diff --git a/src/main/daemon/daemon-pty-startup-delivery.test.ts b/src/main/daemon/daemon-pty-startup-delivery.test.ts
index 4b72070bb42..3cffff8dec2 100644
--- a/src/main/daemon/daemon-pty-startup-delivery.test.ts
+++ b/src/main/daemon/daemon-pty-startup-delivery.test.ts
@@ -52,7 +52,7 @@ describe('DaemonPtyAdapter startup delivery', () => {
       await vi.advanceTimersByTimeAsync(299)
       expect(lastSubprocess.write).not.toHaveBeenCalled()
       await vi.advanceTimersByTimeAsync(1)
-      expect(lastSubprocess.write).toHaveBeenCalledExactlyOnceWith('codex\n')
+      expect(lastSubprocess.write).toHaveBeenCalledExactlyOnceWith('codex\r')
       expect(lastSpawnOpts).not.toEqual(
         expect.objectContaining({ startupCommandDelivery: 'shell-ready' })
       )
@@ -82,7 +82,7 @@ describe('DaemonPtyAdapter startup delivery', () => {
       )
       lastSubprocess._simulateData('\x1b]777;orca-shell-ready\x07\r\nuser@host $ ')
       await waitFor(() => vi.mocked(lastSubprocess.write).mock.calls.length > 0)
-      expect(lastSubprocess.write).toHaveBeenCalledExactlyOnceWith('codex\n')
+      expect(lastSubprocess.write).toHaveBeenCalledExactlyOnceWith('codex\r')
     }
   )
 
@@ -102,6 +102,6 @@ describe('DaemonPtyAdapter startup delivery', () => {
     lastSubprocess._simulateData('\r\nuser@host $ ')
 
     await waitFor(() => vi.mocked(lastSubprocess.write).mock.calls.length > 0)
-    expect(lastSubprocess.write).toHaveBeenCalledExactlyOnceWith(`${startup.command}\n`)
+    expect(lastSubprocess.write).toHaveBeenCalledExactlyOnceWith(`${startup.command}\r`)
   })
 })
diff --git a/src/main/daemon/terminal-host-session-create.ts b/src/main/daemon/terminal-host-session-create.ts
index 15e86a70a72..f490c5d5722 100644
--- a/src/main/daemon/terminal-host-session-create.ts
+++ b/src/main/daemon/terminal-host-session-create.ts
@@ -197,11 +197,9 @@ async function spawnAndPublishSession(
     // Diagnostics must never turn a live PTY into a failed create.
   }
   if (startupCommandWritten && opts.command) {
-    const submit = process.platform === 'win32' ? '\r' : '\n'
     // Why: only Orca-wrapped shells advertise the paste-safe startup barrier.
     session.write(
       buildStartupCommandSubmission(opts.command, {
-        submit,
         bracketedPasteSafe: shellReadySupported
       })
     )
diff --git a/src/main/daemon/terminal-host-startup.test.ts b/src/main/daemon/terminal-host-startup.test.ts
index c6817b1e758..830bf0c40bd 100644
--- a/src/main/daemon/terminal-host-startup.test.ts
+++ b/src/main/daemon/terminal-host-startup.test.ts
@@ -19,11 +19,8 @@ function mockSubprocess(): SubprocessHandle {
   } as SubprocessHandle
 }
 
-// Why: Windows shells (PowerShell/cmd.exe) submit on CR, not LF. Without CR
-// the startup command sits typed at the prompt but unexecuted — forcing the
-// user to press Enter after "claude" (or a setup script) is injected.
-// POSIX shells (bash/zsh) keep the LF behaviour. A caller-supplied terminator
-// must not be doubled.
+// Why: without CR (Enter) the startup command sits typed at the prompt but
+// unexecuted (#23250). A caller-supplied terminator is replaced, not doubled.
 describe('TerminalHost startup command terminator', () => {
   const origPlatform = process.platform
   afterEach(() => {
@@ -39,9 +36,11 @@ describe('TerminalHost startup command terminator', () => {
 
