@@ -5,6 +5,7 @@ import { failure, type Output } from '../output.js'
 import { type ParsedArgv } from '../parse-argv.js'
 import { resolveEndpoint, sshConfigHosts } from '../resolve.js'
 import { blankPane, buildEndpointChoices, defaultLocalPath, Tui } from '../tui/app.js'
+import { runInherited } from '../tui/launch.js'
 
 /**
  * `diskpush tui` — the two-pane browser, in a terminal.
@@ -41,6 +42,31 @@ export async function runTui(parsed: ParsedArgv, store: DiskPushStore, output: O
   const choices = buildEndpointChoices(await store.listConnections(), sshConfigHosts(), defaultLocalPath())
   const tui = new Tui(panes[0]!, panes[1]!, choices)
 
+  try {
+    void tui.loadBoth()
+    // The browser runs until it quits, or until it wants the terminal handed
+    // to a program — `e` outside tmux. Then the program runs with the screen
+    // to itself and the browser starts again, every pane where it was.
+    for (;;) {
+      await runApp(tui)
+      const handoff = tui.takeHandoff()
+      if (!handoff) break
+      try {
+        await runInherited(handoff)
+      } catch (error) {
+        console.error(`could not start ${handoff.argv[0]}: ${error instanceof Error ? error.message : String(error)}`)
+      }
+      await tui.afterHandoff()
+    }
+  } finally {
+    tui.close()
+  }
+
+  return EXIT.ok
+}
+
+/** One run of the screen: from the terminal taken to the terminal restored. */
+async function runApp(tui: Tui): Promise<void> {
   // `q` is not a quit key to the app: inside the host-key prompt it has to
   // reach the Tui first, which is the only thing that knows a dialog is up.
   // Ctrl+C stays with the app so the terminal is restored however it dies.
@@ -61,12 +87,5 @@ export async function runTui(parsed: ParsedArgv, store: DiskPushStore, output: O
     tui.view(ui, theme, width, height)
   })
 
-  try {
-    void tui.loadBoth()
-    await app.start()
-  } finally {
-    tui.close()
-  }
-
-  return EXIT.ok
+  await app.start()
 }
@@ -34,6 +34,7 @@ import {
   endpointString,
   fillDocument,
   listLocal,
+  looksBinary,
   nothingToDo,
   parentPath,
   pushChange,
@@ -46,6 +47,7 @@ import {
 } from './model.js'
 import { type Action, type Tone, type ViewState, draw, filterChoices } from './view.js'
 import { maxScroll, readsAsMarkdown } from './document.js'
+import { type Launch, type Launcher, type Target, editLaunch, openLaunch, systemLauncher } from './launch.js'
 
 export {
   blankPane,
@@ -70,6 +72,8 @@ export class Tui {
   private document: Document | null = null
   /** What the last frame drew of it: its line count and the rows it had, so a scroll can be clamped. */
   private documentLayout = { total: 0, rows: 1 }
+  /** A program waiting for the terminal, once the app has given it up. See `start`. */
+  private handoff: Launch | null = null
   private filtering: Side | null = null
   private status: { text: string; tone: Tone } | null = null
   private busy = false
@@ -86,6 +90,7 @@ export class Tui {
     left: Pane,
     right: Pane,
     private readonly choices: readonly EndpointChoice[] = [],
+    private readonly launcher: Launcher = systemLauncher(),
   ) {
     this.panes = { left, right }
   }
@@ -237,6 +242,12 @@ export class Tui {
       case 'closeDocument':
         this.document = null
         break
+      case 'edit':
+        if (!this.busy) await this.editSelected()
+        break
+      case 'openWith':
+        if (!this.busy) await this.openSelected()
+        break
       case 'preview':
         if (!this.busy) await this.transferTo(true)
         break
@@ -458,6 +469,12 @@ export class Tui {
       case key.char === 'v':
         await this.toggleDocument()
         break
+      case key.char === 'e':
+        await this.editSelected()
+        break
+      case key.char === 'x':
+        await this.openSelected()
+        break
       case key.name === 'r':
         await this.refresh(this.active)
         break
@@ -635,6 +652,106 @@ export class Tui {
     }
   }
 
