feat(ai): AmbientDrift — frame-grounded drift judge

internal/ai/ambient.go

@@ -0,0 +1,79 @@
+// internal/ai/ambient.go
+package ai
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// AmbientDriftJudge judges whether current activity serves the user's standing
+// frame when NO task is declared. Like Nudge it takes primitives, not domain
+// types, so ai stays a leaf. The returned string is a one-sentence advisory, or
+// "" when the activity is plausibly on-track.
+type AmbientDriftJudge interface {
+	AmbientDrift(ctx context.Context, frame string, recentTitles []string) (string, error)
+}
+
+// ErrInvalidAmbientDrift marks a parseable-but-unusable ambient response.
+var ErrInvalidAmbientDrift = errors.New("ai: invalid ambient drift")
+
+// AmbientDrift makes Service satisfy AmbientDriftJudge over the same backend.
+func (s *Service) AmbientDrift(ctx context.Context, frame string, recentTitles []string) (string, error) {
+	out, err := s.backend.Run(ctx, buildAmbientPrompt(frame, recentTitles))
+	if err != nil {
+		return "", err
+	}
+	return parseAmbientDrift(out)
+}
+
+func buildAmbientPrompt(frame string, recentTitles []string) string {
+	return `You are an ambient coach. The user has NOT declared a task. Below is their standing frame — goals, values, and life-domains — and today's tasks, then the recent sequence of window titles. Decide whether the recent activity plausibly serves ANY of what matters to them, or whether it is a slide into drift.
+
+Be forgiving: legitimate breaks, rest, admin, and unplanned-but-useful work are ON-TRACK. Only call drift when the activity clearly serves none of what matters.
+
+Respond with ONLY a JSON object, no prose and no code fences, exactly this shape:
+{"drifting": <true or false>, "message": "<short explanation, one sentence>"}
+
+Rules:
+- drifting: true only if the recent activity serves none of the frame; false otherwise.
+- message: one short sentence naming the drift. REQUIRED when drifting is true.
+
+## Frame
+` + frame + `
+
+## Recent window titles (oldest to newest)
+` + strings.Join(recentTitles, "\n")
+}
+
+type rawAmbientDrift struct {
+	Drifting bool   `json:"drifting"`
+	Message  string `json:"message"`
+}
+
+// parseAmbientDrift extracts the advisory from raw CLI output. On-track yields
+// "". A drift with no message degrades to "" (silence) rather than an error:
+// the ambient signal is advisory, so the safe degenerate is to say nothing —
+// exactly like parseNudge.
+func parseAmbientDrift(s string) (string, error) {
+	if strings.TrimSpace(s) == "" {
+		return "", ErrEmptyResponse
+	}
+	if strings.IndexByte(s, '{') < 0 {
+		return "", ErrNoJSON
+	}
+	jsonStr, err := extractJSON(s)
+	if err != nil {
+		return "", fmt.Errorf("%w: %v", ErrInvalidAmbientDrift, err)
+	}
+	var raw rawAmbientDrift
+	if err := json.Unmarshal([]byte(jsonStr), &raw); err != nil {
+		return "", fmt.Errorf("%w: %v", ErrInvalidAmbientDrift, err)
+	}
+	if !raw.Drifting {
+		return "", nil
+	}
+	return strings.TrimSpace(raw.Message), nil
+}

internal/ai/ambient_test.go

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+// internal/ai/ambient_test.go
+package ai
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestServiceAmbientDriftSuccess(t *testing.T) {
+	fb := &fakeBackend{out: `{"drifting": true, "message": "deep in YouTube, none of today's goals"}`}
+	line, err := NewService(fb).AmbientDrift(context.Background(), "## Goals\nship keel", []string{"YouTube - Brave"})
+	if err != nil {
+		t.Fatalf("ambient drift: %v", err)
+	}
+	if line == "" {
+		t.Fatal("expected a non-empty drift line")
+	}
+	if !strings.Contains(fb.gotPrompt, "ship keel") {
+		t.Fatalf("prompt should embed the frame, got: %s", fb.gotPrompt)
+	}
+	if !strings.Contains(fb.gotPrompt, "YouTube - Brave") {
+		t.Fatalf("prompt should embed the recent titles, got: %s", fb.gotPrompt)
+	}
+}
+
+func TestServiceAmbientDriftBackendError(t *testing.T) {
+	fb := &fakeBackend{err: errors.New("boom")}
+	if _, err := NewService(fb).AmbientDrift(context.Background(), "frame", []string{"x"}); err == nil {
+		t.Fatal("want backend error")
+	}
+}
+
+func TestParseAmbientDrift(t *testing.T) {
+	tests := []struct {
+		name    string
+		in      string
+		want    string
+		wantErr error
+	}{
+		{"on track yields empty", `{"drifting": false, "message": ""}`, "", nil},
+		{"drift returns message", `{"drifting": true, "message": "watching unrelated videos"}`, "watching unrelated videos", nil},
+		{"drift is trimmed", `{"drifting": true, "message": "  slid  "}`, "slid", nil},
+		{"drift without message degrades to silence", `{"drifting": true, "message": ""}`, "", nil},
+		{"json embedded in prose", `ok: {"drifting": true, "message": "off track"} done`, "off track", nil},
+		{"empty response", "   ", "", ErrEmptyResponse},
+		{"no json", "no braces here", "", ErrNoJSON},
+		{"malformed json", `{"drifting": true, "message":`, "", ErrInvalidAmbientDrift},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := parseAmbientDrift(tt.in)
+			if tt.wantErr != nil {
+				if !errors.Is(err, tt.wantErr) {
+					t.Fatalf("err = %v, want %v", err, tt.wantErr)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected err: %v", err)
+			}
+			if got != tt.want {
+				t.Fatalf("got %q, want %q", got, tt.want)
+			}
+		})
+	}
+}