`--temp-dir` was missing from the flag-to-directive map, so it fell back to plain file completion while `--dir` and `--remote-cache-dir` offered directories.
The rest is dead weight: `listTasks` re-defaulted a sorter `NewExecutor` already sets and scanned descriptions for templates even with `--no-descriptions`; `detectTaskName` had a `--` branch `Complete` returns before reaching; the two flag-value branches built the same suggestion slice twice. `os.Args[2:]` is now sliced in one place, `complete.Words()`, instead of three, and the test helpers reuse `slicesext.Convert`.
completion/protocol_test.go built a `task` binary in TestMain and drove it through 21 subprocess spawns. Every one of its table cases already had a one-for-one in-process equivalent in internal/complete, and the wire format is asserted by TestWrite_Format.
The one guarantee worth keeping was the `-t -` guard, which stops a keystroke from blocking on a Taskfile read from the terminal. It moves from cmd/task into complete.NeedsTaskfile, where it reads the flagset instead of the flags package global — testable in-process, and one less global read in cmd/task.
TestCompletionShells moves to internal/complete unchanged, and the in-process wildcard fixture gains `matches-exactly-*`, the only pattern of testdata/wildcards it was missing.
The binary path stays covered end to end by completion/tests/run.sh, which the CI completion job runs against five real shells on Linux and macOS.
The `--new-completion` section landed in website/src/latest/, which only release commits write to. Moved verbatim to website/src/next/, where the two files were byte-identical up to that point.
Bash, Fish, Zsh, Nushell and PowerShell now share a single backend: `task __complete` returns the suggestions plus a directive, and every wrapper is a thin shim around it. All five shells offer the same suggestions — task names, aliases, flags, flag values and per-task CLI variables. The Zsh `show-aliases` and `verbose` zstyles keep working, now backed by the `--no-aliases` and `--no-descriptions` completion flags.
The engine is opt-in via `task --new-completion <shell>`, leaving `--completion` and the legacy scripts untouched; it will become the default in a future release. The new wrappers live under `completion/next/`.
Completing a keystroke never reaches the network, never blocks on a stdin entrypoint, and honors every flag that decides how the Taskfile is loaded. Ref resolution shared by `requires` and enum completion moved to `internal/refs`.
A cross-shell test suite exercises the protocol in Go with thin shell smoke tests, and runs in CI.
