fix(nushell): adapt the completer to the 0.116 contract (#4934)

* fix(nushell): adapt the completer to the 0.116 contract

Nushell 0.116 runs an external completer on a background worker
without the terminal unless the registered closure reaches a
command carrying the @interactive attribute. Interactivity is
seen through the closure to the command it calls, so wrap the
completion logic in an @interactive entry point and register a
closure that ends with the call to it.

Read the named `place` input instead of the deprecated
positional `spans`; $place.command carries the same token list.

An @interactive completer cannot decline with null (null reads
as a dismissed picker), so request the fallback explicitly when
the `**` trigger is absent, keeping plain file completion
working. The previous external completer is still called when
the trigger is absent.

The script now requires Nushell 0.116+, since @interactive is a
parse error on older versions.

Fixes #4932

* fix(nushell): retry the previous completer with the legacy spans input

The fallback to the previously configured external completer always
handed it the new `place` input. A completer that still declares the
legacy `spans` parameter errors on a record, so the fallback silently
produced no completions for pre-0.116 completers (e.g. older Carapace
installs).

Try `place` first, then retry with the token list, which is what the
old positional bridge handed such completers.

* docs(nushell): note the 0.116 requirement and load order

Requires Nushell 0.116.1+, where a completion can take the terminal
through the @interactive attribute, and the wrapper captures the
external completer present at load time.

.github/workflows/linux.yml

@@ -38,9 +38,11 @@ jobs:
         wget -qO- https://apt.fury.io/nushell/gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/fury-nushell.gpg
         echo "deb [signed-by=/etc/apt/keyrings/fury-nushell.gpg] https://apt.fury.io/nushell/ /" | sudo tee /etc/apt/sources.list.d/fury-nushell.list
         sudo apt-get update
-        # Pinned: 0.115.0 runs external completers on a background thread, so
+        # Pinned: the Nushell scripts now require 0.116+, where an external
+        # completer reaches the terminal through the @interactive attribute.
+        # Before that (e.g. 0.115.0), completers run on a background thread, so
         # fzf never receives keystrokes. https://github.com/nushell/nushell/issues/18771
-        sudo apt-get install --yes zsh fish tmux shfmt nushell=0.114.1-0
+        sudo apt-get install --yes zsh fish tmux shfmt nushell=0.116.1-0
 
     - name: Install Ruby gems
       run: bundle install