fix(messages): plain copy for failed uploads and a blocked Send - #3097

…fore the Play click (#3446)

## Why

`composer-attachments.spec.mjs`, "local previews stay interactive during
eager upload and removal collapses the composer", hung once in CI: [11
Nov, Flake check, WebKit
7/9](https://github.com/block/buzz-app/actions/runs/43114573078/job/130840308592),
passed on re-run. The "Play video" click stayed in "performing click
action" past its 10 s action timeout, the test ran to its 120 s timeout,
and the error context holds no page snapshot.

This PR is a mitigation. The root cause is not pinned down.

## What the trace shows

The test pauses the review viewer's autoplaying 2 s clip with `loop =
true; pause()` and then clicks "Play video". The failed attempt's trace
(artifact 13898342784) shows:

- the viewer opening at 12.07 s and the clip at 1.250 s in the dialog
screenshot at 12.52 s;
- a blank stage with the clip reset to 0 at 13.17 s under the same blob
source;
- the clip playing at 1.417 s at 14.08 s, the `loop = true; pause()`
evaluate at 14.11 s (paused at 1.583 s), and the Play click at 14.13 s;
- a last screencast frame at 14.40 s with the clip back on its first
frame. No frame followed in the remaining 110 s and the click never
returned.

The clip was mid-way and never reached its end after `loop` was set, so
a loop seek did not occur. The page froze when the click resumed the
paused pipeline. The exact WebKit mechanism is unknown.

## Change

Set `playbackRate = 0` instead of `loop`, as `messages.spec.mjs` does
since #3058. A zero-rate play turns `paused` false without advancing the
clock, so the Play click leaves the clip on its paused frame and the
clip can neither end nor loop while the eager-upload assertions run. The
Pause button, `paused`, same-element and same-source assertions are
unchanged.

The second commit corrects the code comment, which first attributed the
stall to the loop seek. It now says the cause is not pinned down and
that rate 0 removes both the end and the loop seek.

No timeouts or assertions were relaxed. No browser cases were added or
removed.

## Evidence

Local runs on Linux, WebKit, `-g "local previews stay interactive"`.

| Scope | Unchanged test | With rate 0 |
|---|---|---|
| Idle host, `--workers=1 --repeat-each=10` | 10/10 passed, 12.5 to 13.0
s | 10/10 passed, 13.0 to 17.2 s |
| Pinned to 4 CPUs shared with 5 busy loops, `--repeat-each=6` | 6/6
passed, 24.9 to 31.2 s | 6/6 passed, 26.5 to 31.9 s |
| Whole file, `--workers=2` | | WebKit 10/10, Chromium 10/10 |

A scratch copy that waited for `ended` before taking over passed 3/3
with rate 0 and 3/3 with `loop`, so the ended path needs no extra seek.
After the comment correction, `user-status.spec.mjs` and this spec
passed 11/11 together on WebKit.

## Not reproduced, not run

- The stall was not reproduced locally, with or without the change. The
contended runs matched the 27 to 29 s of the job's passing repeats and
still passed.
- Because the mechanism is unknown, this change removes two candidate
triggers but is not shown to remove the hang. The test needs watching
after it lands.
- No human has tested this yet, so `buzz-review-completed` is not set.

## Left alone

- The earlier reset of the same video element at about 13 s in the
failing run.
- This spec's cold per-test dev server.
- Open PR #3097 edits other parts of `composer-attachments.spec.mjs`. A
trial merge against this change is clean.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: mtoohey <[email protected]>
Signed-off-by: Matt Toohey <[email protected]>
Co-authored-by: Claude Fable 5.1 <[email protected]>