chore(file-viewer): update scroll-anchor tsdoc, remove test separators, add hydrate linger tests

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/home/hooks/use-file-preview-sessions.test.tsx

@@ -176,11 +176,6 @@ describe('reduceFilePreviewSessions', () => {
   })
 
   it('lingers on the completed session when it is the only one (no successor)', () => {
-    // Completing the only session must NOT drop activeSessionId to null.
-    // The linger keeps the completed session active so downstream consumers
-    // continue to receive previewText and the file viewer stays mounted,
-    // preserving the user's scroll position until a new tool call arrives
-    // or the session store is reset.
     const onlyStreaming = reduceFilePreviewSessions(INITIAL_FILE_PREVIEW_SESSIONS_STATE, {
       type: 'upsert',
       session: createSession({
@@ -247,9 +242,6 @@ describe('reduceFilePreviewSessions', () => {
   })
 
   it('holds the linger when an empty pending session arrives (no content yet)', () => {
-    // Between tool calls, a new empty/pending session may arrive before its
-    // first content chunk. The active session must not switch to it so the
-    // file viewer stays mounted and scroll position is preserved.
     const lingered = reduceFilePreviewSessions(INITIAL_FILE_PREVIEW_SESSIONS_STATE, {
       type: 'upsert',
       session: createSession({
@@ -271,7 +263,6 @@ describe('reduceFilePreviewSessions', () => {
       }),
     })
 
-    // New session arrives but with no renderable content (pending, empty).
     const afterEmptyUpsert = reduceFilePreviewSessions(afterComplete, {
       type: 'upsert',
       session: createSession({
@@ -285,7 +276,6 @@ describe('reduceFilePreviewSessions', () => {
 
     expect(afterEmptyUpsert.activeSessionId).toBe('preview-1')
 
-    // Once the first content chunk arrives, active switches.
     const afterContent = reduceFilePreviewSessions(afterEmptyUpsert, {
       type: 'upsert',
       session: createSession({
@@ -467,6 +457,88 @@ describe('reduceFilePreviewSessions', () => {
     expect(hydrated.sessions['preview-2']?.previewText).toBe('new')
   })
 
+  it('hydrate preserves linger when no non-complete session exists in incoming batch', () => {
+    const lingered = reduceFilePreviewSessions(
+      reduceFilePreviewSessions(INITIAL_FILE_PREVIEW_SESSIONS_STATE, {
+        type: 'upsert',
+        session: createSession({
+          id: 'preview-1',
+          toolCallId: 'preview-1',
+          previewVersion: 2,
+          previewText: 'final',
+        }),
+      }),
+      {
+        type: 'complete',
+        session: createSession({
+          id: 'preview-1',
+          toolCallId: 'preview-1',
+          status: 'complete',
+          previewVersion: 3,
+          completedAt: '2026-04-10T00:00:02.000Z',
+          previewText: 'final',
+        }),
+      }
+    )
+
+    // Hydrate with the same completed session — no non-complete successor.
+    const afterHydrate = reduceFilePreviewSessions(lingered, {
+      type: 'hydrate',
+      sessions: [
+        createSession({
+          id: 'preview-1',
+          toolCallId: 'preview-1',
+          status: 'complete',
+          previewVersion: 3,
+          previewText: 'final',
+          completedAt: '2026-04-10T00:00:02.000Z',
+        }),
+      ],
+    })
+
+    expect(afterHydrate.activeSessionId).toBe('preview-1')
+  })
+
+  it('hydrate releases linger when a non-complete session is present in the incoming batch', () => {
+    const lingered = reduceFilePreviewSessions(
+      reduceFilePreviewSessions(INITIAL_FILE_PREVIEW_SESSIONS_STATE, {
+        type: 'upsert',
+        session: createSession({
+          id: 'preview-1',
+          toolCallId: 'preview-1',
+          previewVersion: 2,
+          previewText: 'final',
+        }),
+      }),
+      {
+        type: 'complete',
+        session: createSession({
+          id: 'preview-1',
+          toolCallId: 'preview-1',
+          status: 'complete',
+          previewVersion: 3,
+          completedAt: '2026-04-10T00:00:02.000Z',
+          previewText: 'final',
+        }),
+      }
+    )
+
+    const afterHydrate = reduceFilePreviewSessions(lingered, {
+      type: 'hydrate',
+      sessions: [
+        createSession({
+          id: 'preview-2',
+          toolCallId: 'preview-2',
+          status: 'streaming',
+          previewVersion: 1,
+          previewText: 'new content',
+        }),
+      ],
+    })
+
+    expect(afterHydrate.activeSessionId).toBe('preview-2')
+  })
+
   it('complete for a non-active session updates the session but keeps activeSessionId', () => {
     let state = reduceFilePreviewSessions(INITIAL_FILE_PREVIEW_SESSIONS_STATE, {
       type: 'upsert',

