* feat(frontend): add side conversations for quoted follow-ups
* style(frontend): apply prettier formatting to sidecar-chat files
* fix(frontend): surface sidecar cascade cleanup failures via console.warn
Previously deleteSidecarThreadsForParent silently swallowed both
lookup errors and per-thread deletion failures, so parent thread
deletions could succeed while orphaning sidecar threads with no
signal to the caller. Log a warning that includes the parent id
and the failed thread ids/reasons so the leak is discoverable in
telemetry, matching the existing console.warn/error pattern in
this file.
* fix(frontend): address all sidecar review feedback
Resolve every reviewer comment on PR #3934:
- input-box/hooks/sidecar-panel: clear quoted references only via an
`onSent` callback that fires after the in-flight guard, so a dropped
send no longer silently discards quotes (willem-bd #3550).
- message-list: flip the selection toolbar below the selection when it
would clip above the viewport (willem-bd #3551).
- reference-metadata/thread/input-box: keep referenced ids, roles, and
count arrays 1:1 parallel instead of deduping ids (willem-bd #3552).
- message-list: widen selection containment to the shared assistant-turn
container and hint when a selection crosses messages (willem-bd #3553).
- sidecar/api: coalesce concurrent sidecar creates for one parent behind
a single in-flight promise to prevent duplicates (willem-bd #3554).
- sidecar-trigger/context: force-restore on trigger click so a sidecar
deleted elsewhere self-heals instead of opening a dead thread
(willem-bd #3555).
- threads/hooks: surface sidecar cascade cleanup failures via
console.warn for both lookup and per-thread deletes (Copilot).
Add unit + e2e coverage for parallel metadata, atomic create, and
trigger self-healing.
A reasoning+content AI message with no tool calls was grouped into both an
`assistant:processing` group (the ChainOfThought panel above the bubble) and an
`assistant` group (the bubble's own Reasoning collapsible), so its reasoning
rendered twice. Such a message now becomes only the assistant bubble; the
ChainOfThought panel keeps handling intermediate reasoning and tool steps.
Closes#3868
