diff --git a/src/main/native-chat/agent-session-journal/journal-log-file.ts b/src/main/native-chat/agent-session-journal/journal-log-file.ts
index c2c58471322..f67c6529faf 100644
--- a/src/main/native-chat/agent-session-journal/journal-log-file.ts
+++ b/src/main/native-chat/agent-session-journal/journal-log-file.ts
@@ -16,7 +16,22 @@ import type {
   AgentJournalSubmission
 } from '../../../shared/agent-session-journal-types'
 import { AGENT_SESSION_JOURNAL_SCHEMA_VERSION } from '../../../shared/agent-session-journal-types'
-import { parseJournalRow, serializeJournalRow, type JournalRow } from './journal-row-schema'
+import {
+  isJournalAlias,
+  isJournalReceipt,
+  isJournalRenderItem,
+  isJournalSubmission,
+  isJournalTombstone,
+  isNonEmptyString,
+  isNonNegativeInteger,
+  isRecord
+} from './journal-persisted-shapes'
+import {
+  parseJournalRow,
+  parseJournalRowValue,
+  serializeJournalRow,
+  type JournalRow
+} from './journal-row-schema'
 
 export const JOURNAL_LOG_FILE = 'log.jsonl'
 export const JOURNAL_SNAPSHOT_FILE = 'snapshot.json'
@@ -69,22 +84,57 @@ export async function readJournalSnapshotFile(
 ): Promise<JournalSnapshotReadResult> {
   try {
     const raw = await readFile(join(journalDir, JOURNAL_SNAPSHOT_FILE), 'utf-8')
-    const parsed = JSON.parse(raw) as Partial<JournalSnapshotFile>
-    if (typeof parsed?.v !== 'number' || !Number.isInteger(parsed.v) || parsed.v < 1) {
-      return { snapshot: null, unreadable: false }
-    }
-    if (parsed.v > AGENT_SESSION_JOURNAL_SCHEMA_VERSION) {
-      return { snapshot: null, unreadable: true }
-    }
-    return {
-      snapshot: typeof parsed?.epoch === 'string' ? (parsed as JournalSnapshotFile) : null,
-      unreadable: false
-    }
+    return parseJournalSnapshot(JSON.parse(raw))
   } catch {
     return { snapshot: null, unreadable: false }
   }
 }
 
+function parseJournalSnapshot(value: unknown): JournalSnapshotReadResult {
+  if (!isRecord(value) || !Number.isInteger(value.v) || (value.v as number) < 1) {
+    return { snapshot: null, unreadable: false }
+  }
+  if ((value.v as number) > AGENT_SESSION_JOURNAL_SCHEMA_VERSION) {
+    return { snapshot: null, unreadable: true }
+  }
+  if (
+    !isNonEmptyString(value.epoch) ||
+    !isNonNegativeInteger(value.compactedThrough) ||
+    !(value.highestFence === undefined || isNonNegativeInteger(value.highestFence)) ||
+    !Array.isArray(value.items) ||
+    !value.items.every(isJournalRenderItem) ||
+    !(value.tombstones === undefined || Array.isArray(value.tombstones)) ||
+    (Array.isArray(value.tombstones) && !value.tombstones.every(isJournalTombstone)) ||
+    !Array.isArray(value.submissions) ||
+    !value.submissions.every(isJournalSubmission) ||
+    !Array.isArray(value.receipts) ||
+    !value.receipts.every(isJournalReceipt) ||
+    !Array.isArray(value.aliases) ||
+    !value.aliases.every(isJournalAlias) ||
+    !Array.isArray(value.tail)
+  ) {
+    return { snapshot: null, unreadable: false }
+  }
+
+  const tail: JournalRow[] = []
+  for (const candidate of value.tail) {
+    const parsed = parseJournalRowValue(candidate)
+    if (!parsed.ok) {
+      return { snapshot: null, unreadable: parsed.unreadable }
+    }
+    tail.push(parsed.row)
+  }
+  return {
+    snapshot: {
+      ...value,
+      highestFence: value.highestFence ?? 0,
+      tombstones: value.tombstones ?? [],
+      tail
+    } as JournalSnapshotFile,
+    unreadable: false
+  }
+}
+
 export async function writeJournalSnapshotFile(
