round 1: project the web transcript from append-origin events

Replace the surface-ordered fold with a log-ordered human transcript:
append-origin surface events at their own log positions plus one marker per
landed compaction checkpoint. Command folding, the tool-call index, and the
rev-keyed memo carry over unchanged.

Removes foldDegraded, the padding sentinels, baseSeq, and degradedSeqs() --
they existed only to satisfy the core fold's seq === index assertion. That
also closes the pagination hole A1 exposed: a page can carry a checkpoint
whose shadowed range fell outside the window, and nothing resolves
surfaceOp.start anymore.

apps/web/tests/seeded-history.e2e.ts

@@ -1,8 +1,8 @@
 // Web e2e scenario: seeded history. A recorded session seeded cold through
 // the REAL persistence API renders purely from the log — the surface nothing
 // else covers: sidebar cold listing, the implicit resume/attach inside the
-// history RPC, history-page tool views, and the client fold of historical
-// events — with ZERO model calls in replay (no replay fixture; a stray stream
+// history RPC, history-page tool views, and the client's log-ordered transcript
+// of historical events — with ZERO model calls in replay (no replay fixture; a stray stream
 // fails loud on the open llm seam). The seed is a recorded fixture under the
 // same record discipline as every other: DSH_SNAPSHOT=record drives the turn
 // live through the composer (real read tool against seeded workspace files)
@@ -27,6 +27,77 @@ const SEED_ID = 'seeded-history-web-e2e'
 
 const PROMPT = 'Use the read tool twice in one assistant message: read a.txt and b.txt. Then reply with the single word DONE and stop.'
 
+/**
+ * Append a complete, valid compaction transaction over the recorded turn's own
+ * surface. The recording stays model-authentic and reusable; replay adds this
+ * deterministic condition before seeding it cold, so the scenario pins the bug
+ * this change fixes — a landed compaction must not erase history the reader
+ * already saw — through the real host and the real browser.
+ * @param raw - the committed seed fixture text.
+ * @returns the fixture with a compacted turn appended.
+ */
+function withCompaction(raw: string): string {
+  const lines = raw.trimEnd().split('\n')
+  const events = lines.slice(1).map(line => JSON.parse(line) as {
+    type: string
+    seq: number
+    time: number
+    surfaceOp?: unknown
+  })
+  const surfaceSeqs = events
+    .filter(event => event.surfaceOp === 'append'
+      && (event.type === 'user/message'
+        || event.type === 'assistant/message'
+        || event.type === 'tool/result'
+        || event.type === 'steering/message'))
+    .map(event => event.seq)
+  const first = surfaceSeqs[0]
+  const last = surfaceSeqs.at(-1)
+  const tail = events.at(-1)
+  if (first === undefined || last === undefined || tail === undefined) {
+    throw new Error('seeded-history compaction requires a non-empty closed surface')
+  }
+  let seq = tail.seq + 1
+  let time = tail.time + 1
+  const at = (event: Record<string, unknown>): string => JSON.stringify({ ...event, seq: seq++, time: time++ })
+  // The checkpoint's provenance names the two events appended before it.
+  const startSeq = seq + 1
+  const summarySeq = seq + 2
+  lines.push(
+    at({ type: 'turn/start', data: { turn: 2, trigger: { kind: 'injection', source: { kind: 'plugin', plugin: 'compact' } } } }),
+    at({ type: 'compact/start', data: { turn: 2 } }),
+    at({
+      type: 'compact/summary',
+      data: {
+        summary: [{
+          type: 'text',
+          text: '## Cold resume compact summary\n\n- The exact summary remains available.',
+        }],
+        shadowedRange: { start: first, end: last },
+        shadowedSeqs: surfaceSeqs,
+        shadowedTokenCount: 10_000,
+        provider: 'snapshot',
+        model: 'snapshot-compactor',
+      },
+    }),
+    at({
+      type: 'user/message',
+      data: {
+        content: [{
+          type: 'text',
+          text: '<context_checkpoint>Model-only compact checkpoint.</context_checkpoint>',
+        }],
+        source: { kind: 'plugin', plugin: 'compact' },
+      },
+      surfaceOp: { op: 'replace', start: first, end: last },
+      sourceEventSeqs: [startSeq, summarySeq, ...surfaceSeqs],
+    }),
+    at({ type: 'compact/end', data: { turn: 2 } }),
+    at({ type: 'turn/end', data: { turn: 2, reason: { kind: 'completed' } } }),
+  )
+  return `${lines.join('\n')}\n`
+}
+
 describe('web e2e: seeded history renders through cold resume', () => {
   let scaffold: WebScaffold
   let browser: Browser
@@ -46,7 +117,7 @@ describe('web e2e: seeded history renders through cold resume', () => {
     if (MODE !== 'record') {
       const raw = await readFile(SEED, 'utf8')
       expect(fixtureUserPrompts(raw), 'seed fixture must carry exactly the drive prompt').toEqual([PROMPT])
-      await seedSession(scaffold, raw, SEED_ID)
+      await seedSession(scaffold, withCompaction(raw), SEED_ID)
     }
     browser = await chromium.launch()
     page = await browser.newPage({ viewport: { width: 1680, height: 1000 } })
@@ -112,11 +183,15 @@ describe('web e2e: seeded history renders through cold resume', () => {
     await sessionRow.click()
     // Settled barrier for history: the recorded final assistant text renders.
     await expect.poll(() => page.getByText('DONE', { exact: true }).count(), { timeout: 15_000 }).toBe(1)
+    await expect.poll(() => page.getByText('上下文已压缩', { exact: true }).count(), { timeout: 10_000 }).toBe(1)
     // Tool cards render from logged tool/call + tool/result alone (views are
     // host-recomputed per page; the generic card is the documented default).
     const toolRows = page.locator('[data-variant], [data-sample]')
     await expect.poll(() => toolRows.count(), { timeout: 10_000 }).toBeGreaterThanOrEqual(2)
     expect(await page.getByText('a.txt', { exact: false }).count()).toBeGreaterThan(0)
+    // The bug this fixes: the compaction shadowed the whole recorded surface on
+    // the model side, and the prompt and full tool output are still on screen.
+    expect(await page.getByText(PROMPT, { exact: true }).count()).toBe(1)
   }, 60_000)
 
