Multimodal tool-result retention
工具结果的图文保留
MCP prepares durable images asynchronously while its pure renderer emits text placeholders. Installing prepared content after post-execute policy makes text retention invalidate image replacement. A byte-only limit also cannot compare text with visual input costs.
English
Problem
MCP prepares durable images asynchronously while its pure renderer emits text placeholders. Installing prepared content after post-execute policy makes text retention invalidate image replacement. A byte-only limit also cannot compare text with visual input costs.
Decision
ToolDefinition.projectContent installs execution-prepared content before post-execute policy. The final callback retains its separate role for terminal and job limits. Policy blocks and replacements remain authoritative.
The spill policy prices ordered text/image blocks in estimated tokens, reusing the text estimator and the active route image calculator, including descriptor text. It reserves omission notices, divides remaining tokens between contiguous ends, and omits the middle. Text can split between code points; images remain indivisible at their original positions.
The complete spill file contains accepted text and readable attachment paths in order. Attachments own image bytes. Missing image pricing or a readable recovery path preserves the original result with a diagnostic. PTC program values remain complete; forwarding and logs retain a recovery notice even when every image is omitted.
The spill storage decision still owns backend separation and secure local files. The MCP client decision still owns canonical values and image admission.
Alternatives considered
Restore images after policy edits. This can resurrect blocked images or discarded text. Preparing content before policy lets transformations inspect the actual images.
Keep images outside the budget or charge a fixed maximum. Images must share the result budget with text. The existing route calculator already prices projected dimensions and descriptor text, so it owns that cost.
Embed image bytes in spill text. Base64 inflates the artifact and duplicates attachment storage. Readable attachment paths preserve retrieval and ordering without copying bytes.
Consequences
The shipped result budget is 12,500 estimated tokens, replacing the former 50,000-byte setting. Text estimation remains heuristic; provider usage is authoritative. Unused space at an image boundary stays unused to preserve contiguous ends. Other block types pass through.
中文
Problem
MCP 异步准备持久化图片，而纯渲染器输出文字占位。在执行后策略完成后才安装已准备内容，会让文字保留使图片替换失效。按字节限制也无法比较文字与视觉输入的成本。
Decision
ToolDefinition.projectContent 在执行后策略之前安装执行期间准备的内容。最终回调保留其对终端和任务结果设定上限的独立职责。策略阻止和替换仍然生效。
spill 策略以估算 token 对有序图文块计量，复用文字估算和当前模型图片计算器，并计入说明文字。它预留省略提示，将剩余 token 平分给连续两端，省略中间。文字可在码点之间切分；图片不可切分，并保持原位置。
完整结果文件按顺序保存已接受文字和可读取的附件路径。附件拥有图片字节。缺少图片计量或可读取的恢复路径时，保留原结果并记录诊断。PTC 程序返回值保持完整；全部图片被省略时，转发内容和日志仍保留读取提示。
spill 存储决策继续负责后端拆分和安全的本地文件。MCP 客户端决策继续负责规范值和图片准入。
Alternatives considered
在策略修改后恢复图片。 这可能恢复已阻止图片或已丢弃文字。在策略之前准备内容，让转换能够检查真实图片。
图片不计入预算或按固定上限计费。 图片必须与文字共享结果预算。现有模型计算器已经衡量请求尺寸和说明文字，因此由它负责成本。
把图片字节嵌入 spill 文本。 Base64 会增大产物并重复附件存储。可读取的附件路径在不复制字节的情况下保留读取方式和顺序。
Consequences
随产品提供的结果预算为 12,500 个估算 token，替代此前的 50,000 字节配置。文字计量仍为估算，提供方用量具有权威性。图片分界处剩余空间保持空闲，以维持连续的首尾内容。其他内容块类型原样通过。