   it.each([
     ['win32', 'claude', 'claude\r'],
-    ['darwin', 'claude', 'claude\n'],
+    ['darwin', 'claude', 'claude\r'],
+    ['linux', 'claude', 'claude\r'],
     ['win32', 'claude\r', 'claude\r'],
-    ['darwin', 'claude\n', 'claude\n']
+    ['darwin', 'claude\n', 'claude\r'],
+    ['win32', 'claude\r\n', 'claude\r']
   ])('submits startup with correct terminator on %s', async (platform, cmd, sent) => {
     Object.defineProperty(process, 'platform', { value: platform })
     await host.createOrAttach({
@@ -128,6 +127,6 @@ describe('TerminalHost startup command delivery logging', () => {
         streamClient: { onData: vi.fn(), onExit: vi.fn() }
       })
     ).resolves.toMatchObject({ isNew: true })
-    expect(sub.write).toHaveBeenCalledWith(`codex${process.platform === 'win32' ? '\r' : '\n'}`)
+    expect(sub.write).toHaveBeenCalledWith('codex\r')
   })
 })
diff --git a/src/main/daemon/terminal-host.test.ts b/src/main/daemon/terminal-host.test.ts
index 7ffaadec06d..f7330b3525c 100644
--- a/src/main/daemon/terminal-host.test.ts
+++ b/src/main/daemon/terminal-host.test.ts
@@ -189,9 +189,7 @@ describe('TerminalHost', () => {
 
       lastSubprocess._onDataCb?.('\r\nuser@host $ ')
       await new Promise((r) => setTimeout(r, 40))
-      expect(lastSubprocess.write).toHaveBeenCalledWith(
-        process.platform === 'win32' ? 'echo hello\r' : 'echo hello\n'
-      )
+      expect(lastSubprocess.write).toHaveBeenCalledWith('echo hello\r')
     })
 
     it('uses the short daemon settle path when marker and prompt arrive together', async () => {
@@ -211,9 +209,7 @@ describe('TerminalHost', () => {
         expect(lastSubprocess.write).not.toHaveBeenCalled()
 
         vi.advanceTimersByTime(1)
-        expect(lastSubprocess.write).toHaveBeenCalledWith(
-          process.platform === 'win32' ? 'echo hello\r' : 'echo hello\n'
-        )
+        expect(lastSubprocess.write).toHaveBeenCalledWith('echo hello\r')
       } finally {
         vi.useRealTimers()
       }
@@ -242,9 +238,7 @@ describe('TerminalHost', () => {
         streamClient: { onData: vi.fn(), onExit: vi.fn() }
       })
 
-      expect(lastSubprocess.write).toHaveBeenCalledWith(
-        process.platform === 'win32' ? 'echo hello\r' : 'echo hello\n'
-      )
+      expect(lastSubprocess.write).toHaveBeenCalledWith('echo hello\r')
     })
 
     it('does not bracketed-paste-wrap multiline commands for a fallback shell without paste mode', async () => {
@@ -272,7 +266,8 @@ describe('TerminalHost', () => {
 
       const written = (lastSubprocess.write as ReturnType<typeof vi.fn>).mock.calls[0]?.[0]
       expect(written).not.toContain('\x1b[200~')
-      expect(written).toContain('line one\nline two')
+      // Why CR between the lines: without bracketed paste each break submits its own line.
+      expect(written).toContain('line one\rline two')
     })
 
     it('keeps the shell-ready barrier when the spawned shell supports the marker', async () => {
diff --git a/src/main/ipc/pty-login-shell-startup-commands.test.ts b/src/main/ipc/pty-login-shell-startup-commands.test.ts
index 7ccb0386b9f..a89aca38ea5 100644
--- a/src/main/ipc/pty-login-shell-startup-commands.test.ts
+++ b/src/main/ipc/pty-login-shell-startup-commands.test.ts
@@ -233,7 +233,7 @@ describe('registerPtyHandlers', () => {
         mockProc.emitData('\x1b]133;A\x07% ')
         await Promise.resolve()
         vi.runAllTimers()
-        expect(mockProc.proc.write).toHaveBeenCalledWith('claude\n')
+        expect(mockProc.proc.write).toHaveBeenCalledWith('claude\r')
       } finally {
         vi.useRealTimers()
       }
@@ -396,7 +396,7 @@ describe('registerPtyHandlers', () => {
       vi.advanceTimersByTime(1)
       await Promise.resolve()
       vi.runAllTimers()
-      expect(mockProc.proc.write).toHaveBeenCalledWith('printf "hello"\n')
+      expect(mockProc.proc.write).toHaveBeenCalledWith('printf "hello"\r')
     } finally {
       vi.useRealTimers()
     }
diff --git a/src/main/ipc/pty-spawn-env-codex-resume-provenance.test.ts b/src/main/ipc/pty-spawn-env-codex-resume-provenance.test.ts
index a2a6153e99a..f3b30321c55 100644
--- a/src/main/ipc/pty-spawn-env-codex-resume-provenance.test.ts
+++ b/src/main/ipc/pty-spawn-env-codex-resume-provenance.test.ts
@@ -278,7 +278,7 @@ describe('registerPtyHandlers', () => {
             await Promise.resolve()
             vi.runAllTimers()
 
