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).

tests/sidechat-transcript.spec.ts

@@ -8,7 +8,7 @@
 import { describe, expect, it } from 'vitest'
 import type { SidebarHistoryEntry, SidebarSessionEvent } from '../src/context-types.ts'
 import { SIDE_BOUNDARY_PREFIX, SIDE_BOUNDARY_PROMPT, SIDE_INJECTION_PLUGIN } from '../src/sidechat-core.ts'
-import { collectOwnEvents, toolArgsSummary, transcriptRows, type SidechatTranscriptRow } from '../src/client/sidechat-transcript.ts'
+import { toolArgsSummary, transcriptRows, type SidechatTranscriptRow } from '../src/client/sidechat-transcript.ts'
 
 /** One history entry (event + optional view). */
 function entry(event: SidebarSessionEvent): SidebarHistoryEntry {
@@ -164,69 +164,6 @@ describe('transcriptRows', () => {
   })
 })
 
-describe('collectOwnEvents', () => {
-  /** A paginated fake log: fetchPage(beforeSeq) returns the ≤pageSize events
-   *  ENDING before beforeSeq (exclusive); the tail page when omitted. */
-  function pagedLog(events: SidebarSessionEvent[], pageSize: number) {
-    const calls: Array<number | undefined> = []
-    const fetchPage = async (beforeSeq?: number): Promise<SidebarHistoryEntry[]> => {
-      calls.push(beforeSeq)
-      const window = beforeSeq === undefined ? events : events.filter(e => e.seq < beforeSeq)
-      return window.slice(-pageSize).map(entry)
-    }
-    return { fetchPage, calls }
-  }
-
-  it('finds the seed boundary on the tail page in one fetch', async () => {
-    const { fetchPage, calls } = pagedLog([
-      ev('user/message', 0, { content: textBlocks('inherited'), source: { kind: 'user' } }),
-      ev('session/end-seed', 1),
-      ev('user/message', 2, { content: textBlocks('own'), source: { kind: 'user' } }),
-      ev('assistant/message', 3, { turn: 1, step: 1, message: { content: textBlocks('a') } }),
-    ], 200)
-    const result = await collectOwnEvents(fetchPage)
-    expect(calls).toEqual([undefined])
-    expect(result.seedBoundary).toBe(1)
-    expect(result.entries.map(e => e.event.seq)).toEqual([2, 3])
-  })
-
-  it('walks back across pages until the boundary surfaces', async () => {
-    // A dense chunk tail (cold reads re-expand chunk-rows): the boundary is
-    // several pages back and earlier tool/call events must NOT fall out of
-    // the loaded window (the re-entry tool-row regression).
-    const events = [
-      ev('session/end-seed', 0),
-      ev('tool/call', 1, { turn: 1, step: 1, callId: 'c1', name: 'bash' }),
-      ...Array.from({ length: 12 }, (_, i) => ev('assistant/chunk', 2 + i, { turn: 1, step: 1 })),
-    ]
-    const { fetchPage, calls } = pagedLog(events, 5)
-    const result = await collectOwnEvents(fetchPage)
-    expect(calls.length).toBeGreaterThan(1)
-    expect(result.seedBoundary).toBe(0)
-    // Everything after the marker, oldest-first, deduped.
-    expect(result.entries.map(e => e.event.seq)).toEqual(events.slice(1).map(e => e.seq))
-  })
-
-  it('stops at the log start when no marker exists and reports boundary 0', async () => {
-    const { fetchPage } = pagedLog([
-      ev('user/message', 0, { content: textBlocks('legacy'), source: { kind: 'user' } }),
-      ev('assistant/message', 1, { turn: 1, step: 1, message: { content: textBlocks('a') } }),
-    ], 200)
-    const result = await collectOwnEvents(fetchPage)
-    expect(result.seedBoundary).toBe(0)
-    expect(result.entries.map(e => e.event.seq)).toEqual([0, 1])
-  })
-
-  it('honours the page cap instead of re-walking forever', async () => {
-    const events = Array.from({ length: 30 }, (_, i) => ev('assistant/chunk', i, { turn: 1, step: 1 }))
-    const { fetchPage, calls } = pagedLog(events, 5)
-    const result = await collectOwnEvents(fetchPage, 2)
-    expect(calls).toEqual([undefined, 25])
-    expect(result.seedBoundary).toBe(0)
-    expect(result.entries.map(e => e.event.seq)).toEqual([20, 21, 22, 23, 24, 25, 26, 27, 28, 29])
-  })
-})
-
 describe('toolArgsSummary', () => {
   it('picks the most identifying string field', () => {
     expect(toolArgsSummary('{"command":"ls -la","timeout":1000}')).toBe('ls -la')