     for y in geo.yticks:
         drawing.add(
             String(
                 sx(geo.y_axis_x) - 6, sy(y) - 3, _fmt_num(y),
-                fontName=_FONT, fontSize=_TICK_FONT_SIZE, fillColor=_AXIS_COLOR, textAnchor="end",
+                fontName=_FONT, fontSize=_TICK_FONT_SIZE, fillColor=axis_color, textAnchor="end",
             )
         )
 
@@ -83,7 +86,7 @@ def _build_drawing(geo: PlotGeometry) -> Drawing:
         drawing.add(
             String(
                 geo.width / 2, 10, geo.xlabel,
-                fontName=_FONT, fontSize=_LABEL_FONT_SIZE, fillColor=_LABEL_COLOR, textAnchor="middle",
+                fontName=_FONT, fontSize=_LABEL_FONT_SIZE, fillColor=label_color, textAnchor="middle",
             )
         )
     if geo.ylabel:
@@ -95,7 +98,7 @@ def _build_drawing(geo: PlotGeometry) -> Drawing:
         label.add(
             String(
                 0, 0, geo.ylabel,
-                fontName=_FONT, fontSize=_LABEL_FONT_SIZE, fillColor=_LABEL_COLOR, textAnchor="middle",
+                fontName=_FONT, fontSize=_LABEL_FONT_SIZE, fillColor=label_color, textAnchor="middle",
             )
         )
         label.translate(16, geo.height / 2)
@@ -105,19 +108,25 @@ def _build_drawing(geo: PlotGeometry) -> Drawing:
     return drawing
 
 
-def render_drawing(plot: FunctionPlot, width: float | None = None) -> Drawing:
+def render_drawing(plot: FunctionPlot, width: float | None = None, palette=None, unlimited=False, max_height=None) -> Drawing:
     """把已解析的 FunctionPlot 渲染为 reportlab Drawing（可直接追加到 platypus story）。
 
     ``width`` 为目标输出宽度（点），用于把 640px 的几何缩放到页面内容宽；省略则按
     原始尺寸输出。缩放只影响 PDF 渲染，不改动共享几何。
     """
-    geo = compute_geometry(plot)
-    drawing = _build_drawing(geo)
+    geo = compute_geometry(plot, unlimited=unlimited)
+    if palette:
+        from reportlab.lib.colors import HexColor as color
+        bg = color(palette['surface'])
+        if .2126*bg.red + .7152*bg.green + .0722*bg.blue < .5:
+            colors = ['#79c0ff','#ff9b9b','#7ee787','#d2a8ff','#f2cc60','#ffa657']
+            geo.colors = [value if plot.expressions[i].color else colors[i % len(colors)] for i,value in enumerate(geo.colors)]
+    drawing = _build_drawing(geo, palette)
     legend_height = ((len(plot.expressions)+1)//2)*24
     drawing.height += legend_height
     for index, expression in enumerate(plot.expressions):
         drawing.add(String(24+(index%2)*310,geo.height+legend_height-18-(index//2)*24,
             expression.label or 'y = '+expression.expression,fontName=_FONT,fontSize=12,fillColor=HexColor(geo.colors[index])))
     if width is not None and width > 0:
-        drawing.renderScale = min(1.0, width / geo.width)
+        drawing.renderScale = min(1.0, width / geo.width, max_height / drawing.height if max_height else 1.0)
     return drawing

backend/tests/test_export.py

@@ -334,17 +334,16 @@ def test_pdf_exporter_function_plot_fallback_on_error() -> None:
     assert any("函数图像" in w for w in result.warnings)
 
 
-def test_pdf_exporter_limits_function_plot_count() -> None:
+def test_pdf_exporter_has_no_function_plot_count_quota() -> None:
     from app.export.exporters.pdf import PdfExporter
 
     blocks = "\n\n".join("```function-plot\ny = x\n```" for _ in range(20))
     result = asyncio.run(PdfExporter().export(parse_document(blocks), ExportOptions()))
     assert result.content[:4] == b"%PDF"
-    # 超出数量上限的图块回退占位并记 warning
-    assert any("数量超过上限" in w for w in result.warnings)
+    assert not any("函数图像" in w for w in result.warnings)
 
 
-def test_pdf_exporter_limits_total_plot_nodes(monkeypatch) -> None:
+def test_pdf_exporter_has_no_total_plot_node_quota(monkeypatch) -> None:
     import app.export.exporters._common as common_mod
     from app.export.exporters.pdf import PdfExporter
 
@@ -352,7 +351,7 @@ def test_pdf_exporter_limits_total_plot_nodes(monkeypatch) -> None:
     md = "```function-plot\ny = x\n```\n\n```function-plot\ny = x + x + x + x\n```"
     result = asyncio.run(PdfExporter().export(parse_document(md), ExportOptions()))
     assert result.content[:4] == b"%PDF"
-    assert any("累计复杂度" in w for w in result.warnings)
+    assert not any("函数图像" in w for w in result.warnings)
 
 
 def test_docx_exporter_embeds_plot_and_warns_missing_mermaid() -> None:
@@ -831,7 +830,8 @@ def test_callout_formats(name):
         xml = z.read("word/document.xml").decode()
     assert all(word in xml for word in ["Title", "Body", "item", "second", "w:shd"])
     result = PdfExporter().render(doc, ExportOptions(theme_id="sepia"))
-    assert result.content.startswith(b"%PDF") and len(result.warnings) == 1
+    assert result.content.startswith(b"%PDF")
+    assert not any("浅色打印" in warning for warning in result.warnings)
 