-            expect(mockProc.proc.write).toHaveBeenCalledWith(`${command}\n`)
+            expect(mockProc.proc.write).toHaveBeenCalledWith(`${command}\r`)
             expect(spawned.agentResumeUnavailable).toBeUndefined()
           } finally {
             vi.useRealTimers()
diff --git a/src/main/providers/local-pty-provider-shell-readiness.test.ts b/src/main/providers/local-pty-provider-shell-readiness.test.ts
index 6a46261e793..e33a681ed8c 100644
--- a/src/main/providers/local-pty-provider-shell-readiness.test.ts
+++ b/src/main/providers/local-pty-provider-shell-readiness.test.ts
@@ -217,7 +217,7 @@ describe('LocalPtyProvider', () => {
         expect(mockProc.write).not.toHaveBeenCalled()
 
         await vi.advanceTimersByTimeAsync(200)
-        expect(mockProc.write).toHaveBeenCalledWith(`${command}\n`)
+        expect(mockProc.write).toHaveBeenCalledWith(`${command}\r`)
       } finally {
         vi.useRealTimers()
       }
@@ -269,7 +269,7 @@ describe('LocalPtyProvider', () => {
 
         vi.advanceTimersByTime(1)
         await Promise.resolve()
-        expect(mockProc.write).toHaveBeenCalledWith("printf 'linked issue context'\n")
+        expect(mockProc.write).toHaveBeenCalledWith("printf 'linked issue context'\r")
       } finally {
         vi.useRealTimers()
       }
@@ -298,7 +298,7 @@ describe('LocalPtyProvider', () => {
 
         vi.advanceTimersByTime(200)
         await Promise.resolve()
-        expect(mockProc.write).toHaveBeenCalledWith('printf ready\n')
+        expect(mockProc.write).toHaveBeenCalledWith('printf ready\r')
       } finally {
         vi.useRealTimers()
       }
diff --git a/src/main/providers/local-pty-shell-ready-startup-command.test.ts b/src/main/providers/local-pty-shell-ready-startup-command.test.ts
index da843c6e42a..9b7c50ef521 100644
--- a/src/main/providers/local-pty-shell-ready-startup-command.test.ts
+++ b/src/main/providers/local-pty-shell-ready-startup-command.test.ts
@@ -58,8 +58,8 @@ describe('writeStartupCommandWhenShellReady', () => {
     Object.defineProperty(process, 'platform', { value: origPlatform })
   })
 
-  it('appends LF on POSIX so bash/zsh submit the line', async () => {
-    Object.defineProperty(process, 'platform', { value: 'darwin' })
+  it.each(['darwin', 'linux', 'win32'])('submits with CR on %s', async (platform) => {
+    Object.defineProperty(process, 'platform', { value: platform })
     const proc = createMockProc()
     const ready = Promise.resolve()
     writeStartupCommandWhenShellReady(ready, proc, 'claude', () => {})
@@ -69,39 +69,23 @@ describe('writeStartupCommandWhenShellReady', () => {
     vi.advanceTimersByTime(30)
     await Promise.resolve()
 
-    expect(proc._writes).toEqual(['claude\n'])
+    expect(proc._writes).toEqual(['claude\r'])
   })
 
-  it('appends CR on Windows so PowerShell/cmd.exe submit the line', async () => {
-    Object.defineProperty(process, 'platform', { value: 'win32' })
+  it('replaces a caller-supplied LF terminator with CR', async () => {
     const proc = createMockProc()
     const ready = Promise.resolve()
-    writeStartupCommandWhenShellReady(ready, proc, 'claude', () => {})
+    writeStartupCommandWhenShellReady(ready, proc, 'claude\n', () => {})
 
     await ready
-    proc._emitData('\r\nPS> ')
+    proc._emitData('\r\nuser@host % ')
     vi.advanceTimersByTime(30)
     await Promise.resolve()
 
     expect(proc._writes).toEqual(['claude\r'])
   })
 
-  it('does not re-append a submit byte if the command already ends in CR or LF', async () => {
-    Object.defineProperty(process, 'platform', { value: 'win32' })
-    const proc = createMockProc()
-    const ready = Promise.resolve()
-    writeStartupCommandWhenShellReady(ready, proc, 'claude\n', () => {})
-
-    await ready
-    proc._emitData('\r\nPS> ')
-    vi.advanceTimersByTime(30)
-    await Promise.resolve()
-
-    expect(proc._writes).toEqual(['claude\n'])
-  })
-
   it('keeps the no-prompt fallback conservative to avoid duplicate shell echo', async () => {
-    Object.defineProperty(process, 'platform', { value: 'darwin' })
     const proc = createMockProc()
     const ready = Promise.resolve()
     writeStartupCommandWhenShellReady(ready, proc, 'codex', () => {})
@@ -115,11 +99,10 @@ describe('writeStartupCommandWhenShellReady', () => {
     vi.advanceTimersByTime(150)
     await Promise.resolve()
 
