diff --git a/src/main/runtime/agent-launch-scope-runtime.test.ts b/src/main/runtime/agent-launch-scope-runtime.test.ts
index 9c332190f25..1af616d9b1e 100644
--- a/src/main/runtime/agent-launch-scope-runtime.test.ts
+++ b/src/main/runtime/agent-launch-scope-runtime.test.ts
@@ -127,3 +127,19 @@ it("keeps a folder's WSL Terminal shell where its repo's project is set to Windo
     'posix'
   ])
 })
+
+// TEMPORARY until STA-10231: a pane the window spawns keeps main's Terminal-shell answer.
+it('writes the command for the Terminal shell when the window spawns the pane', () => {
+  const s = store({ global: { kind: 'windows-host' }, shell: 'wsl.exe' })
+  const quoting = (windowSpawnsPane: boolean) =>
+    agentLaunchQuotingShell(
+      resolveAgentLaunchRuntime(
+        s,
+        scope(WIN, { repo: repo(WIN) }),
+        undefined,
+        'codex',
+        windowSpawnsPane
+      )
+    )
+  expect([quoting(true), quoting(false)]).toEqual(['posix', 'powershell'])
+})
diff --git a/src/main/runtime/agent-launch-scope-runtime.ts b/src/main/runtime/agent-launch-scope-runtime.ts
index 91eef3937dd..ecb3361258b 100644
--- a/src/main/runtime/agent-launch-scope-runtime.ts
+++ b/src/main/runtime/agent-launch-scope-runtime.ts
@@ -47,7 +47,9 @@ export function agentLaunchPlatformForScope(
 export function agentLaunchProjectRuntime(
   store: LaunchScopeRuntimeStore,
   scope: TerminalWorkspaceLaunchScope,
-  agent: TuiAgent | undefined
+  agent: TuiAgent | undefined,
+  /** The window spawns the pane, by the Terminal shell, so the command must be written for it. */
+  windowSpawnsPane = false
 ): ProjectExecutionRuntimeResolution | undefined {
   const runtime = resolveLocalLaunchScopeRuntime(store, scope)
   const onWindowsHost = runtime?.status === 'resolved' && runtime.runtime.kind === 'windows-host'
@@ -57,8 +59,9 @@ export function agentLaunchProjectRuntime(
     // PERMANENT fix, not parity: a `\\wsl$` cwd runs in WSL whatever the setting says. Keep it
     // when the temporary terms go; the window adopts it in C2.
     (onWindowsHost && isWslUncPath(scope.path)) ||
-    // TEMPORARY (STA-10231): an explicit Windows host can't be told from the shipped default.
-    (onWindowsHost && mainHadNone) ||
+    // TEMPORARY (STA-10231): an explicit Windows host can't be told from the shipped default, so
+    // folders and panes the window spawns keep main's Terminal-shell answer (often WSL).
+    (onWindowsHost && (mainHadNone || windowSpawnsPane)) ||
     // TEMPORARY (STA-10251): OpenCode models can't yet be verified inside WSL.
