`job send` doesn't collect

Bug report form

• I have done a basic search of the issue tracker to find any existing issues that are similar.
• I have checked that my version is at least the latest stable release available via my installation method.

Describe the bug

When using job send with output piped from external commands, the output is not collected (See discord #help channel discussion). As a result, if used in an each closure, all external command entries will run simultaneously instead of in parallel.

How to reproduce

1. Verify each loop runs in series with built-in commands:

   def long_command [] {
     sleep 1sec
     return "output"
   }
   job spawn {
     1..5 | each {
       long_command | job send 0
     }
   }
   loop {
     job recv | print
   }
   

2. Verify each external command loop runs in series outside job spawn:

   1..5 | each {
     bash -c 'sleep 1s; echo "output"' | print
   }
   

3. Add a job spawn closure with associated job send 0 and job recv and see all entries in the each loop are run in parallel:

   job spawn {
     1..5 | each {
       bash -c 'sleep 1s; echo "output"' | job send 0
     }
   }
   loop {
     job recv | print
   }
   

4. Confirm this does not happen when the output is instead piped into a second each loop or into collect:

   job spawn {
     1..5 | each {
       bash -c 'sleep 1s; echo "output"'
     } | each {
       job send 0
     }
   }; loop {
     job recv | print
   }
   

   job spawn {
     1..5 | each {
       bash -c 'sleep 1s; echo "output"' | collect | job send 0
     }
   }
   loop {
     job recv | print
   }
   

Expected behavior

Piping the output of an external command directly into job send while in an each loop should still cause the command to run to completion before the next item is started.

Configuration

~> version | transpose key value | to md --pretty

Start by reproducing the issue with the provided job spawn, job send, job recv, each, and collect examples, then trace the job send path for output from external commands. Done means a direct pipe into job send waits for each external command to finish, matching the built-in-command behavior.