apps/sim/hooks/use-scroll-anchor.test.ts

@@ -10,8 +10,6 @@ import { describe, expect, it } from 'vitest'
 import { computeSpacerShortage } from '@/hooks/use-scroll-anchor'
 
 describe('computeSpacerShortage', () => {
-  // ── no shortage needed ────────────────────────────────────────────────────
-
   it('returns 0 when content is exactly tall enough', () => {
     // user at 500, viewport 600 → needs 1100; content is exactly 1100
     expect(computeSpacerShortage(500, 600, 1100, 0)).toBe(0)
@@ -31,8 +29,6 @@ describe('computeSpacerShortage', () => {
     expect(computeSpacerShortage(0, 600, 1000, 0)).toBe(0)
   })
 
-  // ── shortage cases ───────────────────────────────────────────────────────
-
   it('returns positive shortage when content shrank to almost nothing', () => {
     // user at 500, viewport 600 → needs 1100; content shrank to 100
     expect(computeSpacerShortage(500, 600, 100, 0)).toBe(1000)
@@ -47,8 +43,6 @@ describe('computeSpacerShortage', () => {
     expect(computeSpacerShortage(500, 600, 1099, 0)).toBe(1)
   })
 
-  // ── spacer already inflated from a previous update ───────────────────────
-
   it('subtracts existing spacer height before recomputing shortage', () => {
     // spacer was 900 from last update; content grew to 1000 natural height
     // scrollHeight = 1000 + 900 = 1900; needed = 500 + 600 = 1100
@@ -76,8 +70,6 @@ describe('computeSpacerShortage', () => {
     expect(computeSpacerShortage(500, 600, 2000, 1200)).toBe(300)
   })
 
-  // ── user scrolled deep into a long document ──────────────────────────────
-
   it('handles large scroll positions correctly', () => {
     // user at 5000, viewport 600 → needs 5600; content shrank to 200
     expect(computeSpacerShortage(5000, 600, 200, 0)).toBe(5400)
@@ -89,8 +81,6 @@ describe('computeSpacerShortage', () => {
     expect(computeSpacerShortage(1400, 600, 100, 0)).toBe(1900)
   })
 
-  // ── edge: zero-height content (first chunk of a fresh write) ─────────────
-
   it('handles zero-height content', () => {
     // first streaming chunk is empty; user was at 500
     expect(computeSpacerShortage(500, 600, 0, 0)).toBe(1100)

apps/sim/hooks/use-scroll-anchor.ts

@@ -21,9 +21,10 @@ export function computeSpacerShortage(
  * Manages scroll for a streaming file-preview container.
  *
  * Never-scrolled: auto-follows new content to the bottom (MutationObserver
- * keeps it pinned). Has-scrolled: position is locked via a spacer element
- * that inflates `scrollHeight` to prevent the browser from clamping `scrollTop`
- * when replace-mode streaming temporarily produces a shorter chunk.
+ * keeps it pinned). Scrolled-up: position is locked via a spacer element that
+ * inflates `scrollHeight` to prevent the browser from clamping `scrollTop` when
+ * replace-mode streaming temporarily produces a shorter chunk. Scrolled back to
+ * the bottom: auto-follow re-engages.
  *
  * @param isStreaming - whether the container is currently receiving streaming content
  * @param content - drives spacer recalculation; pass the current text value