     (agent === 'opencode' && mainHadNone)
   return pathDecides ? undefined : runtime
@@ -70,7 +73,8 @@ export function resolveAgentLaunchRuntime(
   store: AgentLaunchRuntimeStore,
   scope: TerminalWorkspaceLaunchScope,
   requestedShellOverride: string | undefined,
-  agent: TuiAgent | undefined
+  agent: TuiAgent | undefined,
+  windowSpawnsPane = false
 ): AgentLaunchRuntime {
   if (scope.connectionId) {
     return {
@@ -78,7 +82,7 @@ export function resolveAgentLaunchRuntime(
       pty: { shellOverride: undefined, terminalWindowsWslDistro: null }
     }
   }
-  const projectRuntime = agentLaunchProjectRuntime(store, scope, agent)
+  const projectRuntime = agentLaunchProjectRuntime(store, scope, agent, windowSpawnsPane)
   return {
     platform: executionRuntimePlatform(projectRuntime, scope.path, process.platform),
     pty: resolveLocalPtyOptions(store.getSettings(), projectRuntime, requestedShellOverride)
diff --git a/src/main/runtime/orca-runtime-create-agent-session.ts b/src/main/runtime/orca-runtime-create-agent-session.ts
index 8d721333abe..c04afba5450 100644
--- a/src/main/runtime/orca-runtime-create-agent-session.ts
+++ b/src/main/runtime/orca-runtime-create-agent-session.ts
@@ -14,6 +14,7 @@ import { createHash } from 'node:crypto'
 import { isTuiAgentEnabled } from '../../shared/tui-agent-selection'
 import { resolveAgentStartupPlanInputs } from '../../shared/agent-startup-plan-inputs'
 import { agentLaunchQuotingShell } from '../../shared/agent-launch-runtime'
+import { windowSpawnsTerminal } from './orca-runtime-create-terminal-dependencies'
 import { buildExecutionHostAgentStartupPlan } from '../opencode/opencode-model-startup-plan'
 import type { RuntimeTerminalCreate } from '../../shared/runtime-types'
 import type {
@@ -131,7 +132,14 @@ export class OrcaRuntimeWithCreateAgentSession extends OrcaRuntimeWithGetAgentSe
       if (!isTuiAgentEnabled(request.agent, settings.disabledTuiAgents)) {
         throw new Error('Selected agent is disabled. Choose an enabled agent before creating.')
       }
-      const launchRuntime = this.resolveAgentLaunchRuntime(workspace, request.agent)
+      const launchRuntime = this.resolveAgentLaunchRuntime(
+        workspace,
+        request.agent,
+        windowSpawnsTerminal(
+          { presentation: request.presentation ?? 'background' },
+          this.getAvailableAuthoritativeWindow() !== null
+        )
+      )
       const startupArgs = resolveAgentStartupPlanInputs({
         agent: request.agent,
         settings,
diff --git a/src/main/runtime/orca-runtime-create-terminal-dependencies.ts b/src/main/runtime/orca-runtime-create-terminal-dependencies.ts
index 85e4e1e5fdd..a4078247999 100644
--- a/src/main/runtime/orca-runtime-create-terminal-dependencies.ts
+++ b/src/main/runtime/orca-runtime-create-terminal-dependencies.ts
@@ -42,6 +42,22 @@ export const BACKGROUND_TERMINAL_SPAWN_FLAGS = {
   persistHostSessionBinding: true
 } as const
 
+/** Whether the window spawns this create's pane, by its own shell rule, rather than this host. */
+export function windowSpawnsTerminal(
+  opts: Pick<
+    TerminalCreateOptions,
+    'agentSessionClaim' | 'requireFreshPane' | 'presentation' | 'focus' | 'rendererBacked'
+  >,
+  windowAvailable: boolean
+): boolean {
+  return (
+    windowAvailable &&
+    !opts.agentSessionClaim &&
+    !opts.requireFreshPane &&
+    (opts.presentation === 'focused' || opts.focus === true || opts.rendererBacked === true)
+  )
+}
+
 /** The PTY's shell inputs: a requested shell, and an agent launch's runtime fact. */
 export const spawnShellInputs = ({
   shellOverride,
diff --git a/src/main/runtime/orca-runtime-create-terminal-desktop.ts b/src/main/runtime/orca-runtime-create-terminal-desktop.ts
index 6a56bff56b0..631f3b597a9 100644
--- a/src/main/runtime/orca-runtime-create-terminal-desktop.ts
+++ b/src/main/runtime/orca-runtime-create-terminal-desktop.ts
@@ -18,7 +18,7 @@ export async function createDesktopTerminal(
     ? await runtime.resolveTerminalWorkspaceLaunchScope(worktreeSelector, createdWorktree)
     : null
   const launchOpts = workspace
-    ? await runtime.resolveAgentTerminalCreateOptions(workspace, opts)
+    ? await runtime.resolveAgentTerminalCreateOptions(workspace, opts, true)
     : opts
   // `resolveAgentTerminalCreateOptions` refuses an unapplicable shell, and it only runs with a
   // workspace; a worktree-less create has no execution host to apply one to either.
