fix(office-ui): stop progress-row flicker and surface native role replies end to end

Two user-visible defects in company mode, root-caused via project 6666/8888
DB forensics:

Progress-row flicker (thinking preview appearing/disappearing): progress
entries were broadcast to clients before reaching the persistence buffer,
so a tool_call-triggered session_detail snapshot rebuilt from the DB erased
freshly streamed entries from the live log. Buffer now fills before the
broadcast and session_detail flushes it before reading.

Native role transcripts incomplete (thinking only at start, no narration,
no final summary — external agents unaffected):
- thinking deltas shared one stream id per conversation turn while seq
  reset per iteration, collapsing all iterations into one entry and
  silently dropping live thinking from iteration 2 on; now keyed per
  iteration like assistant deltas
- assistant_delta events were mapped to None; company mode now surfaces
  them as streaming 'assistant' progress entries (rendered as Reply cards,
  merged like thinking, excluded from inline chat rows)
- thinking was persisted one row per token, flooding the 1000-entry cap
  and evicting interleaved tool history; append_progress now folds
  streaming deltas per (type, turn, stream) with seq dedup
- the terminal company turn was hidden at summary detail and, worse, its
  id-keyed backfill merge kept the first-inserted intermediate content, so
  the final reply never reached any channel; terminal turns are now
  flagged company_final_turn, visible at summary detail, and carry their
  own ui_message_id so they insert as fresh rows
- appendProgressEntry applied its seq guard against unrelated entries when
  the stream key was absent from the log, killing the first delta of any
  fresh stream; the guard now only applies within the same stream

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

opc/plugins/office_ui/frontend_src/lib/progressLog.ts

@@ -68,7 +68,7 @@ function canMergeProgress(left: ProgressEntry, right: ProgressEntry): boolean {
   if (leftKey && rightKey) return leftKey === rightKey
   if (right.timestamp - left.timestamp > STREAM_MERGE_WINDOW_MS) return false
   if (left.type !== right.type) return false
-  if (left.type === 'thinking') return true
+  if (left.type === 'thinking' || left.type === 'assistant') return true
   if (left.type === 'tool_call') return left.summary === right.summary
   return false
 }
@@ -83,14 +83,15 @@ function isDuplicateProgress(left: ProgressEntry, right: ProgressEntry): boolean
 }
 
 function mergeProgress(left: ProgressEntry, right: ProgressEntry): ProgressEntry {
-  if (left.type === 'thinking') {
+  if (left.type === 'thinking' || left.type === 'assistant') {
     // Merge detail text only: summary is a label/preview ("Thinking",
     // truncated excerpt), so falling back to it would splice label text
-    // into the middle of the merged thinking stream.
+    // into the middle of the merged stream. Assistant reply streams merge
+    // the same way as thinking streams.
     const detail = mergeText(left.detail ?? '', right.detail ?? '', 'thinking')
     return {
       timestamp: right.timestamp,
-      type: 'thinking',
+      type: left.type,
       summary: summarizeThinking(detail, right.summary || left.summary),
       detail: detail || undefined,
       turnId: right.turnId ?? left.turnId,
@@ -136,8 +137,12 @@ export function appendProgressEntry(
   const actualIndex = targetIndex >= 0 ? log.length - 1 - targetIndex : log.length - 1
   const last = log[actualIndex]
   if (!last) return [normalized]
+  // The seq guard only applies within the SAME stream: when the key was not
+  // found, `last` is an unrelated entry and a fresh stream legitimately
+  // restarts at seq 1 (per-iteration thinking/assistant streams).
   if (
     normalizedKey
+    && targetIndex >= 0
     && typeof last.seq === 'number'
     && typeof normalized.seq === 'number'
     && normalized.seq <= last.seq