refactor(compiler): remove unnecessary closure comments

- Fix import order in setup.go (gci)
- Fix variable alignment in experiments.go (gofmt)
- Add nolint:paralleltest directive for TestScopedTaskfiles

cmd/task/task.go

@@ -174,6 +174,8 @@ func run() error {
 
 	// Merge CLI variables first (e.g. FOO=bar) so they take priority over Taskfile defaults
 	e.Taskfile.Vars.Merge(globals, nil)
+	// Store CLI vars for scoped mode where they need highest priority
+	e.Compiler.CLIVars = globals
 
 	// Then ReverseMerge special variables so they're available for templating
 	cliArgsPostDashQuoted, err := args.ToQuotedString(cliArgsPostDash)

compiler.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/go-task/task/v3/experiments"
 	"github.com/go-task/task/v3/internal/env"
 	"github.com/go-task/task/v3/internal/execext"
 	"github.com/go-task/task/v3/internal/filepathext"
@@ -25,6 +26,8 @@ type Compiler struct {
 
 	TaskfileEnv  *ast.Vars
 	TaskfileVars *ast.Vars
+	CLIVars      *ast.Vars // CLI vars passed via command line (e.g., task foo VAR=value)
+	Graph        *ast.TaskfileGraph
 
 	Logger *logger.Logger
 
@@ -44,8 +47,236 @@ func (c *Compiler) FastGetVariables(t *ast.Task, call *Call) (*ast.Vars, error)
 	return c.getVariables(t, call, false)
 }
 
