fix(copilot): 调高无限空白检测阈值 20 → 500 (#2647)

* fix(copilot): raise infinite-whitespace threshold from 20 to 500

The previous threshold of 20 falsely aborted legitimate tool calls whose
arguments contain indented code (write_file / edit_file with 4-8 levels
of indentation in Python / YAML / Rust / Markdown easily exceed 20
consecutive whitespace chars, especially when newlines are counted).

The real infinite-whitespace bug emits hundreds to thousands of
consecutive whitespace characters, so 500 keeps the safety net while
drastically reducing false positives.

Refs #2646

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: clarify whitespace threshold comment

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Jason <farion1231@gmail.com>

src-tauri/src/proxy/providers/streaming.rs

@@ -90,14 +90,14 @@ struct ToolBlockState {
     started: bool,
     pending_args: String,
     /// 连续空白字符计数 — 用于检测 Copilot 无限换行 bug
-    /// 当 function call 参数中出现连续 20+ 空白字符时，强制终止流
+    /// 当 function call 参数中的连续空白字符达到阈值时，强制终止流
     consecutive_whitespace: usize,
     /// 是否已因无限空白 bug 被中止
     aborted: bool,
 }
 
 /// 无限空白 bug 的连续空白字符阈值
-const INFINITE_WHITESPACE_THRESHOLD: usize = 20;
+const INFINITE_WHITESPACE_THRESHOLD: usize = 500;
 
 fn build_anthropic_usage_json(usage: &Usage) -> Value {
     let mut usage_json = json!({