diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 35c46d1297..fec424786c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -58,6 +58,49 @@ jobs:
       - name: 🧪 Test
         run: task test --output group --output-group-begin '::group::{{.TASK}}' --output-group-end '::endgroup::'
 
+  completion:
+    name: 🐚 Completion (${{ matrix.platform }})
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.platform }}
+    steps:
+      - name: 📥 Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: ⬇️ Setup Go
+        uses: actions/setup-go@b7ad1dad31e06c5925ef5d2fc7ad053ef454303e # v7.0.0
+        with:
+          go-version: 1.26.x
+
+      - name: ⬇️ Setup Task
+        uses: go-task/setup-task@v2
+
+      # zsh and pwsh are preinstalled on the runners; only fish is missing
+      # (plus zsh on the Linux image).
+      - name: ⬇️ Install shells (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y zsh fish
+
+      - name: ⬇️ Install shells (macOS)
+        if: runner.os == 'macOS'
+        run: brew install fish
+
+      # Nushell ships in no runner image and is not packaged by apt, so it comes
+      # from its own release archives.
+      - name: ⬇️ Install Nushell
+        uses: hustcer/setup-nu@f3fd65374ffc4d60974c0dd2f7263c6c5c285f81 # v3.26
+        with:
+          version: "*"
+
+      - name: 🧪 Test completion
+        # Strict mode fails the run if any shell is missing, so we never get a
+        # false pass when a runner image stops shipping one (e.g. pwsh).
+        env:
+          TASK_COMPLETION_STRICT: "1"
+        run: task test:completion
+
   lint:
     name: 🔍 Lint (${{ matrix.go-version }})
     strategy:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d67a714e36..6fc7364458 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -56,6 +56,14 @@
   reports exit code `124`. Callers that join a `run: once` or `when_changed`
   task already running now honor their own `timeout`, and inherit that task's
   failure instead of being told it succeeded (#1569, #2898 by @vmaerten).
+- Added a new completion engine that unifies Bash, Fish, Zsh, Nushell and
+  PowerShell behind a single `task __complete` command, so every shell offers
+  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. It is
+  opt-in for now via `task --new-completion <shell>`, leaving `--completion`
+  unchanged, and will become the default in a future release (#2897 by
+  @vmaerten).
 
 ## v3.52.0 - 2026-07-02
 
diff --git a/Taskfile.yml b/Taskfile.yml
index 6b9b69a772..1b90492e5a 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -158,6 +158,15 @@ tasks:
     cmds:
       - go test -bench=. -benchmem -tags=fsbench -run=^$ ./...
 
+  test:completion:
+    desc: Tests the shell completion engine and wrappers (bash, zsh, fish, nu, powershell)
+    sources:
+      - internal/complete/**/*.go
+      - cmd/task/**/*.go
+      - completion/**/*
+    cmds:
+      - bash completion/tests/run.sh
+
   goreleaser:test:
     desc: Tests release process without publishing
     cmds:
diff --git a/cmd/task/complete_cmd.go b/cmd/task/complete_cmd.go
new file mode 100644
index 0000000000..1be8c39cf1
--- /dev/null
+++ b/cmd/task/complete_cmd.go
@@ -0,0 +1,50 @@
+package main
+
+import (
+	"bufio"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/spf13/pflag"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/complete"
+	"github.com/go-task/task/v3/internal/flags"
+)
+
+func runComplete(args []string) error {
+	// Strip the completion-control flags the wrapper prepends; the rest is the
+	// user's command line to complete.
+	opts, args := complete.ParseOptions(args)
+
+	// WithFlags carries every flag that decides which Taskfile is loaded, as the
+	// flag package parsed them from the words being completed. The overrides come
+	// after it: a keystroke must stay silent and must never hit the network,
+	// prompt for trust or write to the remote cache, whatever remote flags the
+	// user typed.
+	e := task.NewExecutor(
+		flags.WithFlags(),
+		task.WithStdout(io.Discard),
+		task.WithStderr(io.Discard),
+		task.WithStdin(strings.NewReader("")),
+		task.WithVersionCheck(false),
+		task.WithOffline(true),
+		task.WithDownload(false),
+	)
+
+	// Loading the Taskfile parses YAML, so skip it entirely when completing flags
+	// or their values. Best-effort: a missing or broken Taskfile must not break
+	// completion. A `-` entrypoint is skipped as well, since reading the Taskfile
+	// from standard input would hang the shell on a keystroke.
+	if complete.NeedsTaskfile(args, pflag.CommandLine) && flags.Entrypoint != "-" {
+		_ = e.Setup()
+	}
+
+	suggs, dirv := complete.Complete(e, pflag.CommandLine, args, opts)
+
+	// Buffered: the whole candidate list is written on every keystroke.
+	out := bufio.NewWriter(os.Stdout)
+	complete.Write(out, suggs, dirv)
+	return out.Flush()
+}
diff --git a/cmd/task/task.go b/cmd/task/task.go
index b81e23dd5f..2332845199 100644
--- a/cmd/task/task.go
+++ b/cmd/task/task.go
@@ -13,6 +13,7 @@ import (
 	"github.com/go-task/task/v3/args"
 	"github.com/go-task/task/v3/errors"
 	"github.com/go-task/task/v3/experiments"
+	"github.com/go-task/task/v3/internal/complete"
 	"github.com/go-task/task/v3/internal/filepathext"
 	"github.com/go-task/task/v3/internal/flags"
 	"github.com/go-task/task/v3/internal/logger"
@@ -58,6 +59,12 @@ func emitCIErrorAnnotation(err error) {
 }
 
 func run() error {
+	// Dispatched before flag validation: the args after __complete are the
+	// user's command line, not Task's own flags.
+	if complete.IsActive() {
+		return runComplete(os.Args[2:])
+	}
+
 	log := &logger.Logger{
 		Stdout:  os.Stdout,
 		Stderr:  os.Stderr,
@@ -126,6 +133,15 @@ func run() error {
 		return nil
 	}
 
+	if flags.NewCompletion != "" {
+		script, err := task.CompletionNext(flags.NewCompletion)
+		if err != nil {
+			return err
+		}
+		fmt.Println(script)
+		return nil
+	}
+
 	e := task.NewExecutor(
 		flags.WithFlags(),
 		task.WithVersionCheck(true),
diff --git a/completion.go b/completion.go
index ab333b7ad4..b5e9d29460 100644
--- a/completion.go
+++ b/completion.go
@@ -20,20 +20,59 @@ var completionPowershell string
 //go:embed completion/zsh/_task
 var completionZsh string
 
