fix(system): roll back service update when the new container fails to start

The service update path stopped and renamed the old container aside before
the new one was confirmed running, but only wired up rollback if
createContainer threw or the 5s health check failed. A throw from
newContainer.start() itself (bad device/GPU config, host port already bound,
image incompatibility) bubbled straight to the outer catch, which returned a
generic 400 and never restored the old container, leaving the service down.

Retrying then wedged: the failed new container still held the service name, so
the next attempt's rename to `<name>_old` collided with the leftover from the
first attempt and threw the same error every time.

- Wrap newContainer.start() so a start failure removes the half-created
  container and rolls back to the previous one.
- Clear any stale `<name>_old` before renaming so retries can't collide.
- Dedupe the three rollback sites into a single rollbackToOld() helper (also
  removes a non-null assertion in the create-failure path that could itself
  throw when no `_old` existed).

Refs #949

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

admin/app/services/docker_service.ts

@@ -1547,8 +1547,36 @@ export class DockerService {
 
       // Step 3: Rename old container as safety net
       const oldName = `${serviceName}_old`
+
+      // Clear any stale rollback container left behind by a previously failed update.
+      // Otherwise the rename below collides with the existing `<name>_old` and throws,
+      // which wedges every subsequent retry on the same error.
+      const staleOld = (await this.docker.listContainers({ all: true })).find((c) =>
+        c.Names.includes(`/${oldName}`)
+      )
+      if (staleOld) {
+        try {
+          await this.docker.getContainer(staleOld.Id).remove({ force: true })
+        } catch {
+          // Best effort — if it can't be removed the rename below will surface the error.
+        }
+      }
+
       await oldContainer.rename({ name: oldName })
 
+      // Restore the previous container after a failed update: rename the renamed-aside
+      // old container back into place and start it, so a failure anywhere between here
+      // and the health check never leaves the service down.
+      const rollbackToOld = async () => {
+        const containers = await this.docker.listContainers({ all: true })
+        const oldRef = containers.find((c) => c.Names.includes(`/${oldName}`))
+        if (oldRef) {
+          const rollbackContainer = this.docker.getContainer(oldRef.Id)
+          await rollbackContainer.rename({ name: serviceName }).catch(() => {})
+          await rollbackContainer.start().catch(() => {})
+        }
+      }
+
       // Step 4: Create new container with inspected config + new image
       this._broadcast(serviceName, 'update-creating', `Creating updated container...`)
 
@@ -1604,16 +1632,35 @@ export class DockerService {
       } catch (createError: any) {
         // Rollback: rename old container back
         this._broadcast(serviceName, 'update-rollback', `Failed to create new container: ${createError.message}. Rolling back...`)
-        const rollbackContainer = this.docker.getContainer((await this.docker.listContainers({ all: true })).find((c) => c.Names.includes(`/${oldName}`))!.Id)
-        await rollbackContainer.rename({ name: serviceName })
-        await rollbackContainer.start()
+        await rollbackToOld()
         this.activeInstallations.delete(serviceName)
         return { success: false, message: `Failed to create updated container: ${createError.message}` }
       }
 
-      // Step 5: Start new container
+      // Step 5: Start new container. If the start itself throws (bad device/GPU config,
+      // a host port already bound, image incompatibility), roll back to the previous
+      // container instead of leaving the service stopped with no replacement running.
       this._broadcast(serviceName, 'update-starting', `Starting updated container...`)
-      await newContainer.start()
+      try {
+        await newContainer.start()
+      } catch (startError: any) {
+        this._broadcast(
+          serviceName,
+          'update-rollback',
+          `Updated container failed to start: ${startError.message}. Rolling back to previous version...`
+        )
+        try {
+          await newContainer.remove({ force: true })
+        } catch {
+          // Best effort — leave the half-created container for manual cleanup if needed.
+        }
+        await rollbackToOld()
+        this.activeInstallations.delete(serviceName)
+        return {
+          success: false,
+          message: `Update failed: new container did not start (${startError.message}). Rolled back to previous version.`,
+        }
+      }
 
       // Step 6: Health check — verify container stays running for 5 seconds
       await new Promise((resolve) => setTimeout(resolve, 5000))
@@ -1659,14 +1706,7 @@ export class DockerService {
           // Best effort cleanup
         }
 
-        // Restore old container
-        const oldContainers = await this.docker.listContainers({ all: true })
-        const oldRef = oldContainers.find((c) => c.Names.includes(`/${oldName}`))
-        if (oldRef) {
-          const rollbackContainer = this.docker.getContainer(oldRef.Id)
-          await rollbackContainer.rename({ name: serviceName })
-          await rollbackContainer.start()
-        }
+        await rollbackToOld()
 
         this.activeInstallations.delete(serviceName)
         return {