 
 @pytest.mark.parametrize("fold", ["", "+", "-"])

backend/tests/test_pdf_theme_resources.py

@@ -0,0 +1,96 @@
+"""PDF theme and resource policy regressions; no real providers or user files."""
+import asyncio
+import base64
+from io import BytesIO
+import pytest
+from PIL import Image
+from pydantic import ValidationError
+from app.contracts import ExportAsset, ExportOptions, ExportRequest
+from app.export.assets import validate_assets, enrich_document, source_hash
+from app.export.exporters.pdf import PdfExporter
+from app.export.markdown import parse_document
+from app.export.themes import PALETTES
+from app.export import service
+
+
+def png_asset(size=(40,30), source='graph LR; A-->B'):
+    out=BytesIO(); Image.new('RGBA',size,(0,0,0,0)).save(out,'PNG')
+    return ExportAsset(kind='mermaid',source_hash=source_hash(source),png_base64=base64.b64encode(out.getvalue()).decode())
+
+
+@pytest.mark.parametrize('theme',list(PALETTES))
+def test_pdf_theme_colors_are_written_on_every_page(theme):
+    import re, zlib
+    palette=PALETTES[theme]
+    doc=parse_document(('## Section\n\nText body\n\n> Quoted text\n\n```python\nprint(1)\n```\n\n')*30)
+    result=PdfExporter().render(doc,ExportOptions(theme_id=theme))
+    streams=[]
+    for match in re.finditer(rb'stream\r?\n(.*?)endstream',result.content,re.S):
+        try: streams.append(zlib.decompress(base64.a85decode(match[1].strip().removesuffix(b'~>'))))
+        except Exception: pass
+    from reportlab.lib.rl_accel import fp_str
+    command=(fp_str(*[int(palette[0][i:i+2],16)/255 for i in (1,3,5)])+' rg').encode()
+    pages=[s for s in streams if b'BT' in s and b'/F' in s]
+    assert len(pages)>1
+    assert all(command in s for s in pages)
+    assert not any('浅色打印' in w for w in result.warnings)
+
+
+def test_pdf_accepts_asset_contract_beyond_previous_count_and_size():
+    assets=[png_asset(source=str(i)) for i in range(65)]
+    assets[0]=assets[0].model_copy(update={'png_base64':'A'*2800004})
+    values=dict(source={'type':'markdown','markdown':'content'},assets=assets)
+    ExportRequest(format='pdf',**values)
+    with pytest.raises(ValidationError): ExportRequest(format='html',**values)
+    with pytest.raises(ValidationError): ExportRequest(format='docx',**values)
+
+
+def test_pdf_large_png_still_requires_valid_format():
+    asset=png_asset((2100,2000))
+    assert validate_assets([asset],unlimited=True)
+    with pytest.raises(Exception): validate_assets([asset])
+    with pytest.raises(Exception): validate_assets([asset.model_copy(update={'png_base64':'invalid'})],unlimited=True)
+
+
+def test_pdf_embeds_more_than_64_resources_with_theme_background():
+    doc=parse_document(('```mermaid\ngraph LR; A-->B\n```\n\n')*65)
+    from app.export.assets import attach_assets
+    attach_assets(doc,validate_assets([png_asset()],unlimited=True))
+    assert not enrich_document(doc,unlimited=True,options=ExportOptions(theme_id='dark'))
+    assert all('static_png' in node.attributes for node in doc.children)
+    with Image.open(BytesIO(doc.children[-1].attributes['static_png'])) as image:
+        assert image.getpixel((0,0)) == (13,17,23)
+    assert PdfExporter().render(doc,ExportOptions(theme_id='dark')).content.startswith(b'%PDF')
+
+
+def test_pdf_pipeline_ignores_source_and_output_quotas(monkeypatch):
+    monkeypatch.setattr(service,'MAX_MARKDOWN_CHARS',8)
+    monkeypatch.setattr(service,'MAX_EXPORT_BYTES',8)
+    async def run():
+        job=await service.create_export(ExportRequest(format='pdf',source={'type':'markdown','markdown':'Beyond the previous quota.'}))
+        done=await service.wait_for_export(job.job_id)
+        assert done.status.value=='completed'
+        assert service.get_export_file(job.job_id).stat().st_size>8
+        with pytest.raises(Exception):
+            await service.create_export(ExportRequest(format='html',source={'type':'markdown','markdown':'Beyond the previous quota.'}))
+    asyncio.run(run())
+
+
+def test_pdf_accepts_more_than_16_curves_and_keeps_expression_safety():
+    doc=parse_document('```function-plot\n'+'\n'.join(f'y=x+{i}' for i in range(17))+'\n```')
+    result=PdfExporter().render(doc,ExportOptions(theme_id='dark'))
+    assert not any('函数图像' in w for w in result.warnings)
+    unsafe=PdfExporter().render(parse_document('```function-plot\ny=__import__("os")\n```'),ExportOptions())
+    assert any('函数图像' in w for w in unsafe.warnings)
+
+
+def test_pdf_custom_palette_and_math_color():
+    palette=dict(zip(('page','surface','text','muted','code','border','accent'),PALETTES['midnight-purple']))
+    options=ExportOptions(theme_id='my-theme',palette=palette)
+    doc=parse_document('Formula $x^2$')
+    assert not enrich_document(doc,unlimited=True,options=options)
+    math=next(n for n in doc.children[0].children if n.type=='math_inline')
+    with Image.open(BytesIO(math.attributes['static_png'])) as image:
+        assert image.getpixel((0,0))==(25,19,34)
+    assert not any('主题' in w for w in PdfExporter().render(doc,options).warnings)
+    with pytest.raises(ValidationError): ExportOptions(palette={**palette,'text':'url(file:///private)'})