-func Completion(completion string) (string, error) {
-	// Get the file extension for the selected shell
-	switch completion {
-	case "bash":
-		return completionBash, nil
-	case "fish":
-		return completionFish, nil
-	case "nu", "nushell":
-		return completionNu, nil
-	case "powershell":
-		return completionPowershell, nil
-	case "zsh":
-		return completionZsh, nil
-	default:
-		return "", fmt.Errorf("unknown shell: %s", completion)
+// The completion/next/* scripts are thin wrappers around the `task __complete`
+// engine. They are served only via `--new-completion` for now (opt-in) and will
+// replace the scripts above once the engine becomes the default.
+
+//go:embed completion/next/bash/task.bash
+var completionBashNext string
+
+//go:embed completion/next/fish/task.fish
+var completionFishNext string
+
+//go:embed completion/next/nu/task-completions.nu
+var completionNuNext string
+
+//go:embed completion/next/ps/task.ps1
+var completionPowershellNext string
+
+//go:embed completion/next/zsh/_task
+var completionZshNext string
+
+// The maps accept `nushell` as an alias of `nu`.
+var completionScripts = map[string]string{
+	"bash":       completionBash,
+	"fish":       completionFish,
+	"nu":         completionNu,
+	"nushell":    completionNu,
+	"powershell": completionPowershell,
+	"zsh":        completionZsh,
+}
+
+var completionScriptsNext = map[string]string{
+	"bash":       completionBashNext,
+	"fish":       completionFishNext,
+	"nu":         completionNuNext,
+	"nushell":    completionNuNext,
+	"powershell": completionPowershellNext,
+	"zsh":        completionZshNext,
+}
+
+// Completion returns the default (stable) completion script for the given shell.
+func Completion(shell string) (string, error) {
+	return completionScript(completionScripts, shell)
+}
+
+// CompletionNext returns the new `task __complete` engine wrapper for the given
+// shell, exposed via `--new-completion` while the engine is opt-in.
+func CompletionNext(shell string) (string, error) {
+	return completionScript(completionScriptsNext, shell)
+}
+
+func completionScript(scripts map[string]string, shell string) (string, error) {
+	script, ok := scripts[shell]
+	if !ok {
+		return "", fmt.Errorf("unknown shell: %s", shell)
 	}
+	return script, nil
 }
diff --git a/completion/next/bash/task.bash b/completion/next/bash/task.bash
new file mode 100644
index 0000000000..f9b8cfaeaa
--- /dev/null
+++ b/completion/next/bash/task.bash
@@ -0,0 +1,95 @@
+# vim: set tabstop=2 shiftwidth=2 expandtab:
+#
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+TASK_CMD="${TASK_EXE:-task}"
+
+# Wraps _filedir so an inline `--flag=` prefix is stripped before completion and
+# re-applied to the results. `=` is kept inside the current word (see the
+# `_init_completion -n =:` below), so the whole `--flag=value` token would
+# otherwise be treated as the path and never match.
+_task_filedir() {
+  local fpfx="" savecur="$cur"
+  if [[ "$cur" == -*=* ]]; then
+    fpfx="${cur%%=*}="
+    cur="${cur#*=}"
+  fi
+  _filedir ${1:+"$1"}
+  cur="$savecur"
+  if [[ -n "$fpfx" ]]; then
+    COMPREPLY=( ${COMPREPLY[@]+"${COMPREPLY[@]/#/$fpfx}"} )
+  fi
+}
+
+_task() {
+  local cur prev words cword
+
+  # Completion directives, mirroring internal/complete/complete.go.
+  local -ri NO_SPACE=2 NO_FILE_COMP=4 FILTER_FILE_EXT=8 FILTER_DIRS=16
+
+  # Exclude both `=` and `:` from the word breaks so `--output=` and
+  # `docs:serve` reach the engine as single tokens.
+  _init_completion -n =: || return
+
+  local -a args=( "${words[@]:1:cword}" )
+  if (( ${#args[@]} == 0 )); then
+    args=( "" )
+  fi
+
+  local output
+  output=$("$TASK_CMD" __complete "${args[@]}" 2>/dev/null)
+  if [[ -z "$output" ]]; then
+    _task_filedir
+    return
+  fi
+
+  local -a lines=()
+  local line
+  while IFS= read -r line; do
+    lines+=( "$line" )
+  done <<< "$output"
+
+  local last_idx=$(( ${#lines[@]} - 1 ))
+  local directive="${lines[$last_idx]#:}"
+  unset 'lines[$last_idx]'
+
+  if (( directive & FILTER_FILE_EXT )); then
+    local exts=""
+    # ${arr[@]+…} guards against "unbound variable" on an empty array under
+    # `set -u` in bash 3.2 (macOS).
+    for line in ${lines[@]+"${lines[@]}"}; do
+      exts+="${exts:+|}$line"
+    done
+    _task_filedir "@($exts)"
+    return
+  fi
+
+  if (( directive & FILTER_DIRS )); then
+    _task_filedir -d
+    return
+  fi
+
+  # Prefix-filter by hand instead of `compgen -W`: the latter joins/splits the
+  # word list on IFS, which mangles any suggestion value containing a space.
+  local value
+  COMPREPLY=()
+  for line in ${lines[@]+"${lines[@]}"}; do
+    value="${line%%$'\t'*}"
+    if [[ -z "$cur" || "$value" == "$cur"* ]]; then
+      COMPREPLY+=( "$value" )
+    fi
+  done
+
+  if (( directive & NO_SPACE )); then
+    compopt -o nospace 2>/dev/null
+  fi
+
+  __ltrim_colon_completions "$cur"
+
+  if (( ${#COMPREPLY[@]} == 0 )) && ! (( directive & NO_FILE_COMP )); then
+    _task_filedir
+  fi
+}
+
+complete -F _task "$TASK_CMD"
diff --git a/completion/next/fish/task.fish b/completion/next/fish/task.fish
new file mode 100644
index 0000000000..66f342190c
--- /dev/null
+++ b/completion/next/fish/task.fish
@@ -0,0 +1,109 @@
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+set -l GO_TASK_PROGNAME (if set -q GO_TASK_PROGNAME; echo $GO_TASK_PROGNAME; else if set -q TASK_EXE; echo $TASK_EXE; else; echo task; end)
+
+# Completion directives, mirroring internal/complete/complete.go. fish's `math`
+# has no bitwise operators, so bits are stored as their power-of-two value and
+# tested with integer division + modulo via __task_test_bit. NoSpace (2) and
+# KeepOrder (32) need no handling: fish appends no space and keeps the order.
+set -g __task_directive_no_file_comp 4
+set -g __task_directive_filter_file_ext 8
+set -g __task_directive_filter_dirs 16
+
+function __task_test_bit --argument-names value bit
+  test (math "floor($value / $bit) % 2") -eq 1
+end
+
+function __task_complete --inherit-variable GO_TASK_PROGNAME
+  set -l tokens (commandline -opc)
+  set -l current (commandline -ct)
+  set -l args
+  if test (count $tokens) -gt 1
+    set args $tokens[2..-1]
+  end
+  set args $args $current
+
+  set -l output ($GO_TASK_PROGNAME __complete $args 2>/dev/null)
+  set -l count (count $output)
+  if test $count -eq 0
+    return
+  end
+
+  set -l last $output[$count]
+  if not string match -q ':*' -- $last
+    # Protocol violation: emit raw lines as a fallback.
+    printf '%s\n' $output
+    return
+  end
+
+  set -l directive (string replace -r '^:' '' -- $last)
+  set -l data
+  if test $count -gt 1
+    set data $output[1..(math $count - 1)]
+  end
+
+  # The main completion is registered with `--no-files`, which disables fish's
+  # native file fallback. Every file-completion directive must therefore be
+  # served here, otherwise nothing is offered (e.g. `--cacert`, after `--`).
+
+  # For an inline `--flag=path`, complete against the path part but keep the
+  # `--flag=` prefix on every candidate (fish replaces the whole token). flagpfx
+  # is empty for the normal case, so the prefixing below is a no-op then.
+  set -l flagpfx ""
+  set -l pathcur $current
+  if string match -qr '^--?[^=]+=' -- $current
+    set flagpfx (string replace -r '=.*$' '=' -- $current)
+    set pathcur (string replace -r '^--?[^=]+=' '' -- $current)
+  end
+
+  # __fish_complete_suffix only *prioritizes* the extension rather than
+  # filtering, so filter the file list ourselves (keeping dirs to descend into).
+  if __task_test_bit $directive $__task_directive_filter_file_ext
+    for entry in (__fish_complete_path $pathcur)
+      set -l name (string split -f1 \t -- $entry)
+      if string match -qr '/$' -- $name
+        printf '%s%s\n' $flagpfx $entry
+        continue
+      end
+      for ext in $data
+        if string match -qr "\.$ext\$" -- $name
+          printf '%s%s\n' $flagpfx $entry
+          break
+        end
+      end
+    end
+    return
+  end
+
+  if __task_test_bit $directive $__task_directive_filter_dirs
+    for entry in (__fish_complete_directories $pathcur)
+      printf '%s%s\n' $flagpfx $entry
+    end
+    return
+  end
+
+  # Emit the candidates verbatim; fish reads the tab as the value/description
+  # separator.
+  for line in $data
+    printf '%s\n' $line
+  end
+
+  # NoFileComp unset → also offer files, since `--no-files` suppressed the
+  # native fallback. Covers DirectiveDefault (e.g. `--cacert`, after `--`).
+  if not __task_test_bit $directive $__task_directive_no_file_comp
+    for entry in (__fish_complete_path $pathcur)
+      printf '%s%s\n' $flagpfx $entry
+    end
+  end
+end
+
+# Erase any inherited rules first: fish accumulates `complete` entries (unlike
+# bash/zsh/PowerShell which replace), so a previously loaded completion would
+# otherwise keep contributing alongside the engine.
+complete -c $GO_TASK_PROGNAME -e
+
+# Single registration: all task names, flags, flag values and file completion
+# flow through the engine. `--no-files` prevents fish from mixing in files when
+# the engine says not to (NoFileComp); `__task_complete` re-adds them otherwise.
+complete -c $GO_TASK_PROGNAME --no-files -a "(__task_complete)"
diff --git a/completion/next/nu/task-completions.nu b/completion/next/nu/task-completions.nu
new file mode 100644
index 0000000000..c78cdc72eb
--- /dev/null
+++ b/completion/next/nu/task-completions.nu
@@ -0,0 +1,113 @@
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+#
+# Nushell has a single, global external completer instead of a per-command
+# registration, so this script chains to the one already installed rather than
+# replacing it: command lines that do not start with Task are handed back.
+
+# Completes a Task command line. `spans` is the tokenised command line Nushell
+# hands to an external completer: the command name, then every argument up to
+# the cursor — the last one empty when the cursor sits on a fresh word.
+#
+# Returns a list of `{value, description}` records, or null to let Nushell run
+# its own file completion (the engine's DirectiveDefault).
+#
+# Only a list or null may be returned here: the `{completions, options}` record
+# documented for `def` completers is rejected for an external completer and
+# yields no suggestion at all.
+def task-external-completer [spans: list<string>] {
+  let exe = ($env.TASK_EXE? | default "task")
+
+  # Words after the program name. The trailing empty word must be preserved:
+  # the engine relies on it to know the cursor sits on a fresh word.
+  let words = ($spans | skip 1)
+  let args = (if ($words | is-empty) { [""] } else { $words })
+  let current = ($args | last)
+
+  # `complete` captures the exit code and keeps stderr off the prompt. A missing
+  # binary raises, hence the `try`.
+  let result = (try { do { ^$exe "__complete" ...$args } | complete } catch { null })
+  if ($result | is-empty) or $result.exit_code != 0 {
+    return null
+  }
+
+  let lines = ($result.stdout | lines)
+  let last = ($lines | last)
+  # Protocol violation: offer nothing rather than garbage.
+  if ($last | is-empty) or (not ($last | str starts-with ":")) {
+    return null
+  }
+  let directive = (try { $last | str substring 1.. | into int } catch { 0 })
+  let data = ($lines | drop 1)
+
+  # Completion directives, mirroring internal/complete/complete.go.
+  # DirectiveNoSpace (2) needs no handling: Nushell never appends a space after
+  # an external completion. DirectiveKeepOrder (32) needs none either: results
+  # are offered in the order they are returned, unsorted.
+  let no_file_comp = (($directive | bits and 4) != 0)
+  let filter_file_ext = (($directive | bits and 8) != 0)
+  let filter_dirs = (($directive | bits and 16) != 0)
+
+  # Nushell replaces the whole token being completed, so an inline `--flag=`
+  # prefix must be re-applied to every path candidate. The directory already
+  # typed is kept by `ls`, which returns paths as matched (`sub/nested.yml`).
+  let inline = ($current | parse --regex '^(?<flag>--?[^=]+=)(?<path>.*)$')
+  let flag_prefix = (if ($inline | is-empty) { "" } else { $inline.0.flag })
+  let path_arg = (if ($inline | is-empty) { $current } else { $inline.0.path })
+
+  if $filter_file_ext or $filter_dirs {
+    # A string variable is a literal path for `ls`; `into glob` turns it into a
+    # pattern. A pattern matching nothing raises, hence the `try`.
+    let entries = (try { ls ($"($path_arg)*" | into glob) } catch { [] })
+    # FilterFileExt keeps directories too, so the user can descend into them.
+    let matched = (if $filter_file_ext {
+      $entries | where {|entry| $entry.type == "dir" or ($entry.name | path parse | get extension) in $data }
+    } else {
+      $entries | where type == "dir"
+    })
+    return ($matched | each {|entry|
+      # Directories get a trailing separator: without it a second <tab> would
+      # match the directory again instead of descending into it.
+      let name = (if $entry.type == "dir" { $"($entry.name)(char path_sep)" } else { $entry.name })
+      { value: $"($flag_prefix)($name)" }
+    })
+  }
+
+  # Nushell does not filter the results of an external completer, so match the
+  # current word here — case-insensitively, like Nushell's own default.
+  let candidates = ($data
+    | each {|line|
+      let parts = ($line | split row --number 2 "\t")
+      let value = ($parts | first)
+      if ($parts | length) > 1 { { value: $value, description: ($parts | last) } } else { { value: $value } }
+    }
+    | where {|candidate| $candidate.value | str starts-with --ignore-case $current })
+
+  # NoFileComp unset and nothing to offer → null hands the word back to
+  # Nushell's file completion (DirectiveDefault: `--cacert`, after `--`, …).
+  if ($candidates | is-empty) and (not $no_file_comp) {
+    return null
+  }
+
+  $candidates
+}
+
+# Chain to the completer already installed, if any: Nushell shares a single
+# external completer between every command, so replacing it outright would break
+# the completions of every other tool. Autoload files are loaded after config.nu,
+# so a completer configured there is picked up here.
+let task_previous_completer = ($env.config.completions.external.completer? | default null)
+
+$env.config.completions.external.completer = {|spans|
+  let exe = ($env.TASK_EXE? | default "task")
+  # Compare basenames so `./task`, `/usr/local/bin/task` and `task.exe` all match.
+  let head = ($spans | first | path basename | str replace --regex '(?i)\.exe$' '')
+  let name = ($exe | path basename | str replace --regex '(?i)\.exe$' '')
+  if $head == $name {
+    task-external-completer $spans
+  } else if $task_previous_completer != null {
+    do $task_previous_completer $spans
+  } else {
+    null
+  }
+}
diff --git a/completion/next/ps/task.ps1 b/completion/next/ps/task.ps1
new file mode 100644
index 0000000000..185f185744
--- /dev/null
+++ b/completion/next/ps/task.ps1
@@ -0,0 +1,124 @@
+using namespace System.Management.Automation
+using namespace System.Management.Automation.Language
+
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+$cmdNames = @('task') + (Get-Alias -Definition task,task.exe,*\task,*\task.exe -ErrorAction SilentlyContinue).Name | Select-Object -Unique
+
+Register-ArgumentCompleter -Native -CommandName $cmdNames -ScriptBlock {
+	param($wordToComplete, $commandAst, $cursorPosition)
+
+	$TaskExe = if ($env:TASK_EXE) { $env:TASK_EXE } else { 'task' }
+
+	# The current word arrives with the quote the user opened; the engine wants
+	# the value, and so does every path we build from it below.
+	$current = $wordToComplete
+	if ($current.Length -ge 1 -and ($current[0] -eq '"' -or $current[0] -eq "'")) {
+		$quoteChar = $current[0]
+		$current = $current.Substring(1)
+		if ($current.EndsWith($quoteChar)) {
+			$current = $current.Substring(0, $current.Length - 1)
+		}
+	}
+
+	# Words after the program name, truncated to the cursor. A string element
+	# yields its Value, not its source text, so `--dir "a b"` does not reach the
+	# engine with its quotes.
+	$argsToPass = @()
+	$elements = $commandAst.CommandElements