+// isScopedMode returns true if scoped variable resolution should be used.
+// Scoped mode requires the experiment to be enabled, a task with location info, and a graph.
+func (c *Compiler) isScopedMode(t *ast.Task) bool {
+	return experiments.ScopedTaskfiles.Enabled() &&
+		t != nil &&
+		t.Location != nil &&
+		c.Graph != nil
+}
+
 func (c *Compiler) getVariables(t *ast.Task, call *Call, evaluateShVars bool) (*ast.Vars, error) {
-	result := env.GetEnviron()
+	if c.isScopedMode(t) {
+		return c.getScopedVariables(t, call, evaluateShVars)
+	}
+	return c.getLegacyVariables(t, call, evaluateShVars)
+}
+
+// getScopedVariables resolves variables in scoped mode.
+// In scoped mode:
+// - OS env vars are in {{.env.XXX}} namespace, not at root
+// - Variables from sibling includes are isolated
+//
+// Variable resolution order (lowest to highest priority):
+// 1. Root Taskfile vars
+// 2. Include Taskfile vars
+// 3. Include passthrough vars (includes: name: vars:)
+// 4. Task vars
+// 5. Call vars
+// 6. CLI vars
+func (c *Compiler) getScopedVariables(t *ast.Task, call *Call, evaluateShVars bool) (*ast.Vars, error) {
+	result := ast.NewVars()
+
+	specialVars, err := c.getSpecialVars(t, call)
+	if err != nil {
+		return nil, err
+	}
+	for k, v := range specialVars {
+		result.Set(k, ast.Var{Value: v})
+	}
+
+	getRangeFunc := func(dir string) func(k string, v ast.Var) error {
+		return func(k string, v ast.Var) error {
+			cache := &templater.Cache{Vars: result}
+			newVar := templater.ReplaceVar(v, cache)
+			if !evaluateShVars && newVar.Value == nil {
+				result.Set(k, ast.Var{Value: "", Sh: newVar.Sh})
+				return nil
+			}
+			if !evaluateShVars {
+				result.Set(k, ast.Var{Value: newVar.Value, Sh: newVar.Sh})
+				return nil
+			}
+			if err := cache.Err(); err != nil {
+				return err
+			}
+			if newVar.Value != nil || newVar.Sh == nil {
+				result.Set(k, ast.Var{Value: newVar.Value})
+				return nil
+			}
+			static, err := c.HandleDynamicVar(newVar, dir, env.GetFromVars(result))
+			if err != nil {
+				return err
+			}
+			result.Set(k, ast.Var{Value: static})
+			return nil
+		}
+	}
+	rangeFunc := getRangeFunc(c.Dir)
+
+	var taskRangeFunc func(k string, v ast.Var) error
+	if t != nil {
+		cache := &templater.Cache{Vars: result}
+		dir := templater.Replace(t.Dir, cache)
+		if err := cache.Err(); err != nil {
+			return nil, err
+		}
+		dir = filepathext.SmartJoin(c.Dir, dir)
+		taskRangeFunc = getRangeFunc(dir)
+	}
+
+	rootVertex, err := c.Graph.Root()
+	if err != nil {
+		return nil, err
+	}
+
+	envMap := make(map[string]any)
+	for _, e := range os.Environ() {
+		k, v, _ := strings.Cut(e, "=")
+		envMap[k] = v
+	}
+
+	resolveEnvToMap := func(k string, v ast.Var, dir string) error {
+		cache := &templater.Cache{Vars: result}
+		newVar := templater.ReplaceVar(v, cache)
+		if err := cache.Err(); err != nil {
+			return err
+		}
+		if newVar.Value != nil || newVar.Sh == nil {
+			if newVar.Value != nil {
+				envMap[k] = newVar.Value
+			}
+			return nil
+		}
+		if evaluateShVars {
+			envSlice := os.Environ()
+			for ek, ev := range envMap {
+				if s, ok := ev.(string); ok {
+					envSlice = append(envSlice, fmt.Sprintf("%s=%s", ek, s))
+				}
+			}
+			static, err := c.HandleDynamicVar(newVar, dir, envSlice)
+			if err != nil {
+				return err
+			}
+			envMap[k] = static
+		}
+		return nil
+	}
+
+	for k, v := range rootVertex.Taskfile.Env.All() {
+		if err := resolveEnvToMap(k, v, c.Dir); err != nil {
+			return nil, err
+		}
+	}
+
+	for k, v := range rootVertex.Taskfile.Vars.All() {
+		if err := rangeFunc(k, v); err != nil {
+			return nil, err
+		}
+	}
+
+	if t.Location.Taskfile != rootVertex.URI {
+		predecessorMap, err := c.Graph.PredecessorMap()
+		if err != nil {
+			return nil, err
+		}
+
+		var parentChain []*ast.TaskfileVertex
+		currentURI := t.Location.Taskfile
+		for {
