diff --git a/src/main/runtime/orca-runtime-files.test.ts b/src/main/runtime/orca-runtime-files.test.ts
index d43e48c4695..eb7723944f7 100644
--- a/src/main/runtime/orca-runtime-files.test.ts
+++ b/src/main/runtime/orca-runtime-files.test.ts
@@ -248,6 +248,7 @@ describe('RuntimeFileCommands', () => {
   it('opens text files through the renderer host (inheriting active runtime env)', async () => {
     const openFile = vi.fn()
     const { commands } = createRuntimeFileCommands({ openFile })
+    statMock.mockResolvedValue({ isDirectory: () => false })
 
     const result = await commands.openMobileFile('id:wt-1', 'docs/readme.md')
 
@@ -268,6 +269,7 @@ describe('RuntimeFileCommands', () => {
   it('opens previewable images through the renderer host as an image tab', async () => {
     const openFile = vi.fn()
     const { commands } = createRuntimeFileCommands({ openFile })
+    statMock.mockResolvedValue({ isDirectory: () => false })
 
     const result = await commands.openMobileFile('id:wt-1', 'assets/logo.png')
 
@@ -285,6 +287,43 @@ describe('RuntimeFileCommands', () => {
     })
   })
 
+  it('fails the open when the resolved local file does not exist', async () => {
+    const openFile = vi.fn()
+    const { commands } = createRuntimeFileCommands({ openFile })
+    statMock.mockRejectedValue(enoent())
+
+    await expect(commands.openMobileFile('id:wt-1', 'spec/does-not-exist.md')).rejects.toThrow(
+      'file_not_found'
+    )
+    expect(openFile).not.toHaveBeenCalled()
+  })
+
+  it('fails the open when the resolved path is a directory', async () => {
+    const openFile = vi.fn()
+    const { commands } = createRuntimeFileCommands({ openFile })
+    statMock.mockResolvedValue({ isDirectory: () => true })
+
+    await expect(commands.openMobileFile('id:wt-1', 'docs')).rejects.toThrow('file_not_found')
+    expect(openFile).not.toHaveBeenCalled()
+  })
+
+  it('fails the open when the remote SSH file does not exist', async () => {
+    const openFile = vi.fn()
+    const resolveRuntimeFileTarget = vi.fn(async () => ({
+      worktree: { id: 'wt-1', repoId: 'repo-1', path: '/repo' },
+      connectionId: 'ssh-1'
+    }))
+    const { commands } = createRuntimeFileCommands({ openFile, resolveRuntimeFileTarget })
+    vi.mocked(getSshFilesystemProvider).mockReturnValue({
+      stat: vi.fn().mockRejectedValue(new Error('No such file or directory'))
+    } as never)
+
+    await expect(commands.openMobileFile('id:wt-1', 'spec/does-not-exist.md')).rejects.toThrow(
+      'file_not_found'
+    )
+    expect(openFile).not.toHaveBeenCalled()
+  })
+
   it('leaves non-previewable binaries unavailable on mobile', async () => {
     const openFile = vi.fn()
     const { commands } = createRuntimeFileCommands({ openFile })
diff --git a/src/main/runtime/orca-runtime-files.ts b/src/main/runtime/orca-runtime-files.ts
index acdf3616f47..6bfeabe5266 100644
--- a/src/main/runtime/orca-runtime-files.ts
+++ b/src/main/runtime/orca-runtime-files.ts
@@ -248,7 +248,7 @@ export class RuntimeFileCommands {
     worktreeSelector: string,
     relativePath: string
   ): Promise<RuntimeFileOpenResult> {
-    const { worktree } = await this.host.resolveRuntimeFileTarget(worktreeSelector)
+    const { worktree, connectionId } = await this.host.resolveRuntimeFileTarget(worktreeSelector)
     if (!isSafeMobileRelativePath(relativePath)) {
       throw new Error('invalid_relative_path')
     }
@@ -265,6 +265,12 @@ export class RuntimeFileCommands {
       return { worktree: worktree.id, relativePath, kind, opened: false }
     }
     const filePath = joinWorktreeRelativePath(worktree.path, relativePath)
+    // Why: a missing (or directory) path used to report opened:true / exit 0
+    // and create a ghost tab that only failed at render time, misleading
+    // CLI-driving agents into trusting the open succeeded (#8844).
+    if (!(await this.resolvedOpenTargetIsFile(filePath, connectionId))) {
+      throw new Error('file_not_found')
+    }
     // Why: the service's internal runtimeId is not a registered runtime env selector
     // (those live in orca-environments.json). Passing it caused Unknown environment
     // errors on content load for CLI-initiated opens (via files.open from orca cli
@@ -482,6 +488,29 @@ export class RuntimeFileCommands {
     return /\bENOENT\b|no such file|not found|does not exist/i.test(message)
   }
 
+  // Existence probe for files.open across local and SSH worktrees. Genuine
+  // not-found (or a directory) → false; transport/permission failures still
+  // throw so a dropped remote session doesn't read as "file missing".
+  private async resolvedOpenTargetIsFile(
+    filePath: string,
+    connectionId: string | undefined
+  ): Promise<boolean> {
+    try {
+      const stats = connectionId
+        ? await this.statRemoteTerminalPath(filePath, connectionId)
+        : await stat(filePath)
+      return !stats.isDirectory()
+    } catch (error) {
+      if (
+        isENOENT(error) ||
+        (connectionId !== undefined && RuntimeFileCommands.isRemoteNotFoundErrorMessage(error))
+      ) {
+        return false
+      }
+      throw error
+    }
+  }
+
   private async statRemoteTerminalPath(
     absolutePath: string,
     connectionId: string
diff --git a/src/main/runtime/rpc/errors.ts b/src/main/runtime/rpc/errors.ts
index bb800b54617..6d94fd3a092 100644
--- a/src/main/runtime/rpc/errors.ts
+++ b/src/main/runtime/rpc/errors.ts
@@ -45,6 +45,7 @@ const RUNTIME_PASSTHROUGH_CODES: ReadonlySet<string> = new Set([
   'terminal_gone',
   'no_active_terminal',
   'repo_not_found',
+  'file_not_found',
   'timeout',
   'invalid_limit'
 ])