diff --git a/src/main/native-chat/agent-session-wire/agent-session-history-byte-accounting.test.ts b/src/main/native-chat/agent-session-wire/agent-session-history-byte-accounting.test.ts
new file mode 100644
index 00000000000..757e7e44084
--- /dev/null
+++ b/src/main/native-chat/agent-session-wire/agent-session-history-byte-accounting.test.ts
@@ -0,0 +1,96 @@
+import { mkdtemp, rm } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, beforeEach, expect, it } from 'vitest'
+import type {
+  AgentJournalItemBody,
+  AgentJournalItemIdentity,
+  AgentSessionJournalIdentity
+} from '../../../shared/agent-session-journal-types'
+import { createTrackedJournalOpener } from '../agent-session-journal/journal-store-test-open'
+import type { AgentSessionJournal } from '../agent-session-journal/journal-store'
+import { readAgentSessionHistory } from './agent-session-history-page'
+
+const IDENTITY: AgentSessionJournalIdentity = {
+  sessionId: 'session-1',
+  workspaceId: 'ws-1',
+  hostId: 'host-1',
+  agent: 'codex',
+  providerHandle: { kind: 'codex', threadId: 'thread-1' }
+}
+
+const journals = createTrackedJournalOpener()
+let root: string
+let clock = 1_000
+let epochs = 0
+let journal: AgentSessionJournal
+
+function tick(): number {
+  clock += 1
+  return clock
+}
+
+function item(ordinal: number): AgentJournalItemIdentity {
+  return { provider: 'codex', threadId: 'thread-1', turnId: 'turn-1', ordinal }
+}
+
+function body(text: string): AgentJournalItemBody {
+  return { kind: 'message', role: 'assistant', blocks: [{ type: 'text', text }] }
+}
+
+async function appendItems(count: number, text: string): Promise<void> {
+  for (let ordinal = 1; ordinal <= count; ordinal += 1) {
+    await journal.appendItem(item(ordinal), body(`${text}-${ordinal}`), { fence: 1 })
+  }
+}
+
+beforeEach(async () => {
+  root = await mkdtemp(join(tmpdir(), 'orca-wire-history-'))
+  clock = 1_000
+  epochs = 0
+  journal = await journals.open({
+    identity: IDENTITY,
+    journalDir: root,
+    now: tick,
+    mintEpoch: () => {
+      epochs += 1
+      return `epoch-${epochs}`
+    }
+  })
+})
+
+afterEach(async () => {
+  await journals.closeAll()
+  await rm(root, { recursive: true, force: true })
+})
+
+it.each([1, 100, 200])('serializes each of %i unchanged forward page items once', async (count) => {
+  const cursor = journal.cursor()
+  await appendItems(count, 'x'.repeat(8_000))
+  const snapshot = journal.snapshot()
+  const stringify = JSON.stringify
+  let itemSerializations = 0
+  JSON.stringify = ((value: unknown, ...args: unknown[]) => {
+    if (value && typeof value === 'object' && 'itemId' in value && 'body' in value) {
+      itemSerializations++
+    }
+    return Reflect.apply(stringify, JSON, [value, ...args])
+  }) as typeof JSON.stringify
+  try {
+    const result = readAgentSessionHistory(
+      journal,
+      {
+        sessionId: 'session-1',
+        direction: 'after',
+        limit: count,
+        cursor
+      },
+      snapshot
+    )
+    expect(result.ok).toBe(true)
+    expect(result.page.items).toHaveLength(count)
+    expect(itemSerializations).toBe(count)
+  } finally {
+    JSON.stringify = stringify
+  }
+})
diff --git a/src/main/native-chat/agent-session-wire/agent-session-history-page.ts b/src/main/native-chat/agent-session-wire/agent-session-history-page.ts
index 231b0b248f7..f7bef47e553 100644
--- a/src/main/native-chat/agent-session-wire/agent-session-history-page.ts
+++ b/src/main/native-chat/agent-session-wire/agent-session-history-page.ts
@@ -196,11 +196,8 @@ function readForward(
   if (!projected.ok) {
     return historyReset(snapshot, projected.reset)
   }
-  while (
-    rows.length > 1 &&
-    pageContentBytes(projected.batch.items, projected.batch.removedItemIds) >
-      HISTORY_PAGE_CONTENT_BUDGET_BYTES
-  ) {
+  let contentBytes = pageContentBytes(projected.batch.items, projected.batch.removedItemIds)
+  while (rows.length > 1 && contentBytes > HISTORY_PAGE_CONTENT_BUDGET_BYTES) {
     rows = rows.slice(0, Math.ceil(rows.length / 2))
     const shrunk = projectJournalBatch({
       rows,
@@ -212,19 +209,18 @@ function readForward(
       return historyReset(snapshot, shrunk.reset)
     }
     projected = shrunk
+    contentBytes = pageContentBytes(projected.batch.items, projected.batch.removedItemIds)
   }
   // One row can still touch an over-budget item; degrade it visibly.
-  const items =
-    pageContentBytes(projected.batch.items, projected.batch.removedItemIds) >
-    HISTORY_PAGE_CONTENT_BUDGET_BYTES
-      ? projected.batch.items.map((item) => {
-          const bytes = historyEntryBytes(item, submissionBytes)
-          return bytes > HISTORY_PAGE_CONTENT_BUDGET_BYTES
-            ? oversizedHistoryItem(item, bytes)
-            : item
-        })
-      : projected.batch.items
-  if (pageContentBytes(items, projected.batch.removedItemIds) > HISTORY_PAGE_CONTENT_BUDGET_BYTES) {
+  let items = projected.batch.items
+  if (contentBytes > HISTORY_PAGE_CONTENT_BUDGET_BYTES) {
+    items = items.map((item) => {
+      const bytes = historyEntryBytes(item, submissionBytes)
+      return bytes > HISTORY_PAGE_CONTENT_BUDGET_BYTES ? oversizedHistoryItem(item, bytes) : item
+    })
+    contentBytes = pageContentBytes(items, projected.batch.removedItemIds)
+  }
+  if (contentBytes > HISTORY_PAGE_CONTENT_BUDGET_BYTES) {
     // A single row's semantic payload — in practice a pre-bounding oversized
     // removal id — can never fit any page, and truncating a removal id would
     // break the client's keying. A bounded tail replaces the client's state