   journalDir: string,
   snapshot: JournalSnapshotFile
diff --git a/src/main/native-chat/agent-session-journal/journal-persisted-shapes.ts b/src/main/native-chat/agent-session-journal/journal-persisted-shapes.ts
new file mode 100644
index 00000000000..1e88be845f7
--- /dev/null
+++ b/src/main/native-chat/agent-session-journal/journal-persisted-shapes.ts
@@ -0,0 +1,215 @@
+import type {
+  AgentJournalItemBody,
+  AgentJournalRenderItem,
+  AgentJournalSubmission,
+  AgentSessionProviderHandle
+} from '../../../shared/agent-session-journal-types'
+import type { NativeChatBlock } from '../../../shared/native-chat-types'
+
+const ROLES = new Set(['user', 'assistant', 'tool', 'reasoning', 'system'])
+const TOOL_STATES = new Set(['running', 'completed', 'failed'])
+const RESOLUTION_STATES = new Set(['pending', 'resolved', 'cancelled'])
+const DISPATCH_STATES = new Set(['pending', 'accepted', 'rejected', 'unknown'])
+
+export function isRecord(value: unknown): value is Record<string, unknown> {
+  return Boolean(value) && typeof value === 'object' && !Array.isArray(value)
+}
+
+export function isNonEmptyString(value: unknown): value is string {
+  return typeof value === 'string' && value.length > 0
+}
+
+export function isFiniteNumber(value: unknown): value is number {
+  return typeof value === 'number' && Number.isFinite(value)
+}
+
+export function isNonNegativeInteger(value: unknown): value is number {
+  return Number.isInteger(value) && (value as number) >= 0
+}
+
+function isOptionalTrue(value: unknown): boolean {
+  return value === undefined || value === true
+}
+
+function isOptionalString(value: unknown): boolean {
+  return value === undefined || typeof value === 'string'
+}
+
+function isNullableString(value: unknown): boolean {
+  return value === null || typeof value === 'string'
+}
+
+function isNullableNumber(value: unknown): boolean {
+  return value === null || isFiniteNumber(value)
+}
+
+function hasOwn(value: Record<string, unknown>, key: string): boolean {
+  return Object.prototype.hasOwnProperty.call(value, key)
+}
+
+export function isAgentSessionProviderHandle(value: unknown): value is AgentSessionProviderHandle {
+  if (!isRecord(value)) {
+    return false
+  }
+  if (value.kind === 'codex') {
+    return isNonEmptyString(value.threadId)
+  }
+  if (value.kind === 'claude') {
+    return isNonEmptyString(value.sessionId) && isNullableString(value.leafUuid)
+  }
+  return value.kind === 'opaque' && isNonEmptyString(value.agent) && isNonEmptyString(value.value)
+}
+
+function isNativeChatBlock(value: unknown): value is NativeChatBlock {
+  if (!isRecord(value)) {
+    return false
+  }
+  if (value.type === 'text') {
+    return typeof value.text === 'string'
+  }
+  if (value.type === 'tool-call') {
+    return typeof value.name === 'string' && hasOwn(value, 'input')
+  }
+  if (value.type === 'tool-result') {
+    return (
+      typeof value.output === 'string' &&
+      (value.isError === undefined || typeof value.isError === 'boolean')
+    )
+  }
+  return (
+    value.type === 'image-ref' &&
+    isOptionalString(value.path) &&
+    isOptionalString(value.url) &&
+    isOptionalString(value.alt)
+  )
+}
+
+function isBoundedPayload(value: unknown): boolean {
+  return (
+    isRecord(value) &&
+    typeof value.head === 'string' &&
+    isNonNegativeInteger(value.byteLength) &&
+    typeof value.digest === 'string' &&
+    typeof value.truncated === 'boolean'
+  )
+}
+
+function isPromptOption(value: unknown): boolean {