-    expect(proc._writes).toEqual(['codex\n'])
+    expect(proc._writes).toEqual(['codex\r'])
   })
 
   it('uses the short settle delay when marker scan already observed post-marker bytes', async () => {
-    Object.defineProperty(process, 'platform', { value: 'darwin' })
     const proc = createMockProc()
     const ready = Promise.resolve({ postMarkerBytesObserved: true })
     writeStartupCommandWhenShellReady(ready, proc, 'codex', () => {})
@@ -131,12 +114,11 @@ describe('writeStartupCommandWhenShellReady', () => {
 
     vi.advanceTimersByTime(1)
     await Promise.resolve()
-    expect(proc._writes).toEqual(['codex\n'])
+    expect(proc._writes).toEqual(['codex\r'])
   })
 
   // Why: multiline startup commands must be bracketed-paste wrapped (ESC[200~ … ESC[201~) so shells insert them literally instead of treating each LF as Enter.
   it('wraps a multiline startup command in bracketed paste when the shell supports it', async () => {
-    Object.defineProperty(process, 'platform', { value: 'darwin' })
     const proc = createMockProc()
     const ready = Promise.resolve()
     const command = "claude '--dangerously-skip-permissions' 'line one\nline two'"
@@ -149,11 +131,10 @@ describe('writeStartupCommandWhenShellReady', () => {
     vi.advanceTimersByTime(30)
     await Promise.resolve()
 
-    expect(proc._writes).toEqual([`\x1b[200~${command}\x1b[201~\n`])
+    expect(proc._writes).toEqual([`\x1b[200~${command}\x1b[201~\r`])
   })
 
   it('leaves a single-line command on the raw submit path even when bracketed paste is safe', async () => {
-    Object.defineProperty(process, 'platform', { value: 'darwin' })
     const proc = createMockProc()
     const ready = Promise.resolve()
     writeStartupCommandWhenShellReady(ready, proc, 'claude', () => {}, {
@@ -165,14 +146,14 @@ describe('writeStartupCommandWhenShellReady', () => {
     vi.advanceTimersByTime(30)
     await Promise.resolve()
 
-    expect(proc._writes).toEqual(['claude\n'])
+    expect(proc._writes).toEqual(['claude\r'])
   })
 
   it('does not bracket-wrap a multiline command when the shell lacks bracketed paste', async () => {
-    Object.defineProperty(process, 'platform', { value: 'darwin' })
     const proc = createMockProc()
     const ready = Promise.resolve()
     const command = 'echo one\necho two'
+    // Why CR between the lines: without bracketed paste each break submits its own line.
     // Why: bracketedPasteSafe defaults false, so keep the raw path to avoid echoing ESC[200~ on shells without bracketed paste.
     writeStartupCommandWhenShellReady(ready, proc, command, () => {})
 
@@ -181,6 +162,6 @@ describe('writeStartupCommandWhenShellReady', () => {
     vi.advanceTimersByTime(30)
     await Promise.resolve()
 
-    expect(proc._writes).toEqual([`${command}\n`])
+    expect(proc._writes).toEqual(['echo one\recho two\r'])
   })
 })
diff --git a/src/main/providers/local-pty-shell-ready-startup-command.ts b/src/main/providers/local-pty-shell-ready-startup-command.ts
index bf7f73c19d7..5fefb5db5fa 100644
--- a/src/main/providers/local-pty-shell-ready-startup-command.ts
+++ b/src/main/providers/local-pty-shell-ready-startup-command.ts
@@ -46,12 +46,9 @@ export function writeStartupCommandWhenShellReady(
       postReadyTimer = null
     }
     // Why: run in the same interactive shell (not `shell -c`) so the session survives after the agent exits.
-    // Why CR on Windows: PSReadLine/cmd.exe submit on `\r`, not LF; POSIX treats either as Enter under ICRNL.
-    const submit = process.platform === 'win32' ? '\r' : '\n'
     // Why: single write after the ready barrier avoids incremental-paste char drops; multiline is bracketed-paste wrapped so newlines don't submit early.
     proc.write(
       buildStartupCommandSubmission(startupCommand, {
-        submit,
         bracketedPasteSafe: options.bracketedPasteSafe === true
       })
     )
diff --git a/src/relay/pty-handler-startup-command-delivery.test.ts b/src/relay/pty-handler-startup-command-delivery.test.ts
index 2215eff9d76..a8d812ed89a 100644
--- a/src/relay/pty-handler-startup-command-delivery.test.ts
+++ b/src/relay/pty-handler-startup-command-delivery.test.ts
@@ -89,8 +89,7 @@ describe('PtyHandler', () => {
     expect(term.write).not.toHaveBeenCalled()
 
     vi.advanceTimersByTime(1)
-    const submit = process.platform === 'win32' ? '\r' : '\n'
-    expect(term.write).toHaveBeenCalledWith(`echo provider-owned${submit}`)
+    expect(term.write).toHaveBeenCalledWith('echo provider-owned\r')
     expect(handler.retainedStartupCommandCount).toBe(0)
   })
 
