From 0d892610c1c7c6197b015ec6fdd864c73b69d194 Mon Sep 17 00:00:00 2001
From: shin-core <153108882+shin-core@users.noreply.github.com>
Date: Tue, 4 Aug 2026 14:59:00 +0900
Subject: [PATCH] fix(review): reserve header length in
 buildUnifiedReviewDiff's no-patch branch

The patched-file branch of buildUnifiedReviewDiff already reserves the header's
length against the remaining budget before appending, but the no-patch branch
(binary/too-large files) appended header + suffix unconditionally. A long enough
file.path made that header overflow the caller's budget, breaking the same
bounded-output invariant the patched branch upholds.

Mirror the patched branch's reservation: when header.length + suffix.length would
exceed the remaining budget, fall through to the existing truncation-notice-and-break
path instead of silently overflowing. The common case (a short path that fits
comfortably) renders byte-for-byte as before.

Closes #10327
---
 src/review/review-diff.ts     | 10 +++++++++-
 test/unit/review-diff.test.ts | 20 ++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/review/review-diff.ts b/src/review/review-diff.ts
index bda991a55..011c3f083 100644
--- a/src/review/review-diff.ts
+++ b/src/review/review-diff.ts
@@ -185,7 +185,15 @@ export function buildUnifiedReviewDiff(files: ReviewDiffFile[], budget: number =
       break;
     }
     if (!file.patch) {
-      diff += `${header}(no inline patch — binary or too large)\n\n`;
+      const suffix = `(no inline patch — binary or too large)\n\n`;
+      // Mirror the patched branch's `header.length + body.length + 2 > remaining` reservation: a long
+      // enough `file.path` can make the header+suffix overflow `budget`, so fall through to the same
+      // truncation-notice-and-break path the `remaining < 240` case uses rather than silently overflowing (#10327).
+      if (header.length + suffix.length > remaining) {
+        diff += truncationNotice;
+        break;
+      }
+      diff += `${header}${suffix}`;
       continue;
     }
     let body = file.patch;
diff --git a/test/unit/review-diff.test.ts b/test/unit/review-diff.test.ts
index 21cb9fc02..981ae4b49 100644
--- a/test/unit/review-diff.test.ts
+++ b/test/unit/review-diff.test.ts
@@ -168,6 +168,26 @@ describe("buildUnifiedReviewDiff — the #1528 fix: never silently drop the file
   });
 });
 
+describe("buildUnifiedReviewDiff — the #10327 fix: a patch-less file's header+suffix respects the remaining budget", () => {
+  it("falls through to the truncation-notice-and-break path when a long path makes header+suffix overflow, staying within budget", () => {
+    // remaining >= 240 (past the `remaining < 240` break), but a ~250-char path makes header+suffix (~310) exceed it,
+    // so the patch-less branch must break with the truncation notice rather than silently overflow `budget` (#10327).
+    const longPath = "a".repeat(250);
+    const budget = 250;
+    const diff = buildUnifiedReviewDiff([{ path: longPath, patch: undefined, status: "added", additions: 0, deletions: 0 }], budget);
+    expect(diff.length).toBeLessThanOrEqual(budget); // the invariant the patched branch already holds
+    expect(diff).toContain("…diff truncated"); // the drop is announced, not silent
+    expect(diff).not.toContain("no inline patch"); // the overflowing file was not appended
+  });
+
+  it("renders a short-path patch-less file unchanged when it comfortably fits (the header+suffix fits, so no break)", () => {
+    const diff = buildUnifiedReviewDiff([{ path: "logo.png", patch: undefined, status: "added", additions: 0, deletions: 0 }]);
+    expect(diff).toContain("### logo.png (added) +0/-0");
+    expect(diff).toContain("(no inline patch — binary or too large)");
+    expect(diff).not.toContain("…diff truncated"); // it fit, so no truncation
+  });
+});
+
 describe("keepHighSignalHunks — non-positive budget guard (#5849)", () => {
   it("returns only the truncation marker when the budget is zero", () => {
     expect(keepHighSignalHunks("@@ a\n+x\n+y", 0)).toBe("… (this file's diff truncated)");