+  return isRecord(value) && isNonEmptyString(value.id) && typeof value.label === 'string'
+}
+
+function isResolution(value: unknown): boolean {
+  return (
+    isRecord(value) &&
+    typeof value.state === 'string' &&
+    RESOLUTION_STATES.has(value.state) &&
+    isNullableString(value.selectedOptionId) &&
+    isNullableString(value.resolvedBy) &&
+    isNullableNumber(value.resolvedAt)
+  )
+}
+
+export function isAgentJournalItemBody(value: unknown): value is AgentJournalItemBody {
+  if (!isRecord(value)) {
+    return false
+  }
+  if (value.kind === 'message') {
+    return (
+      typeof value.role === 'string' &&
+      ROLES.has(value.role) &&
+      Array.isArray(value.blocks) &&
+      value.blocks.every(isNativeChatBlock)
+    )
+  }
+  if (value.kind === 'tool-call') {
+    return (
+      typeof value.name === 'string' &&
+      hasOwn(value, 'input') &&
+      typeof value.state === 'string' &&
+      TOOL_STATES.has(value.state) &&
+      (value.output === undefined || isBoundedPayload(value.output))
+    )
+  }
+  if (value.kind === 'diff') {
+    return typeof value.path === 'string' && isBoundedPayload(value.patch)
+  }
+  if (value.kind === 'approval') {
+    return (
+      typeof value.title === 'string' &&
+      isNullableString(value.detail) &&
+      Array.isArray(value.options) &&
+      value.options.every(isPromptOption) &&
+      isResolution(value.resolution)
+    )
+  }
+  if (value.kind === 'question') {
+    return (
+      typeof value.question === 'string' &&
+      Array.isArray(value.options) &&
+      value.options.every(isPromptOption) &&
+      isResolution(value.resolution)
+    )
+  }
+  return value.kind === 'status' && typeof value.text === 'string'
+}
+
+export function isJournalRenderItem(value: unknown): value is AgentJournalRenderItem {
+  return (
+    isRecord(value) &&
+    isNonEmptyString(value.itemId) &&
+    isNonNegativeInteger(value.revision) &&
+    isAgentJournalItemBody(value.body) &&
+    Number.isInteger(value.sequence) &&
+    (value.sequence as number) >= 1 &&
+    isFiniteNumber(value.observedAt) &&
+    isOptionalTrue(value.recovered)
+  )
+}
+
+export function isJournalSubmission(value: unknown): value is AgentJournalSubmission {
+  if (
+    !isRecord(value) ||
+    !isNonEmptyString(value.clientMessageId) ||
+    !isNonNegativeInteger(value.fence) ||
+    typeof value.payloadFingerprint !== 'string' ||
+    typeof value.dispatchState !== 'string' ||
+    !DISPATCH_STATES.has(value.dispatchState) ||
+    !isNullableString(value.providerItemId) ||
+    !isNullableString(value.reason) ||
+    !isFiniteNumber(value.submittedAt) ||
+    !isNullableNumber(value.resolvedAt)
+  ) {
+    return false
+  }
+  if (value.dispatchState === 'pending') {
+    return value.providerItemId === null && value.reason === null && value.resolvedAt === null
+  }
+  if (value.dispatchState === 'accepted') {
+    return (
+      isNonEmptyString(value.providerItemId) &&
+      value.reason === null &&
+      isFiniteNumber(value.resolvedAt)
+    )
+  }
+  return value.providerItemId === null && isFiniteNumber(value.resolvedAt)
+}
+
+export function isJournalTombstone(value: unknown): boolean {
+  return isRecord(value) && isNonEmptyString(value.itemId) && isNonNegativeInteger(value.revision)
+}
+
+export function isJournalReceipt(value: unknown): boolean {
+  return (
+    isRecord(value) &&
+    isNonEmptyString(value.clientMessageId) &&
+    isNonEmptyString(value.providerItemId) &&