+	for ($i = 1; $i -lt $elements.Count; $i++) {
+		$el = $elements[$i]
+		if ($el.Extent.StartOffset -ge $cursorPosition) { break }
+		$argsToPass += if ($el -is [StringConstantExpressionAst] -or $el -is [ExpandableStringExpressionAst]) {
+			$el.Value
+		} else {
+			$el.ToString()
+		}
+	}
+	# The trailing word (possibly empty) must reach the engine so it knows
+	# the cursor sits on a fresh word. It is already present when it coincides
+	# with the last command element captured above.
+	if ($argsToPass.Count -eq 0 -or $argsToPass[-1] -ne $current) {
+		$argsToPass += $current
+	}
+
+	$output = & $TaskExe __complete @argsToPass 2>$null
+	if (-not $output) { return }
+
+	$lines = @($output)
+	$last = $lines[-1]
+	if (-not $last.StartsWith(':')) { return }
+
+	$directive = [int]($last.Substring(1))
+	$data = if ($lines.Count -gt 1) { $lines[0..($lines.Count - 2)] } else { @() }
+
+	# Completion directives, mirroring internal/complete/complete.go.
+	$NoFileComp    = 4
+	$FilterFileExt = 8
+	$FilterDirs    = 16
+
+	# PowerShell replaces the whole token with the completion text, so both an
+	# inline `--flag=` and any directory the user already typed (e.g. `sub/`)
+	# must be preserved. Query the filesystem with the path portion only
+	# ($pathArg), but prepend the flag + directory prefix to every candidate.
+	$flagPrefix = ''
+	$pathArg = $current
+	if ($current -match '^(--?[^=]+=)(.*)$') {
+		$flagPrefix = $Matches[1]
+		$pathArg = $Matches[2]
+	}
+	$pathPrefix = $flagPrefix + ($pathArg -replace '[^\\/]*$', '')
+
+	# Note: DirectiveNoSpace (bit 2) cannot be honored here — PowerShell's
+	# CompletionResult API has no per-item "no trailing space" option, so a
+	# suggestion like `VAR=` gets a trailing space. This is a PowerShell limit.
+
+	# The completion text replaces the token as-is, so anything holding a space
+	# has to be quoted or it would come back as several arguments.
+	$asCompletionText = {
+		param($text)
+		if ($text -match '[\s'']') { "'" + $text.Replace("'", "''") + "'" } else { $text }
+	}
+
+	$asPathResult = {
+		param($item)
+		$type = if ($item.PSIsContainer) { [CompletionResultType]::ProviderContainer } else { [CompletionResultType]::ProviderItem }
+		[CompletionResult]::new((& $asCompletionText "$pathPrefix$($item.Name)"), $item.Name, $type, $item.Name)
+	}
+
+	# FilterFileExt: keep files whose extension matches, plus directories so the
+	# user can still descend into them. `-Include` is unreliable without
+	# `-Recurse`, so filter with Where-Object instead.
+	if ($directive -band $FilterFileExt) {
+		$exts = $data | ForEach-Object { ".$_" }
+		return Get-ChildItem -Path "$pathArg*" -ErrorAction SilentlyContinue |
+			Where-Object { $_.PSIsContainer -or $exts -contains $_.Extension } |
+			ForEach-Object { & $asPathResult $_ }
+	}
+
+	if ($directive -band $FilterDirs) {
+		return Get-ChildItem -Path "$pathArg*" -Directory -ErrorAction SilentlyContinue |
+			ForEach-Object { & $asPathResult $_ }
+	}
+
+	# Build candidates, filtering by the current word. PowerShell does not filter
+	# native argument-completer results itself, so without this every suggestion
+	# would be offered regardless of what the user typed.
+	$results = @($data | ForEach-Object {
+		$parts = $_ -split "`t", 2
+		$value = $parts[0]
+		if ($current -and -not $value.StartsWith($current, [System.StringComparison]::OrdinalIgnoreCase)) { return }
+		$desc = if ($parts.Count -gt 1 -and $parts[1]) { $parts[1] } else { $value }
+		[CompletionResult]::new((& $asCompletionText $value), $value, [CompletionResultType]::ParameterValue, $desc)
+	})
+
+	# NoFileComp (bit 4) unset and nothing matched → fall back to file completion,
+	# since the engine returned DirectiveDefault (e.g. --cacert, after `--`).
+	if ($results.Count -eq 0 -and -not ($directive -band $NoFileComp)) {
+		return Get-ChildItem -Path "$pathArg*" -ErrorAction SilentlyContinue |
+			ForEach-Object { & $asPathResult $_ }
+	}
+
+	return $results
+}
diff --git a/completion/next/zsh/_task b/completion/next/zsh/_task
new file mode 100755
index 0000000000..b3b26a0aca
--- /dev/null
+++ b/completion/next/zsh/_task
@@ -0,0 +1,84 @@
+#compdef task
+#
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+TASK_CMD="${TASK_EXE:-task}"
+
+_task() {
+	local -a args lines completions describe_opts compadd_opts ctl
+	local output directive line
+
+	# Completion directives, mirroring internal/complete/complete.go.
+	local -ri NO_SPACE=2 NO_FILE_COMP=4 FILTER_FILE_EXT=8 FILTER_DIRS=16 KEEP_ORDER=32
+
+	# Map the zsh completion zstyles to engine flags. `-T` is true when the
+	# style is unset (its default) or explicitly true, so a flag is only passed
+	# when the user turned the style off.
+	zstyle -T ":completion:${curcontext}:" show-aliases || ctl+=(--no-aliases)
+	zstyle -T ":completion:${curcontext}:" verbose      || ctl+=(--no-descriptions)
+
+	# (@) preserves a trailing empty string, which the engine relies on to
+	# know the cursor is on a fresh word.
+	args=("${(@)words[2,CURRENT]}")
+	(( ${#args} == 0 )) && args=("")
+
+	output=$("$TASK_CMD" __complete "${ctl[@]}" "${args[@]}" 2>/dev/null)
+	if [[ -z "$output" ]]; then
+		_files
+		return
+	fi
+
+	lines=("${(f)output}")
+	directive="${lines[-1]#:}"
+	lines=("${(@)lines[1,-2]}")
+
+	if (( directive & FILTER_FILE_EXT )); then
+		local -a globs
+		for line in "${lines[@]}"; do
+			globs+=("*.${line}")
+		done
+		# Strip an inline `--flag=` into IPREFIX so file completion runs on the
+		# value; zsh re-inserts the prefix. Only in the file branches — doing it
+		# globally would break `_describe` matching for inline enums.
+		compset -P '*='
+		_files -g "(${(j:|:)globs})"
+		return
+	fi
+
+	if (( directive & FILTER_DIRS )); then
+		compset -P '*='
+		_path_files -/
+		return
+	fi
+
+	# `:` inside the value must be escaped: _describe splits on the first
+	# unescaped colon (e.g. "docs:serve" would otherwise become value "docs").
+	local value desc
+	for line in "${lines[@]}"; do
+		if [[ "$line" == *$'\t'* ]]; then
+			value="${line%%$'\t'*}"
+			desc="${line#*$'\t'}"
+			completions+=("${value//:/\\:}:$desc")
+		else
+			completions+=("${line//:/\\:}")
+		fi
+	done
+
+	# -S is a compadd option, passed after the array; -V is an option of
+	# _describe itself. In the compadd zone it would take the next argument as a
+	# group name, swallowing the `-d` _describe appends and offering its internal
+	# variables as candidates.
+	(( directive & NO_SPACE ))   && compadd_opts+=(-S '')
+	(( directive & KEEP_ORDER )) && describe_opts+=(-V)
+
+	if (( ${#completions} > 0 )); then
+		_describe "${describe_opts[@]}" -t tasks 'task' completions "${compadd_opts[@]}"
+	fi
+
+	(( directive & NO_FILE_COMP )) && return
+	compset -P '*='
+	_files
+}
+
+compdef _task "$TASK_CMD"
diff --git a/completion/protocol_test.go b/completion/protocol_test.go
new file mode 100644
index 0000000000..6c3776e389
--- /dev/null
+++ b/completion/protocol_test.go
@@ -0,0 +1,344 @@
+// Package completion_test black-box tests the `task __complete` wire protocol:
+// the candidates and directive the real binary emits for a command line. The
+// shell wrappers only need to be smoke-tested for how they interpret the
+// directive (see completion/tests/wrapper.*).
+package completion_test
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/complete"
+)
+
+var taskBin string
+
+func TestMain(m *testing.M) {
+	dir, err := os.MkdirTemp("", "task-completion-test")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	taskBin = filepath.Join(dir, "task")
+	if runtime.GOOS == "windows" {
+		taskBin += ".exe"
+	}
+	if out, err := exec.CommandContext(context.Background(), "go", "build", "-o", taskBin, "github.com/go-task/task/v3/cmd/task").CombinedOutput(); err != nil {
+		fmt.Fprintf(os.Stderr, "failed to build task binary: %v\n%s", err, out)
+		os.RemoveAll(dir)
+		os.Exit(1)
+	}
+	code := m.Run()
+	os.RemoveAll(dir)
+	os.Exit(code)
+}
+
+const fixtureTaskfile = `version: '3'
+
+tasks:
+  build:
+    desc: Build it
+  deploy:
+    desc: Deploy the application
+    aliases: [dep, ship]
+    requires:
+      vars:
+        - name: ENV
+          enum: [dev, staging, prod]
+        - REGION
+  docs:serve:
+    desc: Serve docs locally
+`
+
+// completeArgs runs `task __complete <args>` in a fresh fixture directory and
+// returns the offered candidate values plus the emitted directive.
+func completeArgs(t *testing.T, args ...string) ([]string, complete.Directive) {
+	t.Helper()
+
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(fixtureTaskfile), 0o644))
+
+	// taskBin is the test-built binary and args are test-controlled literals.
+	cmd := exec.CommandContext(t.Context(), taskBin, append([]string{complete.CommandName}, args...)...) //nolint:gosec
+	cmd.Dir = dir
+	out, err := cmd.Output()
+	require.NoError(t, err)
+
+	return parseProtocol(t, out)
+}
+
+// parseProtocol splits the protocol output into candidate values and the
+// trailing directive.
+func parseProtocol(t *testing.T, out []byte) ([]string, complete.Directive) {
+	t.Helper()
+
+	lines := strings.Split(strings.TrimRight(string(out), "\n"), "\n")
+	require.NotEmpty(t, lines, "protocol output must end with a directive line")
+
+	last := lines[len(lines)-1]
+	require.True(t, strings.HasPrefix(last, ":"), "last line must be the :<directive> line, got %q", last)
+	n, err := strconv.Atoi(strings.TrimPrefix(last, ":"))
+	require.NoError(t, err)
+
+	values := make([]string, 0, len(lines)-1)
+	for _, line := range lines[:len(lines)-1] {
+		values = append(values, strings.SplitN(line, "\t", 2)[0])
+	}
+	return values, complete.Directive(n)
+}
+
+func TestProtocol(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name      string
+		args      []string
+		want      []string // candidate values that must be offered
+		absent    []string // candidate values that must NOT be offered
+		directive complete.Directive
+	}{
+		{
+			name:      "task names and aliases",
+			args:      []string{""},
+			want:      []string{"build", "deploy", "dep", "ship", "docs:serve"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "no-aliases drops aliases",
+			args:      []string{"--no-aliases", ""},
+			want:      []string{"build", "deploy"},
+			absent:    []string{"dep", "ship"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "flag names",
+			args:      []string{"-"},
+			want:      []string{"--taskfile", "--dir", "--output"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "separate flag value is bare",
+			args:      []string{"--output", ""},
+			want:      []string{"interleaved", "group", "prefixed"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "inline flag value is full form",
+			args:      []string{"--output="},
+			want:      []string{"--output=interleaved", "--output=group", "--output=prefixed"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "sort enum values",
+			args:      []string{"--sort", ""},
+			want:      []string{"default", "alphanumeric", "none"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "taskfile filters by extension",
+			args:      []string{"--taskfile", ""},
+			want:      []string{"yml", "yaml"},
+			directive: complete.DirectiveFilterFileExt,
+		},
+		{
+			name:      "dir filters to directories",
+			args:      []string{"--dir", ""},
+			directive: complete.DirectiveFilterDirs,
+		},
+		{
+			name:      "task variables keep order and suppress the space",
+			args:      []string{"deploy", ""},
+			want:      []string{"ENV=dev", "ENV=staging", "ENV=prod", "REGION="},
+			directive: complete.DirectiveNoSpace | complete.DirectiveNoFileComp | complete.DirectiveKeepOrder,
+		},
+		{
+			name:      "after -- yields default file completion",
+			args:      []string{"deploy", "--", ""},
+			directive: complete.DirectiveDefault,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			values, directive := completeArgs(t, tt.args...)
+			require.Equal(t, tt.directive, directive)
+			require.Subset(t, values, tt.want)
+			for _, a := range tt.absent {
+				require.NotContains(t, values, a)
+			}
+		})
+	}
+}
+
+// TestProtocol_SortFlagIsApplied checks that the flags deciding how the Taskfile
+// is read reach the engine, --sort being the one with a visible order.
+func TestProtocol_SortFlagIsApplied(t *testing.T) {
+	t.Parallel()
+
+	const taskfile = `version: '3'
+
+tasks:
+  zebra:
+    desc: Declared first, last alphabetically
+  alpha:
+    desc: Declared last, first alphabetically
+`
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(taskfile), 0o644))
+
+	sorted, _ := completeInDir(t, dir, nil, "")
+	require.Equal(t, []string{"alpha", "zebra"}, sorted)
+
+	declared, _ := completeInDir(t, dir, nil, "--sort", "none", "")
+	require.Equal(t, []string{"zebra", "alpha"}, declared)
+}
+
+// TestProtocol_ExperimentGatedFlag checks that a flag only registered under an
+// experiment is parsed instead of breaking the whole command line.
+func TestProtocol_ExperimentGatedFlag(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(fixtureTaskfile), 0o644))
+
+	values, directive := completeInDir(t, dir, []string{"TASK_X_GENTLE_FORCE=1"}, "--force-all", "")
+	require.Equal(t, complete.DirectiveNoFileComp, directive)
+	require.Subset(t, values, []string{"build", "deploy"})
+}
+
+// TestProtocol_RemoteIncludeStaysOffline guards the keystroke path against a
+// remote include with no cache: downloading it would freeze the shell for up to
+// --timeout and prompt for trust.
+func TestProtocol_RemoteIncludeStaysOffline(t *testing.T) {
+	t.Parallel()
+
+	var hits atomic.Int64
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		hits.Add(1)
+		<-r.Context().Done()
+	}))
+	defer srv.Close()
+
+	taskfile := fmt.Sprintf(`version: '3'
+
+includes:
+  remote: %s/Taskfile.yml
+
+tasks:
+  build:
+    desc: Build it
+`, srv.URL)
+
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(taskfile), 0o644))
+
+	ctx, cancel := context.WithTimeout(t.Context(), 15*time.Second)
+	defer cancel()
+
+	// A fresh cache dir: nothing can be served from disk, so a download is the
+	// only way the include could be resolved. The insecure opt-in keeps the
+	// plain-HTTP test server from being rejected before the download.
+	// taskBin is the test-built binary and the arguments are literals.
+	cmd := exec.CommandContext(ctx, taskBin, complete.CommandName, "") //nolint:gosec
+	cmd.Dir = dir
+	cmd.Env = append(os.Environ(),
+		"TASK_REMOTE_DIR="+t.TempDir(),
+		"TASK_REMOTE_INSECURE=1",
+	)
+	out, err := cmd.Output()
+	require.NoError(t, err, "completion must not hang on a remote include")
+
+	_, directive := parseProtocol(t, out)
+	require.Equal(t, complete.DirectiveNoFileComp, directive)
+	require.Zero(t, hits.Load(), "completion must not reach the network")
+}
+
+// TestProtocol_StdinEntrypointDoesNotHang guards the keystroke path against
+// `--taskfile -`, which would otherwise read the Taskfile from the terminal.
+func TestProtocol_StdinEntrypointDoesNotHang(t *testing.T) {
+	t.Parallel()
+
+	// An unwritten pipe: reading it would block until the context expires.
+	r, w, err := os.Pipe()
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		r.Close()
+		w.Close()
+	})
+
+	ctx, cancel := context.WithTimeout(t.Context(), 15*time.Second)
+	defer cancel()
+
+	// taskBin is the test-built binary and the arguments are literals.
+	cmd := exec.CommandContext(ctx, taskBin, complete.CommandName, "-t", "-", "") //nolint:gosec
+	cmd.Dir = t.TempDir()
+	cmd.Stdin = r
+	out, err := cmd.Output()
+	require.NoError(t, err, "completion must not read the Taskfile from stdin")
+
+	_, directive := parseProtocol(t, out)
+	require.Equal(t, complete.DirectiveNoFileComp, directive)
+}
+
+// TestProtocol_WildcardTaskNames checks that a pattern reaches the shell as the
+// prefix to type onto, with the trailing space suppressed.
+func TestProtocol_WildcardTaskNames(t *testing.T) {
+	t.Parallel()
+
+	values, directive := completeInDir(t, filepath.Join("..", "testdata", "wildcards"), nil, "")
+	require.Equal(t, complete.DirectiveNoSpace|complete.DirectiveNoFileComp, directive)
+	require.Subset(t, values, []string{"start-", "s-", "wildcard-", "matches-exactly-"})
+	for _, v := range values {
+		require.NotEmpty(t, v)
