diff --git a/apps/review-desktop/code-oss/src/vs/review/common/reviewLens.test.ts b/apps/review-desktop/code-oss/src/vs/review/common/reviewLens.test.ts
index 4470324ed..2c6efa5c4 100644
--- a/apps/review-desktop/code-oss/src/vs/review/common/reviewLens.test.ts
+++ b/apps/review-desktop/code-oss/src/vs/review/common/reviewLens.test.ts
@@ -24,6 +24,20 @@ test('structural folds within the lens survive, overlapping folds do not', () =>
 	assert.ok(!gaps.includes(outside));
 });
 
+test('an exact document lens (tour step, code peek) clips an added file to its +/-3 window; without it, #502 fills the whole open run', () => {
+	const diff = {
+		...plain,
+		sourceLineAlignment: Array.from({ length: 300 }, (_, i) => [null, i] as const),
+		contextScopes: { original: [], modified: [[0, 300] as const] },
+	};
+	const ranges = [{ side: 'head' as const, file: 'new.ts', fromLine: 80, toLine: 87 }];
+	// #502 behavior (Diff tab): the added file is one open run, so contextScopes fills it whole.
+	assert.deepEqual(lensContextGaps(diff, 0, 300, ranges), []);
+	// exact document lens: withLens strips contextScopes before calling lensContextGaps.
+	const clipped = lensContextGaps({ ...diff, contextScopes: undefined }, 0, 300, ranges);
+	assert.deepEqual(clipped.map(gap => [gap.modifiedStart, gap.modifiedCount]), [[1, 76], [91, 210]]);
+});
+
 test('viewed folds never hide an unread counterpart, and do not overlap structural folds', async () => {
 	const { viewedContextGaps } = await import('./reviewLens.js');
 	const range = (side: 'base' | 'head', fromLine: number, toLine: number) => ({ side, file: 'a.ts', fromLine, toLine });
diff --git a/apps/review-desktop/code-oss/src/vs/review/services/reviewApiSourceService.ts b/apps/review-desktop/code-oss/src/vs/review/services/reviewApiSourceService.ts
index b27f49d51..b50e5bcf3 100644
--- a/apps/review-desktop/code-oss/src/vs/review/services/reviewApiSourceService.ts
+++ b/apps/review-desktop/code-oss/src/vs/review/services/reviewApiSourceService.ts
@@ -287,7 +287,7 @@ export class ReviewApiSourceService extends Disposable implements IReviewApiSour
 			const current = spec.pins ? reviewSourceAnchor(view(), spec.pins) : reviewSourceComparison(view());
 			const lens: ReviewDiffLens = {
 				id: "document:" + JSON.stringify([spec.path, spec.ranges, spec.pins]), title: spec.path,
-				reviewId: current.reviewId, version: current.version,
+				reviewId: current.reviewId, version: current.version, exact: true,
 				ranges: spec.ranges.map(range => ({ file: spec.path, side: range.side ?? spec.side, fromLine: range.startLine, toLine: range.endLine })),
 			};
 			return { lens, source: makeSource(() => current) };
diff --git a/apps/review-desktop/code-oss/src/vs/review/services/reviewLens.ts b/apps/review-desktop/code-oss/src/vs/review/services/reviewLens.ts
index 8cc8a33d2..1b73282bc 100644
--- a/apps/review-desktop/code-oss/src/vs/review/services/reviewLens.ts
+++ b/apps/review-desktop/code-oss/src/vs/review/services/reviewLens.ts
@@ -59,7 +59,10 @@ export function withLens(instantiation: IInstantiationService, entries: readonly
 						}) ? { ...gap, collapsed: false } : gap)
 					};
 					const section = progress()?.sections?.find(section => section.id === entry.sectionId);
-					return lens && !lens.wholeFiles ? { ...diff, contextGaps: lensContextGaps(diff, original.getLineCount(), modified.getLineCount(), lensRanges(section ? { ...lens, ranges: section.sources } : lens, entry)) } : diff;
+					// An exact lens (a tour step, a code peek) is authored to show one chunk;
+					// diffr's structural scope expansion is right for the Diff tab, not here.
+					const scopedDiff = lens?.exact ? { ...diff, contextScopes: undefined } : diff;
+					return lens && !lens.wholeFiles ? { ...diff, contextGaps: lensContextGaps(scopedDiff, original.getLineCount(), modified.getLineCount(), lensRanges(section ? { ...lens, ranges: section.sources } : lens, entry)) } : diff;
 				},
 			};
 		},
diff --git a/packages/review-protocol/src/contracts.ts b/packages/review-protocol/src/contracts.ts
index 67e486393..b1a5478b2 100644
--- a/packages/review-protocol/src/contracts.ts
+++ b/packages/review-protocol/src/contracts.ts
@@ -199,6 +199,8 @@ export interface ReviewInlineEditorFactory {
 export interface ReviewDiffLens {
   /** Filter files while retaining ordinary diff context/folding within them. */
   wholeFiles?: boolean;
+  /** Show only the pinned range, ignoring diffr's structural scope expansion. */
+  exact?: boolean;
   id: string;
   title: string;
   reviewId: string;
diff --git a/packages/review/instructions/authoring.md b/packages/review/instructions/authoring.md
index 438b9e7b5..593eb0094 100644
--- a/packages/review/instructions/authoring.md
+++ b/packages/review/instructions/authoring.md
@@ -34,3 +34,4 @@ follow these first five steps in order, with no tool calls beyond what they need
 - keep whiteboards short and sweet when possible (esp. for small changes.) feel free to omit sections.
 - when something (a phrase in the prose, diagram node, etc.) describes actual code in the codebase, always default to attaching/hyperlink code.
 - Link repository code as `[label](review-source:head/src/file.ts#L10-L24)`; use `base` for old code. Use repository-relative paths and verified line numbers.
+- point each code reference (diagram step, call-stack frame, `code_peek`) at the smallest range that shows the claim, usually 3-15 lines: the call, the branch, the assignment. not the whole function. tour steps and peeks show only that range.