diff --git a/src/main/runtime/orca-runtime-create-terminal.ts b/src/main/runtime/orca-runtime-create-terminal.ts
index a4c7ed44652..dcbc7cdcc00 100644
--- a/src/main/runtime/orca-runtime-create-terminal.ts
+++ b/src/main/runtime/orca-runtime-create-terminal.ts
@@ -22,14 +22,11 @@ export class OrcaRuntimeWithCreateTerminal extends OrcaRuntimeWithTerminalCreate
       dependencies.setPairedViewerColors(callerColors)
     }
     const presentation = dependencies.resolveTerminalPresentation(opts)
-    const requiresRendererFocus = opts.presentation === 'focused' || opts.focus === true
     const availableAuthoritativeWindow = this.getAvailableAuthoritativeWindow()
     const rendererWindow = opts.rendererBacked === true ? availableAuthoritativeWindow : null
     const shouldCreateInBackground =
       worktreeSelector !== undefined &&
-      (Boolean(opts.agentSessionClaim || opts.requireFreshPane) ||
-        (!requiresRendererFocus && opts.rendererBacked !== true) ||
-        availableAuthoritativeWindow === null)
+      !dependencies.windowSpawnsTerminal(opts, availableAuthoritativeWindow !== null)
     if (shouldCreateInBackground) {
       if (!this.ptyController?.spawn) {
         throw new Error('runtime_unavailable')
diff --git a/src/main/runtime/orca-runtime-resolve-mobile-session-terminal-command.ts b/src/main/runtime/orca-runtime-resolve-mobile-session-terminal-command.ts
index 41032c139ef..a2ac5df8682 100644
--- a/src/main/runtime/orca-runtime-resolve-mobile-session-terminal-command.ts
+++ b/src/main/runtime/orca-runtime-resolve-mobile-session-terminal-command.ts
@@ -21,7 +21,9 @@ export class OrcaRuntimeWithResolveMobileSessionTerminalCommand extends OrcaRunt
       agentPrompt?: string
       launchConfig?: SleepingAgentLaunchConfig
       launchAgent?: TuiAgent
-    }
+    },
+    /** The window spawns the tab by its own shell rule. */
+    windowSpawnsPane = false
   ): Promise<{
     command?: string
     env?: Record<string, string>
@@ -49,7 +51,7 @@ export class OrcaRuntimeWithResolveMobileSessionTerminalCommand extends OrcaRunt
     if (!isTuiAgentEnabled(opts.agent, settings.disabledTuiAgents)) {
       throw new Error('Selected agent is disabled. Choose an enabled agent before creating.')
     }
-    const launchRuntime = this.resolveAgentLaunchRuntime(workspace, opts.agent)
+    const launchRuntime = this.resolveAgentLaunchRuntime(workspace, opts.agent, windowSpawnsPane)
     const startupPlan = buildAgentStartupPlan({
       ...resolveAgentStartupPlanInputs({
         agent: opts.agent,
diff --git a/src/main/runtime/orca-runtime-resolve-worktree-removal-target.ts b/src/main/runtime/orca-runtime-resolve-worktree-removal-target.ts
index 79c3726653e..bff92162bd0 100644
--- a/src/main/runtime/orca-runtime-resolve-worktree-removal-target.ts
+++ b/src/main/runtime/orca-runtime-resolve-worktree-removal-target.ts
@@ -237,9 +237,11 @@ export class OrcaRuntimeWithResolveWorktreeRemovalTarget extends OrcaRuntimeWith
 
   protected async resolveAgentTerminalCreateOptions(
     workspace: TerminalWorkspaceLaunchScope,
-    opts: TerminalCreateOptions
+    opts: TerminalCreateOptions,
+    windowSpawnsPane = false
   ): Promise<TerminalCreateOptions> {
     return resolveAgentTerminalCreateOptions(workspace, opts, {
+      windowSpawnsPane,
       store: this.store,
       hostIdentity: this.runtimeId,
       toSessionOptions: (preferences) => this.toAgentSessionOptions(preferences)
diff --git a/src/main/runtime/orca-runtime-restore-structured-agent-session-tabs-once.ts b/src/main/runtime/orca-runtime-restore-structured-agent-session-tabs-once.ts
