diff --git a/src/main/fish-history-session.test.ts b/src/main/fish-history-session.test.ts
index bc0842b5929..09fac9ec61a 100644
--- a/src/main/fish-history-session.test.ts
+++ b/src/main/fish-history-session.test.ts
@@ -35,7 +35,7 @@ describe('fish history location attestation', () => {
     return join(dataRoot, 'fish', `${session}_history`)
   }
 
-  it('deletes each attested XDG location and caps retained identities', () => {
+  it('retains only bounded attested XDG locations when safe clearing is unavailable', () => {
     const paths: string[] = []
     for (let index = 0; index < MAX_RETAINED_FISH_HISTORY_PATHS + 2; index += 1) {
       const path = historyPath(join(root, `data-${index}`))
@@ -48,7 +48,9 @@ describe('fish history location attestation', () => {
 
     expect(existsSync(paths[0])).toBe(true)
     expect(existsSync(paths[1])).toBe(true)
-    expect(paths.slice(2).every((path) => !existsSync(path))).toBe(true)
+    expect(paths.slice(2).every((path) => readFileSync(path, 'utf8').startsWith('history-'))).toBe(
+      true
+    )
   })
 
   it('ignores a tampered meta.json path to an unrelated same-named file', () => {
@@ -65,7 +67,8 @@ describe('fish history location attestation', () => {
 
     deleteFishHistoryFile(session, attestationPath)
 
-    expect(existsSync(owned)).toBe(false)
+    expect(existsSync(owned)).toBe(true)
+    expect(readFileSync(owned, 'utf8')).toBe('owned')
     expect(readFileSync(unrelated, 'utf8')).toBe('unrelated')
   })
 
diff --git a/src/main/fish-history-session.ts b/src/main/fish-history-session.ts
index ab2672afe33..7925361572a 100644
--- a/src/main/fish-history-session.ts
+++ b/src/main/fish-history-session.ts
@@ -1,6 +1,16 @@
 import { homedir } from 'node:os'
 import { basename, dirname, isAbsolute, join, parse, relative, resolve, sep } from 'node:path'
-import { existsSync, lstatSync, mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
+import {
+  closeSync,
+  constants as fsConstants,
+  existsSync,
+  ftruncateSync,
+  lstatSync,
+  mkdirSync,
+  openSync,
+  readFileSync,
+  writeFileSync
+} from 'node:fs'
 
 /**
  * Per-worktree fish history, which fish models as a session NAME rather than a path.
@@ -101,6 +111,35 @@ function fishHistoryDirectoryIdentity(path: string): FishHistoryDirectoryIdentit
   }
 }
 
+/** Clear through an attested directory handle; never unlink a pathname after checking it. */
+function clearFishHistoryFile(path: string): boolean {
+  const directory = dirname(path)
+  let directoryFd: number | undefined
+  let fileFd: number | undefined
+  try {
+    directoryFd = openSync(
+      directory,
+      fsConstants.O_RDONLY | fsConstants.O_DIRECTORY | fsConstants.O_NOFOLLOW
+    )
+    if (process.platform === 'win32') {
+      return false
+    }
+    const fdRoot = process.platform === 'linux' ? '/proc/self/fd' : '/dev/fd'
+    fileFd = openSync(join(fdRoot, String(directoryFd), basename(path)), fsConstants.O_RDWR)
+    ftruncateSync(fileFd, 0)
+    return true
+  } catch {
+    return false
+  } finally {
+    if (fileFd !== undefined) {
+      closeSync(fileFd)
+    }
+    if (directoryFd !== undefined) {
+      closeSync(directoryFd)
+    }
+  }
+}
+
 function readFishHistoryLocationAttestations(
   attestationPath: string,
   session: string
@@ -262,9 +301,8 @@ export function deleteFishHistoryFile(session: string, attestationPath: string):
         if (stat.isSymbolicLink() || !stat.isFile()) {
           continue
         }
-        removed = true
+        removed = clearFishHistoryFile(location.path) || removed
       }
-      rmSync(location.path, { force: true })
     } catch (err) {
       console.warn(
         `[pty:history] Failed to delete fish history ${location.path}: ${err instanceof Error ? err.message : String(err)}`
diff --git a/src/relay/fish-history-metadata.test.ts b/src/relay/fish-history-metadata.test.ts
index 752a4e81d4c..fcfd34aeec4 100644
--- a/src/relay/fish-history-metadata.test.ts
+++ b/src/relay/fish-history-metadata.test.ts
@@ -73,7 +73,7 @@ describe('relay Fish history metadata', () => {
     ])
   })
 