+			edges := predecessorMap[currentURI]
+			if len(edges) == 0 {
+				break
+			}
+			var parentURI string
+			for _, edge := range edges {
+				parentURI = edge.Source
+				break
+			}
+			if parentURI == rootVertex.URI {
+				break
+			}
+			parentVertex, err := c.Graph.Vertex(parentURI)
+			if err != nil {
+				return nil, err
+			}
+			parentChain = append([]*ast.TaskfileVertex{parentVertex}, parentChain...)
+			currentURI = parentURI
+		}
+
+		for _, parent := range parentChain {
+			parentDir := filepath.Dir(parent.URI)
+			for k, v := range parent.Taskfile.Env.All() {
+				if err := resolveEnvToMap(k, v, parentDir); err != nil {
+					return nil, err
+				}
+			}
+			// Vars use the parent's directory too
+			parentRangeFunc := getRangeFunc(parentDir)
+			for k, v := range parent.Taskfile.Vars.All() {
+				if err := parentRangeFunc(k, v); err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		includeVertex, err := c.Graph.Vertex(t.Location.Taskfile)
+		if err != nil {
+			return nil, err
+		}
+		includeDir := filepath.Dir(includeVertex.URI)
+		for k, v := range includeVertex.Taskfile.Env.All() {
+			if err := resolveEnvToMap(k, v, includeDir); err != nil {
+				return nil, err
+			}
+		}
+		includeRangeFunc := getRangeFunc(includeDir)
+		for k, v := range includeVertex.Taskfile.Vars.All() {
+			if err := includeRangeFunc(k, v); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	if t.IncludeVars != nil {
+		for k, v := range t.IncludeVars.All() {
+			if err := rangeFunc(k, v); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	if call != nil {
+		for k, v := range t.Vars.All() {
+			if err := taskRangeFunc(k, v); err != nil {
+				return nil, err
+			}
+		}
+		for k, v := range call.Vars.All() {
+			if err := taskRangeFunc(k, v); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	for k, v := range c.CLIVars.All() {
+		if err := rangeFunc(k, v); err != nil {
+			return nil, err
+		}
+	}
+
+	result.Set("env", ast.Var{Value: envMap})
+
+	return result, nil
+}
+
+// getLegacyVariables resolves variables in legacy mode.
+// In legacy mode, all variables (including OS env) are merged at root level.
+func (c *Compiler) getLegacyVariables(t *ast.Task, call *Call, evaluateShVars bool) (*ast.Vars, error) {
+	result := env.GetEnviron()
+
 	specialVars, err := c.getSpecialVars(t, call)
 	if err != nil {
 		return nil, err
@@ -57,30 +288,22 @@ func (c *Compiler) getVariables(t *ast.Task, call *Call, evaluateShVars bool) (*
 	getRangeFunc := func(dir string) func(k string, v ast.Var) error {
 		return func(k string, v ast.Var) error {
 			cache := &templater.Cache{Vars: result}
-			// Replace values
 			newVar := templater.ReplaceVar(v, cache)
-			// If the variable should not be evaluated, but is nil, set it to an empty string
-			// This stops empty interface errors when using the templater to replace values later
-			// Preserve the Sh field so it can be displayed in summary
 			if !evaluateShVars && newVar.Value == nil {
 				result.Set(k, ast.Var{Value: "", Sh: newVar.Sh})
 				return nil
 			}
-			// If the variable should not be evaluated and it is set, we can set it and return
 			if !evaluateShVars {
 				result.Set(k, ast.Var{Value: newVar.Value, Sh: newVar.Sh})
 				return nil
 			}
-			// Now we can check for errors since we've handled all the cases when we don't want to evaluate
 			if err := cache.Err(); err != nil {
 				return err
 			}
-			// If the variable is already set, we can set it and return
 			if newVar.Value != nil || newVar.Sh == nil {
 				result.Set(k, ast.Var{Value: newVar.Value})
 				return nil
 			}
-			// If the variable is dynamic, we need to resolve it first
 			static, err := c.HandleDynamicVar(newVar, dir, env.GetFromVars(result))
 			if err != nil {
 				return err
@@ -93,8 +316,6 @@ func (c *Compiler) getVariables(t *ast.Task, call *Call, evaluateShVars bool) (*
 