@@ -364,7 +363,7 @@ describe('PtyHandler', () => {
       expect(term.write).not.toHaveBeenCalled()
       vi.advanceTimersByTime(1)
 
-      expect(term.write).toHaveBeenCalledWith('echo after-ready\n')
+      expect(term.write).toHaveBeenCalledWith('echo after-ready\r')
       expect(handler.retainedStartupCommandCount).toBe(0)
       vi.advanceTimersByTime(8)
       expect(dispatcher.notify).toHaveBeenCalledWith('pty.data', {
@@ -421,7 +420,7 @@ describe('PtyHandler', () => {
       promptOptions.onPromptReady()
       await vi.advanceTimersByTimeAsync(50)
 
-      expect(term.write).toHaveBeenCalledWith('echo after-exec\n')
+      expect(term.write).toHaveBeenCalledWith('echo after-exec\r')
       expect(handler.retainedStartupCommandCount).toBe(0)
     }
   )
@@ -635,7 +634,7 @@ describe('PtyHandler', () => {
       dataCallback?.('\x1b]777;orca-shell-ready')
       vi.advanceTimersByTime(1500)
 
-      expect(term.write).toHaveBeenCalledWith('echo fallback\n')
+      expect(term.write).toHaveBeenCalledWith('echo fallback\r')
       vi.advanceTimersByTime(8)
       expect(dispatcher.notify).toHaveBeenCalledWith('pty.data', {
         id: PTY_1,
diff --git a/src/relay/pty-handler.ts b/src/relay/pty-handler.ts
index b96781818e7..162553fe613 100644
--- a/src/relay/pty-handler.ts
+++ b/src/relay/pty-handler.ts
@@ -1025,10 +1025,8 @@ export class PtyHandler {
     if (heldBytes) {
       managed.startupIngress?.accept(heldBytes)
     }
-    const submit = process.platform === 'win32' ? '\r' : '\n'
     // Why: only the shell-ready wrapper arms bracketed-paste; other shells use raw submit so ESC[200~ markers aren't echoed.
     const payload = buildStartupCommandSubmission(startup.command, {
-      submit,
       bracketedPasteSafe: startup.waitForShellReady
     })
     managed.startupCommand = undefined
diff --git a/src/renderer/src/lib/ssh-background-startup-delivery.ts b/src/renderer/src/lib/ssh-background-startup-delivery.ts
index 0e1c08c70ff..239bf6326a5 100644
--- a/src/renderer/src/lib/ssh-background-startup-delivery.ts
+++ b/src/renderer/src/lib/ssh-background-startup-delivery.ts
@@ -139,12 +139,10 @@ export function createSshBackgroundStartupDelivery(
       // PTYs; hidden automation tabs still submit the command themselves.
       // Why bracketed paste: multiline prompts are pasted literally only when we
       // synchronized on the Orca shell-ready marker — that is the bash/zsh overlay
-      // with bracketed-paste mode armed. Submit with CR since the relay drives a
-      // remote shell.
+      // with bracketed-paste mode armed.
       options.write(
         ptyId,
         buildStartupCommandSubmission(command, {
-          submit: '\r',
           bracketedPasteSafe: markerObserved
         })
       )
diff --git a/src/shared/powershell-native-argument.test.ts b/src/shared/powershell-native-argument.test.ts
index b8e1feb8aa2..33d396dc8b0 100644
--- a/src/shared/powershell-native-argument.test.ts
+++ b/src/shared/powershell-native-argument.test.ts
@@ -9,10 +9,27 @@ describe('PowerShell native argument quoting', () => {
     )
   })
 