+    isNonEmptyString(value.epoch) &&
+    Number.isInteger(value.sequence) &&
+    (value.sequence as number) >= 1 &&
+    isFiniteNumber(value.acceptedAt)
+  )
+}
+
+export function isJournalAlias(value: unknown): boolean {
+  return isRecord(value) && isNonEmptyString(value.providerItemId) && isNonEmptyString(value.itemId)
+}
diff --git a/src/main/native-chat/agent-session-journal/journal-persisted-validation.test.ts b/src/main/native-chat/agent-session-journal/journal-persisted-validation.test.ts
new file mode 100644
index 00000000000..7ae5e22fce6
--- /dev/null
+++ b/src/main/native-chat/agent-session-journal/journal-persisted-validation.test.ts
@@ -0,0 +1,88 @@
+import { mkdtemp, readFile, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
+import type {
+  AgentJournalItemBody,
+  AgentSessionJournalIdentity
+} from '../../../shared/agent-session-journal-types'
+import { JOURNAL_LOG_FILE, JOURNAL_SNAPSHOT_FILE } from './journal-log-file'
+import { openAgentSessionJournal } from './journal-store'
+
+const IDENTITY: AgentSessionJournalIdentity = {
+  sessionId: 'session-1',
+  workspaceId: 'ws-1',
+  hostId: 'host-1',
+  agent: 'codex',
+  providerHandle: { kind: 'codex', threadId: 'thread-1' }
+}
+
+let root: string
+let clock = 1_000
+
+function body(text: string): AgentJournalItemBody {
+  return { kind: 'message', role: 'assistant', blocks: [{ type: 'text', text }] }
+}
+
+async function open() {
+  return openAgentSessionJournal({
+    identity: IDENTITY,
+    journalDir: root,
+    now: () => ++clock,
+    mintEpoch: () => `epoch-${clock}`
+  })
+}
+
+beforeEach(async () => {
+  root = await mkdtemp(join(tmpdir(), 'orca-journal-validation-'))
+  clock = 1_000
+})
+
+afterEach(async () => {
+  await rm(root, { recursive: true, force: true })
+})
+
+describe('persisted journal validation', () => {
+  it('does not admit a malformed item body into reducer state', async () => {
+    const journal = await open()
+    const malformed = JSON.stringify({
+      v: 1,
+      kind: 'item',
+      epoch: journal.epoch,
+      seq: 2,
+      fence: 1,
+      ts: 1_002,
+      itemId: 'malformed',
+      revision: 1,
+      body: null
+    })
+    const logPath = join(root, JOURNAL_LOG_FILE)
+    await writeFile(logPath, `${await readFile(logPath, 'utf-8')}${malformed}\n`, 'utf-8')
+
+    const reopened = await open()
+    expect(reopened.snapshot().items).toEqual([])
+    await expect(reopened.compact(1)).resolves.toBeUndefined()
+  })
+
+  it('rebuilds from the log when a snapshot contains a malformed render item', async () => {
+    const journal = await open()
+    await journal.appendItem(
+      { provider: 'codex', threadId: 'thread-1', turnId: 'turn-1', ordinal: 0 },
+      body('valid'),
+      { fence: 1 }
+    )
+    const expected = journal.snapshot()
+    await journal.compact(1)
+
+    const snapshotPath = join(root, JOURNAL_SNAPSHOT_FILE)
+    const snapshot = JSON.parse(await readFile(snapshotPath, 'utf-8')) as {
+      items: { body: unknown }[]
+    }
+    snapshot.items[0]!.body = null
+    await writeFile(snapshotPath, JSON.stringify(snapshot), 'utf-8')
+
+    const reopened = await open()
+    expect(reopened.snapshot()).toEqual(expected)
+    await expect(reopened.compact(1)).resolves.toBeUndefined()
+  })
+})
diff --git a/src/main/native-chat/agent-session-journal/journal-row-schema.ts b/src/main/native-chat/agent-session-journal/journal-row-schema.ts
index f7c15afe1ee..3e741c16598 100644
