diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 88cc398..84e4387 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -145,6 +145,8 @@ fixed dependency relation required by the feature roadmap.
 
 ## Stage 2 — Shared Bounded Plan Selection
 
+**Status: Completed**
+
 ### Goal
 
 Give the application one validated representation of a contiguous canonical
diff --git a/internal/app/planner.go b/internal/app/planner.go
index fb4bf89..9a7a704 100644
--- a/internal/app/planner.go
+++ b/internal/app/planner.go
@@ -2,13 +2,134 @@ package app
 
 import (
 	"fmt"
+	"strings"
 
 	"gitea.maximumdirect.net/eric/narratio/internal/stage"
 )
 
+// BoundedPlan is one validated inclusive range of the canonical pipeline.
+// It owns effective endpoints and membership so command, runner, and
+// composition callers do not independently interpret range bounds.
+type BoundedPlan struct {
+	stages          []stage.Stage
+	canonicalNames  []string
+	startIndex      int
+	endIndex        int
+	explicitFrom    bool
+	explicitThrough bool
+}
+
+// BuildBoundedPlan selects an inclusive contiguous range of the canonical
+// pipeline. Empty endpoints default to the beginning or end respectively.
+func BuildBoundedPlan(from, through string) (BoundedPlan, error) {
+	registry := stage.All()
+	names := make([]string, len(registry))
+	indices := make(map[string]int, len(registry))
+	for index, candidate := range registry {
+		if candidate == nil {
+			return BoundedPlan{}, fmt.Errorf("build bounded plan: canonical stage %d is nil", index)
+		}
+		name := candidate.Name()
+		if _, duplicate := indices[name]; duplicate {
+			return BoundedPlan{}, fmt.Errorf("build bounded plan: duplicate canonical stage %q", name)
+		}
+		names[index] = name
+		indices[name] = index
+	}
+	if len(registry) == 0 {
+		return BoundedPlan{}, fmt.Errorf("build bounded plan: canonical stage registry is empty")
+	}
+
+	start := 0
+	if from != "" {
+		var ok bool
+		start, ok = indices[from]
+		if !ok {
+			return BoundedPlan{}, fmt.Errorf("build bounded plan: unknown from stage %q; valid stages: %s", from, strings.Join(names, ", "))
+		}
+	}
+	end := len(registry) - 1
+	if through != "" {
+		var ok bool
+		end, ok = indices[through]
+		if !ok {
+			return BoundedPlan{}, fmt.Errorf("build bounded plan: unknown through stage %q; valid stages: %s", through, strings.Join(names, ", "))
+		}
+	}
+	if start > end {
+		return BoundedPlan{}, fmt.Errorf("build bounded plan: from stage %q occurs after through stage %q; valid stages: %s", from, through, strings.Join(names, ", "))
+	}
+
+	return BoundedPlan{
+		stages:          append([]stage.Stage(nil), registry[start:end+1]...),
+		canonicalNames:  append([]string(nil), names...),
+		startIndex:      start,
+		endIndex:        end,
+		explicitFrom:    from != "",
+		explicitThrough: through != "",
+	}, nil
+}
+
+// Stages returns a copy of the selected canonical stages.
+func (p BoundedPlan) Stages() []stage.Stage {
+	return append([]stage.Stage(nil), p.stages...)
+}
+
+// Names returns selected stage names in canonical order.
+func (p BoundedPlan) Names() []string {
+	out := make([]string, 0, len(p.stages))
+	for _, candidate := range p.stages {
+		out = append(out, candidate.Name())
+	}
+	return out
+}
+
+// From returns the effective inclusive start stage.
+func (p BoundedPlan) From() string {
+	if len(p.canonicalNames) == 0 || p.startIndex < 0 || p.startIndex >= len(p.canonicalNames) {
+		return ""
+	}
+	return p.canonicalNames[p.startIndex]
+}
+
+// Through returns the effective inclusive end stage.
+func (p BoundedPlan) Through() string {
+	if len(p.canonicalNames) == 0 || p.endIndex < 0 || p.endIndex >= len(p.canonicalNames) {
+		return ""
+	}
+	return p.canonicalNames[p.endIndex]
+}
+
+// Contains reports whether a canonical stage is selected by the range.
+func (p BoundedPlan) Contains(name string) bool {
+	for _, candidate := range p.stages {
+		if candidate.Name() == name {
+			return true
+		}
+	}
+	return false
+}
+
+// PrefixNames returns canonical stages excluded before the selected start.
+func (p BoundedPlan) PrefixNames() []string {
+	if p.startIndex <= 0 || p.startIndex > len(p.canonicalNames) {
+		return nil
+	}
+	return append([]string(nil), p.canonicalNames[:p.startIndex]...)
+}
+
+// HasExplicitBounds reports whether either endpoint was supplied by the caller.
+func (p BoundedPlan) HasExplicitBounds() bool {
+	return p.explicitFrom || p.explicitThrough
+}
+
 // BuildFullPlan returns the canonical full stage list in deterministic order.
 func BuildFullPlan() []stage.Stage {
-	return stage.All()
+	plan, err := BuildBoundedPlan("", "")
+	if err != nil {
+		panic(err)
+	}
+	return plan.Stages()
 }
 