+		require.NotContains(t, v, "*")
+	}
+}
+
+// completeInDir runs `task __complete <args>` in dir, with extra environment
+// variables appended to the current environment.
+func completeInDir(t *testing.T, dir string, env []string, args ...string) ([]string, complete.Directive) {
+	t.Helper()
+
+	// taskBin is the test-built binary and args are test-controlled literals.
+	cmd := exec.CommandContext(t.Context(), taskBin, append([]string{complete.CommandName}, args...)...) //nolint:gosec
+	cmd.Dir = dir
+	cmd.Env = append(os.Environ(), env...)
+	out, err := cmd.Output()
+	require.NoError(t, err)
+
+	return parseProtocol(t, out)
+}
+
+// TestCompletionShells keeps the shells the engine offers for --completion and
+// --new-completion in step with the scripts the root package can actually serve.
+func TestCompletionShells(t *testing.T) {
+	t.Parallel()
+
+	for _, flag := range []string{"--completion", "--new-completion"} {
+		shells, directive := completeArgs(t, flag, "")
+		require.Equal(t, complete.DirectiveNoFileComp, directive)
+		require.NotEmpty(t, shells)
+
+		for _, shell := range shells {
+			_, err := task.Completion(shell)
+			require.NoErrorf(t, err, "%s offers %q", flag, shell)
+			_, err = task.CompletionNext(shell)
+			require.NoErrorf(t, err, "%s offers %q", flag, shell)
+		}
+	}
+}
diff --git a/completion/tests/run.sh b/completion/tests/run.sh
new file mode 100755
index 0000000000..762d752920
--- /dev/null
+++ b/completion/tests/run.sh
@@ -0,0 +1,104 @@
+#!/usr/bin/env bash
+# Runs the completion test suite: builds the task binary, creates a fixture
+# Taskfile with sample files and directories, then exercises the engine and
+# every installed shell wrapper. Skips shells that are not installed.
+set -u
+
+here=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+root=$(cd "$here/../.." && pwd)
+
+# Temp dirs for the binary and the fixture; removed on exit (including on early
+# failure via the trap).
+bindir=$(mktemp -d)
+fixture=$(mktemp -d)
+trap 'rm -rf "$bindir" "$fixture"' EXIT
+
+# Build the binary under test.
+if ! go build -o "$bindir/task" "$root/cmd/task"; then
+  echo "failed to build task binary" >&2
+  exit 1
+fi
+export TASK_BIN="$bindir/task"
+# fish and PowerShell register completion for the command name `task`, so make
+# `task` on PATH resolve to the binary under test.
+export PATH="$bindir:$PATH"
+
+# Fixture: a Taskfile plus files/dirs so file/dir completion has real entries.
+cat > "$fixture/Taskfile.yml" <<'YML'
+version: '3'
+
+tasks:
+  build:
+    desc: Build it
+  deploy:
+    desc: Deploy it
+    aliases: [dep]
+    requires:
+      vars:
+        - name: ENV
+          enum: [dev, prod]
+        - REGION
+  docs:serve:
+    desc: Serve docs
+YML
+touch "$fixture/extra.yaml" "$fixture/notes.txt"
+mkdir -p "$fixture/sub" "$fixture/other"
+# A file inside sub/ so nested-path completion (keeping the dir prefix) is tested.
+touch "$fixture/sub/nested.yml"
+# A directory whose name holds a space, with its own Taskfile: shells must pass
+# the quoted `--dir` value to the engine unquoted, and quote it back on insert.
+mkdir -p "$fixture/with space"
+cat > "$fixture/with space/Taskfile.yml" <<'YML'
+version: '3'
+
+tasks:
+  spaced:
+    desc: Task from the spaced dir
+YML
+export TASK_FIXTURE="$fixture"
+
+# In strict mode (set TASK_COMPLETION_STRICT=1, used in CI) a missing shell is
+# a failure instead of a skip, so we never get a false pass when a shell the
+# environment was expected to provide (e.g. pwsh on CI runners) is absent.
+strict=${TASK_COMPLETION_STRICT:-}
+
+fails=0
+run() { # LABEL COMMAND...
+  echo "== $1 =="
+  "${@:2}" || fails=$((fails + 1))
+  echo
+}
+run_if() { # BIN LABEL COMMAND...
+  if command -v "$1" >/dev/null 2>&1; then run "${@:2}"; else skip "$2"; fi
+}
+skip() { # LABEL
+  if [[ -n "$strict" ]]; then
+    echo "== $1 == (MISSING — required under TASK_COMPLETION_STRICT)"
+    fails=$((fails + 1))
+  else
+    echo "== $1 == (skipped: not installed)"
+  fi
+  echo
+}
+
+# The engine/protocol itself is covered by the Go tests (completion/protocol_test.go
+# and internal/complete); these smokes only check how each shell wrapper
+# interprets the directive.
+run    "bash wrapper" bash "$here/wrapper.bash"
+run_if zsh  "zsh wrapper"  zsh  "$here/wrapper.zsh"
+run_if fish "fish wrapper" fish "$here/wrapper.fish"
+# --no-config-file: the user's own external completer must not interfere.
+run_if nu   "nu wrapper"   nu --no-config-file "$here/wrapper.nu"
+
+pwsh_bin=$(command -v pwsh || command -v pwsh-preview || true)
+if [[ -n "$pwsh_bin" ]]; then
+  run "powershell wrapper" "$pwsh_bin" -NoProfile -File "$here/wrapper.ps1"
+else
+  skip "powershell wrapper"
+fi
+
+if ((fails)); then
+  echo "completion tests: $fails suite(s) failed"
+  exit 1
+fi
+echo "completion tests: all suites passed"
diff --git a/completion/tests/wrapper.bash b/completion/tests/wrapper.bash
new file mode 100755
index 0000000000..1d6599a18e
--- /dev/null
+++ b/completion/tests/wrapper.bash
@@ -0,0 +1,83 @@
+#!/usr/bin/env bash
+# Smoke-tests how the bash wrapper routes each directive by stubbing the
+# bash-completion helpers (_filedir / compopt / …) and asserting what it calls.
+# Suggestion logic lives in the Go tests. Requires TASK_BIN and TASK_FIXTURE.
+set -u
+
+: "${TASK_BIN:?}"; : "${TASK_FIXTURE:?}"
+export TASK_EXE="$TASK_BIN"
+cd "$TASK_FIXTURE" || exit 1
+
+fails=0
+CAP=""
+
+# Stubs standing in for the bash-completion runtime.
+_init_completion() {
+  words=("${TEST_WORDS[@]}")
+  cword=$TEST_CWORD
+  cur="${TEST_WORDS[$TEST_CWORD]}"
+  prev="${TEST_WORDS[$((TEST_CWORD - 1))]}"
+  return 0
+}
+# Records the extension arg and the value of $cur it was called with, so tests
+# can assert the inline `--flag=` prefix was stripped before file completion.
+_filedir() { CAP+="filedir:$* cur=$cur"$'\n'; }
+compopt() { CAP+="compopt:$*"$'\n'; }
+__ltrim_colon_completions() { :; }
+
+source "$(dirname "${BASH_SOURCE[0]}")/../next/bash/task.bash"
+
+run() {
+  CAP=""
+  TEST_WORDS=("$@")
+  TEST_CWORD=$((${#TEST_WORDS[@]} - 1))
+  COMPREPLY=()
+  _task
+}
+
+reply_has() { # LABEL VALUE
+  local v
+  for v in "${COMPREPLY[@]}"; do [[ "$v" == "$2" ]] && { echo "  ok   $1"; return; }; done
+  echo "  FAIL $1 — '$2' missing from COMPREPLY: ${COMPREPLY[*]}"
+  fails=$((fails + 1))
+}
+cap_has() { # LABEL PATTERN
+  if [[ "$CAP" == *"$2"* ]]; then echo "  ok   $1"; else
+    echo "  FAIL $1 — expected '$2' in: $CAP"; fails=$((fails + 1)); fi
+}
+cap_hasnot() { # LABEL PATTERN
+  if [[ "$CAP" == *"$2"* ]]; then
+    echo "  FAIL $1 — '$2' should be absent in: $CAP"; fails=$((fails + 1)); else
+    echo "  ok   $1"; fi
+}
+
+echo "bash: :4 (NoFileComp) forwards candidates, no file fallback"
+run task ''
+reply_has  "candidate forwarded" build
+cap_hasnot "no file fallback"     "filedir:"
+
+echo "bash: :2 (NoSpace) disables the trailing space"
+run task deploy ''
+cap_has    "nospace applied"      "compopt:-o nospace"
+
+echo "bash: :8 (FilterFileExt) routes to extension-filtered files"
+run task --taskfile ''
+cap_has    "filedir ext glob"     "filedir:@(yml|yaml)"
+
+echo "bash: :16 (FilterDirs) routes to directory completion"
+run task --dir ''
+cap_has    "filedir -d"           "filedir:-d"
+
+echo "bash: :0 (Default) falls back to files"
+run task build -- ''
+cap_has    "filedir default"      "filedir:"
+
+echo "bash: inline --flag= strips the prefix before file completion"
+run task --taskfile=sub/x
+cap_has    "inline cur stripped"  "cur=sub/x"
+
+if ((fails)); then
+  echo "bash: $fails failure(s)"
+  exit 1
+fi
+echo "bash: all passed"
diff --git a/completion/tests/wrapper.fish b/completion/tests/wrapper.fish
new file mode 100755
index 0000000000..373406f81c
--- /dev/null
+++ b/completion/tests/wrapper.fish
@@ -0,0 +1,56 @@
+#!/usr/bin/env fish
+# Smoke-tests how the fish wrapper routes each directive, via `complete -C`
+# (real completions, no TTY). Suggestion logic lives in the Go tests.
+# Set up by run.sh: TASK_FIXTURE, and `task` on PATH = the binary under test.
+
+cd $TASK_FIXTURE
+source (dirname (status -f))/../next/fish/task.fish
+
+set -g fails 0
+
+function cands
+    complete -C $argv[1] | string split -f1 \t
+end
+
+function has # LABEL LINE VALUE
+    if contains -- $argv[3] (cands $argv[2])
+        echo "  ok   $argv[1]"
+    else
+        echo "  FAIL $argv[1] — '$argv[3]' missing from: "(cands $argv[2])
+        set fails (math $fails + 1)
+    end
+end
+
+function hasnot # LABEL LINE VALUE
+    if contains -- $argv[3] (cands $argv[2])
+        echo "  FAIL $argv[1] — '$argv[3]' should be absent"
+        set fails (math $fails + 1)
+    else
+        echo "  ok   $argv[1]"
+    end
+end
+
+echo "fish: :4 (NoFileComp) forwards candidates, offers no files"
+has    "candidate forwarded"  'task ' build
+hasnot "no file fallback"     'task ' notes.txt
+
+echo "fish: :16 (FilterDirs) offers directories only"
+has    "dir offered"          'task --dir ' sub/
+hasnot "no plain file"        'task --dir ' notes.txt
+
+echo "fish: :8 (FilterFileExt) filters by extension"
+has    "matching file"        'task --taskfile ' Taskfile.yml
+hasnot "non-matching file"    'task --taskfile ' notes.txt
+
+echo "fish: :0 (Default) falls back to files"
+has    "file offered"         'task build -- ' notes.txt
+
+echo "fish: inline --flag=path keeps the --flag= prefix"
+has    "inline nested"        'task --taskfile=sub/' --taskfile=sub/nested.yml
+hasnot "inline non-matching"  'task --taskfile=' --taskfile=notes.txt
+
+if test $fails -ne 0
+    echo "fish: $fails failure(s)"
+    exit 1
+end
+echo "fish: all passed"
diff --git a/completion/tests/wrapper.nu b/completion/tests/wrapper.nu
new file mode 100644
index 0000000000..4c030c1337
--- /dev/null
+++ b/completion/tests/wrapper.nu
@@ -0,0 +1,97 @@
+#!/usr/bin/env nu
+# Smoke-tests how the Nushell wrapper routes each directive (plus its own prefix
+# filtering), by driving the external completer it installs. Nushell only runs
+# external completers in the interactive REPL, so the closure is called directly.
+# Suggestion logic lives in the Go tests. Set up by run.sh: $env.TASK_FIXTURE,
+# and `task` on PATH = the binary under test.
+
+# `source` needs a parse-time constant path.
+const TASK_NU = (path self "../next/nu/task-completions.nu")
+
+# A completer installed before the wrapper is sourced, so the delegation path
+# can be asserted.
+$env.config.completions.external.completer = {|spans| [{ value: $"prev:($spans | first)" }] }
+
+source $TASK_NU
+
+cd $env.TASK_FIXTURE
+
+let completer = $env.config.completions.external.completer
+
+def cands [spans: list<string>] {
+  let out = (do $completer $spans)
+  if $out == null { [] } else { $out | get value }
+}
+
+def has [label: string, spans: list<string>, value: string] {
+  let values = (cands $spans)
+  if $value in $values {
+    print $"  ok   ($label)"
+    0
+  } else {
+    print $"  FAIL ($label) — '($value)' missing from: ($values | str join ' ')"
+    1
+  }
+}
+
+def hasnot [label: string, spans: list<string>, value: string] {
+  if $value in (cands $spans) {
+    print $"  FAIL ($label) — '($value)' should be absent"
+    1
+  } else {
+    print $"  ok   ($label)"
+    0
+  }
+}
+
+def check [label: string, ok: bool] {
+  if $ok {
+    print $"  ok   ($label)"
+    0
+  } else {
+    print $"  FAIL ($label)"
+    1
+  }
+}
+
+mut fails = 0
+
+print "nu: :4 (NoFileComp) forwards candidates, offers no files"
+$fails += (has    "candidate forwarded" [task ""] "build")
+$fails += (hasnot "no file fallback"    [task ""] "notes.txt")
+
+print "nu: filters candidates by the current word"
+$fails += (has    "prefix keeps match"  [task b] "build")
+$fails += (hasnot "prefix drops others" [task b] "deploy")
+
+print "nu: :16 (FilterDirs) offers directories only"
+$fails += (has    "dir offered"         [task --dir ""] $"sub(char path_sep)")
+$fails += (hasnot "no plain file"       [task --dir ""] "notes.txt")
+
+print "nu: :8 (FilterFileExt) filters by extension"
+$fails += (has    "matching file"       [task --taskfile ""] "Taskfile.yml")
+$fails += (hasnot "non-matching file"   [task --taskfile ""] "notes.txt")
+
+print "nu: nested path completion keeps the directory prefix"
+$fails += (has    "prefix kept"         [task --taskfile $"sub(char path_sep)"] $"sub(char path_sep)nested.yml")
+
+print "nu: inline --flag=path keeps the --flag= prefix"
+$fails += (has    "inline nested"       [task $"--taskfile=sub(char path_sep)"] $"--taskfile=sub(char path_sep)nested.yml")
+$fails += (hasnot "inline non-matching" [task "--taskfile="] "--taskfile=notes.txt")
+
+print "nu: :2|:32 (NoSpace|KeepOrder) keep the order the engine emitted"
+let vars = (cands [task deploy ""])
+$fails += (has   "required var offered" [task deploy ""] "ENV=dev")
+$fails += (check "declaration order kept" (($vars | enumerate | where item == "ENV=dev" | get 0.index) < ($vars | enumerate | where item == "REGION=" | get 0.index)))
+
+print "nu: :0 (Default) returns null so Nushell completes files itself"
+$fails += (check "null returned" ((do $completer [task build "--" ""]) == null))
+
+print "nu: other commands go to the previously installed completer"
+$fails += (has   "delegated"            [git status ""] "prev:git")
+
+if $fails != 0 {
+  print $"nu: ($fails) failure\(s\)"
+  exit 1
+}
+print "nu: all passed"
diff --git a/completion/tests/wrapper.ps1 b/completion/tests/wrapper.ps1
new file mode 100644
index 0000000000..8098cf7214
--- /dev/null
+++ b/completion/tests/wrapper.ps1
@@ -0,0 +1,68 @@
+# Smoke-tests how the PowerShell wrapper routes each directive (plus its own
+# prefix filtering), via the completion API (real completions, no TTY).
+# Suggestion logic lives in the Go tests. Set up by run.sh: $env:TASK_FIXTURE,
+# and `task` on PATH = the binary under test.
+
+Set-Location $env:TASK_FIXTURE
+. "$PSScriptRoot/../next/ps/task.ps1"
+
+$fails = 0
+
+function Cands($line) {
+	([System.Management.Automation.CommandCompletion]::CompleteInput($line, $line.Length, $null)).CompletionMatches |
+		ForEach-Object { $_.CompletionText }
+}
+
+function Has($label, $line, $value) {
+	if ((Cands $line) -contains $value) {
+		Write-Output "  ok   $label"
+	} else {
+		Write-Output "  FAIL $label — '$value' missing from: $((Cands $line) -join ' ')"
+		$script:fails++
+	}
+}
+
+function HasNot($label, $line, $value) {
+	if ((Cands $line) -contains $value) {
+		Write-Output "  FAIL $label — '$value' should be absent"
+		$script:fails++
+	} else {
+		Write-Output "  ok   $label"
+	}
+}
+
+Write-Output "powershell: :4 (NoFileComp) forwards candidates, offers no files"
+Has    "candidate forwarded" 'task ' 'build'
+HasNot "no file fallback"    'task ' 'notes.txt'
+
+Write-Output "powershell: filters candidates by the current word"
+Has    "prefix keeps match"  'task b' 'build'
+HasNot "prefix drops others" 'task b' 'deploy'
+
+Write-Output "powershell: :16 (FilterDirs) offers directories only"
+Has    "dir offered"         'task --dir ' 'sub'
+HasNot "no plain file"       'task --dir ' 'notes.txt'
+
+Write-Output "powershell: :8 (FilterFileExt) filters by extension"
+Has    "matching file"       'task --taskfile ' 'Taskfile.yml'
+HasNot "non-matching file"   'task --taskfile ' 'notes.txt'
+
+Write-Output "powershell: nested path completion keeps the directory prefix"
+Has    "prefix kept"         'task --taskfile sub/' 'sub/nested.yml'
+
+Write-Output "powershell: inline --flag=path keeps the --flag= prefix"
+Has    "inline nested"       'task --taskfile=sub/' '--taskfile=sub/nested.yml'
+HasNot "inline non-matching" 'task --taskfile=' '--taskfile=notes.txt'
+
+Write-Output "powershell: a quoted argument reaches the engine unquoted"
+Has    "single-quoted dir"   "task --dir 'with space' " 'spaced'
+Has    "double-quoted dir"   'task --dir "with space" ' 'spaced'
+
+Write-Output "powershell: a candidate holding a space is quoted for insertion"
+Has    "dir quoted"          'task --dir w' "'with space'"
+
+if ($fails -ne 0) {
+	Write-Output "powershell: $fails failure(s)"
+	exit 1
+}
+Write-Output "powershell: all passed"
diff --git a/completion/tests/wrapper.zsh b/completion/tests/wrapper.zsh