 	var taskRangeFunc func(k string, v ast.Var) error
 	if t != nil {
-		// NOTE(@andreynering): We're manually joining these paths here because
-		// this is the raw task, not the compiled one.
 		cache := &templater.Cache{Vars: result}
 		dir := templater.Replace(t.Dir, cache)
 		if err := cache.Err(); err != nil {
@@ -114,6 +335,7 @@ func (c *Compiler) getVariables(t *ast.Task, call *Call, evaluateShVars bool) (*
 			return nil, err
 		}
 	}
+
 	if t != nil {
 		for k, v := range t.IncludeVars.All() {
 			if err := rangeFunc(k, v); err != nil {
@@ -149,7 +371,6 @@ func (c *Compiler) HandleDynamicVar(v ast.Var, dir string, e []string) (string,
 	c.muDynamicCache.Lock()
 	defer c.muDynamicCache.Unlock()
 
-	// If the variable is not dynamic or it is empty, return an empty string
 	if v.Sh == nil || *v.Sh == "" {
 		return "", nil
 	}

executor.go

@@ -63,6 +63,7 @@ type (
 
 		// Internal
 		Taskfile           *ast.Taskfile
+		Graph              *ast.TaskfileGraph
 		Logger             *logger.Logger
 		Compiler           *Compiler
 		Output             output.Output

