diff --git a/src/renderer/src/components/editor/check-run-details-fix-with-ai.ts b/src/renderer/src/components/editor/check-run-details-fix-with-ai.ts
index 394bcac8123..0fa2c9b67f5 100644
--- a/src/renderer/src/components/editor/check-run-details-fix-with-ai.ts
+++ b/src/renderer/src/components/editor/check-run-details-fix-with-ai.ts
@@ -12,7 +12,7 @@ import { openSourceControlAiSettingsTarget } from '@/components/right-sidebar/so
 import { getConnectionId } from '@/lib/connection-context'
 import { startFixChecksAgent } from '@/lib/fix-checks-agent-launch'
 import { readSourceControlLaunchRecipeAgentId } from '../../../../shared/source-control-launch-agent-selection'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
+import { resolveRepoWorktreeLaunchPlatform } from '@/lib/execution-host-facts'
 import { useAppStore } from '@/store'
 import { findWorktreeById } from '@/store/slices/worktree-helpers'
 import { resolveSourceControlActionRecipe } from '../../../../shared/source-control-ai'
@@ -147,10 +147,15 @@ export function useCheckRunDetailsFixWithAI(args: {
   const connectionId = args.worktreeId
     ? (getConnectionId(args.worktreeId) ?? repo?.connectionId ?? null)
     : null
-  const launchPlatform = resolveSourceControlLaunchPlatform({
-    connectionId,
-    worktreePath: worktree?.path ?? null
-  })
+  // Why: the fix agent runs on the workspace's execution host, so its OS decides quoting (#27971).
+  const launchPlatform =
+    args.worktreeId && repo
+      ? resolveRepoWorktreeLaunchPlatform(
+          useAppStore.getState(),
+          repo,
+          worktree ?? { id: args.worktreeId }
+        )
+      : undefined
   const fixChecksRecipe = useMemo(
     () =>
       resolveSourceControlActionRecipe({
diff --git a/src/renderer/src/components/pull-request-page/checks/fix-dialog.tsx b/src/renderer/src/components/pull-request-page/checks/fix-dialog.tsx
index f43c6f6be53..0759c82442c 100644
--- a/src/renderer/src/components/pull-request-page/checks/fix-dialog.tsx
+++ b/src/renderer/src/components/pull-request-page/checks/fix-dialog.tsx
@@ -22,7 +22,8 @@ export function ChecksFixDialog({
   fixChecksComposerPrompt: string | null
   setFixChecksComposerPrompt: (value: string | null) => void
   fixChecksRecipe: SourceControlActionRecipe
-  fixChecksLaunchPlatform: NodeJS.Platform
+  /** Unset when the repo's host has not reported its OS; the launch then reports why. */
+  fixChecksLaunchPlatform: NodeJS.Platform | undefined
   repoConnectionId: string | null
   targetRepoId: string | null
   item: GitHubWorkItem
diff --git a/src/renderer/src/components/pull-request-page/checks/tab.tsx b/src/renderer/src/components/pull-request-page/checks/tab.tsx
index 0c12d91ae7e..9b94d3b3e08 100644
--- a/src/renderer/src/components/pull-request-page/checks/tab.tsx
+++ b/src/renderer/src/components/pull-request-page/checks/tab.tsx
@@ -23,7 +23,7 @@ import {
 } from '@/lib/github-source-runtime-context'
 import { getLocalRepoProjectExecutionRuntimeContext } from '@/lib/local-preflight-context'
 import { CLIENT_PLATFORM } from '@/lib/new-workspace'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
+import { resolveRepoExecutionHostPlatform } from '@/lib/execution-host-facts'
 import { resolveSourceControlActionRecipe } from '../../../../../shared/source-control-ai'
 import type {
   GitHubWorkItem,
@@ -119,29 +119,42 @@ export function ChecksTab({
       }),
     [repo, settings]
   )
-  const fixChecksLaunchPlatform = useMemo(
-    () =>
-      resolveSourceControlLaunchPlatform({
-        connectionId: repo?.connectionId ?? null,
-        worktreePath: repo?.path ?? null,
-        projectRuntime: repo?.connectionId
-          ? undefined
-          : getLocalRepoProjectExecutionRuntimeContext(
-              // Why: repo-scoped resolution only reads repos/projects/settings, and subscribing keeps the launch platform fresh.
-              {
-                activeRepoId: null,
-                activeWorktreeId: null,
-                projects,
-                repos,
-                settings,
-                worktreesByRepo: {}
-              },
-              repo?.id,
-              CLIENT_PLATFORM
-            )
-      }),
-    [projects, repo?.connectionId, repo?.id, repo?.path, repos, settings]
-  )
+  const sshConnectionStates = useAppStore((s) => s.sshConnectionStates)
+  const sshStateByEnvironment = useAppStore((s) => s.sshStateByEnvironment)
+  const runtimeStatusByEnvironmentId = useAppStore((s) => s.runtimeStatusByEnvironmentId)
+  // Why: the fix agent runs on the repo's execution host, so its OS decides quoting (#27971).
+  const fixChecksLaunchPlatform = useMemo(() => {
+    if (!repo) {
+      return undefined
+    }
+    const fact = resolveRepoExecutionHostPlatform(
+      { sshConnectionStates, sshStateByEnvironment, runtimeStatusByEnvironmentId },
+      repo,
+      () =>
+        getLocalRepoProjectExecutionRuntimeContext(
+          // Why: repo-scoped resolution only reads repos/projects/settings, and subscribing keeps the launch platform fresh.
+          {
+            activeRepoId: null,
+            activeWorktreeId: null,
+            projects,
+            repos,
+            settings,
+            worktreesByRepo: {}
+          },
+          repo.id,
+          CLIENT_PLATFORM
+        )
+    )
+    return fact.kind === 'known' ? fact.platform : undefined
+  }, [
+    projects,
+    repo,
+    repos,
+    runtimeStatusByEnvironmentId,
+    settings,
+    sshConnectionStates,
+    sshStateByEnvironment
+  ])
   // Why: parses a fresh host object per call, so memoize to keep the check action callbacks stable.
   const runtimeHost = useMemo(() => getGitHubSourceRuntimeHost(sourceContext), [sourceContext])
   const canUseChecksRepoContext = canUseGitHubRepoContext(repoPath, sourceContext)
diff --git a/src/renderer/src/components/right-sidebar/SourceControl.preview-open.test.tsx b/src/renderer/src/components/right-sidebar/SourceControl.preview-open.test.tsx
index c69dfeb608c..f28414592cd 100644
--- a/src/renderer/src/components/right-sidebar/SourceControl.preview-open.test.tsx
+++ b/src/renderer/src/components/right-sidebar/SourceControl.preview-open.test.tsx
@@ -151,6 +151,9 @@ function resetState(overrides: Partial<Record<string, unknown>> = {}): void {
     groupsByWorktree: { [mocks.activeWorktree.id]: [{ id: 'group-1', activeTabId: null }] },
     repos: [mocks.activeRepo],
     worktreesByRepo: { [mocks.activeRepo.id]: [mocks.activeWorktree] },
+    sshConnectionStates: new Map(),
+    sshStateByEnvironment: new Map(),
+    runtimeStatusByEnvironmentId: new Map(),
     rightSidebarOpen: false,
     rightSidebarTab: 'source-control',
     gitStatusByWorktree: { [mocks.activeWorktree.id]: [] },
diff --git a/src/renderer/src/components/right-sidebar/checks-panel/use-checks-panel-controller-state.tsx b/src/renderer/src/components/right-sidebar/checks-panel/use-checks-panel-controller-state.tsx
index fb54b599386..71c3ce6b703 100644
--- a/src/renderer/src/components/right-sidebar/checks-panel/use-checks-panel-controller-state.tsx
+++ b/src/renderer/src/components/right-sidebar/checks-panel/use-checks-panel-controller-state.tsx
@@ -8,8 +8,7 @@ import { readDetectedAgentsForWorktree } from '@/lib/agent-detection-target-inve
 import { useMountedRef } from '@/hooks/useMountedRef'
 import { useConfirmationDialog } from '@/components/confirmation-dialog-context'
 import { getWorktreeGitIdentityDisplay } from '../../../../../shared/worktree/git-identity-display'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
-import { getLocalProjectExecutionRuntimeContext } from '@/lib/local-preflight-context'
+import { resolveRepoWorktreeLaunchPlatform } from '@/lib/execution-host-facts'
 import { getRuntimeEnvironmentIdForWorktree } from '@/lib/worktree-runtime-owner'
 import { normalizeGlobalWindowsRuntimeDefault } from '../../../../../shared/project-execution-runtime'
 import {
@@ -218,13 +217,11 @@ export function useChecksPanelControllerState() {
   const branch = gitIdentityDisplay?.kind === 'branch' ? gitIdentityDisplay.branchName : ''
   const activeWorktreePath = activeWorktree?.path ?? null
   const activeWorktreePushTarget = activeWorktree?.pushTarget ?? null
-  const activeSourceControlLaunchPlatform = resolveSourceControlLaunchPlatform({
-    connectionId: activeConnectionId,
-    worktreePath: activeWorktreePath,
-    projectRuntime: activeConnectionId
-      ? undefined
-      : getLocalProjectExecutionRuntimeContext(useAppStore.getState(), activeWorktreeId)
-  })
+  // Why: agents run on the workspace's execution host, so its OS decides quoting (#27971).
+  const activeSourceControlLaunchPlatform =
+    activeWorktree && repo
