#2523 · Copying a chat text selection pastes invisible trailing newlines

Bug Low priority Effort: unset ui open on GitHub 2026-08-27 · base ad79bbb5ec909524f8f281e62d860c588a86f332

Verdict: REPRODUCED · Root-cause confidence: high

1. TL;DR

Chromium can extend a visible assistant-text selection into the next timeline row.

The highlight shows only the sentence, but the native selection and clipboard contain six final newline characters.

The selection controller removes this whitespace only from its menu payload. It does not change the native browser range.

The composer keeps normal plain-text newline characters, so the paste increases its height from 22 to 155 pixels.

The submit path removes the final newline characters. Thus, the defect affects the draft but not the sent message.

2. Claims vs findings

Claim from the issue	Status	Evidence
A visible sentence selection can paste extra blank lines.	Verified	The real app pasted six clipboard newline characters as seven editor breaks.
The native selection and clipboard contain seven newline characters.	Partly verified	This fixture produced six clipboard newline characters. The exact count changes with the range endpoint and DOM shape.
The provider does not affect the defect after the message exists.	Verified	Trusted browser copy and paste actions reproduced the defect without a provider request.
The defect occurs only in the draft.	Verified	The stored user row contained only the sentence after the test submitted the expanded draft.
Issue #1590 is not a duplicate.	Verified	Issue #1590 covers Clipboard API failure on an insecure remote origin.

3. Environment

bb 0.40.0 at ad79bbb5ec909524f8f281e62d860c588a86f332.
Linux 7.0.0-30-generic on x86-64.
The investigation shell used Node.js v24.18.0 with ABI 137.
The isolated development server used Node.js v22.23.2 with ABI 127.
Headless Chrome 152.0.0.0 through doobie 0.1.2.
Codex CLI 0.150.1 created the fixture messages.
App localhost:11116, server localhost:19116, and host daemon 127.0.0.1:27116.
The launcher used a worktree-specific directory under ~/.bb-dev/.

4. Minimal reproduction

Use an isolated development instance and a thread with two completed turns.

scripts/bb-dev-app current
eval "$(scripts/bb-dev-app env)"
app_url=$(scripts/bb-dev-app status | sed -n 's/^App: //p')

spawn_json=$(node packages/scripts/dist/commands/run-cli.js thread spawn \
  --project proj_personal \
  --machine bee \
  --provider codex \
  --permission-mode accept-edits \
  --title "Issue 2523 reproduction" \
  --prompt "Reply with exactly this sentence: The clipboard should contain only the text that the user can see selected." \
  --json)
thread_id=$(printf '%s' "$spawn_json" | jq -r '.id')
node packages/scripts/dist/commands/run-cli.js thread wait \
  "$thread_id" --status idle --timeout 120
node packages/scripts/dist/commands/run-cli.js thread tell \
  "$thread_id" "Reply with exactly: OK."
node packages/scripts/dist/commands/run-cli.js thread wait \
  "$thread_id" --status idle --timeout 120

if test -f /home/sawyer/.bb/reports-work/issues/2523/repro/reproduce.js; then
  cp /home/sawyer/.bb/reports-work/issues/2523/repro/reproduce.js \
    reproduce-2523.js
else
  curl -fsSL \
    https://get-bb.github.io/reports/issues/2523/repro/reproduce.js \
    -o reproduce-2523.js
fi
doobie --headless -b bb-report-2523 -e \
  "const page = await browser.getPage('issue-2523-repro'); await page.goto('${app_url}/threads/${thread_id}'); page.url();"
doobie --headless -b bb-report-2523 run reproduce-2523.js

The first download path supports this workflow host. The public URL supports readers after publication.

Both paths create reproduce-2523.js in the checkout.

Source artifact: reproduce.js.

The base commit produced this output:

selection.trailingWhitespace: 6
clipboard.trailingWhitespace: 6
composer.beforeHeight: 22.09375
composer.height: 154.65625
submittedUserRow.text:
"The clipboard should contain only the text that the user can see selected."
submittedUserRow.trailingWhitespace: 0

The real bb thread with only the assistant sentence visibly selected — The visible highlight ends after the period. The native range continues to the next row boundary.

The bb composer after the selected sentence was pasted with blank lines — The pasted sentence occupies the top line. Six invisible newline characters expand the composer.