--- a/src/main/native-chat/agent-session-journal/journal-row-schema.ts
+++ b/src/main/native-chat/agent-session-journal/journal-row-schema.ts
@@ -12,6 +12,13 @@ import {
   type AgentJournalMessageItem,
   type AgentSessionProviderHandle
 } from '../../../shared/agent-session-journal-types'
+import {
+  isAgentJournalItemBody,
+  isAgentSessionProviderHandle,
+  isFiniteNumber,
+  isNonEmptyString,
+  isNonNegativeInteger
+} from './journal-persisted-shapes'
 
 export type JournalRowBase = {
   /** Schema version of THIS row. */
@@ -91,6 +98,8 @@ export type JournalRowParse =
   | { ok: false; unreadable: true }
 
 const ROW_KINDS = new Set(['epoch', 'item', 'tombstone', 'submission', 'dispatch'])
+const EPOCH_REASONS = new Set(AGENT_JOURNAL_EPOCH_REASONS)
+const DISPATCH_STATES = new Set(['accepted', 'rejected', 'unknown'])
 
 export function journalRowBase(
   epoch: string,
@@ -116,6 +125,10 @@ export function parseJournalRow(line: string): JournalRowParse {
   } catch {
     return { ok: false, unreadable: false }
   }
+  return parseJournalRowValue(parsed)
+}
+
+export function parseJournalRowValue(parsed: unknown): JournalRowParse {
   if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
     return { ok: false, unreadable: false }
   }
@@ -148,22 +161,52 @@ function isJournalRow(record: Record<string, unknown>): record is JournalRow {
     return false
   }
   if (
-    typeof record.epoch !== 'string' ||
-    !record.epoch ||
+    !isNonEmptyString(record.epoch) ||
     !Number.isInteger(record.seq) ||
     (record.seq as number) < 1 ||
-    !Number.isInteger(record.fence) ||
-    typeof record.ts !== 'number'
+    !isNonNegativeInteger(record.fence) ||
+    !isFiniteNumber(record.ts) ||
+    (record.recovered !== undefined && record.recovered !== true)
   ) {
     return false
   }
-  if (record.kind === 'item' || record.kind === 'tombstone') {
-    return typeof record.itemId === 'string' && Number.isInteger(record.revision)
+  if (record.kind === 'epoch') {
+    return (
+      typeof record.reason === 'string' &&
+      EPOCH_REASONS.has(record.reason as AgentJournalEpochReason) &&
+      isAgentSessionProviderHandle(record.providerHandle)
+    )
   }
-  if (record.kind === 'submission' || record.kind === 'dispatch') {
-    return typeof record.clientMessageId === 'string' && record.clientMessageId.length > 0
+  if (record.kind === 'item') {
+    return (
+      isNonEmptyString(record.itemId) &&
+      isNonNegativeInteger(record.revision) &&
+      isAgentJournalItemBody(record.body)
+    )
   }
-  return typeof record.reason === 'string'
+  if (record.kind === 'tombstone') {
+    return isNonEmptyString(record.itemId) && isNonNegativeInteger(record.revision)
+  }
+  if (record.kind === 'submission') {
+    return (
+      isNonEmptyString(record.clientMessageId) &&
+      typeof record.payloadFingerprint === 'string' &&
+      isAgentSessionProviderHandle(record.providerHandle) &&
+      isAgentJournalItemBody(record.body) &&
+      record.body.kind === 'message'
+    )
+  }
+  if (
+    !isNonEmptyString(record.clientMessageId) ||
+    typeof record.state !== 'string' ||
+    !DISPATCH_STATES.has(record.state) ||
+    !(record.reason === null || typeof record.reason === 'string')
+  ) {
+    return false
+  }
+  return record.state === 'accepted'
+    ? isNonEmptyString(record.providerItemId) && record.reason === null
+    : record.providerItemId === null
 }
 
 /** Approximate on-disk cost of a row, used for the per-session size bound. */