   it.skipIf(MODE === 'record')('matches the historical conversation aria golden', async () => {
@@ -147,6 +222,22 @@ describe('web e2e: seeded history renders through cold resume', () => {
     await expect.poll(() => page.getByText('a.txt', { exact: false }).count(), { timeout: 5_000 }).toBeGreaterThan(0)
   })
 
+  it.skipIf(MODE === 'record')('expands the cold-resumed compact summary', async () => {
+    onTestFailed(() => saveFailureShot(page, 'web-e2e-seeded-compaction'))
+    const marker = page.getByRole('button', { name: /上下文已压缩/ })
+    await marker.waitFor({ timeout: 10_000 })
+    expect(await marker.getAttribute('aria-expanded')).toBe('false')
+    await marker.click()
+    await expect.poll(() => marker.getAttribute('aria-expanded'), { timeout: 5_000 }).toBe('true')
+    await expect.poll(() => page.getByRole('heading', { name: 'Cold resume compact summary' }).count(), {
+      timeout: 5_000,
+    }).toBe(1)
+    expect(await page.getByText('The exact summary remains available.', { exact: false }).count()).toBeGreaterThan(0)
+    // Collapse again so the aria golden captured after this case is unaffected.
+    await marker.click()
+    await expect.poll(() => marker.getAttribute('aria-expanded'), { timeout: 5_000 }).toBe('false')
+  })
+
   it.skipIf(MODE === 'record')('issued zero model calls and stayed clean', async () => {
     // No replay fixture was installed and the llm seam is open — any stray
     // stream would have failed the turn loudly. Cleanliness pins the wire.

apps/web/tests/snapshots/seeded-history/ui.expected.md

@@ -36,7 +36,11 @@
   - img
 - button "在新对话中分支":
   - img
-- text: {{clock}} cache hit 98% · 15,962 tokens · 1 turns · 2 steps
+- text: {{clock}}
+- button "上下文已压缩 点击查看压缩摘要":
+  - img
+  - text: 上下文已压缩 点击查看压缩摘要
+- text: cache hit 98% · 15,962 tokens · 1 turns · 2 steps
 - textbox "Message the agent"
 - button "Add attachment":
   - img