chore: import upstream snapshot with attribution

open-sse/services/compression/engines/rtk/renderers/gitDiff.ts

@@ -0,0 +1,39 @@
+import type { RenderResult, CommandDetectionResult } from "./types.ts";
+import { NO_RENDER } from "./types.ts";
+
+/**
+ * RTK semantic renderer for `git diff` / `git show` output.
+ *
+ * Keeps only:
+ *  - `diff --git a/... b/...` file header lines
+ *  - `@@ ... @@` hunk headers
+ *  - change lines starting with `+` or `-` (but NOT `+++`/`---`)
+ *
+ * Everything else (context lines, index lines, mode lines, etc.) is dropped.
+ * If no hunk header is found, returns no-op (input is not a real diff).
+ */
+export function renderGitDiff(text: string, _detection: CommandDetectionResult): RenderResult {
+  // Guard: must have at least one hunk header
+  if (!text.includes("@@ ")) {
+    return NO_RENDER(text);
+  }
+
+  const kept: string[] = [];
+  for (const line of text.split("\n")) {
+    if (
+      line.startsWith("diff --git ") ||
+      line.startsWith("@@ ")
+    ) {
+      kept.push(line);
+    } else if (/^[+-](?![+-])/.test(line)) {
+      // change line (+foo or -foo) but NOT +++ or ---
+      kept.push(line);
+    }
+    // drop: context lines (space), index lines, --- a/, +++ b/, mode lines, etc.
+  }
+
+  const out = kept.join("\n");
+  if (out === text) return NO_RENDER(text);
+
+  return { text: out, changed: true, renderer: "git-diff" };
+}