executor_test.go

@@ -1180,3 +1180,114 @@ func TestIf(t *testing.T) {
 		NewExecutorTest(t, opts...)
 	}
 }
+
+//nolint:paralleltest // enableExperimentForTest modifies global state
+func TestScopedTaskfiles(t *testing.T) {
+	// Legacy tests (without experiment) - vars should be merged globally
+	t.Run("legacy", func(t *testing.T) {
+		// Test with scoped taskfiles disabled (legacy) - vars should be merged globally
+		NewExecutorTest(t,
+			WithName("default"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+		)
+		// In legacy mode, UNIQUE_B should be accessible (merged globally)
+		NewExecutorTest(t,
+			WithName("cross-include"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("a:try-access-b"),
+		)
+	})
+
+	// Scoped tests (with experiment enabled) - vars should be isolated
+	t.Run("scoped", func(t *testing.T) {
+		enableExperimentForTest(t, &experiments.ScopedTaskfiles, 1)
+
+		// Test with scoped taskfiles enabled - vars should be isolated
+		NewExecutorTest(t,
+			WithName("default"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+		)
+		// Test inheritance: include can access root vars
+		NewExecutorTest(t,
+			WithName("inheritance-a"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("a:print"),
+		)
+		// Test isolation: each include sees its own vars
+		NewExecutorTest(t,
+			WithName("isolation-b"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("b:print"),
+		)
+		// In scoped mode, UNIQUE_B should be empty (isolated)
+		NewExecutorTest(t,
+			WithName("cross-include"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("a:try-access-b"),
+		)
+		// Test env namespace: {{.env.XXX}} should access env vars
+		NewExecutorTest(t,
+			WithName("env-namespace"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("print-env"),
+		)
+		// Test env separation: {{.ROOT_ENV}} at root should be empty (env not at root level)
+		NewExecutorTest(t,
+			WithName("env-separation"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("test-env-separation"),
+		)
+		// Test include env: include's env is accessible via {{.env.XXX}}
+		NewExecutorTest(t,
+			WithName("include-env"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("a:print-env"),
+		)
+		// Test call vars: vars passed when calling a task override task vars
+		NewExecutorTest(t,
+			WithName("call-vars"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("call-with-vars"),
+		)
+		// Test nested includes (3 levels: root → a → nested)
+		// Verifies that nested includes inherit vars from their parent chain
+		NewExecutorTest(t,
+			WithName("nested"),
+			WithExecutorOptions(
+				task.WithDir("testdata/scoped_taskfiles"),
+				task.WithSilent(true),
+			),
+			WithTask("a:nested:print"),
+		)
+	})
+}

experiments/experiments.go

@@ -19,6 +19,7 @@ var (
 	GentleForce     Experiment
 	RemoteTaskfiles Experiment
 	EnvPrecedence   Experiment
+	ScopedTaskfiles Experiment
 )
 
 // Inactive experiments. These are experiments that cannot be enabled, but are
@@ -43,6 +44,7 @@ func ParseWithConfig(dir string, config *ast.TaskRC) {
 	GentleForce = New("GENTLE_FORCE", config, 1)
 	RemoteTaskfiles = New("REMOTE_TASKFILES", config, 1)
 	EnvPrecedence = New("ENV_PRECEDENCE", config, 1)
+	ScopedTaskfiles = New("SCOPED_TASKFILES", config, 1)
 	AnyVariables = New("ANY_VARIABLES", config)
 	MapVariables = New("MAP_VARIABLES", config)
 }

setup.go

@@ -13,6 +13,7 @@ import (
 	"github.com/sajari/fuzzy"
 
 	"github.com/go-task/task/v3/errors"
+	"github.com/go-task/task/v3/experiments"
 	"github.com/go-task/task/v3/internal/env"
 	"github.com/go-task/task/v3/internal/execext"
 	"github.com/go-task/task/v3/internal/filepathext"
@@ -104,7 +105,8 @@ func (e *Executor) readTaskfile(node taskfile.Node) error {
 		}
 		return err
 	}
-	if e.Taskfile, err = graph.Merge(); err != nil {
+	e.Graph = graph
+	if e.Taskfile, err = graph.Merge(experiments.ScopedTaskfiles.Enabled()); err != nil {
 		return err
 	}
 	return nil
@@ -226,6 +228,7 @@ func (e *Executor) setupCompiler() error {
 		UserWorkingDir: e.UserWorkingDir,
 		TaskfileEnv:    e.Taskfile.Env,
 		TaskfileVars:   e.Taskfile.Vars,
+		Graph:          e.Graph,
 		Logger:         e.Logger,
 	}
 	return nil

taskfile/ast/graph.go

@@ -45,7 +45,21 @@ func (tfg *TaskfileGraph) Visualize(filename string) error {
 	return draw.DOT(tfg.Graph, f)
 }
 
-func (tfg *TaskfileGraph) Merge() (*Taskfile, error) {
+// Root returns the root vertex of the graph (the entrypoint Taskfile).
+func (tfg *TaskfileGraph) Root() (*TaskfileVertex, error) {
+	hashes, err := graph.TopologicalSort(tfg.Graph)
+	if err != nil {
+		return nil, err
+	}
+	if len(hashes) == 0 {
+		return nil, fmt.Errorf("task: graph has no vertices")
+	}
+	return tfg.Vertex(hashes[0])
+}
+
+// Merge merges all included Taskfiles into the root Taskfile.
+// If skipVarsMerge is true, variables are not merged (used for scoped includes).
+func (tfg *TaskfileGraph) Merge(skipVarsMerge bool) (*Taskfile, error) {
 	hashes, err := graph.TopologicalSort(tfg.Graph)
 	if err != nil {
 		return nil, err
@@ -92,6 +106,7 @@ func (tfg *TaskfileGraph) Merge() (*Taskfile, error) {
 					if err := vertex.Taskfile.Merge(
 						includedVertex.Taskfile,
 						include,
+						skipVarsMerge,
 					); err != nil {
 						return err
 					}