new file mode 100755
index 0000000000..42a0766bf3
--- /dev/null
+++ b/completion/tests/wrapper.zsh
@@ -0,0 +1,92 @@
+#!/usr/bin/env zsh
+# Smoke-tests how the zsh wrapper routes each directive by stubbing the
+# completion functions (_describe / _files / _path_files) and asserting what it
+# calls. Suggestion logic lives in the Go tests. Requires TASK_BIN, TASK_FIXTURE.
+
+export TASK_EXE=$TASK_BIN
+cd $TASK_FIXTURE
+
+integer fails=0
+local CAP
+compdef() { }   # no-op: we call _task directly, not through compinit
+
+# Mirrors the real signature — `_describe [-12JVoOx] [-t tag] descr array
+# [compadd-opt ...]` — so that an option landing in the wrong zone is visible.
+# zsh's own _describe forwards the trailing zone to compadd, where -J and -V
+# require a group name and would swallow the next argument.
+_describe() {
+    local -a flags
+    while [[ $1 == -* ]]; do
+        case $1 in
+            (-t) flags+=($1 $2); shift 2 ;;
+            (*)  flags+=($1); shift ;;
+        esac
+    done
+    local arr=$2                       # $1 is descr
+    CAP+="describe_flags:[${flags[*]}]"$'\n'
+    CAP+="compadd_opts:[${@[3,-1]}]"$'\n'
+    local c; for c in ${(P)arr}; do CAP+="cand:$c"$'\n'; done
+}
+_files()      { CAP+="files:$*"$'\n' }
+_path_files() { CAP+="path_files:$*"$'\n' }
+
+# Sourcing (not autoloading) defines _task and avoids the autoload first-call
+# quirk; the trailing `compdef` call is stubbed above.
+source ${0:A:h}/../next/zsh/_task
+
+run() {
+    CAP=""
+    local -a words=("$@")
+    integer CURRENT=$#words
+    local curcontext=":completion:complete:task:"
+    _task
+}
+
+has() { # LABEL PATTERN
+    if [[ "$CAP" == *"$2"* ]]; then
+        echo "  ok   $1"
+    else
+        echo "  FAIL $1 — expected '$2' in:"$'\n'"$CAP"
+        (( fails++ ))
+    fi
+}
+hasnot() { # LABEL PATTERN
+    if [[ "$CAP" == *"$2"* ]]; then
+        echo "  FAIL $1 — '$2' should be absent in:"$'\n'"$CAP"
+        (( fails++ ))
+    else
+        echo "  ok   $1"
+    fi
+}
+
+echo "zsh: :4 (NoFileComp) forwards candidates, no file fallback"
+run task ''
+has    "candidate forwarded"  "cand:build"
+hasnot "no file fallback"     "files:"
+
+# -V belongs to _describe itself. In the compadd zone it would take the next
+# argument as a group name, swallowing _describe's own `-d`, which offers its
+# internal _tmpd/_tmpm variables as candidates.
+echo "zsh: :2|:32 (NoSpace|KeepOrder) reach the right option zones"
+run task deploy ''
+has    "KeepOrder -> _describe -V"  "describe_flags:[-V"
+has    "NoSpace -> compadd -S"      "compadd_opts:[-S ]"
+
+echo "zsh: :8 (FilterFileExt) routes to extension-filtered files"
+run task --taskfile ''
+has    "files glob"            "files:"
+has    "yml in glob"           "yml"
+
+echo "zsh: :16 (FilterDirs) routes to directory completion"
+run task --dir ''
+has    "path_files -/"         "path_files:-/"
+
+echo "zsh: :0 (Default) falls back to files"
+run task build -- ''
+has    "files default"         "files:"
+
+if (( fails )); then
+    echo "zsh: $fails failure(s)"
+    exit 1
+fi
+echo "zsh: all passed"
diff --git a/internal/complete/complete.go b/internal/complete/complete.go
new file mode 100644
index 0000000000..ddeac16f72
--- /dev/null
+++ b/internal/complete/complete.go
@@ -0,0 +1,86 @@
+// Package complete implements the `task __complete` protocol consumed by the
+// shell completion wrappers. The protocol mirrors cobra v2 so a future
+// migration stays cheap.
+package complete
+
+import "os"
+
+// CommandName is the hidden subcommand the shell wrappers invoke to drive
+// completion: `task __complete <words...>`.
+const CommandName = "__complete"
+
+// IsActive reports whether the process was invoked in completion mode, i.e.
+// the first argument is the __complete subcommand.
+func IsActive() bool {
+	return len(os.Args) >= 2 && os.Args[1] == CommandName
+}
+
+// Directive mirrors cobra's ShellCompDirective bitfield. It is emitted on the
+// final output line as `:<directive>` and tells the shell wrapper how to treat
+// the suggestions (file fallback, trailing space, ordering, …).
+type Directive int
+
+const (
+	// DirectiveDefault leaves the shell to perform its default file completion.
+	DirectiveDefault Directive = 0
+	// DirectiveError signals an error; the shell should not offer completion.
+	// Reserved by the protocol: the engine never emits it, since a failure to
+	// load the Taskfile still leaves flags worth completing.
+	DirectiveError Directive = 1 << 0
+	// DirectiveNoSpace prevents the shell from appending a space after the
+	// suggestion (e.g. so `VAR=` can be followed by a value).
+	DirectiveNoSpace Directive = 1 << 1
+	// DirectiveNoFileComp disables the shell's fallback file completion.
+	DirectiveNoFileComp Directive = 1 << 2
+	// DirectiveFilterFileExt restricts file completion to the emitted extensions.
+	DirectiveFilterFileExt Directive = 1 << 3
+	// DirectiveFilterDirs restricts completion to directories.
+	DirectiveFilterDirs Directive = 1 << 4
+	// DirectiveKeepOrder tells the shell to preserve the emitted order instead
+	// of sorting alphabetically.
+	DirectiveKeepOrder Directive = 1 << 5
+)
+
+// Suggestion is a single completion candidate: the Value inserted on the
+// command line and an optional human-readable Description.
+type Suggestion struct {
+	Value       string
+	Description string
+}
+
+// Options tunes what the engine emits. The fields are named after the
+// __complete control flags so the zero value is the standard set: aliases and
+// descriptions shown.
+type Options struct {
+	NoAliases      bool
+	NoDescriptions bool
+}
+
+// Completion-control flags. Shell wrappers prepend these to the __complete
+// invocation to tune the output (e.g. zsh maps its show-aliases / verbose
+// zstyles to them). They are consumed by ParseOptions before the remaining
+// args are treated as the user's command line.
+const (
+	FlagNoAliases      = "--no-aliases"
+	FlagNoDescriptions = "--no-descriptions"
+)
+
+// ParseOptions peels the leading completion-control flags off args and returns
+// the resulting Options together with the remaining args (the user's command
+// line to complete). Only leading flags are consumed, so a `--no-aliases` typed
+// by the user further down the line is left untouched.
+func ParseOptions(args []string) (Options, []string) {
+	var opts Options
+	for len(args) > 0 {
+		switch args[0] {
+		case FlagNoAliases:
+			opts.NoAliases = true
+		case FlagNoDescriptions:
+			opts.NoDescriptions = true
+		default:
+			return opts, args
+		}
+		args = args[1:]
+	}
+	return opts, args
+}
diff --git a/internal/complete/complete_test.go b/internal/complete/complete_test.go
new file mode 100644
index 0000000000..b3d9520dcc
--- /dev/null
+++ b/internal/complete/complete_test.go
@@ -0,0 +1,416 @@
+package complete_test
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/pflag"
+	"github.com/stretchr/testify/require"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/complete"
+)
+
+func newTestFlagSet() *pflag.FlagSet {
+	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	var b bool
+	var s string
+	fs.BoolVarP(&b, "list-all", "a", false, "Lists all tasks")
+	fs.BoolVarP(&b, "list", "l", false, "Lists tasks with descriptions")
+	fs.BoolVarP(&b, "verbose", "v", false, "Verbose mode")
+	fs.StringVarP(&s, "taskfile", "t", "", "Taskfile path")
+	fs.StringVarP(&s, "dir", "d", "", "Run dir")
+	fs.StringVarP(&s, "output", "o", "", "Output style")
+	fs.StringVar(&s, "sort", "", "Sort order")
+	fs.StringVar(&s, "cacert", "", "CA cert path")
+	return fs
+}
+
+const testTaskfile = `version: '3'
+
+vars:
+  ALLOWED_ENVS:
+    - dev
+    - staging
+    - prod
+
+tasks:
+  deploy:
+    desc: Deploy the application
+    aliases: [dep, ship]
+    requires:
+      vars:
+        - name: ENV
+          enum:
+            - dev
+            - staging
+            - prod
+        - REGION
+    cmds:
+      - 'echo {{.ENV}} {{.REGION}}'
+
+  build:
+    desc: Build it
+    cmds:
+      - 'echo build'
+
+  dynenum:
+    desc: Dynamic enum
+    requires:
+      vars:
+        - name: ENV
+          enum:
+            ref: .ALLOWED_ENVS
+    cmds:
+      - 'echo {{.ENV}}'
+
+  docs:serve:
+    desc: Serve docs locally
+    cmds:
+      - 'echo serving'
+`
+
+const wildcardTaskfile = `version: '3'
+
+tasks:
+  wildcard-*:
+    cmds:
+      - 'echo {{index .MATCH 0}}'
+
+  wildcard-*-*:
+    cmds:
+      - 'echo {{index .MATCH 0}}'
+
+  '*-wildcard-*':
+    cmds:
+      - 'echo {{index .MATCH 0}}'
+
+  start-*:
+    desc: Start a service
+    aliases: [s-*]
+    cmds:
+      - 'echo {{index .MATCH 0}}'
+
+  build:
+    desc: Build it
+    cmds:
+      - 'echo build'
+`
+
+func setupExecutor(t *testing.T) *task.Executor {
+	t.Helper()
+	return setupExecutorWith(t, testTaskfile)
+}
+
+func setupExecutorWith(t *testing.T, taskfile string) *task.Executor {
+	t.Helper()
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(taskfile), 0o644))
+
+	e := task.NewExecutor(
+		task.WithDir(dir),
+		task.WithStdout(io.Discard),
+		task.WithStderr(io.Discard),
+		task.WithVersionCheck(false),
+	)
+	require.NoError(t, e.Setup())
+	return e
+}
+
+func TestComplete_TaskNames(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{""}, complete.Options{})
+
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dep", "ship", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+	require.Contains(t, descriptions(suggs), "Deploy the application")
+}
+
+func TestComplete_WildcardTaskNames(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutorWith(t, wildcardTaskfile)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{""}, complete.Options{})
+
+	// Patterns are cut at their first `*`: `wildcard-*` and `wildcard-*-*`
+	// collapse into one candidate, and `*-wildcard-*` leaves nothing to insert.
+	require.Equal(t, []string{"build", "start-", "s-", "wildcard-"}, values(suggs))
+	require.Equal(t, complete.DirectiveNoSpace|complete.DirectiveNoFileComp, dir)
+	// Without a desc, the pattern says what the prefix stands for.
+	require.Contains(t, descriptions(suggs), "wildcard-*")
+
+	suggs, _ = complete.Complete(e, newTestFlagSet(), []string{""}, complete.Options{NoDescriptions: true})
+	require.Equal(t, []string{"", "", "", ""}, descriptions(suggs))
+}
+
+func TestComplete_AliasResolvesToTaskVars(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"dep", ""}, complete.Options{})
+	require.Equal(t, []string{"ENV=dev", "ENV=staging", "ENV=prod", "REGION="}, values(suggs))
+	require.Equal(t, complete.DirectiveNoSpace|complete.DirectiveNoFileComp|complete.DirectiveKeepOrder, dir)
+}
+
+func TestComplete_StaticEnum(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"deploy", ""}, complete.Options{})
+
+	require.Equal(t, []string{"ENV=dev", "ENV=staging", "ENV=prod", "REGION="}, values(suggs))
+	require.Equal(t, complete.DirectiveNoSpace|complete.DirectiveNoFileComp|complete.DirectiveKeepOrder, dir)
+}
+
+func TestComplete_EnumRef(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, _ := complete.Complete(e, newTestFlagSet(), []string{"dynenum", ""}, complete.Options{})
+	require.Equal(t, []string{"ENV=dev", "ENV=staging", "ENV=prod"}, values(suggs))
+}
+
+func TestComplete_NoRequires(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"build", ""}, complete.Options{})
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_FlagValueNotConfusedWithTaskName(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--dir", "deploy", ""}, complete.Options{})
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dep", "ship", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_NamespacedTaskName(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"docs:serve", ""}, complete.Options{})
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_FlagValueInlineEquals(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--output="}, complete.Options{})
+	// Inline form returns full `--output=value` tokens so the shell can match
+	// against the whole current word.
+	require.Equal(t, []string{"--output=interleaved", "--output=group", "--output=prefixed"}, values(suggs))
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_AfterDash(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"deploy", "--", ""}, complete.Options{})
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveDefault, dir)
+}
+
+func TestComplete_FlagNames(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"-"}, complete.Options{})
+	require.NotEmpty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+
+	vals := values(suggs)
+	require.Contains(t, vals, "--list-all")
+	require.Contains(t, vals, "--taskfile")
+	require.Contains(t, vals, "-a")
+}
+
+func TestComplete_EnumFlagValue_Output(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--output", ""}, complete.Options{})
+	require.Equal(t, []string{"interleaved", "group", "prefixed"}, values(suggs))
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_EnumFlagValue_Sort(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, _ := complete.Complete(e, newTestFlagSet(), []string{"--sort", ""}, complete.Options{})
+	require.Equal(t, []string{"default", "alphanumeric", "none"}, values(suggs))
+}
+
+func TestComplete_PathFlag_Taskfile(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--taskfile", ""}, complete.Options{})
+	require.Equal(t, []string{"yml", "yaml"}, values(suggs))
+	require.Equal(t, complete.DirectiveFilterFileExt, dir)
+}
+
+func TestComplete_PathFlag_Dir(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--dir", ""}, complete.Options{})
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveFilterDirs, dir)
+}
+
+func TestComplete_PathFlag_Cacert(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--cacert", ""}, complete.Options{})
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveDefault, dir)
+}
+
+func TestComplete_NilExecutor(t *testing.T) {
+	t.Parallel()
+
+	suggs, dir := complete.Complete(nil, newTestFlagSet(), []string{"-"}, complete.Options{})
+	require.NotEmpty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_NoAliases(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	opts := complete.Options{NoAliases: true}
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{""}, opts)
+
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	require.NotContains(t, values(suggs), "dep")
+	require.NotContains(t, values(suggs), "ship")
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_NoDescriptions(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	opts := complete.Options{NoDescriptions: true}
+	suggs, _ := complete.Complete(e, newTestFlagSet(), []string{""}, opts)
+
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dep", "ship", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	for _, d := range descriptions(suggs) {
+		require.Empty(t, d)
+	}
+}
+
+func TestParseOptions(t *testing.T) {
+	t.Parallel()
+
+	t.Run("defaults", func(t *testing.T) {
+		t.Parallel()
+		opts, rest := complete.ParseOptions([]string{"deploy", ""})
+		require.Equal(t, complete.Options{}, opts)
+		require.Equal(t, []string{"deploy", ""}, rest)
+	})
+
+	t.Run("both flags", func(t *testing.T) {
+		t.Parallel()
+		opts, rest := complete.ParseOptions([]string{"--no-aliases", "--no-descriptions", "deploy", ""})
+		require.True(t, opts.NoAliases)
+		require.True(t, opts.NoDescriptions)
+		require.Equal(t, []string{"deploy", ""}, rest)
+	})
+
+	t.Run("only leading flags consumed", func(t *testing.T) {
+		t.Parallel()
+		// A flag appearing after the user's words is left in the command line.
+		opts, rest := complete.ParseOptions([]string{"deploy", "--no-aliases"})
+		require.False(t, opts.NoAliases)
+		require.Equal(t, []string{"deploy", "--no-aliases"}, rest)
+	})
+}
+
+func TestNeedsTaskfile(t *testing.T) {
+	t.Parallel()
+
+	tests := map[string]struct {
+		args []string
+		want bool
+	}{
+		"task name":            {[]string{""}, true},
+		"partial task name":    {[]string{"bui"}, true},
+		"task var":             {[]string{"deploy", ""}, true},
+		"value flag then name": {[]string{"--dir", "/tmp", ""}, true},
+		"flag name":            {[]string{"-"}, false},