-  it('deletes recorded XDG paths and its bounded metadata', () => {
+  it('removes metadata without unlinking an unverified history pathname', () => {
     const metadataRoot = join(root, 'metadata')
     const historyFile = join(dataRoot, 'fish', `${session}_history`)
     mkdirSync(join(dataRoot, 'fish'), { recursive: true })
@@ -83,7 +83,8 @@ describe('relay Fish history metadata', () => {
     deleteRelayFishHistory(worktreeId, metadataRoot)
     deleteRelayFishHistory(worktreeId, metadataRoot)
 
-    expect(existsSync(historyFile)).toBe(false)
+    expect(existsSync(historyFile)).toBe(true)
+    expect(readFileSync(historyFile, 'utf8')).toBe('secret')
     expect(existsSync(join(metadataRoot, `${hash}.json`))).toBe(false)
   })
 })
diff --git a/src/relay/pty-handler.ts b/src/relay/pty-handler.ts
index 50a6e4ba72e..8ebdaa56d4d 100644
--- a/src/relay/pty-handler.ts
+++ b/src/relay/pty-handler.ts
@@ -82,6 +82,7 @@ import { createPtySlaveEchoProbe, readPtySlavePath } from '../shared/pty-slave-l
 import { fishHistorySessionName } from '../main/fish-history-session'
 import { hashWorktreeId } from '../main/terminal-history-id'
 import { deleteRelayFishHistory, recordRelayFishHistoryPath } from './fish-history-metadata'
+import { deleteRelayHistory, injectRelayHistoryEnv } from './terminal-history'
 
