Attachments carousel loading optimizations

[szymonzalarski98]

PR #82282 was reverted because it exposed a pre-existing bug:
convertFileToAttachment() did not set attachmentID, causing
every Lightbox to resolve to page = 0 via findIndex. With
FALLBACK_OFFSET=2, pages beyond ±2 of the incorrect page 0
showed blank on Android (NUMBER_OF_CONCURRENT_LIGHTBOXES=1).

Explanation of Change

• Set attachmentID in convertFileToAttachment() using
  file.uri (root cause fix)
• Add source-based fallback in Lightbox findIndex when
  attachmentID is undefined (defense-in-depth)
• Re-introduce FALLBACK_OFFSET=2 to limit fallback image
  rendering to ±2 pages
• Re-introduce image priority prop (HIGH/NORMAL/LOW) for
  expo-image loading order
• Add IMAGE_LOADING_PRIORITY constant and priority prop to
  Image types
• Add unit tests covering page resolution, fallback range,
  and priority assignment

Fixed Issues

$ #81250
PROPOSAL:

Tests

Prerequisites: Use a chat room with 30+ image attachments.
Each scenario below should be tested twice — once after a
hard refresh of the app (to ensure no cached images give
false positives), and once without a refresh (normal warm
state).

Scenario 1: Sequential swipe from first to last and back

1. Open the chat room
2. Tap on the first image attachment to open the carousel
3. Verify the image loads within 1-2 seconds
4. Swipe forward through every single image one by one until
   the last one
5. Verify each image displays correctly (no blank screens, no
   excessive loading time)
6. Swipe backward through every single image back to the
   first one
7. Verify each image still displays correctly on the way back

Scenario 2: Opening from the middle and swiping in both
directions

1. Open the chat room
2. Tap on an image somewhere in the middle of the
   conversation
3. Verify the image loads within 1-2 seconds
4. Swipe 5 images backward (toward the beginning) — verify
   each one displays
5. Swipe 10 images forward (5 back to start + 5 past it) —
   verify each one displays
6. Swipe back to the original image — verify it still
   displays

Scenario 3: Opening the last image

1. Open the chat room
2. Tap on the last image in the conversation
3. Verify the image loads within 1-2 seconds (previously took
   4-5+ seconds)
4. Swipe backward through 5 images — verify each displays
   correctly

Scenario 4: Zoom and gestures

1. Open any image in the carousel
2. Verify zoom (pinch) and pan gestures work correctly
3. Swipe to adjacent images — verify gestures still work
4. Verify no errors appear in the JS console

Offline tests

QA Steps

Same as tests

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I verified there are no new alerts related to the canBeMissing param for useOnyx
• I followed proper code patterns (see Reviewing the code)
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    • If any non-english text was added/modified, I used JaimeGPT to get English > Spanish translation. I then posted it in #expensify-open-source and it was approved by an internal Expensify engineer. Link to Slack message:
  • I verified all numbers, amounts, dates and phone numbers shown in the product are using the localization methods
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
  • I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
  • I verified the JSDocs style guidelines (in STYLE.md) were followed
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
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• If any new file was added I verified that:
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  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• If new assets were added or existing ones were modified, I verified that:
  • The assets are optimized and compressed (for SVG files, run npm run compress-svg)
  • The assets load correctly across all supported platforms.
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

recording_images_android_fix.mov

Android: mWeb Chrome

iOS: Native

recording_images_ios_fix.mov

iOS: mWeb Safari

MacOS: Chrome / Safari

[melvin-bot]

@abzokhattab Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

[codecov]

Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
src/CONST/index.ts	92.43% <ø> (+5.04%)	⬆️
src/components/Lightbox/index.tsx	89.06% <100.00%> (+24.35%)	⬆️
...entModalContent/AddAttachmentModalCarouselView.tsx	5.26% <12.50%> (-1.41%)	⬇️
... and 136 files with indirect coverage changes

[chatgpt-codex-connector]

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Reviewed commit: bfdc21b735

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[chatgpt-codex-connector]

Guard missing pager matches before setting page index

findIndex can return -1 here when the current attachment is not present in pagerItems (for example on web carousels where the context only provides a single source entry). In that case this component treats the visible item as inactive, and isImageLoaded short-circuits to true, so the loading indicator is skipped and users can see a blank frame until the image finishes loading. Please handle the -1 case explicitly (e.g., fallback to activePage/0) before deriving active/loading state.

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[szymonzalarski98]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

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[abzokhattab]

reviewing it today

[abzokhattab]

Reviewer Checklist

• I have verified the author checklist is complete (all boxes are checked off).
• I verified the correct issue is linked in the ### Fixed Issues section above
• I verified testing steps are clear and they cover the changes made in this PR
  • I verified the steps for local testing are in the Tests section
  • I verified the steps for Staging and/or Production testing are in the QA steps section
  • I verified the steps cover any possible failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
• I checked that screenshots or videos are included for tests on all platforms
• I included screenshots or videos for tests on all platforms
• I verified that the composer does not automatically focus or open the keyboard on mobile unless explicitly intended. This includes checking that returning the app from the background does not unexpectedly open the keyboard.
• I verified tests pass on all platforms & I tested again on:
  • Android: HybridApp
  • Android: mWeb Chrome
  • iOS: HybridApp
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• If there are any errors in the console that are unrelated to this PR, I either fixed them (preferred) or linked to where I reported them in Slack
• I verified there are no new alerts related to the canBeMissing param for useOnyx
• I verified proper code patterns were followed (see Reviewing the code)
  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick).
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text shown in the product is localized by adding it to src/languages/* files and using the translation method
  • I verified all numbers, amounts, dates and phone numbers shown in the product are using the localization methods
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
  • I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
  • I verified the JSDocs style guidelines (in STYLE.md) were followed
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I verified that this PR follows the guidelines as stated in the Review Guidelines
• I verified other components that can be impacted by these changes have been tested, and I retested again (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar have been tested & I retested again)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.ts or at the top of the file that uses the constant) are defined as such
• If a new component is created I verified that:
  • A similar component doesn't exist in the codebase
  • All props are defined accurately and each prop has a /** comment above it */
  • The file is named correctly
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• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG)
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
• For any bug fix or new feature in this PR, I verified that sufficient unit tests are included to prevent regressions in this flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.
• I have checked off every checkbox in the PR reviewer checklist, including those that don't apply to this PR.

Screenshots/Videos

Android: HybridApp

Screen.Recording.2026-02-25.at.02.06.26.mov

Screen.Recording.2026-02-25.at.02.08.07.mov

Screen.Recording.2026-02-25.at.02.10.01.mov

Screen.Recording.2026-02-25.at.02.11.30.mov

Android: mWeb Chrome

Screen.Recording.2026-02-25.at.02.15.01.mov

iOS: HybridApp

Screen.Recording.2026-02-25.at.01.29.41.mov

Screen.Recording.2026-02-25.at.01.57.38.mov

Screen.Recording.2026-02-25.at.01.59.25.mov

iOS: mWeb Safari

Screen.Recording.2026-02-25.at.02.01.47.mov

MacOS: Chrome / Safari

Screen.Recording.2026-02-25.at.01.20.53.mov

Screen.Recording.2026-02-25.at.01.22.15.mov

[abzokhattab]

LGTM

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