+  // --------------------------------------------------------------- launching
+
+  /** The row under the cursor, as something to hand to a program. */
+  private target(): (Target & { isDirectory: boolean }) | null {
+    const pane = this.current
+    const row = selectedRow(pane)
+    if (!row) return null
+    const path = pane.connection ? posix.join(pane.path, row.rel) : join(pane.path, row.rel)
+    return { path, name: row.entry.name, connection: pane.connection, isDirectory: row.entry.isDirectory }
+  }
+
+  /** `e`: the file under the cursor, in the system editor. */
+  private async editSelected(): Promise<void> {
+    const target = this.target()
+    if (!target) return
+    if (target.isDirectory) {
+      this.say('e edits a file; ⏎ unfolds a directory', 'warn')
+      return
+    }
+    const launch = editLaunch(target, this.launcher.env, this.launcher.available)
+    if ('error' in launch) {
+      this.say(launch.error, 'warn')
+      return
+    }
+    await this.start(launch, `Editing ${target.name}`)
+  }
+
+  /** `x`: the file under the cursor, with whatever the system opens it with. */
+  private async openSelected(): Promise<void> {
+    const target = this.target()
+    if (!target) return
+    // The bytes decide text against media before the name gets a say.
+    let text = false
+    if (!target.connection && !target.isDirectory) {
+      try {
+        text = !looksBinary(readLocalHead(target.path, 8192).bytes)
+      } catch {
+        // Unreadable: let the opener report it.
+      }
+    }
+    const launch = openLaunch(target, this.launcher.env, this.launcher.available, process.platform, { text })
+    if ('error' in launch) {
+      this.say(launch.error, 'warn')
+      return
+    }
+    await this.start(launch, `Opened ${target.name}`)
+  }
+
+  /**
+   * Gets a program on screen.
+   *
+   * A desktop opener returns at once and wants no terminal. Under tmux the
+   * program gets a window of its own and the browser stays up beside it.
+   * Otherwise the browser hands the terminal over: it stops, the runner in
+   * commands/tui.ts runs the program, and starts the browser again with every
+   * pane where it was — vim's `:sh`, from the other side.
+   */
+  private async start(launch: Launch, done: string): Promise<void> {
+    if (launch.detached) {
+      this.launcher.detach(launch)
+      this.say(done)
+      return
+    }
+    if (this.launcher.inTmux) {
+      try {
+        await this.launcher.tmux(launch)
+        this.say(`${done} in a new tmux window`)
+      } catch (error) {
+        this.say(`tmux: ${error instanceof Error ? error.message : String(error)}`, 'error')
+      }
+      return
+    }
+    this.handoff = launch
+    this.app?.quit()
+  }
+
+  /** The program the app quit for, if it quit for one. Taken once. */
+  takeHandoff(): Launch | null {
+    const launch = this.handoff
+    this.handoff = null
+    return launch
+  }
+
+  /**
+   * Back from a hand-off. The program may have changed anything, so both
+   * listings are re-read in place, and the open document is read again —
+   * an edit is the most likely thing to have just happened to it.
+   */
+  async afterHandoff(): Promise<void> {
+    await this.refresh('left')
+    await this.refresh('right')
+    const doc = this.document
+    if (!doc) return
+    const pane = this.panes[doc.side]
+    const row = visibleRows(pane).find((candidate) => endpointString(pane, candidate.rel, false) === doc.location)
+    this.document = null
+    if (row) await this.viewRow(doc.side, row)
+    this.invalidate()
+  }
+
   private async readRemoteHead(pane: Pane, path: string): Promise<{ bytes: Uint8Array; size: number }> {
     const browser = await SftpBrowser.open(await this.session(pane.connection!))
     try {
 
@@ -12,6 +12,7 @@ import type { App, MouseEvent } from '@profullstack/hqtui'
 import { renderToScreen } from '@profullstack/hqtui/testing'
 import { key } from './keys.fixture.js'
 import { visibleRows, type Entry, type Pane, type Side } from './model.js'
+import type { Launch, Launcher } from './launch.js'
 