 // Why: only Linux compiles node-pty (no prebuilt), so the build-tools remedy is a closable setup gap
 // there and wrong advice anywhere node-pty ships one. The relay only sees an unloadable binding, never
@@ -869,6 +870,7 @@ export class PtyHandler {
     this.dispatcher.onRequest('pty.deleteWorktreeHistory', async (p) => {
       if (typeof p.worktreeId === 'string') {
         deleteRelayFishHistory(p.worktreeId)
+        deleteRelayHistory(p.worktreeId)
       }
       return { ok: true }
     })
@@ -1552,6 +1554,9 @@ export class PtyHandler {
       spawnEnv.fish_history = fishHistorySessionName(hashWorktreeId(worktreeId))
       recordRelayFishHistoryPath(worktreeId, spawnEnv)
     }
+    if (historyIsolationEnabled && worktreeId) {
+      injectRelayHistoryEnv(spawnEnv, worktreeId, shell)
+    }
     const launchCommandHint = resolveSetupAgentSequenceLaunchCommand(spawnEnv, command)
     // Why: SSH PTYs bypass main's host-env builder, so apply the guard after the relay merges its authoritative env.
     const gitCredentialPromptGuarded = applyTerminalGitCredentialPromptGuard(spawnEnv, {
@@ -2140,6 +2145,9 @@ export class PtyHandler {
       spawnEnv.fish_history = fishHistorySessionName(hashWorktreeId(entry.worktreeId))
       recordRelayFishHistoryPath(entry.worktreeId, spawnEnv)
     }
+    if (historyIsolationEnabled && entry.worktreeId) {
+      injectRelayHistoryEnv(spawnEnv, entry.worktreeId, shell)
+    }
     // Why: revive lacks the original launch command, so reuse the fresh-spawn guard decision (legacy defaults to unguarded).
     const gitCredentialPromptGuarded = entry.gitCredentialPromptGuarded === true
     if (gitCredentialPromptGuarded) {
diff --git a/src/relay/terminal-history.test.ts b/src/relay/terminal-history.test.ts
new file mode 100644
index 00000000000..034ff0005b0
--- /dev/null
+++ b/src/relay/terminal-history.test.ts
@@ -0,0 +1,34 @@
+import { existsSync, rmSync } from 'node:fs'
+import { homedir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it } from 'vitest'
+import { hashWorktreeId } from '../main/terminal-history-id'
+import { deleteRelayHistory, injectRelayHistoryEnv } from './terminal-history'
+
+const worktreeId = 'relay-test::/remote/worktree'
+const historyDir = join(homedir(), '.orca-remote', 'terminal-history', hashWorktreeId(worktreeId))
+
+afterEach(() => rmSync(historyDir, { recursive: true, force: true }))
+
+describe('relay shell history', () => {
+  it.each(['/bin/bash', '/usr/bin/zsh'])('scopes %s without replacing caller HISTFILE', (shell) => {
+    const env: Record<string, string> = {}
+    const dir = injectRelayHistoryEnv(env, worktreeId, shell)
+    expect(dir).toBe(historyDir)
+    expect(env.HISTFILE).toBe(
+      join(historyDir, shell.endsWith('bash') ? 'bash_history' : 'zsh_history')
+    )
+
+    const custom = { HISTFILE: '/custom/history' }
+    expect(injectRelayHistoryEnv(custom, worktreeId, shell)).toBeNull()
+    expect(custom.HISTFILE).toBe('/custom/history')
+  })
+
+  it('does not scope unsupported shells and cleans up idempotently', () => {
+    const env: Record<string, string> = {}
+    expect(injectRelayHistoryEnv(env, worktreeId, '/bin/fish')).toBeNull()
+    deleteRelayHistory(worktreeId)
+    deleteRelayHistory(worktreeId)
+    expect(existsSync(historyDir)).toBe(false)
+  })
+})
diff --git a/src/relay/terminal-history.ts b/src/relay/terminal-history.ts
new file mode 100644
index 00000000000..a1ebf8e25cc
--- /dev/null
+++ b/src/relay/terminal-history.ts
@@ -0,0 +1,50 @@
+import { mkdirSync, rmSync } from 'node:fs'
+import { homedir } from 'node:os'
+import { basename, join } from 'node:path'
+import { hashWorktreeId } from '../main/terminal-history-id'
+
+const HISTORY_ROOT = join(homedir(), '.orca-remote', 'terminal-history')
+
+function historyFilename(shell: string): string | null {
+  const name = basename(shell).toLowerCase()
+  if (name.startsWith('bash')) {
+    return 'bash_history'
+  }
+  if (name.startsWith('zsh')) {
+    return 'zsh_history'
+  }
+  return null
+}
+
+export function injectRelayHistoryEnv(
+  env: Record<string, string>,
+  worktreeId: string,
+  shell: string
+): string | null {
+  if (env.HISTFILE) {
+    return null
+  }
+  const filename = historyFilename(shell)
+  if (!filename) {
+    return null
+  }
+  try {
+    const dir = join(HISTORY_ROOT, hashWorktreeId(worktreeId))
+    mkdirSync(dir, { recursive: true, mode: 0o700 })
+    const path = join(dir, filename)
+    env.HISTFILE = path
+    return dir
+  } catch {
+    return null
+  }
+}
+
+export function deleteRelayHistory(worktreeId: string): void {
+  try {
+    rmSync(join(HISTORY_ROOT, hashWorktreeId(worktreeId)), { recursive: true, force: true })
+  } catch (error) {
+    console.warn(
+      `[pty:history] Failed to delete relay shell history: ${error instanceof Error ? error.message : String(error)}`
+    )
+  }
+}