+      ? resolveRepoWorktreeLaunchPlatform(useAppStore.getState(), repo, activeWorktree)
+      : undefined
   const runtimeEnvironmentId = useAppStore((s) =>
     getRuntimeEnvironmentIdForWorktree(s, activeWorktreeId)
   )
diff --git a/src/renderer/src/components/right-sidebar/source-control/ai/controller-types.ts b/src/renderer/src/components/right-sidebar/source-control/ai/controller-types.ts
index 32f00e18e24..c7721c631f6 100644
--- a/src/renderer/src/components/right-sidebar/source-control/ai/controller-types.ts
+++ b/src/renderer/src/components/right-sidebar/source-control/ai/controller-types.ts
@@ -19,7 +19,7 @@ export type SourceControlAiControllerParams = {
   activeWorktreeId: string | null | undefined
   activeConnectionId: string | null | undefined
   activeGroupId: string | null | undefined
-  activeSourceControlLaunchPlatform: NodeJS.Platform
+  activeSourceControlLaunchPlatform: NodeJS.Platform | undefined
   conflictOperation: GitConflictOperation
   unresolvedConflicts: Pick<GitStatusEntry, 'path' | 'conflictKind'>[]
   stagedEntries: Pick<GitStatusEntry, 'path' | 'status' | 'area'>[]
diff --git a/src/renderer/src/components/right-sidebar/source-control/ai/recovery-launch.ts b/src/renderer/src/components/right-sidebar/source-control/ai/recovery-launch.ts
index a16e3723073..ac7c96ef060 100644
--- a/src/renderer/src/components/right-sidebar/source-control/ai/recovery-launch.ts
+++ b/src/renderer/src/components/right-sidebar/source-control/ai/recovery-launch.ts
@@ -90,7 +90,7 @@ export async function launchSourceControlRecoveryAgentWithDefault({
 }: {
   activeWorktreeId: string
   activeGroupId: string | null | undefined
-  activeSourceControlLaunchPlatform: NodeJS.Platform
+  activeSourceControlLaunchPlatform: NodeJS.Platform | undefined
   sourceRepoConnectionId?: string | null
   actionId: SourceControlLaunchActionId
   basePrompt: string | null
diff --git a/src/renderer/src/components/right-sidebar/source-control/ai/use-recovery-ai.ts b/src/renderer/src/components/right-sidebar/source-control/ai/use-recovery-ai.ts
index 3ee965b7ef8..e9268ed12b6 100644
--- a/src/renderer/src/components/right-sidebar/source-control/ai/use-recovery-ai.ts
+++ b/src/renderer/src/components/right-sidebar/source-control/ai/use-recovery-ai.ts
@@ -15,7 +15,7 @@ import type { SourceControlAiStoreSnapshot } from './controller-types'
 type SourceControlRecoveryAiParams = {
   activeWorktreeId: string | null | undefined
   activeGroupId: string | null | undefined
-  activeSourceControlLaunchPlatform: NodeJS.Platform
+  activeSourceControlLaunchPlatform: NodeJS.Platform | undefined
   sourceRepoConnectionId?: string | null
   worktreePath: string | null
   commitMessage: string
diff --git a/src/renderer/src/components/right-sidebar/source-control/listing/use-worktree-context.ts b/src/renderer/src/components/right-sidebar/source-control/listing/use-worktree-context.ts
index 2501e3aaec4..7f234a8915c 100644
--- a/src/renderer/src/components/right-sidebar/source-control/listing/use-worktree-context.ts
+++ b/src/renderer/src/components/right-sidebar/source-control/listing/use-worktree-context.ts
@@ -1,8 +1,7 @@
 import { useMemo } from 'react'
 import { getConnectionId } from '@/lib/connection-context'
-import { getLocalProjectExecutionRuntimeContext } from '@/lib/local-preflight-context'
 import { ipcOrRuntimeTargetForHostId } from '@/runtime/runtime-client-target'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
+import { resolveRepoWorktreeLaunchPlatform } from '@/lib/execution-host-facts'
 import { getWorktreeGitIdentityDisplay } from '../../../../../../shared/worktree/git-identity-display'
 import { useAppStore } from '@/store'
 import { useActiveWorktree, useRepoById, useWorktreeMap } from '@/store/selectors'
@@ -129,13 +128,11 @@ export function useSourceControlWorktreeContext() {
   const activeConnectionId = activeWorktreeId
     ? (getConnectionId(activeWorktreeId) ?? activeRepoConnectionId)
     : null
-  const activeSourceControlLaunchPlatform = resolveSourceControlLaunchPlatform({
-    connectionId: activeConnectionId,
-    worktreePath,
-    projectRuntime: activeConnectionId
-      ? undefined
-      : getLocalProjectExecutionRuntimeContext(useAppStore.getState(), activeWorktreeId)
-  })
+  // Why: agents run on the workspace's execution host, so its OS decides quoting (#27971).
+  const activeSourceControlLaunchPlatform =
+    activeWorktree && activeRepo
+      ? resolveRepoWorktreeLaunchPlatform(useAppStore.getState(), activeRepo, activeWorktree)
+      : undefined
   // Why: the sidebar stays mounted when closed, so gate polling on tab AND open or branchCompare/PR fetch would run with no visible consumer.
   const isBranchVisible = rightSidebarTab === 'source-control' && rightSidebarOpen
   const hasUncommittedEntries = entries.length > 0
diff --git a/src/renderer/src/lib/execution-host-facts.test.ts b/src/renderer/src/lib/execution-host-facts.test.ts
new file mode 100644
index 00000000000..69e703e18a5
--- /dev/null
+++ b/src/renderer/src/lib/execution-host-facts.test.ts
@@ -0,0 +1,112 @@
+import { describe, expect, it, vi } from 'vitest'
+import type { RuntimeEnvironmentStatus } from '../../../shared/runtime-host-status'
+import { resolveRepoWorktreeLaunchPlatform } from './execution-host-facts'
+
+vi.mock('./new-workspace', async (importOriginal) => ({
+  ...(await importOriginal<Record<string, unknown>>()),
+  CLIENT_PLATFORM: 'win32'
+}))
+
+type State = Parameters<typeof resolveRepoWorktreeLaunchPlatform>[0]
+
+function linuxServer(): Map<string, RuntimeEnvironmentStatus> {
+  return new Map([
+    [
+      'linux-box',
+      {
+        checkedAt: 1,
+        status: {
+          runtimeId: 'rt',
+          rendererGraphEpoch: 0,
+          graphStatus: 'ready',
+          authoritativeWindowId: null,
+          liveTabCount: 0,
+          liveLeafCount: 0,
+          hostPlatform: 'linux'
+        }
+      }
+    ]
+  ])
+}
+
+function state(): State {
+  return {
+    repos: [],
+    worktreesByRepo: {},
+    detectedWorktreesByRepo: {},
+    folderWorkspaces: [],
+    projectGroups: [],
+    projects: [],
+    activeRepoId: null,
+    activeWorktreeId: null,
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the resolver reads no other setting.
+    settings: {} as State['settings'],
+    sshConnectionStates: new Map(),
+    sshStateByEnvironment: new Map(),
+    runtimeStatusByEnvironmentId: linuxServer()
+  }
+}
+
+const serverRepo = { path: '/srv/repo', executionHostId: 'runtime:linux-box' }
+
+describe('resolveRepoWorktreeLaunchPlatform from a Windows client', () => {
+  it("reads a server project's worktree as the server's OS (#27971)", () => {
+    expect(
+      resolveRepoWorktreeLaunchPlatform(state(), serverRepo, { id: 'wt', path: '/srv/wt' })
+    ).toBe('linux')
+  })
+
+  it("lets a worktree's own host outrank its repo's", () => {
+    expect(
+      resolveRepoWorktreeLaunchPlatform(state(), serverRepo, {
+        id: 'wt',
+        path: 'C:\\wt',
+        hostId: 'local'
+      })
+    ).toBe('win32')
+  })
+
+  it("reads a server-projected SSH worktree through that server's connection", () => {
+    const nested = {
+      ...state(),
+      sshStateByEnvironment: new Map([
+        [
+          'linux-box',
+          {
+            connectionStates: new Map([
+              [
+                'box',
+                {
+                  targetId: 'box',
+                  status: 'connected' as const,
+                  error: null,
+                  reconnectAttempt: 0,
+                  remotePlatform: 'linux' as const
+                }
+              ]
+            ]),
+            targetLabels: new Map(),
+            targetGenerations: new Map(),
+            removedTargetLabels: new Map(),
+            targetsHydrated: true
+          }
+        ]
+      ])
+    }
+    expect(
+      resolveRepoWorktreeLaunchPlatform(nested, serverRepo, {
+        id: 'wt',
+        path: '/home/a/wt',
+        hostId: 'ssh:box',
+        runtimeOwnerEnvironmentId: 'linux-box'
+      })
+    ).toBe('linux')
+  })
+
+  it('is undefined when the server has not reported its OS', () => {
+    const withheld = { ...state(), runtimeStatusByEnvironmentId: new Map() }
+    expect(
+      resolveRepoWorktreeLaunchPlatform(withheld, serverRepo, { id: 'wt', path: '/srv/wt' })
+    ).toBeUndefined()
+  })
+})
diff --git a/src/renderer/src/lib/execution-host-facts.ts b/src/renderer/src/lib/execution-host-facts.ts
index d6635931161..5ef43967c7f 100644
--- a/src/renderer/src/lib/execution-host-facts.ts
+++ b/src/renderer/src/lib/execution-host-facts.ts
@@ -115,18 +115,22 @@ function resolveHostPlatform(
   return { kind: 'known', platform, hostKind: 'runtime' }
 }
 