+  it('keeps a value with a line break on one physical line', () => {
+    expect(quotePowerShellLiteral('line one\nline two')).toBe('"line one`nline two"')
+    expect(quotePowerShellLiteral('a\r\nb\rc')).toBe('"a`r`nb`rc"')
+  })
+
+  it('escapes the double-quoted specials in a multi-line value', () => {
+    expect(
+      quotePowerShellLiteral('$(Remove-Item x) `t "q" \u201Cl\u201D \u201Elow \'single\'\nend')
+    ).toBe('"`$(Remove-Item x) ``t `"q`" `\u201Cl`\u201D `\u201Elow \'single\'`nend"')
+  })
+
+  it('leaves single-line values on the single-quoted form', () => {
+    expect(quotePowerShellLiteral('a $b `c "d"')).toBe('\'a $b `c "d"\'')
+  })
+
   it('pre-escapes embedded quotes for Windows native argv parsing', () => {
     expect(quotePowerShellNativeArgument('eval "decoded"')).toBe(String.raw`'eval \"decoded\"'`)
     expect(quotePowerShellNativeArgument(String.raw`before\"after`)).toBe(
       String.raw`'before\\\"after'`
     )
+    // Why: the argv pre-escape survives the multi-line form, so 5.1 still passes `\"` to argv.
+    expect(quotePowerShellNativeArgument('say "hi"\nbye')).toBe('"say \\`"hi\\`"`nbye"')
   })
 })
diff --git a/src/shared/powershell-native-argument.ts b/src/shared/powershell-native-argument.ts
index f357a8e8fb7..23e517505f0 100644
--- a/src/shared/powershell-native-argument.ts
+++ b/src/shared/powershell-native-argument.ts
@@ -1,8 +1,24 @@
 export function quotePowerShellLiteral(value: string): string {
+  if (/[\r\n]/.test(value)) {
+    return quotePowerShellMultilineLiteral(value)
+  }
   // Why: PowerShell also ends single-quoted strings at typographic single quotes.
   return `'${value.replace(/['\u2018\u2019\u201A\u201B]/g, '$&$&')}'`
 }
 
+/**
+ * Why one physical line: a raw line break typed into PowerShell submits the line, and Windows
+ * PowerShell 5.1 without PSReadLine then waits at `>>` for an empty line that never comes.
+ * Backtick escapes keep every byte, so `\r\n` stays `\r\n` exactly as the single-quoted form
+ * delivered it.
+ */
+function quotePowerShellMultilineLiteral(value: string): string {
+  const escaped = value.replace(/[`$"\u201C\u201D\u201E\r\n]/g, (char) =>
+    char === '\r' ? '`r' : char === '\n' ? '`n' : `\`${char}`
+  )
+  return `"${escaped}"`
+}
+
 export function quotePowerShellNativeArgument(value: string): string {
   // Why: Windows PowerShell 5.1 drops unescaped embedded quotes when it
   // constructs argv for native executables such as wsl.exe.
diff --git a/src/shared/powershell-native-argument.windows.test.ts b/src/shared/powershell-native-argument.windows.test.ts
new file mode 100644
index 00000000000..1bd81a27721
--- /dev/null
+++ b/src/shared/powershell-native-argument.windows.test.ts
@@ -0,0 +1,50 @@
+import { mkdtemp, readFile, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { expect, it } from 'vitest'
+import { runProcess } from './child-process/run-process'
+import { quotePowerShellLiteral } from './powershell-native-argument'
+
+async function captureNativeArgv(root: string, quotedArg: string): Promise<string[]> {
+  const capturePath = join(root, 'argv.json')
+  const scriptPath = join(root, 'capture.js')
+  await writeFile(
+    scriptPath,
+    `require('node:fs').writeFileSync(${JSON.stringify(capturePath)}, JSON.stringify(process.argv.slice(2)))`
+  )
+  const result = await runProcess({
+    program: 'powershell.exe',
+    args: [
+      '-NoProfile',
+      '-NonInteractive',
+      '-Command',
+      `& ${quotePowerShellLiteral(process.execPath)} ${quotePowerShellLiteral(scriptPath)} ${quotedArg}`
+    ],
+    cwd: root
+  })
+  expect(result.code, JSON.stringify(result)).toBe(0)
+  const argv: string[] = JSON.parse(await readFile(capturePath, 'utf8'))
+  return argv
+}
+
+// Why native: argv marshalling, not the generated text, is what a launched agent actually receives.
+it.skipIf(process.platform !== 'win32')(
+  'passes a multi-line value to a native program exactly as the single-quoted form did',
+  async () => {
+    const root = await mkdtemp(join(tmpdir(), 'orca-ps-multiline-'))
+    try {
+      const plain = 'line one\r\nline two $HOME `tick\nO\u2019Brien \u201Cdouble\u201D end'
+      expect(await captureNativeArgv(root, quotePowerShellLiteral(plain))).toEqual([plain])
+
+      // Why compare with the old raw single-quoted form: 5.1 drops embedded `"` from native argv
+      // either way, and the one-line form must not change what reaches the program.
+      const withQuotes = 'say "hi"\nbye'
+      const legacy = `'${withQuotes.replace(/'/g, "''")}'`
+      expect(await captureNativeArgv(root, quotePowerShellLiteral(withQuotes))).toEqual(
+        await captureNativeArgv(root, legacy)
+      )
+    } finally {
+      await rm(root, { recursive: true, force: true })
+    }
+  }
+)
diff --git a/src/shared/startup-command-submission.test.ts b/src/shared/startup-command-submission.test.ts
index e25ee4c4105..6d85f4d14bc 100644
--- a/src/shared/startup-command-submission.test.ts
+++ b/src/shared/startup-command-submission.test.ts
@@ -5,46 +5,52 @@ import {
 } from './startup-command-submission'
 
