[matt2e]

Composer attachment failures didn't say which file or conversation they were about. A background send that failed in one conversation surfaced unnamed in whichever conversation was open, and a multi-file pick with one bad file attached nothing.

What changed for users

Background sends

• The pill reads "Uploading to #Design", plus "and N more" while several sends run. It stays on one line, and Cancel stays at the end of the row as the text changes. Cancel's accessible name names the send it stops: "Cancel upload to #Random".
• Failure toasts are titled "Upload to #Design failed" or "Message to #Design failed to send", with the reason as the description. The recovery notices name the conversation too.
• Notices offer Open #Design, or Open thread in #Design for a reply, when that conversation isn't on screen. Huddles get no Open, because a huddle opens only from its entry point.
• Names follow channelText, so DMs, Solo chats and private channels get no #.

Multi-file picks

• Picking, pasting or dropping several files attaches the ones that fit, in pick order. A file is left out if it's empty, past 10 per message (counting chips already attached), over the size limit, or past the 1,000 MiB drafts budget.
• The toast names what was left out, with one sentence per reason and up to three names plus a count. For example: "Could not attach 1 of 5 files / cloud-placeholder.png is empty."
• A single file or voice note that doesn't fit is refused as before. The one change: an empty file now says " is empty." instead of claiming to exceed the size limit.

Docs: buzz-help.md describes the named pill, Cancel and notices, and when Open appears. It also says the files that fit attach and the rest are named. contributing.md no longer calls Background Send separate work. It now describes the current behaviour: background send in the main window, and paused uploads resume when their composer returns.

Deliberate decisions

• Cancel still stops the newest send, as Desktop does. So in #Design the pill can read "Uploading to #Random and 1 more". The label is now accurate. Stopping only the current conversation's sends is a product call, left for a follow-up.
• Open isn't gated on canOpenLink. That predicate reports registered panel targets only, so it's false for buzz://channel and buzz://message links and would hide Open in every channel host.
• Attaching the first files in pick order, up to the limit, is a judgement call. The alternative was to refuse the whole pick and say how many more fit.

Known follow-ups

• Cancel during publish restores sent files (predates this branch). Cancel doesn't stop a publish already in flight. The message sends, then its caption and chips come back, which invites a double send.
• The refusal toast covers Send (predates this branch). This matters more now that the files that fit stay attached.
• A covered main-pane tab hides Open. When a thread tab in the main pane covers the channel's own composer, Open doesn't show, though the toast still names the conversation. Fixing it means passing shown to that composer, which also changes mention and agent reseeding.

Before and after

Left: before, on main at 8668dbd. Right: after, on this branch at 06ab014. Recorded in Chromium against the fixture relay. The upload failure is a 200 response with an unusable {} body. Each side asserts its own expected state.

1. A send from #Design fails while #Random is open. Before, the pill says only "Uploading", and the failure is one unnamed line with only Dismiss. You find #Design yourself, and the toast follows you there over Send. After, the pill reads "Uploading to #Design". The toast is titled "Upload to #Design failed" with the reason below, and Open #Design lands on the restored caption and failed chip and closes the toast.

ce01-failed-send-before-after.mp4

2. Two sends running. Before, the pill reads "Uploading" and the button's accessible name is just "Cancel". After, the pill reads "Uploading to #Random and 1 more" and Cancel's accessible name is "Cancel upload to #Random". The video shows that name in a label, since it isn't drawn on screen. On both sides, Cancel in #Design stops #Random's send, the newest, and lunch.png comes back to #Random paused. After, the pill then reads "Uploading to #Design", and Cancel doesn't move under the pointer (0 px measured).

ce02-two-sends-before-after.mp4

3. Mixed picks. Four PNGs plus a 0-byte file: before attaches nothing and calls the empty file over the size limit. After attaches the four and says "cloud-placeholder.png is empty." Eleven photos into an empty composer: before attaches nothing. After attaches ten and names offsite-11.png.

ce03-mixed-picks-before-after.mp4

Single-side videos (960 px wide)

Before: 1. failed send from #Design

ce01-failed-send-named-before.mp4

After: 1. failed send from #Design

ce01-failed-send-named-after.mp4

Before: 2. two sends and Cancel

ce02-two-sends-cancel-named-before.mp4

After: 2. two sends and Cancel

ce02-two-sends-cancel-named-after.mp4

Before: 3. mixed picks

ce03-mixed-picks-before.mp4

After: 3. mixed picks

ce03-mixed-picks-after.mp4

Testing

• Vitest: BackgroundUploadStatus, MessageComposer, attachment-draft and attachment-panes. Each new case was shown to fail before its fix.
• Browser: no cases were added or removed. In composer-attachments.spec.mjs, the background-send journey now asserts the named pill, progress bar and Cancel. It also checks a browser-only geometry contract: Cancel ends the row. Without 06ab014 that check fails, with Cancel 535 px short of the row's end. The spec ran in Chromium at the head; WebKit ran only at an earlier commit.
• Not checked: the native desktop app, a real drag and drop, dark theme, and a real 4xx/5xx upload failure. Thread replies, huddles and the recovery notices have unit tests only.

🤖 Generated with Claude Code

[kalvinnchau]

🤖 One test synchronization issue found.

[wesbillman]

🤖 Guardians review — recommend approval; no new blocking findings.

Reviewed the full feature at head 5767d920c2d3b19400e6169ba1bb52587368aee5, target base 9f14241db4f37ebba5eba651b466a241fcfdd655 (merge base 8668dbd46a12d01fb5583c1b520093ff96930a6b).

The prior restored-chip visibility P2 is repaired: MessageComposer.test.tsx:3114–3116 now waits for visibility. Partial attachment admission preserves pick order and existing count/retained-byte limits, charges only admitted files, and returns the actual added IDs. Background sends retain their captured destinations; the label and Cancel action select the same newest live job. Recovery remains with the session-owned draft, and Open uses the existing navigation handler without dismissing a pending recovery.

The disclosed boundaries remain explicit: cancellation after publication starts can restore an already-sent draft, creating a duplicate-send risk; toast overlap with Send predates this patch. The covered main-pane composer can still omit Open because its host does not pass presentation state. Newest-send cancellation can target another conversation, now named accurately. These are not newly discovered regressions or claims that the product tradeoffs have been accepted.

Optional coverage follow-up: exercise Open navigation and focus destination, plus a partial-pick notice, in the real browser journey. Current coverage for these behaviors is at the component level; the browser change checks the Cancel geometry and status labels.

Validation: source-only review; no tests, builds or apps run by reviewers. The inspected hosted snapshot at this head has 41 successful checks and one skipped Windows native check, including successful Vitest flake shards and Chromium/WebKit flake checks. This is CI status evidence, not independent runtime reproduction. The nine videos were not viewed. Native picker/relay-error behavior, screen-reader behavior and narrow/dark rendering remain unverified.