fix(sidechat): read the transcript through the plugin's own events route

DSH 0.1.2-alpha.1 removed the client `ctx.connection.api` face (Remote
gateway migration), so every Side Chat transcript poll (`sessions.history`)
threw TypeError into the view's catch and was swallowed — the tab rendered
an empty transcript forever, silently (no console error, so the mount lane
never caught it). The successor APIs are not a drop-in either:
session/follow|page reject plain session addresses for origin:'subagent'
logs (agent-busy fence) and paging cannot read past the current cursor.

Move the transcript to the plugin's own wire — one transport for every
DSH generation:

- new `sidechat.events` route: live threads read the in-memory
  `agent.session.events`; cold threads read `sessionPersistence.inspect`
  (both seams exist since 0.1.0-rc.8; alpha.1's inspect returns the
  expanded logical log, never the packed chunk-row encoding). The
  inherited seed is cut host-side (`threadOwnLogEvents`), polls ride an
  `afterSeq` delta, and the response is tail-capped at 8000 events (the
  old client walk ceiling).
- SideChatView.fetchThread is single-path; collectOwnEvents (the client
  walk) is gone, and so are the ctx.connection mirror and inject entry
  (no consumer left).
- transcriptRows keeps re-cutting at session/end-seed as defense in
  depth.

Verification:
- unit: sidechat.events route (seed cut, afterSeq delta + never
  resurrecting the seed, cap, cold/live sources, 404/503/bad-request),
  full suite 1104 passed; typecheck and build (purity gate) green.
- mount e2e vs a real dsh-v0.1.2-alpha.1 source build: 14/14, including
  the Side Chat tab sweep polling sidechat.events (performance resource
  assertion) and live + post-dispose (persisted) route reads.
- mount e2e vs PATH dsh 0.1.0-rc.8: 14/14 (no regression).

src/sidechat-core.ts

@@ -416,13 +416,18 @@ export interface SidechatThreadInfo {
 }
 
 /** The events a thread produced itself: everything after the LAST
- *  `session/end-seed` marker (the fork-seed boundary). */
-export function threadOwnEvents(entries: readonly SidebarHistoryEntry[]): SidechatLogEvent[] {
-  const events = entries.map(entry => entry.event)
+ *  `session/end-seed` marker (the fork-seed boundary). A log with no marker
+ *  (a thread created before seeding existed) is returned whole. */
+export function threadOwnLogEvents(events: readonly SidechatLogEvent[]): SidechatLogEvent[] {
   for (let index = events.length - 1; index >= 0; index--) {
     if (events[index]?.type === 'session/end-seed') return events.slice(index + 1)
   }
-  return events
+  return [...events]
+}
+
+/** {@link threadOwnLogEvents} over history rows (the client cache shape). */
+export function threadOwnEvents(entries: readonly SidebarHistoryEntry[]): SidechatLogEvent[] {
+  return threadOwnLogEvents(entries.map(entry => entry.event))
 }
 
 /**