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/context-types.ts

@@ -304,39 +304,6 @@ export interface SidebarSessionPersistenceService {
   }>
 }
 
-/** RPC result slot mirror (`RpcResult<T>` on the wire). */
-export type SidebarRpcResult<T> = { ok: true; value: T } | { ok: false; error: { code: string; message: string } }
-
-/** Unary response mirror (`RpcResponse<T>` on the wire). */
-export interface SidebarRpcResponse<T> {
-  rpcId: unknown
-  result: SidebarRpcResult<T>
-}
-
-/** The generic session-history RPC face the Side Chat transcript polls
- *  (subagent.history verifies subagent-catalog membership, which our custom
- *  side-thread children do not have — the generic session.history reads any
- *  durable log directly). */
-export interface SidebarSessionHistoryRpc {
-  history(
-    payload: { sessionId: string; beforeSeq?: number; maxMessages?: number },
-    signal?: AbortSignal,
-  ): Promise<SidebarRpcResponse<{ events: SidebarHistoryEntry[]; hasMore: boolean }>>
-}
-
-/** The wire face the Subagent activity summary needs (subset of `ctx.connection`). */
-export interface SidebarConnectionHandle {
-  api: {
-    sessions: SidebarSessionHistoryRpc
-    subagents: {
-      history(
-        payload: SidebarSubagentAddress & { beforeSeq?: number; maxMessages?: number },
-        signal?: AbortSignal,
-      ): Promise<SidebarRpcResponse<{ events: SidebarHistoryEntry[]; hasMore: boolean }>>
-    }
-  }
-}
-
 /** The client session list snapshot the sidebar subscribes to. */
 export interface SidebarSessionList {
   current: string | undefined
@@ -527,8 +494,6 @@ export interface SidebarContextShape {
   webServer: SidebarWebServer
   /** The session store (host `.get`) and the client list feed (`.list`) faces. */
   sessions: SidebarSessionStore & SidebarSessionsService
-  /** The wire handle the Side Chat transcript polls through. */
-  connection: SidebarConnectionHandle
   /** The web runtime trust list (bind-derived). */
   webRuntime: SidebarWebRuntime
   /** The client slot registry (register/inject). */