Work diff canvas drops blank context lines when the user's Git config sets diff.suppressBlankEmpty #285

Expected and actual behavior / 实际现象与期望

With diff.suppressBlankEmpty=true in the user's Git config, git diff writes a blank context line as an empty line instead of a single space. Git apply and GNU patch read that empty line as context. parse_unified_diff (server/unified_diff.py) drops it, so the Work attempt diff canvas loses every blank context line, and every following line in the hunk shows an old/new line number that is one too low per dropped line.

Expected: a blank context line is shown with its line numbers, and the rest of the hunk keeps the right numbers.

Steps to reproduce / 复现步骤

git config diff.suppressBlankEmpty true
printf 'a\n\nb\nc\n' > notes.txt && git add notes.txt && git commit -m base

Run an attempt that changes b to B, then open the attempt diff.

The attempt patch is

@@ -1,4 +1,4 @@
 a

-b
+B
 c

Actual: lines a (1/1), -b (old 2), +B (new 2), c (3/3). The blank line is missing.
Expected: a (1/1), blank (2/2), -b (old 3), +B (new 3), c (4/4).

Relevant environment / 使用环境

Platform-independent; current main (f86c72a). Reproduced with Git 2.43 and 2.54. There is no git diff command-line option that overrides this setting.

Sanitized evidence / 错误信息或截图（请先脱敏）

The parser skips every empty line (if current_hunk is None or not raw_line: continue), including one that the hunk header still counts as a context line.

Related issues or fixes / 相关问题或修复

Follow-up to #279 / #284, which pinned the other Git settings that change the patch format.