* fix: hide archived section and empty folders when no sessions remain
- Only push archived group in useSessionGrouping when there are archived
sessions, preventing an empty archived section from rendering
- Hide empty folders in archived bucket via shouldKeepFolder check in
SessionGroupSection (folders with no sessions and no content in
children are filtered out)
- Always filter folders through shouldKeepFolder, not just during search
* perf: memoize archived folder filtering
* perf(sync): per-directory event queues to eliminate cross-session HoL blocking
The SSE event pipeline previously used a single global queue and a single
flush timer shared across all directories. Under concurrent multi-session
workloads, a busy directory's delta storm would block other directories'
status and state events from reaching the UI until the next flush tick,
producing the "multi-session latency" symptom users report.
Split the queue into one DirectoryQueue per directory, each with its own
coalesce map, stale-delta set, and flush timer. Directories flush
independently so a busy directory can no longer starve a quiet one. Coalesce
keys are now scoped to a single directory's queue, so the directory prefix
is removed from the key strings.
Cross-directory behavior only; same-directory multi-session behavior is
unchanged (React 18 auto-batching still collapses a single directory's
flush into one render).
* perf(sync): coalesce consecutive message.part.delta events per flush window
Within a 16ms flush window, consecutive delta events for the same
(messageID, partID, field) tuple are string-concatenated into a single
accumulated delta rather than being queued individually.
This directly addresses same-project multi-session workloads — most
notably parent sessions with subagent tasks (child sessions share the
same directory queue). Both parties stream deltas concurrently, which
previously multiplied raw event count proportionally to the number of
active sessions. Coalescing can reduce queue depth by 10-100x during
active streaming.
Safety: verified against event-reducer.ts — the delta handler is a pure
string append (existingValue + props.delta) with no per-event side
effects (no time.updated, no notifications, no diff calculations). The
merged result is semantically identical to applying each delta separately.
The staleDeltas skip mechanism is unaffected: accumulated delta payloads
retain their type and identifiers, so message.part.updated supersession
still works correctly.
* test(sync): cover per-directory queues and delta coalescing
Extend event-pipeline.test.js with behavioural coverage for both
optimizations landed in 98d013a and 258acf0:
P1 (per-directory queues)
- Delivers events from two directories without loss
- Keeps distinct sessionIDs in the same directory as independent coalesce
slots (session.status is not overwritten across sessions)
- Collapses repeated session.status for the same session down to latest
Option C (delta coalescing)
- Accumulates consecutive deltas for the same (messageID, partID, field)
into a single dispatched event with concatenated content
- Does not merge deltas across different fields on the same part
- Does not merge deltas across different parts on the same message
- Does not merge deltas across different directories (per-dir queues)
- Skips accumulated deltas when message.part.updated is coalesced onto
an earlier update, proving staleDeltas still works with C
- Leaves non-delta coalescing (session.status replace semantics) intact
All 13 tests pass under bun:test.
Also adds event-pipeline.bench.js, a runnable synthetic benchmark that
reports delta reduction and byte integrity across 8 workload scenarios
from "single session, 500 tokens" up to "10 projects × 5 sessions ×
1000 tokens". Run with:
bun packages/ui/src/sync/__tests__/event-pipeline.bench.js
Current numbers on this machine: 99.5% - 99.9% delta event reduction
with full byte-level integrity (concatenated delta bytes always equal
the input total).
* fix(sync): remove staleDeltas — it silently drops delta events
---------
Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>