-/** Platform of the host that runs agents for a repo that has no workspace yet. */
+/**
+ * Platform of the host that runs agents for a repo's workspaces, read from the repo row's owner.
+ * `workspacePath` names a workspace on that host (e.g. a WSL worktree); it defaults to the repo.
+ */
 export function resolveRepoExecutionHostPlatform(
   state: HostFactsState,
   repo: { connectionId?: string | null; executionHostId?: string | null; path: string },
-  projectRuntime: () => ProjectExecutionRuntimeResolution | undefined
+  projectRuntime: () => ProjectExecutionRuntimeResolution | undefined,
+  workspacePath: string | null | undefined = repo.path
 ): ExecutionHostPlatformFact {
   const host = parseExecutionHostId(getRepoExecutionHostId(repo))
   return resolveHostPlatform(state, {
     host,
     nestedSshTargetId: host?.kind === 'runtime' ? repo.connectionId?.trim() || null : null,
     sshOwnerEnvironmentId: null,
-    workspacePath: repo.path,
+    workspacePath,
     projectRuntime
   })
 }
@@ -150,6 +154,50 @@ export function resolveWorktreeExecutionHostPlatform(
   })
 }
 
+export type KnownExecutionHostPlatform = Extract<ExecutionHostPlatformFact, { kind: 'known' }>
+
+/** A caller's platform only refines a local launch (e.g. WSL); a remote host's own OS wins. */
+export function refineLocalLaunchPlatform(
+  fact: KnownExecutionHostPlatform,
+  callerPlatform: NodeJS.Platform | undefined
+): KnownExecutionHostPlatform {
+  return fact.hostKind === 'local' && callerPlatform ? { ...fact, platform: callerPlatform } : fact
+}
+
+/**
+ * Preflight platform for a worktree's agent launch: the worktree's own host when its row names
+ * one, else its repo's owner. `undefined` when withheld: the launch itself resolves the host and
+ * tells the user why it stopped.
+ */
+export function resolveRepoWorktreeLaunchPlatform(
+  state: WorktreeHostFactsState,
+  repo: { connectionId?: string | null; executionHostId?: string | null; path: string },
+  worktree: {
+    id: string
+    path?: string | null
+    hostId?: string | null
+    runtimeOwnerEnvironmentId?: string | null
+  }
+): NodeJS.Platform | undefined {
+  const repoHost = parseExecutionHostId(getRepoExecutionHostId(repo))
+  const ownHost = parseExecutionHostId(worktree.hostId)
+  // Why: a per-worktree host (e.g. a local checkout of a server project) outranks the repo's.
+  const host = ownHost && ownHost.id !== repoHost?.id ? ownHost : repoHost
+  const serverOwner =
+    worktree.runtimeOwnerEnvironmentId?.trim() ||
+    (repoHost?.kind === 'runtime' ? repoHost.environmentId : null)
+  const fact = resolveHostPlatform(state, {
+    host,
+    nestedSshTargetId:
+      host?.kind === 'runtime' && host === repoHost ? repo.connectionId?.trim() || null : null,
+    // Why: a server-projected SSH worktree is reached through that server's own connection.
+    sshOwnerEnvironmentId: host?.kind === 'ssh' ? serverOwner : null,
+    workspacePath: worktree.path ?? repo.path,
+    projectRuntime: () => getLocalProjectExecutionRuntimeContext(state, worktree.id)
+  })
+  return fact.kind === 'known' ? fact.platform : undefined
+}
+
 export function requireExecutionHostPlatform(fact: ExecutionHostPlatformFact): NodeJS.Platform {
   if (fact.kind === 'withheld') {
     throw new Error(fact.reason)
diff --git a/src/renderer/src/lib/fix-checks-agent-launch.test.ts b/src/renderer/src/lib/fix-checks-agent-launch.test.ts
index 9d1c71bfaf9..0b18fa505d5 100644
--- a/src/renderer/src/lib/fix-checks-agent-launch.test.ts
+++ b/src/renderer/src/lib/fix-checks-agent-launch.test.ts
@@ -1,4 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
+import type * as ExecutionHostFactsModule from '@/lib/execution-host-facts'
 
 const mocks = vi.hoisted(() => {
   const store = {
@@ -54,7 +55,7 @@ const mocks = vi.hoisted(() => {
     pickSourceControlLaunchAgent: vi.fn(),
     readSourceControlLaunchRecipeAgentId: vi.fn(),
     resolveSourceControlActionRecipe: vi.fn(),
-    resolveSourceControlLaunchPlatform: vi.fn(),
+    resolveRepoWorktreeLaunchPlatform: vi.fn(),
     toastError: vi.fn(),
     toastMessage: vi.fn()
   }
@@ -102,9 +103,15 @@ vi.mock('../../../shared/source-control-launch-agent-selection', () => ({
   readSourceControlLaunchRecipeAgentId: mocks.readSourceControlLaunchRecipeAgentId
 }))
 
-vi.mock('@/lib/source-control-launch-platform', () => ({
-  resolveSourceControlLaunchPlatform: mocks.resolveSourceControlLaunchPlatform
-}))
+vi.mock('@/lib/execution-host-facts', async () => {
+  const actual = await vi.importActual<typeof ExecutionHostFactsModule>(
+    '@/lib/execution-host-facts'
+  )
+  return {
+    ...actual,
+    resolveRepoWorktreeLaunchPlatform: mocks.resolveRepoWorktreeLaunchPlatform
+  }
+})
 
 vi.mock('@/lib/worktree-activation', () => ({
   activateAndRevealWorktree: mocks.activateAndRevealWorktree
@@ -158,7 +165,7 @@ describe('startFixChecksAgent', () => {
     mocks.resolveSourceControlActionRecipe.mockReturnValue({
       commandInputTemplate: '{basePrompt}'
     })
-    mocks.resolveSourceControlLaunchPlatform.mockReturnValue('darwin')
+    mocks.resolveRepoWorktreeLaunchPlatform.mockReturnValue('darwin')
   })
 
   it('activates the attached workspace as a surface-providing caller', async () => {
@@ -230,7 +237,7 @@ describe('startFixChecksAgent', () => {
     expect(mocks.launchAgentInNewTab).not.toHaveBeenCalled()
   })
 
-  it('falls back to the repo connection when an attached workspace lookup is unresolved', async () => {
+  it("resolves the attached workspace's own execution host", async () => {
     mocks.store.repos = [
       {
         ...mocks.store.repos[0],
@@ -250,44 +257,15 @@ describe('startFixChecksAgent', () => {
     ).resolves.toBe(true)
 
     expect(mocks.store.ensureRemoteDetectedAgents).toHaveBeenCalledWith('ssh-1')
-    expect(mocks.resolveSourceControlLaunchPlatform).toHaveBeenCalledWith({
-      connectionId: 'ssh-1',
-      worktreePath: '/repo/wt-1',
-      projectRuntime: undefined
-    })
+    expect(mocks.resolveRepoWorktreeLaunchPlatform).toHaveBeenCalledWith(
+      mocks.store,
+      expect.objectContaining({ id: 'repo-1', connectionId: 'ssh-1' }),
+      expect.objectContaining({ id: 'wt-1', path: '/repo/wt-1' })
+    )
   })
 