index c848374caa7..f2409f14600 100644
--- a/src/main/runtime/orca-runtime-restore-structured-agent-session-tabs-once.ts
+++ b/src/main/runtime/orca-runtime-restore-structured-agent-session-tabs-once.ts
@@ -276,9 +276,10 @@ export class OrcaRuntimeWithRestoreStructuredAgentSessionTabsOnce extends OrcaRu
 
   protected resolveAgentLaunchRuntime(
     scope: TerminalWorkspaceLaunchScope,
-    agent: TuiAgent | undefined
+    agent: TuiAgent | undefined,
+    windowSpawnsPane = false
   ): AgentLaunchRuntime {
-    return resolveAgentLaunchRuntime(this.requireStore(), scope, undefined, agent)
+    return resolveAgentLaunchRuntime(this.requireStore(), scope, undefined, agent, windowSpawnsPane)
   }
 
   /** A startup's fact: the workspace it starts in, else the new worktree a create is making. */
diff --git a/src/main/runtime/orca-runtime-run-create-mobile-session-terminal.ts b/src/main/runtime/orca-runtime-run-create-mobile-session-terminal.ts
index 0813497d2de..f0cbaef2893 100644
--- a/src/main/runtime/orca-runtime-run-create-mobile-session-terminal.ts
+++ b/src/main/runtime/orca-runtime-run-create-mobile-session-terminal.ts
@@ -62,7 +62,12 @@ export class OrcaRuntimeWithRunCreateMobileSessionTerminal extends OrcaRuntimeWi
         afterDesktopTabId = anchor.type === 'terminal' ? anchor.parentTabId : anchor.id
       }
     }
-    const startupCommand = await this.resolveMobileSessionTerminalCommand(workspace, opts)
+    // With a window, it creates the tab and spawns the pane, so the command is written for that pane.
+    const startupCommand = await this.resolveMobileSessionTerminalCommand(
+      workspace,
+      opts,
+      this.getAvailableAuthoritativeWindow() !== null
+    )
     this.assertStableReadyGraph(graphEpoch)
     if (opts.signal?.aborted) {
       throw new Error('client_disconnected')
diff --git a/src/main/runtime/runtime-agent-terminal-startup.ts b/src/main/runtime/runtime-agent-terminal-startup.ts
index e641108001e..7ad57724caa 100644
--- a/src/main/runtime/runtime-agent-terminal-startup.ts
+++ b/src/main/runtime/runtime-agent-terminal-startup.ts
@@ -40,6 +40,8 @@ type AgentTerminalPlanHost = {
   toSessionOptions: (
     preferences: AgentLaunchPreferences | undefined
   ) => Record<string, SessionOptionValue> | undefined
+  /** The window spawns this pane by its own shell rule (`windowSpawnsTerminal`). */
+  windowSpawnsPane?: boolean
 }
 
 /**
@@ -81,7 +83,12 @@ export async function resolveAgentTerminalCreateOptions(
     projectRuntime:
       opts.shellOverride && store
         ? plannedAgent || opts.launchRuntime
-          ? agentLaunchProjectRuntime(store, workspace, plannedAgent ?? opts.launchAgent)
+          ? agentLaunchProjectRuntime(
+              store,
+              workspace,
+              plannedAgent ?? opts.launchAgent,
+              host.windowSpawnsPane
+            )
           : resolveLocalProjectRuntimeForWorktreeId(store, workspace.id)
         : undefined,
     cwd: resolveTerminalStartupCwd(workspace.path, opts.cwd) ?? workspace.path,
@@ -109,7 +116,13 @@ export async function resolveAgentTerminalCreateOptions(
   const runtime =
     opts.launchRuntime ??
     (plannedAgent
-      ? resolveAgentLaunchRuntime(store, workspace, opts.shellOverride, plannedAgent)
+      ? resolveAgentLaunchRuntime(
+          store,
+          workspace,
+          opts.shellOverride,
+          plannedAgent,
+          host.windowSpawnsPane
+        )
       : undefined)
   const launch =
     plannedAgent && runtime