diff --git a/src/renderer/src/hooks/useComposerState.ts b/src/renderer/src/hooks/useComposerState.ts
index 3dd8822eb04..f6d19f12604 100644
--- a/src/renderer/src/hooks/useComposerState.ts
+++ b/src/renderer/src/hooks/useComposerState.ts
@@ -1496,7 +1496,8 @@ export function useComposerState(options: UseComposerStateOptions): UseComposerS
                 agent,
                 draft: quickDraftPrompt,
                 cmdOverrides: settings?.agentCmdOverrides ?? {},
-                platform: CLIENT_PLATFORM
+                platform: CLIENT_PLATFORM,
+                windowsShell: settings?.terminalWindowsShell
               })
 
         let startupPlan: ReturnType<typeof buildAgentStartupPlan> = null
@@ -1589,6 +1590,7 @@ export function useComposerState(options: UseComposerStateOptions): UseComposerS
       resolvedSetupDecision,
       selectedRepo,
       settings?.agentCmdOverrides,
+      settings?.terminalWindowsShell,
       settings?.rightSidebarOpenByDefault,
       setRightSidebarOpen,
       setRightSidebarTab,
diff --git a/src/renderer/src/lib/launch-work-item-direct.ts b/src/renderer/src/lib/launch-work-item-direct.ts
index 85aaf9ef879..e6aea6aecf5 100644
--- a/src/renderer/src/lib/launch-work-item-direct.ts
+++ b/src/renderer/src/lib/launch-work-item-direct.ts
@@ -286,7 +286,8 @@ export async function launchWorkItemDirect(args: LaunchWorkItemDirectArgs): Prom
             agent: effectiveAgent,
             draft: draftContent,
             cmdOverrides: settings?.agentCmdOverrides ?? {},
-            platform: CLIENT_PLATFORM
+            platform: CLIENT_PLATFORM,
+            windowsShell: settings?.terminalWindowsShell
           })
     if (draftLaunchPlan) {
       startupPlan = {
diff --git a/src/renderer/src/lib/tui-agent-startup.test.ts b/src/renderer/src/lib/tui-agent-startup.test.ts
index 1adc0dd4a7b..1b1190820f1 100644
--- a/src/renderer/src/lib/tui-agent-startup.test.ts
+++ b/src/renderer/src/lib/tui-agent-startup.test.ts
@@ -194,6 +194,60 @@ describe('buildAgentDraftLaunchPlan', () => {
     })
   })
 
+  it('uses cmd.exe syntax to clear the pi prefill var when Windows shell is cmd', () => {
+    expect(
+      buildAgentDraftLaunchPlan({
+        agent: 'pi',
+        draft: 'https://github.com/acme/repo/issues/42',
+        cmdOverrides: {},
+        platform: 'win32',
+        windowsShell: 'cmd.exe'
+      })
+    ).toEqual({
+      agent: 'pi',
+      launchCommand: 'pi; set "ORCA_PI_PREFILL="',
+      expectedProcess: 'pi',
+      env: { ORCA_PI_PREFILL: 'https://github.com/acme/repo/issues/42' }
+    })
+  })
+
+  it('uses Remove-Item Env: to clear the pi prefill var on PowerShell', () => {
+    // Why: `set "FOO="` is cmd-only; PowerShell parses it as the Set-Variable
+    // alias and never clears the env var, so re-running pi re-prefills with
+    // the stale URL. Use the portable PowerShell form instead.
+    expect(
+      buildAgentDraftLaunchPlan({
+        agent: 'pi',
+        draft: 'https://github.com/acme/repo/issues/42',
+        cmdOverrides: {},
+        platform: 'win32',
+        windowsShell: 'powershell.exe'
+      })
+    ).toEqual({
+      agent: 'pi',
+      launchCommand: 'pi; Remove-Item Env:ORCA_PI_PREFILL -ErrorAction SilentlyContinue',
+      expectedProcess: 'pi',
+      env: { ORCA_PI_PREFILL: 'https://github.com/acme/repo/issues/42' }
+    })
+  })
+
+  it('treats pwsh.exe as PowerShell for the prefill clear-var', () => {
+    expect(
+      buildAgentDraftLaunchPlan({
+        agent: 'pi',
+        draft: 'https://github.com/acme/repo/issues/42',
+        cmdOverrides: {},
+        platform: 'win32',
+        windowsShell: 'pwsh.exe'
+      })
+    ).toEqual({
+      agent: 'pi',
+      launchCommand: 'pi; Remove-Item Env:ORCA_PI_PREFILL -ErrorAction SilentlyContinue',
+      expectedProcess: 'pi',
+      env: { ORCA_PI_PREFILL: 'https://github.com/acme/repo/issues/42' }
+    })
+  })
+
   it('returns null for an empty draft so callers fall back cleanly', () => {
     expect(
       buildAgentDraftLaunchPlan({
diff --git a/src/renderer/src/lib/tui-agent-startup.ts b/src/renderer/src/lib/tui-agent-startup.ts
index 65964af5ee4..9259442e4b1 100644
--- a/src/renderer/src/lib/tui-agent-startup.ts
+++ b/src/renderer/src/lib/tui-agent-startup.ts
@@ -23,6 +23,14 @@ export type AgentStartupPlan = {
   env?: Record<string, string>
 }
 
+function isPowerShellLike(shell: string | undefined): boolean {
+  if (!shell) {
+    return false
+  }
+  const normalized = shell.toLowerCase().replace(/\\/g, '/').split('/').pop() ?? ''
+  return normalized === 'powershell.exe' || normalized === 'pwsh.exe' || normalized === 'pwsh'
+}
+
 function quoteStartupArg(value: string, platform: NodeJS.Platform): string {
   if (platform === 'win32') {
     return `"${value.replace(/"/g, '""')}"`
@@ -133,8 +141,15 @@ export function buildAgentDraftLaunchPlan(args: {
   draft: string
   cmdOverrides: Partial<Record<TuiAgent, string>>
   platform: NodeJS.Platform
+  /** Why: the post-exit clear-var command differs per Windows shell. cmd.exe
+   *  uses `set "FOO="`, but PowerShell parses that as the `Set-Variable`
+   *  alias and never clears the env var — so re-running the agent re-prefills
+   *  with the stale URL. Callers on Windows pass the configured shell
+   *  (`terminalWindowsShell`) so we can emit `Remove-Item Env:FOO` for
+   *  PowerShell/pwsh. POSIX platforms ignore this. */
+  windowsShell?: string
 }): AgentDraftLaunchPlan | null {
-  const { agent, draft, cmdOverrides, platform } = args
+  const { agent, draft, cmdOverrides, platform, windowsShell } = args
   const config = TUI_AGENT_CONFIG[agent]
   const trimmed = draft.trim()
   if (!trimmed) {
@@ -158,7 +173,9 @@ export function buildAgentDraftLaunchPlan(args: {
     // terminal would inherit the stale value and re-prefill with the old URL.
     const clearVar =
       platform === 'win32'
-        ? `set "${config.draftPromptEnvVar}="`
+        ? isPowerShellLike(windowsShell)
+          ? `Remove-Item Env:${config.draftPromptEnvVar} -ErrorAction SilentlyContinue`
+          : `set "${config.draftPromptEnvVar}="`
         : `unset ${config.draftPromptEnvVar}`
     return {
       agent,