-  it('passes the local project runtime when resolving an attached WSL workspace launch platform', async () => {
-    mocks.store.repos = [
-      {
-        ...mocks.store.repos[0],
-        path: 'C:\\Users\\alice\\repo'
-      }
-    ]
-    mocks.store.worktrees = [
-      {
-        id: 'wt-1',
-        repoId: 'repo-1',
-        path: 'C:\\Users\\alice\\repo-worktree'
-      }
-    ]
-    mocks.store.worktreesByRepo = { 'repo-1': mocks.store.worktrees }
-    mocks.store.projects = [
-      {
-        id: 'repo-1',
-        displayName: 'Repo',
-        badgeColor: '#000000',
-        sourceRepoIds: ['repo-1'],
-        createdAt: 1,
-        updatedAt: 1,
-        localWindowsRuntimePreference: { kind: 'wsl', distro: 'Ubuntu' }
-      }
-    ]
-    mocks.resolveSourceControlLaunchPlatform.mockImplementation(({ projectRuntime }) =>
-      projectRuntime?.status === 'resolved' && projectRuntime.runtime.kind === 'wsl'
-        ? 'linux'
-        : 'win32'
-    )
+  it("plans a Linux server's launch for that server from a Windows client (#27971)", async () => {
+    mocks.resolveRepoWorktreeLaunchPlatform.mockReturnValue('linux')
     const { startFixChecksAgent } = await import('./fix-checks-agent-launch')
 
     await expect(
@@ -299,21 +277,13 @@ describe('startFixChecksAgent', () => {
       })
     ).resolves.toBe(true)
 
-    expect(mocks.resolveSourceControlLaunchPlatform).toHaveBeenCalledWith({
-      connectionId: null,
-      worktreePath: 'C:\\Users\\alice\\repo-worktree',
-      projectRuntime: expect.objectContaining({
-        status: 'resolved',
-        runtime: expect.objectContaining({ kind: 'wsl', distro: 'Ubuntu' })
-      })
-    })
     expect(mocks.launchAgentInNewTab).toHaveBeenCalledWith(
       expect.objectContaining({ launchPlatform: 'linux' })
     )
   })
 
-  it('fails without launching when the launch platform cannot be resolved', async () => {
-    mocks.resolveSourceControlLaunchPlatform.mockReturnValue(undefined)
+  it('fails without launching when the execution host has not reported its OS', async () => {
+    mocks.resolveRepoWorktreeLaunchPlatform.mockReturnValue(undefined)
     const { startFixChecksAgent } = await import('./fix-checks-agent-launch')
 