 vi.mock('@diskpush/ssh-core', () => ({
   SshSession: { connect: async () => ({ close: () => {} }) },
@@ -645,3 +646,144 @@ describe('viewing a file', () => {
     expect(state(app).transfer).not.toBeNull()
   })
 })
+
+describe('editing and opening with the system', () => {
+  /** A launcher that records what would have run. */
+  function fakeLauncher(over: Partial<Launcher> = {}) {
+    const launched: { how: 'tmux' | 'detach'; launch: Launch }[] = []
+    const launcher: Launcher = {
+      env: { EDITOR: 'vim', PATH: '/usr/bin' },
+      available: (bin) => ['vim', 'mpv'].includes(bin),
+      inTmux: true,
+      tmux: async (launch) => {
+        launched.push({ how: 'tmux', launch })
+      },
+      detach: (launch) => {
+        launched.push({ how: 'detach', launch })
+      },
+      ...over,
+    }
+    return { launcher, launched }
+  }
+  function browser(over: Partial<Launcher> = {}) {
+    const root = mkdtempSync(join(tmpdir(), 'diskpush-edit-'))
+    mkdirSync(join(root, 'src'))
+    writeFileSync(join(root, 'notes.md'), '# notes\n')
+    writeFileSync(join(root, 'talk.mp4'), Buffer.from([0, 0, 0, 0x18, 0x66, 0x74, 0x79, 0x70]))
+    const left = blankPane('Local', root)
+    left.entries = listLocal(root)
+    const { launcher, launched } = fakeLauncher(over)
+    const app = new Tui(left, blankPane('Local', '/tmp/b'), [], launcher)
+    return { app, root, launched }
+  }
+  const goto = (app: Tui, name: string) => {
+    const p = pane(app, 'left')
+    p.index = visibleRows(p).findIndex((row) => row.entry.name === name)
+    expect(p.index).toBeGreaterThanOrEqual(0)
+  }
+
+  it('e opens the file under the cursor in $EDITOR, in a tmux window, and says so', async () => {
+    const { app, root, launched } = browser()
+    goto(app, 'notes.md')
+    await press(app, 'e')
+    expect(launched).toEqual([
+      { how: 'tmux', launch: { argv: ['vim', join(root, 'notes.md')], cwd: root, title: 'notes.md' } },
+    ])
+    expect(state(app).status?.text).toBe('Editing notes.md in a new tmux window')
+    expect(app.takeHandoff()).toBeNull()
+  })
+
+  it('e on a directory edits nothing', async () => {
+    const { app, launched } = browser()
+    goto(app, 'src')
+    await press(app, 'e')
+    expect(launched).toEqual([])
+    expect(state(app).status?.text).toContain('e edits a file')
+  })
+
+  it('without tmux, e hands the terminal over: the app quits and the runner gets the program', async () => {
+    const { app, root, launched } = browser({ inTmux: false })
+    const quit = vi.fn()
+    app.attach({ quit, invalidate: () => {}, height: 30 } as unknown as App)
+    goto(app, 'notes.md')
+    await press(app, 'e')
+    expect(launched).toEqual([])
+    expect(quit).toHaveBeenCalledTimes(1)
+    const handoff = app.takeHandoff()
+    expect(handoff).toEqual({ argv: ['vim', join(root, 'notes.md')], cwd: root, title: 'notes.md' })
+    // Taken once: the next run of the app is not a hand-off.
+    expect(app.takeHandoff()).toBeNull()
+  })
+
+  it('coming back from a hand-off re-reads the panes and the open file', async () => {
+    const { app, root } = browser({ inTmux: false })
+    app.attach({ quit: () => {}, invalidate: () => {}, height: 30 } as unknown as App)
+    goto(app, 'notes.md')
+    await press(app, 'v')
+    expect(state(app).document?.text).toBe('# notes\n')
+    await press(app, 'e')
+    app.takeHandoff()
+    writeFileSync(join(root, 'notes.md'), '# notes, edited\n')
+    writeFileSync(join(root, 'new.txt'), 'x')
+    await app.afterHandoff()
+    expect(state(app).document?.text).toBe('# notes, edited\n')
+    expect(pane(app, 'left').entries.some((entry) => entry.name === 'new.txt')).toBe(true)
+  })
+
+  it('x sends a video to a player in a tmux window, and a file to the desktop when there is one', async () => {
+    const { app, root, launched } = browser()
+    goto(app, 'talk.mp4')
+    await press(app, 'x')
+    expect(launched).toEqual([
+      { how: 'tmux', launch: { argv: ['mpv', join(root, 'talk.mp4')], cwd: root, title: 'talk.mp4' } },
+    ])
+    expect(state(app).status?.text).toBe('Opened talk.mp4 in a new tmux window')
+
+    const desktop = browser({ env: { DISPLAY: ':0' }, available: (bin) => bin === 'xdg-open' })
+    goto(desktop.app, 'notes.md')
+    await press(desktop.app, 'x')
+    expect(desktop.launched).toEqual([
+      { how: 'detach', launch: { argv: ['xdg-open', join(desktop.root, 'notes.md')], title: 'notes.md', detached: true } },
+    ])
+  })
+
+  it('x on a text file named like a video does not start a player', async () => {
+    const { app, root, launched } = browser({ available: (bin) => bin === 'ffplay' })
+    writeFileSync(join(root, 'code.ts'), 'const a = 1\n')
+    pane(app, 'left').entries = listLocal(root)
+    goto(app, 'code.ts')
+    await press(app, 'x')
+    expect(launched).toEqual([])
+    expect(state(app).status?.text).toBe('code.ts is a text file: v views it, e edits it.')
+  })
+
+  it('x says what is missing when nothing opens the file', async () => {
+    const { app, launched } = browser({ available: () => false })
+    goto(app, 'talk.mp4')
+    await press(app, 'x')
+    expect(launched).toEqual([])
+    expect(state(app).status?.text).toBe('No video player found: install mpv or ffplay.')
+  })
+
+  it('a tmux that refuses is reported, not swallowed', async () => {
+    const { app } = browser({
+      tmux: async () => {
+        throw new Error('no server running')
+      },
+    })
+    goto(app, 'notes.md')
+    await press(app, 'e')
+    expect(state(app).status).toEqual({ text: 'tmux: no server running', tone: 'error' })
+  })
+
+  it('the footer caps do the same', async () => {
+    const { app, launched } = browser()
+    goto(app, 'notes.md')
+    const screen = frame(app)
+    const cap = screen.find('e edit')!
+    screen.click(cap.x, cap.y)
+    await settle()
+    expect(launched).toHaveLength(1)
+    expect(launched[0]?.launch.argv[0]).toBe('vim')
+  })
+})