fix(hub): throw when restarting a session with a closed stream

restart() silently returned once a startChildProcess()/startPtySession()
session's streamClosed flag was set — after a natural process exit or
terminate(). That flag guards a single-use ReadableStream controller
which cannot be reopened, so restarting in place genuinely cannot
work; the defect was that a caller had no way to distinguish success
from a no-op (hub:terminals:restart resolves either way).

Throw a new DF8206 diagnostic instead, pointing callers at
remove(session) + a fresh start*() with a new id. This is a behaviour
change on a case #148 (four days ago) deliberately pinned as a silent
no-op — the two host-terminals tests that pinned it are updated to
assert the rejection while keeping their original assertions (stream
stays closed / status stays 'stopped'): only the silence changes.

Not reusing DF8205 (its fix text describes restartable: false, which
would misdescribe a spent stream) and not flipping `restartable` in
closeStream() (a different concept — "lifecycle owned elsewhere" vs.
"stream spent").

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: dvcolomban

docs/errors/DF8206.md

@@ -0,0 +1,21 @@
+---
+outline: deep
+---
+
+# DF8206: Terminal Session Restart on Closed Stream
+
+## Message
+
+> Terminal session "`{id}`" cannot be restarted — its output stream is already closed
+
+## Cause
+
+`restart()` was called on a `startChildProcess()` or `startPtySession()` session whose output stream is already closed. The stream closes irreversibly on a natural process exit or after `terminate()` — it backs a single-use `ReadableStream` controller that cannot be reopened, so restarting in place is not possible once it has closed.
+
+## Fix
+
+`ctx.terminals.remove(session)` the spent session, then spawn a fresh one via `startChildProcess()` / `startPtySession()` with a new id.
+
+## Source
+
+- [`packages/hub/src/node/host-terminals.ts`](https://github.com/devframes/devframe/blob/main/packages/hub/src/node/host-terminals.ts) — the `restart()` handle returned by `startChildProcess()` and `startPtySession()` throws this once the session's stream has closed.

packages/hub/src/node/__tests__/host-terminals.test.ts

@@ -163,7 +163,7 @@ describe('devframeTerminalHost stream lifecycle', () => {
     expect(session.buffer!.includes('line-0')).toBe(false)
   })
 
-  it('does not restart a terminated child-process session', async () => {
+  it('rejects restarting a terminated child-process session', async () => {
     const { host, sinks } = createTerminalHost()
     const session = await host.startChildProcess(
       { command: process.execPath, args: ['-e', 'setInterval(() => {}, 1000)'] },
@@ -173,7 +173,7 @@ describe('devframeTerminalHost stream lifecycle', () => {
     await waitUntil(() => {
       expect(sinks.get('child')?.closed).toBe(true)
     })
-    await session.restart()
+    await expect(session.restart()).rejects.toThrow(expect.objectContaining({ code: 'DF8206' }))
     // Stream stays closed; no orphan output stream.
     expect(sinks.get('child')?.closed).toBe(true)
   })
@@ -509,9 +509,9 @@ describe('devframeTerminalHost PTY status lifecycle', () => {
     await waitUntil(() => {
       expect(session.status).toBe('stopped')
     })
-    // The stream is closed for good, so `restart()` is a no-op — the session
+    // The stream is closed for good, so `restart()` rejects — the session
     // stays reported as stopped rather than flipping back to running.
-    await session.restart()
+    await expect(session.restart()).rejects.toThrow(expect.objectContaining({ code: 'DF8206' }))
     expect(session.status).toBe('stopped')
   })
 })

packages/hub/src/node/diagnostics.ts

@@ -67,6 +67,10 @@ export const diagnostics = defineDiagnostics({
       why: (p: { id: string }) => `Terminal session "${p.id}" is not restartable`,
       fix: 'It was registered with `restartable: false`; restart it through its owner\'s controls, or spawn it with `restartable: true` (the default) to allow in-place restarts.',
     },
+    DF8206: {
+      why: (p: { id: string }) => `Terminal session "${p.id}" cannot be restarted — its output stream is already closed`,
+      fix: 'The session already exited (or was terminated) and its stream is spent. `ctx.terminals.remove(session)` then re-`startChildProcess()`/`startPtySession()` with a fresh id instead.',
+    },
     DF8400: {
       why: (p: { id: string }) => `Command "${p.id}" is already registered`,
     },

packages/hub/src/node/host-terminals.ts

@@ -322,7 +322,7 @@ export class DevframeTerminalsHost implements DevframeTerminalsHostType {
 
     const restart = async () => {
       if (streamClosed)
-        return
+        throw diagnostics.DF8206({ id: terminal.id })
       cp?.kill()
       cp = createChildProcess()
       markStatus('running')
@@ -497,7 +497,7 @@ export class DevframeTerminalsHost implements DevframeTerminalsHostType {
       },
       restart: async () => {
         if (streamClosed)
-          return
+          throw diagnostics.DF8206({ id: terminal.id })
         pty?.kill()
         pty = spawnPty()
         markStatus('running')

packages/hub/src/types/terminals.ts

@@ -114,6 +114,7 @@ export interface DevframeChildProcessTerminalSession extends DevframeTerminalSes
    */
   getResult: () => DevframeChildProcessResult
   terminate: () => Promise<void>
+  /** Throws `DF8206` once the session's output stream has closed (after a natural exit or `terminate()`) — `remove()` it and start a fresh session instead. */
   restart: () => Promise<void>
 }
 
@@ -139,5 +140,6 @@ export interface DevframePtyTerminalSession extends DevframeTerminalSession {
   /** Current foreground process name, when the backend can resolve it. */
   getProcessName: () => string | undefined
   terminate: () => Promise<void>
+  /** Throws `DF8206` once the session's output stream has closed (after a natural exit or `terminate()`) — `remove()` it and start a fresh session instead. */
   restart: () => Promise<void>
 }