+		"long flag name":       {[]string{"--li"}, false},
+		"inline flag value":    {[]string{"--output="}, false},
+		"flag value":           {[]string{"--output", ""}, false},
+		"path flag value":      {[]string{"--taskfile", ""}, false},
+		"after dash":           {[]string{"deploy", "--", ""}, false},
+	}
+
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			require.Equal(t, tt.want, complete.NeedsTaskfile(tt.args, newTestFlagSet()))
+		})
+	}
+}
+
+func TestWrite_Format(t *testing.T) {
+	t.Parallel()
+
+	var buf bytes.Buffer
+	complete.Write(&buf, []complete.Suggestion{
+		{Value: "deploy", Description: "Deploy the app"},
+		{Value: "build"},
+	}, complete.DirectiveNoSpace|complete.DirectiveNoFileComp)
+	require.Equal(t, "deploy\tDeploy the app\nbuild\n:6\n", buf.String())
+}
+
+func TestWrite_EmptyWithDirective(t *testing.T) {
+	t.Parallel()
+
+	var buf bytes.Buffer
+	complete.Write(&buf, nil, complete.DirectiveFilterDirs)
+	require.Equal(t, ":16\n", buf.String())
+}
+
+func values(suggs []complete.Suggestion) []string {
+	out := make([]string, 0, len(suggs))
+	for _, s := range suggs {
+		out = append(out, s.Value)
+	}
+	return out
+}
+
+func descriptions(suggs []complete.Suggestion) []string {
+	out := make([]string, 0, len(suggs))
+	for _, s := range suggs {
+		out = append(out, s.Description)
+	}
+	return out
+}
diff --git a/internal/complete/context.go b/internal/complete/context.go
new file mode 100644
index 0000000000..56c8397dec
--- /dev/null
+++ b/internal/complete/context.go
@@ -0,0 +1,86 @@
+package complete
+
+import (
+	"slices"
+	"strings"
+
+	"github.com/spf13/pflag"
+)
+
+type completionContext struct {
+	toComplete string
+	prev       string
+	afterDash  bool
+}
+
+// parseContext infers the cursor position from args alone. It deliberately
+// avoids the task list so flag completion never pays to load it; the task word
+// is resolved separately by detectTaskName only once a task context is reached.
+func parseContext(args []string) completionContext {
+	ctx := completionContext{}
+	if len(args) == 0 {
+		return ctx
+	}
+
+	ctx.toComplete = args[len(args)-1]
+	if len(args) >= 2 {
+		ctx.prev = args[len(args)-2]
+	}
+
+	ctx.afterDash = slices.Contains(args[:len(args)-1], "--")
+
+	return ctx
+}
+
+// flagValue returns the flag whose value the cursor is completing, as in
+// `task --output <tab>`.
+func (ctx completionContext) flagValue(fs *pflag.FlagSet) *pflag.Flag {
+	if f := matchFlagName(fs, ctx.prev); f != nil && flagTakesValue(f) {
+		return f
+	}
+	return nil
+}
+
+// inTaskContext reports whether the cursor completes a task name or a task
+// variable, rather than a flag, a flag value or a word after `--`.
+func (ctx completionContext) inTaskContext(fs *pflag.FlagSet) bool {
+	return !ctx.afterDash && ctx.flagValue(fs) == nil && !strings.HasPrefix(ctx.toComplete, "-")
+}
+
+// detectTaskName scans args for the task word the cursor is completing under
+// (e.g. "deploy" in `task deploy ENV=<tab>`). fs is needed to skip the word
+// following a value-taking flag, otherwise `task --dir deploy` would mistake
+// "deploy" (the directory) for a task name.
+func detectTaskName(args []string, knownTasks []string, fs *pflag.FlagSet) string {
+	if len(args) <= 1 {
+		return ""
+	}
+
+	taskName := ""
+	skipNext := false
+	for _, w := range args[:len(args)-1] {
+		if skipNext {
+			skipNext = false
+			continue
+		}
+		if w == "--" {
+			return taskName
+		}
+		if strings.HasPrefix(w, "-") {
+			if !strings.Contains(w, "=") {
+				if f := matchFlagName(fs, w); f != nil && flagTakesValue(f) {
+					skipNext = true
+				}
+			}
+			continue
+		}
+		if strings.Contains(w, "=") {
+			continue
+		}
+		if slices.Contains(knownTasks, w) {
+			taskName = w
+		}
+	}
+
+	return taskName
+}
diff --git a/internal/complete/engine.go b/internal/complete/engine.go
new file mode 100644
index 0000000000..804a74c8e4
--- /dev/null
+++ b/internal/complete/engine.go
@@ -0,0 +1,229 @@
+package complete
+
+import (
+	"strings"
+
+	"github.com/spf13/pflag"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/refs"
+	"github.com/go-task/task/v3/internal/slicesext"
+	"github.com/go-task/task/v3/internal/sort"
+	"github.com/go-task/task/v3/taskfile/ast"
+)
+
+// Complete is the single entry point used by `task __complete`. e may be nil
+// when the Taskfile failed to load; flag completion still works in that case.
+func Complete(e *task.Executor, fs *pflag.FlagSet, args []string, opts Options) ([]Suggestion, Directive) {
+	ctx := parseContext(args)
+
+	if ctx.afterDash {
+		return nil, DirectiveDefault
+	}
+
+	if flag := ctx.flagValue(fs); flag != nil {
+		return completeFlagValue(flag.Name, "")
+	}
+
+	if strings.HasPrefix(ctx.toComplete, "-") {
+		if flagWord, _, ok := strings.Cut(ctx.toComplete, "="); ok {
+			if f := matchFlagName(fs, flagWord); f != nil && flagTakesValue(f) {
+				// Return full `--flag=value` candidates: shells match/insert
+				// against the whole current token, so bare values never match.
+				return completeFlagValue(f.Name, flagWord+"=")
+			}
+		}
+		return listFlags(fs), DirectiveNoFileComp
+	}
+
+	// A task-var context needs the task list to spot the task word under the
+	// cursor, but that only exists once a prior word is present. Guard on
+	// len(args) > 1 so `task <tab>` / `task buil<tab>` never pay to build it.
+	if e != nil && e.Taskfile != nil && len(args) > 1 {
+		if taskName := detectTaskName(args, taskNames(e), fs); taskName != "" {
+			return completeTaskVars(e, taskName)
+		}
+	}
+
+	return completeTaskNames(e, opts)
+}
+
+// NeedsTaskfile reports whether completing args requires a loaded Taskfile.
+// Flag-name and flag-value completion (and words after `--`) do not, so the
+// caller can skip the potentially expensive Taskfile parse for those keystrokes.
+func NeedsTaskfile(args []string, fs *pflag.FlagSet) bool {
+	return parseContext(args).inTaskContext(fs)
+}
+
+func taskNames(e *task.Executor) []string {
+	if e == nil || e.Taskfile == nil {
+		return nil
+	}
+	var out []string
+	for t := range e.Taskfile.Tasks.Values(nil) {
+		if t.Internal {
+			continue
+		}
+		name, _ := suggestedName(t.Task)
+		out = append(out, name)
+		for _, alias := range t.Aliases {
+			name, _ := suggestedName(alias)
+			out = append(out, name)
+		}
+	}
+	return out
+}
+
+func completeTaskNames(e *task.Executor, opts Options) ([]Suggestion, Directive) {
+	if e == nil || e.Taskfile == nil {
+		return nil, DirectiveNoFileComp
+	}
+	tasks := listTasks(e, opts)
+	desc := func(t *ast.Task) string {
+		if opts.NoDescriptions {
+			return ""
+		}
+		return t.Desc
+	}
+
+	out := make([]Suggestion, 0, len(tasks))
+	seen := make(map[string]bool, len(tasks))
+	anyPartial := false
+	add := func(name, desc string) {
+		value, partial := suggestedName(name)
+		// `*-wildcard-*` has no prefix to insert, and two patterns can share
+		// one (`wildcard-*` and `wildcard-*-*`).
+		if value == "" || seen[value] {
+			return
+		}
+		seen[value] = true
+		if partial {
+			anyPartial = true
+			if desc == "" && !opts.NoDescriptions {
+				desc = name
+			}
+		}
+		out = append(out, Suggestion{Value: value, Description: desc})
+	}
+
+	for _, t := range tasks {
+		add(t.Task, desc(t))
+		if opts.NoAliases {
+			continue
+		}
+		for _, alias := range t.Aliases {
+			add(alias, desc(t))
+		}
+	}
+
+	// A truncated pattern is only half a name: the shell must leave the cursor
+	// against it so the rest can be typed.
+	if anyPartial {
+		return out, DirectiveNoSpace | DirectiveNoFileComp
+	}
+	return out, DirectiveNoFileComp
+}
+
+// listTasks returns the tasks to suggest. Descriptions are the only compiled
+// field read, so GetTaskList — which compiles every task, on every keystroke —
+// is only worth its cost when a description holds a template.
+func listTasks(e *task.Executor, opts Options) []*ast.Task {
+	sorter := e.TaskSorter
+	if sorter == nil {
+		sorter = sort.AlphaNumericWithRootTasksFirst
+	}
+
+	out := make([]*ast.Task, 0, e.Taskfile.Tasks.Len())
+	templated := false
+	for t := range e.Taskfile.Tasks.Values(sorter) {
+		if t.Internal {
+			continue
+		}
+		templated = templated || strings.Contains(t.Desc, "{{")
+		out = append(out, t)
+	}
+
+	if !opts.NoDescriptions && templated {
+		// On error, the uncompiled tasks keep a single broken task from emptying
+		// the whole suggestion list.
+		if compiled, err := e.GetTaskList(task.FilterOutInternal); err == nil {
+			return compiled
+		}
+	}
+	return out
+}
+
+// suggestedName returns the text to insert for a task name, and whether that
+// text is partial: a wildcard pattern is truncated at its first `*`, since the
+// pattern itself is not a runnable name — running it leaves `.MATCH` empty.
+func suggestedName(name string) (string, bool) {
+	if prefix, _, ok := strings.Cut(name, "*"); ok {
+		return prefix, true
+	}
+	return strings.TrimRight(name, ":"), false
+}
+
+// completeFlagValue completes the value of a value-taking flag. prefix is empty
+// for the separate-argument form (`--output <TAB>`) and `<flag>=` for the inline
+// form (`--output=<TAB>`), so enum candidates come back as full `--output=value`
+// tokens the shell can match against the current word.
+func completeFlagValue(flagName, prefix string) ([]Suggestion, Directive) {
+	// Absent keys yield the zero value (DirectiveDefault), which falls through
+	// to the enum lookup below.
+	switch flagDirective[flagName] {
+	case DirectiveFilterFileExt:
+		exts := slicesext.Convert(taskfileExtensions, func(ext string) Suggestion {
+			return Suggestion{Value: ext}
+		})
+		return exts, DirectiveFilterFileExt
+	case DirectiveFilterDirs:
+		return nil, DirectiveFilterDirs
+	}
+
+	if values, ok := flagEnums[flagName]; ok {
+		out := slicesext.Convert(values, func(v string) Suggestion {
+			return Suggestion{Value: prefix + v}
+		})
+		return out, DirectiveNoFileComp
+	}
+
+	return nil, DirectiveDefault
+}
+
+func completeTaskVars(e *task.Executor, taskName string) ([]Suggestion, Directive) {
+	compiled, err := e.FastCompiledTask(&task.Call{Task: taskName})
+	if err != nil || compiled == nil || compiled.Requires == nil {
+		return nil, DirectiveNoFileComp
+	}
+
+	out := make([]Suggestion, 0, 8)
+	for _, v := range compiled.Requires.Vars {
+		if v == nil || v.Name == "" {
+			continue
+		}
+		values := enumValues(v, compiled.Vars)
+		if len(values) == 0 {
+			out = append(out, Suggestion{Value: v.Name + "="})
+			continue
+		}
+		for _, val := range values {
+			out = append(out, Suggestion{Value: v.Name + "=" + val})
+		}
+	}
+	if len(out) == 0 {
+		return nil, DirectiveNoFileComp
+	}
+	// KeepOrder preserves the declaration order of the `requires` block instead
+	// of letting the shell sort the variables alphabetically.
+	return out, DirectiveNoSpace | DirectiveNoFileComp | DirectiveKeepOrder
+}
+
+// enumValues returns the allowed values of a required var, resolving an
+// `enum.ref` against vars.
+func enumValues(v *ast.VarsWithValidation, vars *ast.Vars) []string {
+	resolved := refs.ResolveEnum(v, vars)
+	if resolved.Enum == nil {
+		return nil
+	}
+	return resolved.Enum.Value
+}
diff --git a/internal/complete/flags.go b/internal/complete/flags.go
new file mode 100644
index 0000000000..b9604aa370
--- /dev/null
+++ b/internal/complete/flags.go
@@ -0,0 +1,76 @@
+package complete
+
+import (
+	"slices"
+	"strings"
+
+	"github.com/spf13/pflag"
+)
+
+// completionShells are the values --completion accepts. The scripts themselves
+// are served by the root package, which embeds them; TestCompletionShells keeps
+// the two in step.
+var completionShells = []string{"bash", "zsh", "fish", "powershell", "nu"}
+
+// flagEnums lists allowed values for enum-style flags. Keep in sync with the
+// help strings in internal/flags/flags.go.
+var flagEnums = map[string][]string{
+	"output":         {"interleaved", "group", "prefixed"},
+	"sort":           {"default", "alphanumeric", "none"},
+	"completion":     completionShells,
+	"new-completion": completionShells,
+}
+
+// flagDirective maps value-taking flags to a file-completion directive. Any
+// flag absent here falls back to the shell's default file completion.
+var flagDirective = map[string]Directive{
+	"taskfile":         DirectiveFilterFileExt,
+	"dir":              DirectiveFilterDirs,
+	"remote-cache-dir": DirectiveFilterDirs,
+}
+
+var taskfileExtensions = []string{"yml", "yaml"}
+
+// flagTakesValue is false for boolean switches (NoOptDefVal == "true").
+func flagTakesValue(f *pflag.Flag) bool {
+	return f.NoOptDefVal == ""
+}
+
+// listFlags walks fs at call time so experiment-gated flags appear or
+// disappear based on the active experiments.
+func listFlags(fs *pflag.FlagSet) []Suggestion {
+	if fs == nil {
+		return nil
+	}
+	out := make([]Suggestion, 0, 64)
+	fs.VisitAll(func(f *pflag.Flag) {
+		if f.Hidden || f.Deprecated != "" {
+			return
+		}
+		out = append(out, Suggestion{
+			Value:       "--" + f.Name,
+			Description: f.Usage,
+		})
+		if f.Shorthand != "" {
+			out = append(out, Suggestion{
+				Value:       "-" + f.Shorthand,
+				Description: f.Usage,
+			})
+		}
+	})
+	slices.SortFunc(out, func(a, b Suggestion) int { return strings.Compare(a.Value, b.Value) })
+	return out
+}
+
+func matchFlagName(fs *pflag.FlagSet, word string) *pflag.Flag {
+	if fs == nil {
+		return nil
+	}
+	switch {
+	case strings.HasPrefix(word, "--"):
+		return fs.Lookup(strings.TrimPrefix(word, "--"))
+	case strings.HasPrefix(word, "-") && len(word) == 2:
+		return fs.ShorthandLookup(word[1:])
+	}
+	return nil
+}
diff --git a/internal/complete/output.go b/internal/complete/output.go
new file mode 100644
index 0000000000..158a539c6b
--- /dev/null
+++ b/internal/complete/output.go
@@ -0,0 +1,31 @@
+package complete
+
+import (
+	"fmt"
+	"io"
+	"strings"
+)
+
+// Write emits the cobra-v2 completion protocol: one `value\tdescription` (or
+// bare `value`) per suggestion, followed by a trailing `:<directive>` line
+// that shell wrappers split off even when there are zero suggestions.
+func Write(w io.Writer, suggs []Suggestion, dir Directive) {
+	for _, s := range suggs {
+		value := sanitize(s.Value)
+		desc := sanitize(s.Description)
+		if desc == "" {
+			fmt.Fprintln(w, value)
+			continue
+		}
+		fmt.Fprintf(w, "%s\t%s\n", value, desc)
+	}
+	fmt.Fprintf(w, ":%d\n", dir)
+}
+
+// completionSanitizer collapses the bytes that would corrupt the line-based
+// protocol (a value's tab/newline would be read as a field/record separator).
+var completionSanitizer = strings.NewReplacer("\n", " ", "\r", " ", "\t", " ")
+
+func sanitize(s string) string {
+	return completionSanitizer.Replace(s)
+}
diff --git a/internal/flags/flags.go b/internal/flags/flags.go
index 9e43d4a943..13f28b536e 100644
--- a/internal/flags/flags.go
+++ b/internal/flags/flags.go
@@ -14,6 +14,7 @@ import (
 	"github.com/go-task/task/v3"
 	"github.com/go-task/task/v3/errors"
 	"github.com/go-task/task/v3/experiments"
+	"github.com/go-task/task/v3/internal/complete"
 	"github.com/go-task/task/v3/internal/env"
 	"github.com/go-task/task/v3/internal/sort"
 	"github.com/go-task/task/v3/taskfile/ast"
@@ -48,6 +49,7 @@ var (
 	Help                bool
 	Init                bool
 	Completion          string
+	NewCompletion       string
 	List                bool
 	ListAll             bool
 	ListJson            bool
@@ -124,6 +126,7 @@ func init() {
 	pflag.BoolVarP(&Help, "help", "h", false, "Shows Task usage.")
 	pflag.BoolVarP(&Init, "init", "i", false, "Creates a new Taskfile.yml in the current folder.")
 	pflag.StringVar(&Completion, "completion", "", "Generates shell completion script.")
+	pflag.StringVar(&NewCompletion, "new-completion", "", "Generates the new (experimental) shell completion script, powered by the `task __complete` engine.")
 	pflag.BoolVarP(&List, "list", "l", false, "Lists tasks with description of current Taskfile.")
 	pflag.BoolVarP(&ListAll, "list-all", "a", false, "Lists tasks with or without a description.")
 	pflag.BoolVarP(&ListJson, "json", "j", false, "Formats task list as JSON.")
@@ -174,6 +177,19 @@ func init() {
 		pflag.BoolVarP(&ForceAll, "force", "f", false, "Forces execution even when the task is up-to-date.")
 	}
 