taskfile/ast/taskfile.go

@@ -36,8 +36,9 @@ type Taskfile struct {
 	Interval time.Duration
 }
 
-// Merge merges the second Taskfile into the first
-func (t1 *Taskfile) Merge(t2 *Taskfile, include *Include) error {
+// Merge merges the second Taskfile into the first.
+// If skipVarsMerge is true, variables are not merged (used for scoped includes).
+func (t1 *Taskfile) Merge(t2 *Taskfile, include *Include, skipVarsMerge bool) error {
 	if !t1.Version.Equal(t2.Version) {
 		return fmt.Errorf(`task: Taskfiles versions should match. First is "%s" but second is "%s"`, t1.Version, t2.Version)
 	}
@@ -67,8 +68,11 @@ func (t1 *Taskfile) Merge(t2 *Taskfile, include *Include) error {
 			}
 		}
 	}
-	t1.Vars.Merge(t2.Vars, include)
-	t1.Env.Merge(t2.Env, include)
+	// Only merge vars if not using scoped includes, or if flattening
+	if !skipVarsMerge || include.Flatten {
+		t1.Vars.Merge(t2.Vars, include)
+		t1.Env.Merge(t2.Env, include)
+	}
 	return t1.Tasks.Merge(t2.Tasks, include, t1.Vars)
 }
 

testdata/scoped_taskfiles/Taskfile.yml

@@ -0,0 +1,57 @@
+version: "3"
+
+env:
+  ROOT_ENV: env_from_root
+  SHARED_ENV: shared_from_root
+
+vars:
+  ROOT_VAR: from_root
+
+includes:
+  a: ./inc_a
+  b: ./inc_b
+
+tasks:
+  default:
+    desc: Test scoped includes - vars should be isolated
+    cmds:
+      - task: a:print
+      - task: b:print
+
+  print-root-var:
+    desc: Print ROOT_VAR from root
+    cmds:
+      - echo "ROOT_VAR={{.ROOT_VAR}}"
+
+  print-env:
+    desc: Print env vars using {{.env.XXX}} syntax
+    cmds:
+      - echo "ROOT_ENV={{.env.ROOT_ENV}}"
+      - echo "SHARED_ENV={{.env.SHARED_ENV}}"
+      - echo "PATH_EXISTS={{if .env.PATH}}yes{{else}}no{{end}}"
+
+  test-env-separation:
+    desc: Test that env is NOT at root level in scoped mode
+    cmds:
+      # In scoped mode, {{.ROOT_ENV}} should be empty (env not at root)
+      # In legacy mode, {{.ROOT_ENV}} would have the value
+      - echo "ROOT_ENV_AT_ROOT={{.ROOT_ENV}}"
+
+  prout:
+    vars:
+      LOL: prout_from_root
+    cmds:
+      - echo "{{.LOL}}"
+
+  call-with-vars:
+    desc: Test calling a task with vars override
+    cmds:
+      - task: print-name
+        vars:
+          NAME: from_caller
+
+  print-name:
+    vars:
+      NAME: default_name
+    cmds:
+      - echo "NAME={{.NAME}}"

testdata/scoped_taskfiles/inc_a/Taskfile.yml

@@ -0,0 +1,38 @@
+version: "3"
+
+env:
+  INC_A_ENV: env_from_a
+  SHARED_ENV: shared_from_a
+
+vars:
+  VAR: value_from_a
+  UNIQUE_A: only_in_a
+
+includes:
+  nested: ./nested
+
+tasks:
+  print:
+    desc: Print vars from include A
+    cmds:
+      - echo "A:UNIQUE_A={{.UNIQUE_A}}"
+      - echo "A:ROOT_VAR={{.ROOT_VAR}}"
+
+  try-access-b:
+    desc: Try to access B's unique var (should fail in scoped mode)
+    cmds:
+      - echo "A:UNIQUE_B={{.UNIQUE_B}}"
+
+  print-env:
+    desc: Print env vars from include A
+    cmds:
+      - echo "A:INC_A_ENV={{.env.INC_A_ENV}}"
+      - echo "A:ROOT_ENV={{.env.ROOT_ENV}}"
+      - echo "A:SHARED_ENV={{.env.SHARED_ENV}}"
+
+  test-env-in-var:
+    desc: Test using env in a var template
+    vars:
+      COMPOSED: "env={{.env.ROOT_ENV}}"
+    cmds:
+      - echo "{{.COMPOSED}}"

