Generalize the focus controller into a harness hosting swappable modes

Loosen AntiDrift's session controller into Keel's general collect→brain→act
loop. A new internal/harness runs at most one mode.Mode at a time, fanning
async completions out to the web SSE and status-bar surfaces.

- internal/mode: the Mode contract (Kind/Command/View/Active) plus optional
  EvidenceConsumer and Expirer ports, and the surfacing Envelope.
- internal/mode/focus: the former session/domain/statemachine packages moved
  under the mode, now satisfying the harness contracts unchanged.
- internal/mode/offscreen: a one-shot away-from-desk mode built on the new
  ai.Proposer, which turns a life-domain brief into one off-screen action.
- cmd/keeld replaces cmd/antidriftd; daemon wires focus + offscreen factories
  with per-mode persistence under ~/.keel/modes/<kind>.
- Finish the rename: KEEL_* env refs in the README, /keeld build artifact
  ignored, stale antidriftd binary removed.

Include the design + implementation plan this refactor was built from under
docs/superpowers/{specs,plans}/2026-06-04-controller-refactor*.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/mode/focus/domain/domain_test.go

@@ -0,0 +1,95 @@
+package domain
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestNewManualRejectsEmptyNextAction(t *testing.T) {
+	_, err := NewManual("", "tests pass", 25*time.Minute)
+	if err != ErrMissingNextAction {
+		t.Fatalf("want ErrMissingNextAction, got %v", err)
+	}
+}
+
+func TestNewManualRejectsEmptySuccessCondition(t *testing.T) {
+	_, err := NewManual("Refactor state", "  ", 25*time.Minute)
+	if err != ErrMissingSuccessCondition {
+		t.Fatalf("want ErrMissingSuccessCondition, got %v", err)
+	}
+}
+
+func TestNewManualRejectsZeroTimebox(t *testing.T) {
+	_, err := NewManual("Refactor state", "tests pass", 0)
+	if err != ErrMissingTimebox {
+		t.Fatalf("want ErrMissingTimebox, got %v", err)
+	}
+}
+
+func TestNewManualPopulatesDraftCommitment(t *testing.T) {
+	c, err := NewManual("  Port domain  ", "domain tests pass", 25*time.Minute)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if c.NextAction != "Port domain" {
+		t.Errorf("next action not trimmed: %q", c.NextAction)
+	}
+	if c.SuccessCondition != "domain tests pass" {
+		t.Errorf("success condition wrong: %q", c.SuccessCondition)
+	}
+	if c.TimeboxSecs != 1500 {
+		t.Errorf("timebox secs wrong: %d", c.TimeboxSecs)
+	}
+	if c.State != CommitmentDraft {
+		t.Errorf("state should be draft, got %s", c.State)
+	}
+	if c.Source != SourceManual {
+		t.Errorf("source should be manual, got %s", c.Source)
+	}
+	if !strings.HasPrefix(c.ID, "commitment-") {
+		t.Errorf("id should be prefixed, got %s", c.ID)
+	}
+}
+
+func TestNewManualRejectsSubSecondTimebox(t *testing.T) {
+	_, err := NewManual("Refactor state", "tests pass", 500*time.Millisecond)
+	if err != ErrMissingTimebox {
+		t.Fatalf("want ErrMissingTimebox, got %v", err)
+	}
+}
+
+func TestForRuntimePopulatesPolicySnapshot(t *testing.T) {
+	p := ForRuntime("commitment-123", RuntimeActive, EnforcementObserve)
+	if !strings.HasPrefix(p.ID, "policy-") {
+		t.Errorf("id should be prefixed, got %s", p.ID)
+	}
+	if p.CommitmentID != "commitment-123" {
+		t.Errorf("commitment id wrong: %s", p.CommitmentID)
+	}
+	if p.SchemaVersion != PolicySchemaVersion {
+		t.Errorf("schema version wrong: %d", p.SchemaVersion)
+	}
+	if p.RuntimeState != RuntimeActive {
+		t.Errorf("runtime state wrong: %s", p.RuntimeState)
+	}
+	if p.EnforcementLevel != EnforcementObserve {
+		t.Errorf("enforcement level wrong: %s", p.EnforcementLevel)
+	}
+}
+
+func TestCommitmentSerializesSnakeCaseEnums(t *testing.T) {
+	c, _ := NewManual("Port domain", "domain tests pass", 25*time.Minute)
+	data, err := json.Marshal(c)
+	if err != nil {
+		t.Fatalf("marshal failed: %v", err)
+	}
+	s := string(data)
+	if !strings.Contains(s, `"source":"manual"`) {
+		t.Errorf("missing snake_case source in %s", s)
+	}
+	if !strings.Contains(s, `"state":"draft"`) {
+		t.Errorf("missing snake_case state in %s", s)
+	}
+}