+	// In completion mode the words being completed are parsed leniently: they
+	// hold partially typed and unknown flags, yet the values of the flags that
+	// decide which Taskfile is loaded (--dir, --taskfile, the remote options, …)
+	// must reach the engine. ContinueOnError returns the error without printing
+	// anything, and flags parsed before it are kept.
+	if complete.IsActive() {
+		_, words := complete.ParseOptions(os.Args[2:])
+		pflag.CommandLine.Init(pflag.CommandLine.Name(), pflag.ContinueOnError)
+		pflag.CommandLine.ParseErrorsAllowlist.UnknownFlags = true
+		_ = pflag.CommandLine.Parse(words)
+		return
+	}
+
 	pflag.Parse()
 
 	// Auto-detect color based on environment when not explicitly configured
diff --git a/internal/refs/refs.go b/internal/refs/refs.go
new file mode 100644
index 0000000000..a7898a82ae
--- /dev/null
+++ b/internal/refs/refs.go
@@ -0,0 +1,72 @@
+// Package refs resolves the `ref` fields of a Taskfile into concrete values.
+// A ref is a template expression evaluated against a var set, which callers
+// then expect as a list: `for: matrix` rows and `requires` enums.
+package refs
+
+import (
+	"fmt"
+
+	"github.com/go-task/task/v3/internal/slicesext"
+	"github.com/go-task/task/v3/internal/templater"
+	"github.com/go-task/task/v3/taskfile/ast"
+)
+
+// AsList converts a resolved ref into a []any. A ref does not always resolve to
+// a []any: lists declared in a Taskfile do, but template functions such as
+// `keys` and `splitList` return a []string. The accepted types mirror the list
+// types itemsFromFor supports.
+func AsList(v any) ([]any, bool) {
+	switch value := v.(type) {
+	case []any:
+		return value, true
+	case []string:
+		return slicesext.AsAny(value), true
+	case []int:
+		return slicesext.AsAny(value), true
+	}
+	return nil, false
+}
+
+// ResolveEnums fills in the values of every `enum.ref` in requires.
+func ResolveEnums(requires *ast.Requires, cache *templater.Cache) error {
+	if requires == nil || len(requires.Vars) == 0 {
+		return nil
+	}
+	for _, v := range requires.Vars {
+		if v.Enum == nil || v.Enum.Ref == "" {
+			continue
+		}
+		resolved := templater.ResolveRef(v.Enum.Ref, cache)
+		if cache.Err() != nil {
+			return cache.Err()
+		}
+		arr, ok := AsList(resolved)
+		if !ok {
+			return fmt.Errorf("enum reference %q must resolve to a list", v.Enum.Ref)
+		}
+		strValues := make([]string, 0, len(arr))
+		for _, item := range arr {
+			s, ok := item.(string)
+			if !ok {
+				return fmt.Errorf("enum reference %q must contain only strings", v.Enum.Ref)
+			}
+			strValues = append(strValues, s)
+		}
+		v.Enum.Value = strValues
+	}
+	return nil
+}
+
+// ResolveEnum returns a copy of v with its enum ref resolved into concrete
+// values, so a caller can offer them as a list. Refs that depend on dynamic
+// vars may not resolve here: v is then returned with its enum values empty,
+// which the interactive prompter treats as free-form input.
+func ResolveEnum(v *ast.VarsWithValidation, vars *ast.Vars) *ast.VarsWithValidation {
+	if v.Enum == nil || v.Enum.Ref == "" || len(v.Enum.Value) > 0 {
+		return v
+	}
+	vCopy := v.DeepCopy()
+	cache := &templater.Cache{Vars: vars}
+	_ = ResolveEnums(&ast.Requires{Vars: []*ast.VarsWithValidation{vCopy}}, cache)
+	return vCopy
+}
diff --git a/requires_internal_test.go b/internal/refs/refs_test.go
similarity index 55%
rename from requires_internal_test.go
rename to internal/refs/refs_test.go
index fcfd6a1af9..202a52f544 100644
--- a/requires_internal_test.go
+++ b/internal/refs/refs_test.go
@@ -1,14 +1,15 @@
-package task
+package refs_test
 