testdata/scoped_taskfiles/inc_a/nested/Taskfile.yml

@@ -0,0 +1,22 @@
+version: "3"
+
+env:
+  NESTED_ENV: env_from_nested
+
+vars:
+  NESTED_VAR: from_nested
+
+tasks:
+  print:
+    desc: Print vars from nested include (3 levels deep)
+    cmds:
+      - echo "NESTED:ROOT_VAR={{.ROOT_VAR}}"
+      - echo "NESTED:UNIQUE_A={{.UNIQUE_A}}"
+      - echo "NESTED:NESTED_VAR={{.NESTED_VAR}}"
+      - echo "NESTED:NESTED_ENV={{.env.NESTED_ENV}}"
+      - echo "NESTED:ROOT_ENV={{.env.ROOT_ENV}}"
+
+  try-access-b:
+    desc: Try to access B's unique var (should fail - sibling isolation)
+    cmds:
+      - echo "NESTED:UNIQUE_B={{.UNIQUE_B}}"

testdata/scoped_taskfiles/inc_b/Taskfile.yml

@@ -0,0 +1,23 @@
+version: "3"
+
+env:
+  INC_B_ENV: env_from_b
+  SHARED_ENV: shared_from_b
+
+vars:
+  VAR: value_from_b
+  UNIQUE_B: only_in_b
+
+tasks:
+  print:
+    desc: Print vars from include B
+    cmds:
+      - echo "B:UNIQUE_B={{.UNIQUE_B}}"
+      - echo "B:ROOT_VAR={{.ROOT_VAR}}"
+
+  print-env:
+    desc: Print env vars from include B
+    cmds:
+      - echo "B:INC_B_ENV={{.env.INC_B_ENV}}"
+      - echo "B:ROOT_ENV={{.env.ROOT_ENV}}"
+      - echo "B:SHARED_ENV={{.env.SHARED_ENV}}"

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-legacy-cross-include.golden

@@ -0,0 +1 @@
+A:UNIQUE_B=only_in_b

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-legacy-default.golden

@@ -0,0 +1,4 @@
+A:UNIQUE_A=only_in_a
+A:ROOT_VAR=from_root
+B:UNIQUE_B=only_in_b
+B:ROOT_VAR=from_root

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-call-vars.golden

@@ -0,0 +1 @@
+NAME=from_caller

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-cross-include.golden

@@ -0,0 +1 @@
+A:UNIQUE_B=

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-default.golden

@@ -0,0 +1,4 @@
+A:UNIQUE_A=only_in_a
+A:ROOT_VAR=from_root
+B:UNIQUE_B=only_in_b
+B:ROOT_VAR=from_root

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-env-namespace.golden

@@ -0,0 +1,3 @@
+ROOT_ENV=env_from_root
+SHARED_ENV=shared_from_root
+PATH_EXISTS=yes

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-env-separation.golden

@@ -0,0 +1 @@
+ROOT_ENV_AT_ROOT=

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-include-env.golden

@@ -0,0 +1,3 @@
+A:INC_A_ENV=env_from_a
+A:ROOT_ENV=env_from_root
+A:SHARED_ENV=shared_from_a

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-inheritance-a.golden

@@ -0,0 +1,2 @@
+A:UNIQUE_A=only_in_a
+A:ROOT_VAR=from_root

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-isolation-b.golden

@@ -0,0 +1,2 @@
+B:UNIQUE_B=only_in_b
+B:ROOT_VAR=from_root

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-nested.golden

@@ -0,0 +1,5 @@
+NESTED:ROOT_VAR=from_root
+NESTED:UNIQUE_A=only_in_a
+NESTED:NESTED_VAR=from_nested
+NESTED:NESTED_ENV=env_from_nested
+NESTED:ROOT_ENV=env_from_root

website/.vitepress/config.ts

@@ -302,6 +302,10 @@ export default defineConfig({
             {
               text: 'Remote Taskfiles (#1317)',
               link: '/docs/experiments/remote-taskfiles'
+            },
+            {
+              text: 'Scoped Taskfiles',
+              link: '/docs/experiments/scoped-taskfiles'
             }
           ]
         },