 describe('buildStartupCommandSubmission', () => {
-  it('appends the submit byte to a single-line command unchanged', () => {
-    expect(
-      buildStartupCommandSubmission('claude', { submit: '\n', bracketedPasteSafe: true })
-    ).toBe('claude\n')
-    expect(
-      buildStartupCommandSubmission('claude', { submit: '\r', bracketedPasteSafe: true })
-    ).toBe('claude\r')
+  it('submits a single-line command with CR', () => {
+    expect(buildStartupCommandSubmission('claude', { bracketedPasteSafe: true })).toBe('claude\r')
+    expect(buildStartupCommandSubmission('claude', { bracketedPasteSafe: false })).toBe('claude\r')
   })
 
-  it('preserves a caller-supplied trailing submit byte on single-line commands', () => {
-    expect(
-      buildStartupCommandSubmission('claude\n', { submit: '\r', bracketedPasteSafe: true })
-    ).toBe('claude\n')
-  })
-
-  it('treats a CRLF-terminated single-line command as single-line', () => {
-    expect(
-      buildStartupCommandSubmission('claude\r\n', { submit: '\r', bracketedPasteSafe: true })
-    ).toBe('claude\r\n')
+  it('replaces a caller-supplied trailing terminator with CR', () => {
+    for (const command of ['claude\n', 'claude\r', 'claude\r\n']) {
+      expect(buildStartupCommandSubmission(command, { bracketedPasteSafe: true })).toBe('claude\r')
+    }
   })
 
   it('wraps a multiline command in bracketed paste with a trailing submit byte', () => {
     const command = "claude 'first\nsecond'"
-    expect(buildStartupCommandSubmission(command, { submit: '\n', bracketedPasteSafe: true })).toBe(
-      `\x1b[200~${command}\x1b[201~\n`
+    expect(buildStartupCommandSubmission(command, { bracketedPasteSafe: true })).toBe(
+      `\x1b[200~${command}\x1b[201~\r`
     )
   })
 
   it('strips a trailing submit byte before bracket-wrapping the multiline body', () => {
     const body = "claude 'first\nsecond'"
-    expect(
-      buildStartupCommandSubmission(`${body}\n`, { submit: '\r', bracketedPasteSafe: true })
-    ).toBe(`\x1b[200~${body}\x1b[201~\r`)
+    expect(buildStartupCommandSubmission(`${body}\n`, { bracketedPasteSafe: true })).toBe(
+      `\x1b[200~${body}\x1b[201~\r`
+    )
   })
 
   it('keeps the raw path for multiline commands when bracketed paste is unsafe', () => {
-    const command = 'echo one\necho two'
-    expect(
-      buildStartupCommandSubmission(command, { submit: '\n', bracketedPasteSafe: false })
-    ).toBe(`${command}\n`)
+    expect(buildStartupCommandSubmission('echo one\necho two', { bracketedPasteSafe: false })).toBe(
+      'echo one\recho two\r'
+    )
+  })
+
+  // Why: on the raw path every line break submits a line, so an interior LF is the same
+  // remappable Ctrl+J the trailing terminator was (#23250).
+  it('submits every line of a raw multiline command with CR', () => {
+    for (const command of ['echo one\necho two', 'echo one\r\necho two', 'echo one\recho two']) {
+      expect(buildStartupCommandSubmission(command, { bracketedPasteSafe: false })).toBe(
+        'echo one\recho two\r'
+      )
+    }
+  })
+
+  it('leaves interior line breaks intact inside a bracketed-paste payload', () => {
+    const command = "claude 'first\nsecond'"
+    expect(buildStartupCommandSubmission(command, { bracketedPasteSafe: true })).toBe(
+      `\x1b[200~${command}\x1b[201~\r`
+    )
   })
 })
 