Raw evidence: live-result.json and verification.txt.

5. Root cause

Chromium serializes block boundaries when a native range ends at the start of the next timeline row.

The code knows about this browser behavior. It accepts a whitespace-only boundary spill for the selection menu.

See the boundary-spill check.

The controller calls trim() before it sends text to the menu.

See the selection read.

This operation does not change the native Range. The browser still owns the Ctrl+C result.

The shared event registry has no copy event listener.

See the registered event list.

The normal paste path reads text/plain and inserts the full value.

See the normal paste branch.

The plain-text normalizer changes only line-end format. It keeps final newline characters.

See the normalizer.

An existing test models the same whitespace spill but checks only the menu payload.

See the boundary-spill test.

6. Proposed fix (first principles)

Add one shared copy listener beside the selection listeners.

Handle only a range with visible text in one message and whitespace outside that message.

Clip that spill during native serialization. Restore the original range after Chromium creates both clipboard formats.

Keep deliberate cross-message text, selected media, newer selections, and multiple ranges unchanged.

Do not trim all composer pastes. Users can intentionally paste final blank lines from other applications.

Add a DOM test for the copy payload. Add a real Chrome test for the final clipboard value.

This UI-only fix does not change a server or host-daemon wire contract.

7. PR review

PR #2556 · Fix copied chat selections with invisible trailing newlines

The PR changes two app files. It adds a shared copy listener and 187 lines of focused event tests.

The listener clips only a whitespace boundary spill. It restores the range in the next task if no newer selection exists.

Review item	Finding
Root cause	The fix acts before Chromium serializes the native range. It does not change the paste path.
Selection safety	The code keeps cross-message text, selected media, multiple ranges, and newer selections.
Live Chromium result	The native selection kept six newlines. The clipboard had zero, and the composer stayed at 22.09375 pixels.
Tests	Direct Vitest passed 18 tests. Turbo typecheck passed three tasks.
Current main	`git merge-tree --write-tree` completed without conflicts against `3d57259ab032301d08c1cd9a7e3562f659ac1b3e`.
CI	All app tests passed. Linux Package Smoke failed when the AppImage exited with `SIGTRAP`.

The failing smoke check is outside the two-file UI change. The matching macOS package smoke check passed.

Verdict: MERGE AFTER CI RERUN. The fix removes the defect and preserves the important selection cases.

8. Related issues

#1590 covers copy failures on insecure remote origins. It has a different cause.
PR #274 documented Chromium’s whitespace-only boundary spill for triple-click selection.

9. Appendix

Checks

pnpm install --frozen-lockfile --prefer-offline --package-import-method=copy completed.
pnpm exec turbo run build passed 18 tasks.
Three direct Vitest files passed 127 tests.
The Turbo test gate stopped in native-module setup with signal 139 before Vitest started.
The revised browser script reproduced the selection, clipboard, composer, and stored user row.
PR #2556 removed the clipboard spill in the same live Chromium test.
PR #2556 merges without conflicts against origin/main at 3d57259ab032301d08c1cd9a7e3562f659ac1b3e.

Commands

gh issue view 2523 --comments
gh issue view 2523 --json number,title,body,comments,labels,projectItems,url
pnpm install --frozen-lockfile --prefer-offline --package-import-method=copy
pnpm exec turbo run build
scripts/bb-dev-app current
node packages/scripts/dist/commands/run-cli.js thread spawn ...
node packages/scripts/dist/commands/run-cli.js thread tell ...
doobie --headless -b bb-report-2523 ...
pnpm exec turbo run test --filter=@bb/app -- ...
pnpm exec vitest run ...
pnpm exec turbo run typecheck --filter=@bb/app
gh pr view 2556 ...
git fetch origin pull/2556/head:refs/remotes/origin/pr-2556
git diff "$(git merge-base origin/main origin/pr-2556)"..origin/pr-2556 -- ...
git merge-tree --write-tree origin/main origin/pr-2556
git blame ...
git log ad79bbb5ec90..origin/main -- ...

Verification

The verifier ran the original commands twice. The JSON capture and script path failed.

This revision uses the built CLI for clean JSON. It downloads the script to a local file.

The revised script now submits the draft and reads the new user row from the server timeline.

The revision also reviews PR #2556, its diff, tests, current checks, live fix, and main compatibility.