     await expect(
diff --git a/src/renderer/src/lib/fix-checks-agent-launch.ts b/src/renderer/src/lib/fix-checks-agent-launch.ts
index d5f04bfae68..2c6e3632802 100644
--- a/src/renderer/src/lib/fix-checks-agent-launch.ts
+++ b/src/renderer/src/lib/fix-checks-agent-launch.ts
@@ -1,5 +1,4 @@
 import { toast } from 'sonner'
-import { getConnectionId } from '@/lib/connection-context'
 import {
   ensureDetectedAgentsForRepo,
   ensureDetectedAgentsForWorktree,
@@ -10,14 +9,12 @@ import { findGithubPrWorkspaceAttachment } from '@/lib/github-work-item-workspac
 import { launchAgentInNewTab } from '@/lib/launch-agent-in-new-tab'
 import { newAgentLaunchRequestId } from '@/lib/agent-launch-request-id'
 import { launchWorkItemDirect } from '@/lib/launch-work-item-direct'
-import { getLocalProjectExecutionRuntimeContext } from '@/lib/local-preflight-context'
-import { CLIENT_PLATFORM } from '@/lib/new-workspace'
 import { planAgentCliArgsSuffix } from '@/lib/tui-agent-startup'
 import {
   pickSourceControlLaunchAgent,
   readSourceControlLaunchRecipeAgentId
 } from '../../../shared/source-control-launch-agent-selection'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
+import { resolveRepoWorktreeLaunchPlatform } from '@/lib/execution-host-facts'
 import { activateAndRevealWorktree } from '@/lib/worktree-activation'
 import { useAppStore } from '@/store'
 import { resolveSourceControlActionRecipe } from '../../../shared/source-control-ai'
@@ -158,18 +155,17 @@ export async function startFixChecksAgent(args: StartFixChecksAgentArgs): Promis
       )
       return false
     }
-    const targetConnectionId = getConnectionId(targetWorktreeId) ?? repo?.connectionId ?? null
     const agent = await pickExistingWorktreeAgent(targetWorktreeId, savedAgentId)
     if (!agent) {
       return false
     }
-    const launchPlatform = resolveSourceControlLaunchPlatform({
-      connectionId: targetConnectionId,
-      worktreePath: targetWorktree.path,
-      projectRuntime: targetConnectionId
-        ? undefined
-        : getLocalProjectExecutionRuntimeContext(store, targetWorktreeId, CLIENT_PLATFORM)
-    })
+    // Why: the agent runs on the workspace's execution host, so its OS decides quoting (#27971).
+    const latestStore = useAppStore.getState()
+    const targetRepo =
+      latestStore.repos.find((candidate) => candidate.id === targetWorktree.repoId) ?? repo
+    const launchPlatform = targetRepo
+      ? resolveRepoWorktreeLaunchPlatform(latestStore, targetRepo, targetWorktree)
+      : undefined
     if (!launchPlatform) {
       toast.error(
         translate(
diff --git a/src/renderer/src/lib/launch-agent-execution-context.ts b/src/renderer/src/lib/launch-agent-execution-context.ts
index 0ec03f3cdd3..76ae016082c 100644
--- a/src/renderer/src/lib/launch-agent-execution-context.ts
+++ b/src/renderer/src/lib/launch-agent-execution-context.ts
@@ -2,6 +2,7 @@ import { toast } from 'sonner'
 import type { AgentStartupShell } from '../../../shared/tui-agent-startup-shell'
 import { getConnectionIdFromState } from '@/lib/connection-context'
 import {
+  refineLocalLaunchPlatform,
   resolveExecutionHostAgentStartupShell,
   resolveWorktreeExecutionHostPlatform
 } from '@/lib/execution-host-facts'
@@ -37,15 +38,13 @@ export function resolveAgentLaunchExecutionContext(
     toast.error(fact.reason)
     return null
   }
-  // Why: a caller's platform only refines a local launch (e.g. WSL); a remote host's own OS wins.
-  const resolvedLaunchPlatform =
-    fact.hostKind === 'local' && args.launchPlatform ? args.launchPlatform : fact.platform
+  const launchHost = refineLocalLaunchPlatform(fact, args.launchPlatform)
   return {
     worktreeSshConnectionId,
-    resolvedLaunchPlatform,
+    resolvedLaunchPlatform: launchHost.platform,
     isRemote,
     queuedShell: resolveExecutionHostAgentStartupShell(
-      { ...fact, platform: resolvedLaunchPlatform },
+      launchHost,
       store.settings?.terminalWindowsShell
     )
   }
diff --git a/src/renderer/src/lib/launch-work-item-direct-agent-routing.ts b/src/renderer/src/lib/launch-work-item-direct-agent-routing.ts
index d5abd264a3f..3033e3f4b20 100644
--- a/src/renderer/src/lib/launch-work-item-direct-agent-routing.ts
+++ b/src/renderer/src/lib/launch-work-item-direct-agent-routing.ts
@@ -4,7 +4,10 @@ import { TUI_AGENT_CONFIG } from '../../../shared/tui-agent-config'
 import { isTuiAgentEnabled, pickTuiAgent } from '../../../shared/tui-agent-selection'
 import { buildDirectWorkItemAgentStartupPlan } from '@/lib/launch-work-item-direct-agent'
 import type { AgentSessionLaunchPlan } from '@/lib/agent-session-launch-plan'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
+import {
+  resolveExecutionHostAgentStartupShell,
+  type KnownExecutionHostPlatform
+} from '@/lib/execution-host-facts'
 import { beginStructuredAgentSessionProvisionalLaunch } from '@/lib/structured-agent-session-provisional-tab'
 import type { DeclinedStructuredLaunchTerminalOptions } from '@/lib/structured-agent-session-launch-admission'
 import {
@@ -18,25 +21,21 @@ export function buildDirectWorkItemStartup(args: {
   draftContent: string
   promptDelivery: PromptDelivery
   settings: AppState['settings']
-  launchPlatform?: NodeJS.Platform
+  /** The workspace's execution host; its OS and shell decide quoting, not this client's. */
+  launchHost: KnownExecutionHostPlatform
+  /** This client's Windows shell, which only shapes a local launch. */
+  terminalWindowsShell: string | null | undefined
   launchConnectionId: string | null
-  worktreePath: string
-  repoProjectRuntime?: Parameters<typeof resolveSourceControlLaunchPlatform>[0]['projectRuntime']
 }): ReturnType<typeof buildDirectWorkItemAgentStartupPlan> {
-  const launchPlatform =
-    args.launchPlatform ??
-    resolveSourceControlLaunchPlatform({
-      connectionId: args.launchConnectionId,
-      worktreePath: args.worktreePath,
-      projectRuntime: args.repoProjectRuntime
-    })
+  const shell = resolveExecutionHostAgentStartupShell(args.launchHost, args.terminalWindowsShell)
   return buildDirectWorkItemAgentStartupPlan({
     agent: args.agent,
     agentArgs: args.agentArgs,
     draftContent: args.draftContent,
     promptDelivery: args.promptDelivery,
     settings: args.settings,
-    launchPlatform,
+    launchPlatform: args.launchHost.platform,
+    ...(shell ? { shell } : {}),
     // Why: SSH hosts run the plain `orca` shim, so the Linux-only `orca-ide` rename is not applied.
     isRemote: typeof args.launchConnectionId === 'string'
   })
diff --git a/src/renderer/src/lib/launch-work-item-direct-agent.ts b/src/renderer/src/lib/launch-work-item-direct-agent.ts
index b9175034e7b..f55bcf3cadf 100644
--- a/src/renderer/src/lib/launch-work-item-direct-agent.ts
+++ b/src/renderer/src/lib/launch-work-item-direct-agent.ts
@@ -10,6 +10,7 @@ import type { SleepingAgentLaunchConfig } from '../../../shared/agent-session-re
 import type { LaunchSource } from '../../../shared/telemetry-events'
 import type { StartupCommandDelivery } from '../../../shared/codex-startup-delivery'
 import type { TuiAgent } from '../../../shared/tui-agent'
+import type { AgentStartupShell } from '../../../shared/tui-agent-startup-shell'
 import {
   resolveTuiAgentLaunchArgs,
   resolveTuiAgentLaunchEnv
@@ -30,6 +31,8 @@ export function buildDirectWorkItemAgentStartupPlan(args: {
     | null
     | undefined
   launchPlatform: NodeJS.Platform
+  /** Unset keeps the platform default: PowerShell on win32, POSIX elsewhere. */
+  shell?: AgentStartupShell
   /** Why: SSH remotes deploy the CLI shim as plain `orca`, so the Linux-only
    * `orca-ide` rename must not be applied for remote launches. */
   isRemote?: boolean
@@ -55,6 +58,7 @@ export function buildDirectWorkItemAgentStartupPlan(args: {
           draft: args.draftContent,
           cmdOverrides: args.settings?.agentCmdOverrides ?? {},
           platform: args.launchPlatform,
+          ...(args.shell ? { shell: args.shell } : {}),
           isRemote: args.isRemote,
           agentArgs: effectiveAgentArgs,
           agentEnv: effectiveAgentEnv
@@ -83,6 +87,7 @@ export function buildDirectWorkItemAgentStartupPlan(args: {
     prompt: '',
     cmdOverrides: args.settings?.agentCmdOverrides ?? {},
     platform: args.launchPlatform,
+    ...(args.shell ? { shell: args.shell } : {}),
     isRemote: args.isRemote,
     agentArgs: effectiveAgentArgs,
     agentEnv: effectiveAgentEnv,
diff --git a/src/renderer/src/lib/launch-work-item-direct-host-platform.test.ts b/src/renderer/src/lib/launch-work-item-direct-host-platform.test.ts
new file mode 100644
index 00000000000..3d9494de987
--- /dev/null
+++ b/src/renderer/src/lib/launch-work-item-direct-host-platform.test.ts
@@ -0,0 +1,277 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import type { RuntimeEnvironmentStatus } from '../../../shared/runtime-host-status'
+import type { SshConnectionState } from '../../../shared/ssh-types'
+import type * as TuiAgentStartupModule from '@/lib/tui-agent-startup'
+
+const mocks = vi.hoisted(() => {
+  // Why declared: an inferred literal `'win32'` would reject the other client platforms.
+  const mutable: { clientPlatform: NodeJS.Platform; store: Record<string, unknown> } = {
+    clientPlatform: 'win32',
+    store: {}
+  }
+  return {
+    ...mutable,
+    toastError: vi.fn(),
+    createWorktree: vi.fn(),
+    activateAndRevealWorktree: vi.fn()
+  }
+})
+
+vi.mock('@/store', () => ({ useAppStore: { getState: () => mocks.store } }))
+vi.mock('sonner', () => ({ toast: { error: mocks.toastError, message: vi.fn() } }))
+vi.mock('@/lib/worktree-activation', () => ({
+  activateAndRevealWorktree: mocks.activateAndRevealWorktree
+}))
+vi.mock('@/lib/ensure-hooks-confirmed', () => ({
+  ensureHooksConfirmed: vi.fn().mockResolvedValue('run')
+}))
+vi.mock('@/lib/launch-work-item-direct-preflight', async (importOriginal) => ({
+  ...(await importOriginal<Record<string, unknown>>()),
+  resolveDirectSetupDecision: vi.fn().mockResolvedValue({ kind: 'resolved', decision: 'inherit' })
+}))
+vi.mock('@/lib/agent-detection-target-inventory', () => ({
+  ensureDetectedAgentsForRepo: vi.fn().mockResolvedValue(['claude']),
+  ensureDetectedAgentsForNewWorktree: vi.fn().mockResolvedValue(['claude'])
+}))
+vi.mock('@/lib/agent-session-launch-plan', () => ({
+  planAgentSessionLaunch: vi.fn(() => ({ route: 'terminal' }))
+}))
+vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
+  deliverLaunchPromptToAgentTab: vi.fn(),
+  seedNativeChatLaunchDraftForAgentTab: vi.fn()
+}))
+vi.mock('@/lib/telemetry', () => ({ track: vi.fn(), tuiAgentToAgentKind: (a: string) => a }))
+vi.mock('@/lib/new-workspace', async (importOriginal) => ({
+  ...(await importOriginal<Record<string, unknown>>()),
+  get CLIENT_PLATFORM() {
+    return mocks.clientPlatform
+  }
+}))
+vi.mock('@/lib/tui-agent-startup', async () => {
+  const actual = await vi.importActual<typeof TuiAgentStartupModule>('@/lib/tui-agent-startup')
+  return { ...actual, buildAgentDraftLaunchPlan: vi.fn(actual.buildAgentDraftLaunchPlan) }
+})
+
+import { launchWorkItemDirect } from './launch-work-item-direct'
+import { buildAgentDraftLaunchPlan } from '@/lib/tui-agent-startup'
+
+function runtimeStatus(hostPlatform?: NodeJS.Platform): RuntimeEnvironmentStatus {
+  return {
+    checkedAt: 1,
+    status: {
+      runtimeId: 'rt',
+      rendererGraphEpoch: 0,
+      graphStatus: 'ready',
+      authoritativeWindowId: null,
+      liveTabCount: 0,
+      liveLeafCount: 0,
+      ...(hostPlatform ? { hostPlatform } : {})
+    }
+  }
+}
+
+function sshState(remotePlatform: 'linux' | 'win32'): SshConnectionState {
+  return { targetId: 'box', status: 'connected', error: null, reconnectAttempt: 0, remotePlatform }
+}
+
+type HostCase = {
+  name: string
+  client: NodeJS.Platform
+  repo: { path: string; connectionId?: string; executionHostId?: string }
+  ssh?: Map<string, SshConnectionState>
+  runtime?: Map<string, RuntimeEnvironmentStatus>
+  expected: NodeJS.Platform
+}
+
+function setStore(hostCase: HostCase): void {
+  mocks.clientPlatform = hostCase.client
+  mocks.store = {
+    repos: [{ id: 'repo-1', displayName: 'Repo', addedAt: 1, ...hostCase.repo }],
+    activeRepoId: null,
+    activeWorktreeId: null,
+    projects: [],
+    projectGroups: [],
+    folderWorkspaces: [],
+    worktreesByRepo: {},
+    detectedWorktreesByRepo: {},
+    settings: { defaultTuiAgent: 'claude', disabledTuiAgents: [], agentCmdOverrides: {} },
+    sshConnectionStates: hostCase.ssh ?? new Map(),
+    sshStateByEnvironment: new Map(),
+    runtimeStatusByEnvironmentId: hostCase.runtime ?? new Map(),
+    createWorktree: mocks.createWorktree,
+    updateWorktreeMeta: vi.fn().mockResolvedValue(undefined),
+    setSidebarOpen: vi.fn()
+  }
+}
+
+function startLinearIssue(): Promise<boolean> {
+  return launchWorkItemDirect({
+    repoId: 'repo-1',
+    launchSource: 'task_page',
+    openModalFallback: vi.fn(),
+    agentOverride: 'claude',
+    item: {
+      type: 'issue',
+      number: null,
+      title: 'Ship it',
+      url: 'https://linear.app/acme/issue/ENG-1/ship-it',
+      linearIdentifier: 'ENG-1'
+    }
+  })
+}
+
+const HOST_CASES: HostCase[] = [
+  {
+    name: 'Windows client -> paired Linux Orca server',
+    client: 'win32',
+    repo: { path: '/srv/repo', executionHostId: 'runtime:linux-box' },
+    runtime: new Map([['linux-box', runtimeStatus('linux')]]),
+    expected: 'linux'
+  },
+  {
+    name: 'Windows client -> Linux SSH host',
+    client: 'win32',
+    repo: { path: '/home/alice/repo', connectionId: 'box' },
+    ssh: new Map([['box', sshState('linux')]]),
+    expected: 'linux'
+  },
+  {
+    name: 'Linux client -> paired Windows Orca server',
+    client: 'linux',
+    repo: { path: 'D:\\repo', executionHostId: 'runtime:win-box' },
+    runtime: new Map([['win-box', runtimeStatus('win32')]]),
+    expected: 'win32'
+  },
+  {
+    name: 'macOS client -> Windows SSH host',
+    client: 'darwin',
+    repo: { path: 'C:\\Users\\alice\\repo', connectionId: 'box' },
+    ssh: new Map([['box', sshState('win32')]]),
+    expected: 'win32'
+  },
+  {
+    name: 'Linux client -> paired Linux Orca server',
+    client: 'linux',
+    repo: { path: '/srv/repo', executionHostId: 'runtime:linux-box' },
+    runtime: new Map([['linux-box', runtimeStatus('linux')]]),
+    expected: 'linux'
+  },
+  {
+    name: 'Windows client -> paired Windows Orca server',
+    client: 'win32',
+    repo: { path: 'D:\\repo', executionHostId: 'runtime:win-box' },
+    runtime: new Map([['win-box', runtimeStatus('win32')]]),
+    expected: 'win32'
+  },
+  { name: 'local Linux', client: 'linux', repo: { path: '/repo' }, expected: 'linux' },
+  { name: 'local Windows', client: 'win32', repo: { path: 'C:\\repo' }, expected: 'win32' }
+]
+
+describe('launchWorkItemDirect quotes for the execution host (#27971)', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    mocks.createWorktree.mockResolvedValue({
+      worktree: { id: 'repo-1::/wt', path: '/wt' },
+      setup: undefined
+    })
+    mocks.activateAndRevealWorktree.mockReturnValue({ primaryTabId: 'tab-1' })
+  })
+
+  it.each(HOST_CASES)('$name', async (hostCase) => {
+    setStore(hostCase)
+
+    await expect(startLinearIssue()).resolves.toBe(true)
+
+    expect(buildAgentDraftLaunchPlan).toHaveBeenCalledWith(
+      expect.objectContaining({ platform: hostCase.expected })
+    )
+    const command: string = mocks.activateAndRevealWorktree.mock.calls[0]?.[1]?.startup?.command
+    expect(command).toContain('Linked Linear issue: ENG-1')
+    if (hostCase.expected === 'win32') {
+      expect(command).toContain('`n')
+    } else {
+      // Why: a PowerShell "`n" draft leaves bash waiting at its continuation prompt.
+      expect(command).not.toContain('`n')
+    }
+  })
+
+  it("keeps the server's OS when the created worktree is not hydrated yet", async () => {
+    setStore(HOST_CASES[0])
+    mocks.createWorktree.mockResolvedValue({ worktree: { id: 'wt-new', path: '/wt' } })
+
+    await expect(startLinearIssue()).resolves.toBe(true)
+
+    expect(buildAgentDraftLaunchPlan).toHaveBeenCalledWith(
+      expect.objectContaining({ platform: 'linux' })
+    )
+  })
+
+  it("quotes a Windows server's new WSL worktree for that distro", async () => {
+    setStore(HOST_CASES[5])
+    mocks.createWorktree.mockResolvedValue({
+      worktree: { id: 'wt-wsl', path: '\\\\wsl.localhost\\Ubuntu\\home\\alice\\wt' }
+    })
+
+    await expect(startLinearIssue()).resolves.toBe(true)
+
+    expect(buildAgentDraftLaunchPlan).toHaveBeenCalledWith(
+      expect.objectContaining({ platform: 'linux' })
+    )
+  })
+
+  it("quotes a local Windows project's WSL runtime for that distro", async () => {
+    setStore({ name: 'wsl', client: 'win32', repo: { path: 'C:\\repo' }, expected: 'linux' })
+    mocks.store.projects = [
+      {
+        id: 'repo-1',
+        displayName: 'Repo',
+        badgeColor: '#000000',
+        sourceRepoIds: ['repo-1'],
+        createdAt: 1,
+        updatedAt: 1,
+        localWindowsRuntimePreference: { kind: 'wsl', distro: 'Ubuntu' }
+      }
+    ]
+    mocks.createWorktree.mockResolvedValue({
+      worktree: { id: 'repo-1::C:\\repo-wt', path: 'C:\\repo-wt' }
+    })
+
+    await expect(startLinearIssue()).resolves.toBe(true)
+
+    expect(buildAgentDraftLaunchPlan).toHaveBeenCalledWith(
+      expect.objectContaining({ platform: 'linux' })
+    )
+  })
+
+  it("applies this client's Windows shell only to a local launch", async () => {
+    setStore({ name: 'local', client: 'win32', repo: { path: 'C:\\repo' }, expected: 'win32' })
+    mocks.store.settings = {
+      defaultTuiAgent: 'claude',
+      agentCmdOverrides: {},
+      terminalWindowsShell: 'cmd.exe'
+    }
+
+    await expect(startLinearIssue()).resolves.toBe(true)
+
+    expect(buildAgentDraftLaunchPlan).toHaveBeenCalledWith(
+      expect.objectContaining({ platform: 'win32', shell: 'cmd' })
+    )
+  })
+
+  it('stops before creating a workspace when the server has not reported its OS', async () => {
+    setStore({
+      name: 'unreported',
+      client: 'win32',
+      repo: { path: '/srv/repo', executionHostId: 'runtime:linux-box' },
+      runtime: new Map([['linux-box', runtimeStatus()]]),
+      expected: 'linux'
+    })
+
+    await expect(startLinearIssue()).resolves.toBe(false)
+
+    expect(mocks.createWorktree).not.toHaveBeenCalled()
+    expect(mocks.toastError).toHaveBeenCalledWith(
+      'This Orca server does not report its operating system. Update the server to launch agents on it.'
+    )
+  })
+})
diff --git a/src/renderer/src/lib/launch-work-item-direct-owner-row.test.ts b/src/renderer/src/lib/launch-work-item-direct-owner-row.test.ts
index aea09f69b40..6dc2a0e7098 100644
--- a/src/renderer/src/lib/launch-work-item-direct-owner-row.test.ts
+++ b/src/renderer/src/lib/launch-work-item-direct-owner-row.test.ts
@@ -40,6 +40,12 @@ describe('launchWorkItemDirect owner row', () => {
     mocks.store = {
       repos: [],
       worktreesByRepo: {},
+      sshConnectionStates: new Map(),
+      sshStateByEnvironment: new Map(),
+      // Why: a launch stops before creating anything on a server that has not reported its OS.
+      runtimeStatusByEnvironmentId: new Map([
+        ['env-b', { checkedAt: 1, status: { hostPlatform: 'linux' } }]
+      ]),
       settings: {},
       ensureDetectedAgents: vi.fn().mockResolvedValue([]),
       ensureRemoteDetectedAgents: vi.fn().mockResolvedValue([]),
diff --git a/src/renderer/src/lib/launch-work-item-direct-route-preparation.ts b/src/renderer/src/lib/launch-work-item-direct-route-preparation.ts
index 9dbc6ea0aa4..5d00b080de4 100644
--- a/src/renderer/src/lib/launch-work-item-direct-route-preparation.ts
+++ b/src/renderer/src/lib/launch-work-item-direct-route-preparation.ts
@@ -2,8 +2,16 @@ import type { TuiAgent } from '../../../shared/tui-agent'
 import type { AppState } from '@/store/types'
 import { getConnectionId } from '@/lib/connection-context'
 import type { RepoHostFields } from '@/lib/agent-detection-target-inventory'
+import type { ProjectExecutionRuntimeResolution } from '../../../shared/project-execution-runtime'
+import {
+  refineLocalLaunchPlatform,
+  resolveRepoExecutionHostPlatform,
+  type KnownExecutionHostPlatform
+} from '@/lib/execution-host-facts'
 import { CLIENT_PLATFORM } from '@/lib/new-workspace'
 import { getLocalProjectExecutionRuntimeContext } from '@/lib/local-preflight-context'
+import { resolveLocalWindowsTerminalShellOverrideForTab } from '../../../shared/local-windows-terminal-runtime'
+import { isWslUncPath } from '../../../shared/wsl-paths'
 import type {
   AgentSessionLaunchPlan,
   planAgentSessionLaunch
@@ -26,6 +34,50 @@ export type DirectWorkItemAgentLaunchPreparation = {
   plan: AgentSessionLaunchPlan | null
 }
 