diff --git a/src/shared/startup-command-submission.ts b/src/shared/startup-command-submission.ts
index 33d84cd82b2..5b8b225614a 100644
--- a/src/shared/startup-command-submission.ts
+++ b/src/shared/startup-command-submission.ts
@@ -3,12 +3,12 @@
  * submit a startup command (agent launch, setup script, etc.).
  *
  * Why bracketed paste: agent launch prompts are single-quoted, but their
- * literal embedded newlines survive quoting. bash readline / zsh zle read every
- * raw LF as accept-line (Enter), so the first newline inside a multiline prompt
+ * literal embedded newlines survive quoting. bash readline / zsh zle read a raw
+ * LF as accept-line by default, so the first newline inside a multiline prompt
  * submits an unterminated single-quoted command and drops the shell into PS2
  * continuation — the prompt is executed piecemeal and mangled. Wrapping the
  * payload in bracketed-paste markers (ESC[200~ … ESC[201~) tells the line
- * editor to insert the whole multiline text literally; only the trailing CR/LF
+ * editor to insert the whole multiline text literally; only the trailing CR
  * written after the end marker submits it. Single-line commands keep the proven
  * raw-write path unchanged so the fast path never regresses.
  */
@@ -16,12 +16,11 @@
 // DEC 2004 bracketed-paste bracket sequences.
 const BRACKETED_PASTE_START = '\x1b[200~'
 const BRACKETED_PASTE_END = '\x1b[201~'
+// Why CR on every platform: it is the byte the Enter key sends. A line editor reads
+// the tty raw, so LF arrives as Ctrl+J — a key users rebind (e.g. vi-mode newline).
+const STARTUP_COMMAND_SUBMIT = '\r'
 
 export type StartupCommandSubmissionOptions = {
-  /** Byte that submits the line: CR on Windows (PSReadLine/cmd.exe), LF on
-   *  POSIX; SSH relays remote shells with CR. A caller-supplied trailing submit
-   *  byte on `command` is preserved as-is. */
-  submit: string
   /** Whether the target line editor has bracketed-paste mode active (Orca's
    *  wrapped bash/zsh/fish). Only wrap multiline payloads when true — a shell
    *  without bracketed paste would echo the ESC[200~ markers as literal garbage. */
@@ -52,15 +51,14 @@ export function isBracketedPasteSafeShell(args: {
 
 export function buildStartupCommandSubmission(
   command: string,
-  { submit, bracketedPasteSafe }: StartupCommandSubmissionOptions
+  { bracketedPasteSafe }: StartupCommandSubmissionOptions
 ): string {
-  // Strip a full CRLF (or lone CR/LF) terminator so a single-line command ending
-  // in \r\n isn't misread as multiline by the \r/\n body check below.
-  const trailingTerminator = /\r\n$|\r$|\n$/.exec(command)?.[0] ?? ''
-  const endsWithSubmit = trailingTerminator.length > 0
-  const body = endsWithSubmit ? command.slice(0, -trailingTerminator.length) : command
+  // Why replace a caller's terminator: a trailing LF is Ctrl+J again, and CRLF submits twice.
+  const body = command.replace(/\r\n$|\r$|\n$/, '')
   if (bracketedPasteSafe && (body.includes('\n') || body.includes('\r'))) {
-    return `${BRACKETED_PASTE_START}${body}${BRACKETED_PASTE_END}${submit}`
+    return `${BRACKETED_PASTE_START}${body}${BRACKETED_PASTE_END}${STARTUP_COMMAND_SUBMIT}`
   }
-  return endsWithSubmit ? command : `${command}${submit}`
+  // Why normalise interior breaks too: without bracketed paste each line submits itself, and an
+  // interior LF is the same remappable Ctrl+J as a trailing one.
+  return `${body.replace(/\r?\n/g, STARTUP_COMMAND_SUBMIT)}${STARTUP_COMMAND_SUBMIT}`
 }
diff --git a/src/shared/tui-agent-startup.test.ts b/src/shared/tui-agent-startup.test.ts
index 31690889e9f..c9a62b747b6 100644
--- a/src/shared/tui-agent-startup.test.ts
+++ b/src/shared/tui-agent-startup.test.ts
@@ -85,6 +85,19 @@ describe('tui agent startup plans', () => {
     expect(plan?.launchCommand).toBe("claude 'fix Bob''s \"quoted\" branch'")
   })
 
+  // Why: a typed line break submits early, and PowerShell 5.1 without PSReadLine then hangs at `>>`.
+  it('keeps a multi-line PowerShell launch on one physical line', () => {
+    const plan = buildAgentStartupPlan({
+      agent: 'claude',
+      prompt: 'first line\nsecond $line',
+      cmdOverrides: {},
+      platform: 'win32'
+    })
+
+    expect(plan?.launchCommand).not.toMatch(/[\r\n]/)
+    expect(plan?.launchCommand).toBe('claude "first line`nsecond `$line"')
+  })
+
   it('invokes fully quoted argv commands in PowerShell', () => {
     expect(buildShellCommandFromArgv(['codex', 'resume', 's1'], 'powershell')).toBe(
       "& 'codex' 'resume' 's1'"