 import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/go-task/task/v3/internal/refs"
 	"github.com/go-task/task/v3/taskfile/ast"
 )
 
-func TestResolveEnumRefForPrompt(t *testing.T) {
+func TestResolveEnum(t *testing.T) {
 	t.Parallel()
 
 	vars := ast.NewVars()
@@ -19,9 +20,9 @@ func TestResolveEnumRefForPrompt(t *testing.T) {
 
 		v := &ast.VarsWithValidation{Name: "ENV", Enum: &ast.Enum{Ref: ".ALLOWED_ENVS"}}
 
-		resolved := resolveEnumRefForPrompt(v, vars)
+		resolved := refs.ResolveEnum(v, vars)
 
-		require.Equal(t, []string{"dev", "staging", "prod"}, getEnumValues(resolved.Enum))
+		require.Equal(t, []string{"dev", "staging", "prod"}, resolved.Enum.Value)
 		require.Empty(t, v.Enum.Value, "input var must not be mutated")
 		require.Equal(t, ".ALLOWED_ENVS", v.Enum.Ref)
 	})
@@ -31,7 +32,7 @@ func TestResolveEnumRefForPrompt(t *testing.T) {
 
 		v := &ast.VarsWithValidation{Name: "ENV", Enum: &ast.Enum{Ref: ".NONEXISTENT"}}
 
-		require.Empty(t, getEnumValues(resolveEnumRefForPrompt(v, vars).Enum))
+		require.Empty(t, refs.ResolveEnum(v, vars).Enum.Value)
 	})
 
 	t.Run("passes through a static enum unchanged", func(t *testing.T) {
@@ -39,6 +40,17 @@ func TestResolveEnumRefForPrompt(t *testing.T) {
 
 		v := &ast.VarsWithValidation{Name: "ENV", Enum: &ast.Enum{Value: []string{"a", "b"}}}
 
-		require.Same(t, v, resolveEnumRefForPrompt(v, vars))
+		require.Same(t, v, refs.ResolveEnum(v, vars))
+	})
+
+	t.Run("accepts the list types template functions return", func(t *testing.T) {
+		t.Parallel()
+
+		vars := ast.NewVars()
+		vars.Set("MAP", ast.Var{Value: map[string]any{"dev": 1, "prod": 2}})
+
+		v := &ast.VarsWithValidation{Name: "ENV", Enum: &ast.Enum{Ref: "keys .MAP | sortAlpha"}}
+
+		require.Equal(t, []string{"dev", "prod"}, refs.ResolveEnum(v, vars).Enum.Value)
 	})
 }
diff --git a/internal/slicesext/slicesext.go b/internal/slicesext/slicesext.go
index 2aba5beb15..9376d19962 100644
--- a/internal/slicesext/slicesext.go
+++ b/internal/slicesext/slicesext.go
@@ -30,3 +30,8 @@ func Convert[T, U any](s []T, f func(T) U) []U {
 
 	return result
 }
+
+// AsAny converts a typed slice into a []any.
+func AsAny[T any](s []T) []any {
+	return Convert(s, func(v T) any { return v })
+}
diff --git a/requires.go b/requires.go
index e425f83ce3..2903d25eef 100644
--- a/requires.go
+++ b/requires.go
@@ -7,7 +7,7 @@ import (
 
 	"github.com/go-task/task/v3/errors"
 	"github.com/go-task/task/v3/internal/input"
-	"github.com/go-task/task/v3/internal/templater"
+	"github.com/go-task/task/v3/internal/refs"
 	"github.com/go-task/task/v3/internal/term"
 	"github.com/go-task/task/v3/taskfile/ast"
 )
@@ -46,7 +46,7 @@ func (e *Executor) promptDepsVars(calls []*Call) error {
 
 		for _, v := range getMissingRequiredVars(compiledTask) {
 			if !varsMap.Has(v.Name) {
-				varsMap.Set(v.Name, resolveEnumRefForPrompt(v, compiledTask.Vars))
+				varsMap.Set(v.Name, refs.ResolveEnum(v, compiledTask.Vars))
 			}
 		}
 
@@ -217,16 +217,3 @@ func getEnumValues(e *ast.Enum) []string {
 	}
 	return e.Value
 }
-
-// resolveEnumRefForPrompt returns a copy of v with its enum ref resolved into
-// concrete values, so the interactive prompter can show a Select. Refs that
-// depend on dynamic vars may not resolve here and fall back to free-form input.
-func resolveEnumRefForPrompt(v *ast.VarsWithValidation, vars *ast.Vars) *ast.VarsWithValidation {
-	if v.Enum == nil || v.Enum.Ref == "" || len(v.Enum.Value) > 0 {
-		return v
-	}
-	vCopy := v.DeepCopy()
-	cache := &templater.Cache{Vars: vars}
-	_ = resolveEnumRefs(&ast.Requires{Vars: []*ast.VarsWithValidation{vCopy}}, cache)
-	return vCopy
-}
diff --git a/variables.go b/variables.go
index c2085bd1ea..2742b26312 100644
--- a/variables.go
+++ b/variables.go
@@ -15,6 +15,8 @@ import (
 	"github.com/go-task/task/v3/internal/execext"
 	"github.com/go-task/task/v3/internal/filepathext"
 	"github.com/go-task/task/v3/internal/fingerprint"
+	"github.com/go-task/task/v3/internal/refs"
+	"github.com/go-task/task/v3/internal/slicesext"
 	"github.com/go-task/task/v3/internal/templater"
 	"github.com/go-task/task/v3/taskfile/ast"
 )
@@ -118,7 +120,7 @@ func (e *Executor) compiledTask(call *Call, evaluateShVars bool) (*ast.Task, err
 	requires := origTask.Requires
 	if evaluateShVars {
 		requires = origTask.Requires.DeepCopy()
-		if err := resolveEnumRefs(requires, cache); err != nil {
+		if err := refs.ResolveEnums(requires, cache); err != nil {
 			return nil, err
 		}
 	}
@@ -347,30 +349,6 @@ func (e *Executor) compiledTask(call *Call, evaluateShVars bool) (*ast.Task, err
 	return &new, nil
 }
 
-func asAnySlice[T any](slice []T) []any {
-	ret := make([]any, len(slice))
-	for i, v := range slice {
-		ret[i] = v
-	}
-	return ret
-}
-
-// resolvedAsAnySlice converts a value resolved from a reference into a []any.
-// A reference does not always resolve to a []any: lists declared in a Taskfile
-// do, but template functions such as `keys` and `splitList` return a []string.
-// The accepted types mirror the list types itemsFromFor already supports.
-func resolvedAsAnySlice(v any) ([]any, bool) {
-	switch value := v.(type) {
-	case []any:
-		return value, true
-	case []string:
-		return asAnySlice(value), true
-	case []int:
-		return asAnySlice(value), true
-	}
-	return nil, false
-}
-
 func itemsFromFor(
 	f *ast.For,
 	dir string,
@@ -392,7 +370,7 @@ func itemsFromFor(
 				Err: err,
 			}
 		}
-		return asAnySlice(product(resolvedMatrix)), nil, nil
+		return slicesext.AsAny(product(resolvedMatrix)), nil, nil
 	}
 	// Get the list from the explicit for list
 	if len(f.List) > 0 {
@@ -410,7 +388,7 @@ func itemsFromFor(
 				return nil, nil, err
 			}
 		}
-		values = asAnySlice(glist)
+		values = slicesext.AsAny(glist)
 	}
 	// Get the list from the task generates
 	if f.From == "generates" {
@@ -424,7 +402,7 @@ func itemsFromFor(
 				return nil, nil, err
 			}
 		}
-		values = asAnySlice(glist)
+		values = slicesext.AsAny(glist)
 	}
 	// Get the list from a variable and split it up
 	if f.Var != "" {
@@ -437,14 +415,14 @@ func itemsFromFor(
 				switch value := v.Value.(type) {
 				case string:
 					if f.Split != "" {
-						values = asAnySlice(strings.Split(value, f.Split))
+						values = slicesext.AsAny(strings.Split(value, f.Split))
 					} else {
-						values = asAnySlice(strings.Fields(value))
+						values = slicesext.AsAny(strings.Fields(value))
 					}
 				case []string:
-					values = asAnySlice(value)
+					values = slicesext.AsAny(value)
 				case []int:
-					values = asAnySlice(value)
+					values = slicesext.AsAny(value)
 				case []any:
 					values = value
 				case map[string]any:
@@ -492,7 +470,7 @@ func resolveMatrixRefs(matrix *ast.Matrix, cache *templater.Cache) (*ast.Matrix,
 			if cache.Err() != nil {
 				return nil, cache.Err()
 			}
-			value, ok := resolvedAsAnySlice(v)
+			value, ok := refs.AsList(v)
 			if !ok {
 				return nil, fmt.Errorf("matrix reference %q must resolve to a list", row.Ref)
 			}
@@ -502,35 +480,6 @@ func resolveMatrixRefs(matrix *ast.Matrix, cache *templater.Cache) (*ast.Matrix,
 	return resolved, nil
 }
 
-func resolveEnumRefs(requires *ast.Requires, cache *templater.Cache) error {
-	if requires == nil || len(requires.Vars) == 0 {
-		return nil
-	}
-	for _, v := range requires.Vars {
-		if v.Enum == nil || v.Enum.Ref == "" {
-			continue
-		}
-		resolved := templater.ResolveRef(v.Enum.Ref, cache)
-		if cache.Err() != nil {
-			return cache.Err()
-		}
-		arr, ok := resolvedAsAnySlice(resolved)
-		if !ok {
-			return fmt.Errorf("enum reference %q must resolve to a list", v.Enum.Ref)
-		}
-		strValues := make([]string, 0, len(arr))
-		for _, item := range arr {
-			s, ok := item.(string)
-			if !ok {
-				return fmt.Errorf("enum reference %q must contain only strings", v.Enum.Ref)
-			}
-			strValues = append(strValues, s)
-		}
-		v.Enum.Value = strValues
-	}
-	return nil
-}
-
 // product generates the cartesian product of the input map of slices.
 func product(matrix *ast.Matrix) []map[string]any {
 	if matrix.Len() == 0 {
diff --git a/website/src/docs/installation.md b/website/src/docs/installation.md
index 3d3f660c54..39ec242216 100644
--- a/website/src/docs/installation.md
+++ b/website/src/docs/installation.md
@@ -486,3 +486,66 @@ requires to be static. Three consequences are worth knowing:
 use ($nu.data-dir | path join "vendor/autoload/task-completions.nu") *
 alias go-task = task
 ```
+
+### Trying the new completion engine (experimental)
+
+Task is migrating to a new completion engine, where every shell shares a single
+source of truth: the `task __complete` command. This gives Bash, Zsh, Fish,
+Nushell and PowerShell the exact same suggestions (task names, aliases, flags,
+flag values and `requires` vars, including their enums). It is currently
+**opt-in** and will become the default of `--completion` in a future release.
+
+To try it, swap `--completion` for `--new-completion` in any of the snippets
+above, for example:
+
+::: code-group
+
+```shell [bash]
+# ~/.bashrc
+eval "$(task --new-completion bash)"
+```
+
+```shell [zsh]
+# ~/.zshrc
+eval "$(task --new-completion zsh)"
+```
+
+```shell [fish]
+# ~/.config/fish/config.fish
+task --new-completion fish | source
+```
+
+```powershell [powershell]
+# $PROFILE\Microsoft.PowerShell_profile.ps1
+Invoke-Expression  (&task --new-completion powershell | Out-String)
+```
+
+```nu [nushell]
+# ~/.config/nushell/config.nu
+mkdir ($nu.data-dir | path join "vendor/autoload")
+task --new-completion nu | save --force ($nu.data-dir | path join "vendor/autoload/task-completions.nu")
+```
+
+:::
+
+The `verbose` and `show-aliases` zstyles documented above work with the new Zsh
+completion too.
+
+Nushell shares a single external completer between every command, so the script
+chains to the one already configured — carapace and friends keep working. Load
+it from an autoload directory as shown above rather than from `config.nu`, so
+that your own completer is the one being chained to. If you would rather wire it
+yourself, the script also exposes a `task-external-completer` command:
+
+```nu
+$env.config.completions.external.completer = {|spans|
+    match ($spans | first) {
+        task => (task-external-completer $spans)
+        _ => (do $my_other_completer $spans)
+    }
+}
+```
+
+Two engine directives behave differently under Nushell by design: it never
+appends a space after an external completion (so `NoSpace` is a no-op) and never
+re-sorts the results (so `KeepOrder` is always honoured).