+type DirectLaunchHostArgs = {
+  latestStore: AppState
+  worktreeId: string
+  worktreePath: string
+  repoHost: RepoHostFields & { path: string }
+  launchPlatform?: NodeJS.Platform
+  repoLaunchHost: KnownExecutionHostPlatform
+  repoProjectRuntime?: ProjectExecutionRuntimeResolution
+}
+
+function directLaunchProjectRuntime(
+  args: DirectLaunchHostArgs
+): ProjectExecutionRuntimeResolution | undefined {
+  return (
+    getLocalProjectExecutionRuntimeContext(args.latestStore, args.worktreeId, CLIENT_PLATFORM) ??
+    args.repoProjectRuntime
+  )
+}
+
+function resolveDirectWorkItemLaunchHost(args: DirectLaunchHostArgs): KnownExecutionHostPlatform {
+  // Why the repo's owner: the worktree was created on that host and may not be hydrated yet; its
+  // own path and runtime still refine the OS (a WSL worktree on a Windows host runs in Linux).
+  const fact = resolveRepoExecutionHostPlatform(
+    args.latestStore,
+    args.repoHost,
+    () => directLaunchProjectRuntime(args),
+    args.worktreePath
+  )
+  return refineLocalLaunchPlatform(
+    fact.kind === 'known' ? fact : args.repoLaunchHost,
+    args.launchPlatform
+  )
+}
+
+/** The shell the local tab actually spawns, which a project runtime can override (e.g. WSL setting, Windows runtime). */
+function resolveDirectWorkItemTabShell(args: DirectLaunchHostArgs): string | undefined {
+  return resolveLocalWindowsTerminalShellOverrideForTab({
+    explicitShellOverride: undefined,
+    defaultWindowsShell: args.latestStore.settings?.terminalWindowsShell ?? undefined,
+    isWslWorktree: isWslUncPath(args.worktreePath),
+    projectRuntime: directLaunchProjectRuntime(args)
+  })
+}
+
 export async function prepareDirectWorkItemAgentLaunch(args: {
   worktreeId: string
   worktreePath: string
@@ -33,14 +85,16 @@ export async function prepareDirectWorkItemAgentLaunch(args: {
   agentOverride?: TuiAgent
   agentArgs?: string | null
   repoConnectionId: string | null
-  repoHost: RepoHostFields
+  repoHost: RepoHostFields & { path: string }
   detectedAgentsPromise: Promise<string[]> | null
   latestStore: AppState
   settings: AppState['settings']
   draftContent: string
   promptDelivery: 'draft' | 'submit-after-ready'
   launchPlatform?: NodeJS.Platform
-  repoProjectRuntime?: Parameters<typeof buildDirectWorkItemStartup>[0]['repoProjectRuntime']
+  /** Host the repo creates worktrees on; stands in while the new worktree is not hydrated. */
+  repoLaunchHost: KnownExecutionHostPlatform
+  repoProjectRuntime?: ProjectExecutionRuntimeResolution
   planLaunch: typeof planAgentSessionLaunch
   /** The start action this launch serves. */
   requestId: AgentLaunchRequestId
@@ -83,17 +137,9 @@ export async function prepareDirectWorkItemAgentLaunch(args: {
     draftContent: args.draftContent,
     promptDelivery: args.promptDelivery,
     settings: args.settings,
-    launchPlatform: args.launchPlatform,
-    launchConnectionId,
-    worktreePath: args.worktreePath,
-    repoProjectRuntime:
-      launchConnectionId === null
-        ? (getLocalProjectExecutionRuntimeContext(
-            args.latestStore,
-            args.worktreeId,
-            CLIENT_PLATFORM
-          ) ?? args.repoProjectRuntime)
-        : undefined
+    launchHost: resolveDirectWorkItemLaunchHost(args),
+    terminalWindowsShell: resolveDirectWorkItemTabShell(args),
+    launchConnectionId
   })
 