 // BuildSingleStagePlan returns a one-stage plan for an exact stage name.
diff --git a/internal/app/planner_test.go b/internal/app/planner_test.go
index 88da2dd..80314bb 100644
--- a/internal/app/planner_test.go
+++ b/internal/app/planner_test.go
@@ -1,6 +1,12 @@
 package app
 
-import "testing"
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/stage"
+)
 
 func TestBuildFullPlanOrder(t *testing.T) {
 	got := BuildFullPlan()
@@ -34,3 +40,113 @@ func TestBuildSingleStagePlanUnknown(t *testing.T) {
 		t.Fatal("expected error for unknown stage, got nil")
 	}
 }
+
+func TestBuildBoundedPlanEndpoints(t *testing.T) {
+	canonical := stageNames(BuildFullPlan())
+	for index, name := range canonical {
+		t.Run(name, func(t *testing.T) {
+			one, err := BuildBoundedPlan(name, name)
+			if err != nil {
+				t.Fatalf("BuildBoundedPlan(%q, %q) error = %v", name, name, err)
+			}
+			if got := one.Names(); !reflect.DeepEqual(got, []string{name}) {
+				t.Fatalf("one-stage names = %#v, want %q", got, name)
+			}
+			if one.From() != name || one.Through() != name || !one.Contains(name) || !one.HasExplicitBounds() {
+				t.Fatalf("one-stage plan endpoints or membership = %#v", one)
+			}
+
+			from, err := BuildBoundedPlan(name, "")
+			if err != nil {
+				t.Fatalf("BuildBoundedPlan(%q, empty) error = %v", name, err)
+			}
+			if got := from.Names(); !reflect.DeepEqual(got, canonical[index:]) {
+				t.Fatalf("from names = %#v, want %#v", got, canonical[index:])
+			}
+
+			through, err := BuildBoundedPlan("", name)
+			if err != nil {
+				t.Fatalf("BuildBoundedPlan(empty, %q) error = %v", name, err)
+			}
+			if got := through.Names(); !reflect.DeepEqual(got, canonical[:index+1]) {
+				t.Fatalf("through names = %#v, want %#v", got, canonical[:index+1])
+			}
+		})
+	}
+}
+
+func TestBuildBoundedPlanDefaultsToFullCanonicalPlan(t *testing.T) {
+	plan, err := BuildBoundedPlan("", "")
+	if err != nil {
+		t.Fatalf("BuildBoundedPlan() error = %v", err)
+	}
+	want := stageNames(BuildFullPlan())
+	if got := plan.Names(); !reflect.DeepEqual(got, want) {
+		t.Fatalf("bounded names = %#v, want %#v", got, want)
+	}
+	if plan.From() != want[0] || plan.Through() != want[len(want)-1] || plan.HasExplicitBounds() {
+		t.Fatalf("default endpoints = %q through %q explicit=%t", plan.From(), plan.Through(), plan.HasExplicitBounds())
+	}
+	if got := plan.PrefixNames(); len(got) != 0 {
+		t.Fatalf("default prefix = %#v, want empty", got)
+	}
+}
+
+func TestBuildBoundedPlanRejectsInvalidBounds(t *testing.T) {
+	tests := []struct {
+		name    string
+		from    string
+		through string
+		want    []string
+	}{
+		{name: "unknown from", from: "missing", through: "analyze", want: []string{"unknown from stage", "missing", "prepare", "notify"}},
+		{name: "unknown through", from: "extract", through: "missing", want: []string{"unknown through stage", "missing", "prepare", "notify"}},
+		{name: "reversed", from: "publish", through: "render", want: []string{"publish", "occurs after", "render", "prepare", "notify"}},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			_, err := BuildBoundedPlan(test.from, test.through)
+			if err == nil {
+				t.Fatal("BuildBoundedPlan() error = nil")
+			}
+			for _, fragment := range test.want {
+				if !strings.Contains(err.Error(), fragment) {
+					t.Fatalf("error = %q, want fragment %q", err, fragment)
+				}
+			}
+		})
+	}
+}
+
+func TestBoundedPlanIsContiguousAndCannotMutateRegistry(t *testing.T) {
+	before := stageNames(BuildFullPlan())
+	plan, err := BuildBoundedPlan("trim", "analyze")
+	if err != nil {
+		t.Fatalf("BuildBoundedPlan() error = %v", err)
+	}
+	want := []string{"trim", "render", "extract", "analyze"}
+	if got := plan.Names(); !reflect.DeepEqual(got, want) {
+		t.Fatalf("names = %#v, want contiguous %#v", got, want)
+	}
+	if got := plan.PrefixNames(); !reflect.DeepEqual(got, before[:5]) {
+		t.Fatalf("prefix = %#v, want %#v", got, before[:5])
+	}
+	stages := plan.Stages()
+	stages[0] = nil
+	names := plan.Names()
+	names[0] = "changed"
+	if got := plan.Names(); !reflect.DeepEqual(got, want) {
+		t.Fatalf("mutated plan names = %#v, want %#v", got, want)
+	}
+	if got := stageNames(BuildFullPlan()); !reflect.DeepEqual(got, before) {
+		t.Fatalf("canonical registry changed = %#v, want %#v", got, before)
+	}
+}
+
+func stageNames(stages []stage.Stage) []string {
+	names := make([]string, 0, len(stages))
+	for _, candidate := range stages {
+		names = append(names, candidate.Name())
+	}
+	return names
+}