website/src/docs/experiments/scoped-taskfiles.md

@@ -0,0 +1,281 @@
+---
+title: 'Scoped Taskfiles (#2035)'
+description:
+  Experiment for variable isolation and env namespace in included Taskfiles
+outline: deep
+---
+
+# Scoped Taskfiles (#2035)
+
+::: warning
+
+All experimental features are subject to breaking changes and/or removal _at any
+time_. We strongly recommend that you do not use these features in a production
+environment. They are intended for testing and feedback only.
+
+:::
+
+::: danger
+
+This experiment breaks the following functionality:
+
+- **Environment variables are no longer available at root level in templates**
+  - Before: <span v-pre>`{{.PATH}}`</span>, <span v-pre>`{{.MY_ENV}}`</span>
+  - After: <span v-pre>`{{.env.PATH}}`</span>,
+    <span v-pre>`{{.env.MY_ENV}}`</span>
+- **Variables from sibling includes are no longer visible**
+  - Include A cannot access variables defined in Include B
+  - Each include only sees: root vars + its own vars + parent vars
+
+:::
+
+::: info
+
+To enable this experiment, set the environment variable:
+`TASK_X_SCOPED_TASKFILES=1`. Check out
+[our guide to enabling experiments](./index.md#enabling-experiments) for more
+information.
+
+:::
+
+This experiment introduces two major changes to how variables work in Task:
+
+1. **Environment namespace**: Environment variables (both OS and Taskfile `env:`
+   sections) are moved to a dedicated <span v-pre>`{{.env.XXX}}`</span>
+   namespace, separating them from regular variables
+2. **Variable scoping**: Variables defined in included Taskfiles are isolated -
+   sibling includes cannot see each other's variables
+
+## Environment Namespace
+
+With this experiment enabled, environment variables are no longer mixed with
+regular variables at the template root level. Instead, they are accessible
+through the <span v-pre>`{{.env.XXX}}`</span> namespace.
+
+### Comparison Table
+
+| Template                                        | Legacy | SCOPED_TASKFILES          |
+| ----------------------------------------------- | ------ | ------------------------- |
+| <span v-pre>`{{.MY_VAR}}`</span> (from `vars:`) | Works  | Works                     |
+| <span v-pre>`{{.MY_ENV}}`</span> (from `env:`)  | Works  | `<no value>`              |
+| <span v-pre>`{{.env.MY_ENV}}`</span>            | -      | Works                     |
+| <span v-pre>`{{.PATH}}`</span> (OS)             | Works  | `<no value>`              |
+| <span v-pre>`{{.env.PATH}}`</span> (OS)         | -      | Works                     |
+| <span v-pre>`{{.TASK}}`</span> (special)        | Works  | Works (stays at root)     |
+
+### Example
+
+```yaml
+version: '3'
+
+env:
+  DB_HOST: localhost
+
+vars:
+  DB_NAME: mydb
+
+tasks:
+  show:
+    cmds:
+      # Access Taskfile env: section
+      - echo "Host: {{.env.DB_HOST}}"
+
+      # Access regular vars (unchanged)
+      - echo "Name: {{.DB_NAME}}"
+
+      # Access OS environment variables
+      - echo "Path: {{.env.PATH}}"
+
+      # Special variables stay at root level
+      - echo "Task: {{.TASK}}"
+```
+
+## Variable Scoping
+
+Variables defined in included Taskfiles are now isolated from each other.
+Sibling includes cannot access each other's variables, but child includes can
+still inherit variables from their parent.
+
+### Example
+
+::: code-group
+
+```yaml [Taskfile.yml]
+version: '3'
+
+vars:
+  ROOT_VAR: from_root
+
+includes:
+  api: ./api
+  web: ./web
+```
+
+```yaml [api/Taskfile.yml]
+version: '3'
+
+vars:
+  API_VAR: from_api
+
+tasks:
+  show:
+    cmds:
+      # Inherited from root - works
+      - echo "ROOT_VAR={{.ROOT_VAR}}"
+
+      # Own variable - works
+      - echo "API_VAR={{.API_VAR}}"
+
+      # From sibling include - NOT visible
+      - echo "WEB_VAR={{.WEB_VAR}}"
+```
+
+```yaml [web/Taskfile.yml]
+version: '3'
+
+vars:
+  WEB_VAR: from_web
+
+tasks:
+  show:
+    cmds:
+      # Inherited from root - works
+      - echo "ROOT_VAR={{.ROOT_VAR}}"
+
+      # Own variable - works
+      - echo "WEB_VAR={{.WEB_VAR}}"
+
+      # From sibling include - NOT visible
+      - echo "API_VAR={{.API_VAR}}"
+```
+
+:::
+
+## Variable Priority
+
+With this experiment, variables follow a clear priority order (lowest to
+highest):
+
+| Priority | Source                   | Description                              |
+| -------- | ------------------------ | ---------------------------------------- |
+| 1        | Root Taskfile vars       | `vars:` in the root Taskfile             |
+| 2        | Include Taskfile vars    | `vars:` in the included Taskfile         |
+| 3        | Include passthrough vars | `includes: name: vars:` from parent      |
+| 4        | Task vars                | `tasks: name: vars:` in the task         |
+| 5        | Call vars                | `task: name` with `vars:` when calling   |
+| 6        | CLI vars                 | `task foo VAR=value` on command line     |
+
+### Example: Call vars override task vars
+
+```yaml
+version: '3'
+
+tasks:
+  greet:
+    vars:
+      NAME: default
+    cmds:
+      - echo "Hello {{.NAME}}"
+
+  caller:
+    cmds:
+      - task: greet
+        vars:
+          NAME: from_caller
+```
+
+```bash
+# Direct call uses task default
+task greet
+# Output: Hello default
+
+# Call vars override task vars
+task caller
+# Output: Hello from_caller
+
+# CLI vars override everything
+task greet NAME=cli
+# Output: Hello cli
+```
+
+## Migration Guide
+
+To migrate your Taskfiles to use this experiment:
+
+1. **Update environment variable references** in your templates:
+
+   - <span v-pre>`{{.PATH}}`</span> becomes
+     <span v-pre>`{{.env.PATH}}`</span>
+   - <span v-pre>`{{.HOME}}`</span> becomes
+     <span v-pre>`{{.env.HOME}}`</span>
+   - <span v-pre>`{{.MY_TASKFILE_ENV}}`</span> becomes
+     <span v-pre>`{{.env.MY_TASKFILE_ENV}}`</span>
+
+2. **Variables in `vars:` sections remain unchanged**:
+
+   - <span v-pre>`{{.MY_VAR}}`</span> still works the same way
+
+3. **Special variables stay at root level**:
+
+   - <span v-pre>`{{.TASK}}`</span>, <span v-pre>`{{.ROOT_DIR}}`</span>,
+     <span v-pre>`{{.TASKFILE}}`</span>, <span v-pre>`{{.TASKFILE_DIR}}`</span>,
+     etc.
+
+4. **Review cross-include variable dependencies**:
+   - If your included Taskfiles rely on variables from sibling includes, you'll
+     need to either move those variables to the root Taskfile or pass them
+     explicitly via the `vars:` attribute in the `includes:` section.
+
+5. **Use `flatten: true` for gradual migration**:
+   - If an include needs the legacy behavior (access to sibling variables), you
+     can use `flatten: true` on that include as an escape hatch.
+
+## Using `flatten: true`
+
+The `flatten: true` option on includes bypasses scoping for that specific
+include. When an include has `flatten: true`:
+
+- Its variables are merged globally (legacy behavior)
+- It can access variables from sibling includes
+- Sibling includes can access its variables
+
+This is useful for gradual migration or when you have includes that genuinely
+need to share variables.
+
+### Example
+
+```yaml
+version: '3'
+
+vars:
+  ROOT_VAR: from_root
+
+includes:
+  # Scoped include - isolated from siblings
+  api:
+    taskfile: ./api
+
+  # Flattened include - uses legacy merge behavior
+  shared:
+    taskfile: ./shared
+    flatten: true
+
+  # Another scoped include
+  web:
+    taskfile: ./web
+```
+
+In this example:
+
+- `api` and `web` are isolated from each other (cannot see each other's vars)
+- `shared` uses legacy behavior: its vars are merged globally
+- Both `api` and `web` can access variables from `shared`
+- `shared` can access variables from `api` and `web`
+
+::: tip
+
+Use `flatten: true` sparingly. The goal of scoped taskfiles is to improve
+isolation and predictability. Flattening should be a temporary measure during
+migration or for utility includes that genuinely need global scope.
+
+:::