   const plan =
diff --git a/src/renderer/src/lib/launch-work-item-direct.test.ts b/src/renderer/src/lib/launch-work-item-direct.test.ts
index d1b9c032132..a5084518e48 100644
--- a/src/renderer/src/lib/launch-work-item-direct.test.ts
+++ b/src/renderer/src/lib/launch-work-item-direct.test.ts
@@ -207,6 +207,21 @@ describe('launchWorkItemDirect', () => {
       seedNativeChatLaunchDraft: mocks.seedNativeChatLaunchDraft,
       markNativeChatLaunchPromptFailed: mocks.markNativeChatLaunchPromptFailed
     } as typeof mocks.store
+    // Why: SSH fixtures use target `ssh-1`, which reports a Linux host once connected.
+    mocks.store.sshConnectionStates = new Map([
+      [
+        'ssh-1',
+        {
+          targetId: 'ssh-1',
+          status: 'connected',
+          error: null,
+          reconnectAttempt: 0,
+          remotePlatform: 'linux'
+        }
+      ]
+    ])
+    mocks.store.sshStateByEnvironment = new Map()
+    mocks.store.runtimeStatusByEnvironmentId = new Map()
     // @ts-expect-error -- test shim
     globalThis.window = { api: mockApi }
   })
@@ -418,6 +433,7 @@ describe('launchWorkItemDirect', () => {
       agentArgs: '--dangerously-skip-permissions',
       agentEnv: {},
       platform: 'win32',
+      shell: 'powershell',
       isRemote: false
     })
     expect(buildAgentStartupPlan).not.toHaveBeenCalledWith(
@@ -812,57 +828,4 @@ describe('launchWorkItemDirect', () => {
       `command test -n "$fish_pid" && set --erase -g ORCA_PI_PREFILL; command test -z "$fish_pid" && unset ORCA_PI_PREFILL; true`
     )
   })
-
-  it('plans direct local Windows-path launches with POSIX startup for WSL project runtime', async () => {
-    mocks.store.repos = [
-      {
-        id: 'repo-1',
-        path: 'C:\\Users\\alice\\repo',
-        displayName: 'Repo',
-        addedAt: 1
-      }
-    ]
-    mocks.store.projects = [
-      {
-        id: 'repo-1',
-        displayName: 'Repo',
-        badgeColor: '#000000',
-        sourceRepoIds: ['repo-1'],
-        createdAt: 1,
-        updatedAt: 1,
-        localWindowsRuntimePreference: { kind: 'wsl', distro: 'Ubuntu' }
-      }
-    ]
-    mocks.store.createWorktree.mockResolvedValue({
-      worktree: {
-        id: 'repo-1::C:\\Users\\alice\\repo-worktree',
-        path: 'C:\\Users\\alice\\repo-worktree'
-      }
-    })
-    const { launchWorkItemDirect } = await import('./launch-work-item-direct')
-
-    await expect(
-      launchWorkItemDirect({
-        item: {
-          title: 'Fix failing checks',
-          url: 'https://github.com/acme/repo/pull/1',
-          type: 'issue',
-          number: 1,
-          pasteContent: 'Fix the failing checks.'
-        },
-        repoId: 'repo-1',
-        openModalFallback: mocks.openModalFallback,
-        launchSource: 'task_page',
-        agentOverride: 'codex',
-        promptDelivery: 'submit-after-ready'
-      })
-    ).resolves.toBe(true)
-
-    expect(buildAgentStartupPlan).toHaveBeenCalledWith(
-      expect.objectContaining({
-        agent: 'codex',
-        platform: 'linux'
-      })
-    )
-  })
 })
diff --git a/src/renderer/src/lib/launch-work-item-direct.ts b/src/renderer/src/lib/launch-work-item-direct.ts
index 3eec4417918..b3f6f3bfd2c 100644
--- a/src/renderer/src/lib/launch-work-item-direct.ts
+++ b/src/renderer/src/lib/launch-work-item-direct.ts
@@ -32,7 +32,10 @@ import {
   resolveDirectSetupDecision
 } from '@/lib/launch-work-item-direct-preflight'
 import type { LaunchWorkItemDirectArgs } from '@/lib/launch-work-item-direct-types'
-import { resolveSourceControlLaunchPlatform } from '@/lib/source-control-launch-platform'
+import {
+  refineLocalLaunchPlatform,
+  resolveRepoExecutionHostPlatform
+} from '@/lib/execution-host-facts'
 import { getLocalRepoProjectExecutionRuntimeContext } from '@/lib/local-preflight-context'
 import { beginDirectWorkItemStructuredLaunch } from '@/lib/launch-work-item-direct-agent-routing'
 import { prepareDirectWorkItemAgentLaunch } from '@/lib/launch-work-item-direct-route-preparation'
@@ -90,14 +93,14 @@ export async function launchWorkItemDirect(args: LaunchWorkItemDirectArgs): Prom
   const repoProjectRuntime = repoConnectionId
     ? undefined
     : getLocalRepoProjectExecutionRuntimeContext(store, repoId, CLIENT_PLATFORM)
-  const preflightLaunchPlatform =
-    args.launchPlatform ??
-    resolveSourceControlLaunchPlatform({
-      connectionId: repoConnectionId,
-      worktreePath: repo.path,
-      projectRuntime: repoProjectRuntime
-    })
-  const shell = preflightLaunchPlatform === 'win32' ? 'powershell' : 'posix'
+  // Why: the agent runs on the repo's execution host, so its OS decides quoting, not this client's (#27971).
+  const repoLaunchFact = resolveRepoExecutionHostPlatform(store, repo, () => repoProjectRuntime)
+  if (repoLaunchFact.kind === 'withheld') {
+    toast.error(repoLaunchFact.reason)
+    return false
+  }
+  const repoLaunchHost = refineLocalLaunchPlatform(repoLaunchFact, args.launchPlatform)
+  const shell = repoLaunchHost.platform === 'win32' ? 'powershell' : 'posix'
   const agentArgsPlan = planAgentCliArgsSuffix(agentArgs, shell)
   if (!agentArgsPlan.ok) {
     // Why: direct launches may create a worktree before the agent startup plan
@@ -216,6 +219,7 @@ export async function launchWorkItemDirect(args: LaunchWorkItemDirectArgs): Prom
       draftContent,
       promptDelivery,
       launchPlatform: args.launchPlatform,
+      repoLaunchHost,
       repoProjectRuntime,
       planLaunch: planAgentSessionLaunch,
       requestId: newAgentLaunchRequestId()
diff --git a/src/renderer/src/lib/source-control-launch-platform.test.ts b/src/renderer/src/lib/source-control-launch-platform.test.ts
deleted file mode 100644
index 89bf9ce96a0..00000000000
--- a/src/renderer/src/lib/source-control-launch-platform.test.ts
+++ /dev/null
@@ -1,55 +0,0 @@
-import { describe, expect, it, vi } from 'vitest'
-
-vi.mock('./new-workspace', () => ({ CLIENT_PLATFORM: 'darwin' }))
-
-describe('resolveSourceControlLaunchPlatform', () => {
-  it('uses linux shell planning for ssh POSIX paths and local WSL paths', async () => {
-    const { resolveSourceControlLaunchPlatform } = await import('./source-control-launch-platform')
-
-    expect(
-      resolveSourceControlLaunchPlatform({
-        connectionId: 'ssh-1',
-        worktreePath: '/home/alice/repo'
-      })
-    ).toBe('linux')
-    expect(
-      resolveSourceControlLaunchPlatform({
-        connectionId: null,
-        worktreePath: String.raw`\\wsl.localhost\Ubuntu\home\alice\repo`
-      })
-    ).toBe('linux')
-  })
-
-  it('uses windows shell planning for ssh Windows paths', async () => {
-    const { resolveSourceControlLaunchPlatform } = await import('./source-control-launch-platform')
-
-    expect(
-      resolveSourceControlLaunchPlatform({
-        connectionId: 'ssh-1',
-        worktreePath: String.raw`C:\Users\alice\repo`
-      })
-    ).toBe('win32')
-  })
-
-  it('uses linux shell planning for Windows paths forced to local WSL runtime', async () => {
-    const { resolveSourceControlLaunchPlatform } = await import('./source-control-launch-platform')
-
-    expect(
-      resolveSourceControlLaunchPlatform({
-        connectionId: null,
-        worktreePath: String.raw`C:\Users\alice\repo`,
-        projectRuntime: {
-          status: 'resolved',
-          runtime: {
-            kind: 'wsl',
-            hostPlatform: 'wsl',
-            distro: 'Ubuntu',
-            reason: 'project-override',
-            projectId: 'project-1',
-            cacheKey: 'project-1:wsl:Ubuntu'
-          }
-        }
-      })
-    ).toBe('linux')
-  })
-})
diff --git a/src/renderer/src/lib/source-control-launch-platform.ts b/src/renderer/src/lib/source-control-launch-platform.ts
deleted file mode 100644
index 43cff0ff7e4..00000000000
--- a/src/renderer/src/lib/source-control-launch-platform.ts
+++ /dev/null
@@ -1,25 +0,0 @@
-import { isWindowsAbsolutePathLike } from '../../../shared/cross-platform-path'
-import { isWslUncPath } from '../../../shared/wsl-paths'
-import { CLIENT_PLATFORM } from './new-workspace'
-import type { ProjectExecutionRuntimeResolution } from '../../../shared/project-execution-runtime'
-
-export function resolveSourceControlLaunchPlatform(args: {
-  connectionId?: string | null
-  worktreePath?: string | null
-  projectRuntime?: ProjectExecutionRuntimeResolution
-}): NodeJS.Platform {
-  const path = args.worktreePath?.trim() ?? ''
-  if (typeof args.connectionId === 'string') {
-    return path && isWindowsAbsolutePathLike(path) && !isWslUncPath(path) ? 'win32' : 'linux'
-  }
-  if (args.projectRuntime?.status === 'repair-required') {
-    return args.projectRuntime.repair.preferredRuntime.kind === 'wsl' ? 'linux' : CLIENT_PLATFORM
-  }
-  if (args.projectRuntime?.status === 'resolved' && args.projectRuntime.runtime.kind === 'wsl') {
-    return 'linux'
-  }
-  if (path && isWslUncPath(path)) {
-    return 'linux'
-  }
-  return CLIENT_PLATFORM
-}
diff --git a/src/shared/launch-parity-workspace-start-cases.test-fixture.ts b/src/shared/launch-parity-workspace-start-cases.test-fixture.ts
index aec8125eebb..4fb52e8137b 100644
--- a/src/shared/launch-parity-workspace-start-cases.test-fixture.ts
+++ b/src/shared/launch-parity-workspace-start-cases.test-fixture.ts
@@ -69,16 +69,15 @@ export const WORKSPACE_START_LAUNCH_CASES: WindowLaunchCase[] = [
     { command: `${POSIX_CLAUDE} --prefill 'fix Bob'"'"'s bug'`, agentCommand: POSIX_CLAUDE },
     ZSH
   ),
-  // main today: the work item quotes for PowerShell on Windows even when cmd.exe is the shell
-  // (C4 keeps it; C4-fix flips this row to cmd.exe quoting).
+  // The work item quotes for the cmd.exe tab it spawns (#27971 passes the local shell).
   start(
     'work item, Windows C: repo, cmd.exe set',
     'win32',
     repo(WIN_PATH),
     draft,
     {
-      command: `${POSIX_CLAUDE} --prefill 'fix Bob''s bug'`,
-      agentCommand: POSIX_CLAUDE,
+      command: `${CMD_CLAUDE} --prefill "fix Bob's bug"`,
+      agentCommand: CMD_CLAUDE,
       ...IN_CMD
     },
     CMD_EXE,
diff --git a/src/shared/tui-agent-startup-shell.spec.ts b/src/shared/tui-agent-startup-shell.spec.ts
index 1698e86b08b..64eca460df4 100644
--- a/src/shared/tui-agent-startup-shell.spec.ts
+++ b/src/shared/tui-agent-startup-shell.spec.ts
@@ -147,4 +147,14 @@ describe('one Unix startup dialect', () => {
     )
     expect(plan?.env?.ORCA_PI_PREFILL).toBe('hello')
   })
+
+  it('leaves a multi-line argv draft to the paste fallback in cmd.exe', () => {
+    const draft = 'Linked Linear issue: ENG-1\nhttps://linear.app/acme/issue/ENG-1'
+    const args = { agent: 'claude' as const, draft, cmdOverrides: {}, platform: 'win32' as const }
+
+    expect(buildAgentDraftLaunchPlan({ ...args, shell: 'cmd' })).toBeNull()
+    expect(buildAgentDraftLaunchPlan({ ...args, shell: 'powershell' })?.launchCommand).toContain(
+      '`n'
+    )
+  })
 })
diff --git a/src/shared/tui-agent-startup.ts b/src/shared/tui-agent-startup.ts
index 8c56c1d9d95..ba516c97f15 100644
--- a/src/shared/tui-agent-startup.ts
+++ b/src/shared/tui-agent-startup.ts
@@ -253,6 +253,10 @@ export function buildAgentDraftLaunchPlan(args: {
     agentCommand: baseCommand.commandWithoutSessionOptions
   })
   let plan: AgentDraftLaunchPlan | null = null
+  if (config.draftPromptFlag && shell === 'cmd' && /[\r\n]/.test(trimmed)) {
+    // Why: cmd.exe cannot quote a newline, so each one would submit the line early; paste instead.
+    return null
+  }
   if (config.draftPromptFlag) {
     const quoted = quoteStartupArg(trimmed, shell)
     plan = {