Split session time into on/off/unclassified buckets

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

internal/session/stats.go

@@ -11,14 +11,17 @@ type bucketKey struct{ Class, Title string }
 
 // EvidenceStats is the in-memory accounting for the current session only.
 type EvidenceStats struct {
-	SessionID   string
-	StartedUnix int64
-	Buckets     map[bucketKey]time.Duration
-	SwitchCount int
-	Current     evidence.WindowSnapshot
-	lastFocusAt time.Time
-	lastKey     bucketKey
-	hasLast     bool
+	SessionID    string
+	StartedUnix  int64
+	Buckets      map[bucketKey]time.Duration // total time per bucket (unchanged)
+	OnTask       map[bucketKey]time.Duration // on-task portion per bucket
+	OffTask      map[bucketKey]time.Duration // off-task portion per bucket
+	unclassified time.Duration               // idle/pending time; aggregate only
+	SwitchCount  int
+	Current      evidence.WindowSnapshot
+	lastFocusAt  time.Time
+	lastKey      bucketKey
+	hasLast      bool
 }
 
 // applyEvent advances stats by one observation: it credits the prior segment to
@@ -26,7 +29,7 @@ type EvidenceStats struct {
 // current window. Used by both live tracking and crash replay. Caller holds mu.
 func (c *Controller) applyEvent(now time.Time, snap evidence.WindowSnapshot) {
 	if c.stats.hasLast {
-		c.stats.Buckets[c.stats.lastKey] += now.Sub(c.stats.lastFocusAt)
+		c.creditLocked(c.stats.lastKey, now.Sub(c.stats.lastFocusAt))
 	}
 	newKey := keyFor(snap)
 	if c.stats.hasLast && newKey != c.stats.lastKey {
@@ -38,6 +41,24 @@ func (c *Controller) applyEvent(now time.Time, snap evidence.WindowSnapshot) {
 	c.stats.Current = snap
 }
 
+// creditLocked credits duration d to bucket k: always to the running total, and
+// to the on/off/unclassified split per the live drift status — which, at every
+// credit site, is the classification of the segment being credited (applyEvent
+// runs before evaluateDriftLocked reclassifies; the end-of-session flush runs
+// before the state transition). idle/pending route to unclassified: honest, never
+// falsely on-task. Caller holds mu.
+func (c *Controller) creditLocked(k bucketKey, d time.Duration) {
+	c.stats.Buckets[k] += d
+	switch c.driftStatus {
+	case driftOnTask:
+		c.stats.OnTask[k] += d
+	case driftDrifting:
+		c.stats.OffTask[k] += d
+	default: // driftIdle, driftPending
+		c.stats.unclassified += d
+	}
+}
+
 // replayStats rebuilds in-memory stats from the raw session log after a crash.
 func (c *Controller) replayStats(sessionID string) {
 	events, err := store.ReplaySession(c.sessionsDir, sessionID)
@@ -46,6 +67,8 @@ func (c *Controller) replayStats(sessionID string) {
 			SessionID:   sessionID,
 			StartedUnix: c.clock().Unix(),
 			Buckets:     map[bucketKey]time.Duration{},
+			OnTask:      map[bucketKey]time.Duration{},
+			OffTask:     map[bucketKey]time.Duration{},
 		}
 		return
 	}
@@ -53,7 +76,12 @@ func (c *Controller) replayStats(sessionID string) {
 		SessionID:   sessionID,
 		StartedUnix: events[0].AtUnixMillis / 1000,
 		Buckets:     map[bucketKey]time.Duration{},
+		OnTask:      map[bucketKey]time.Duration{},
+		OffTask:     map[bucketKey]time.Duration{},
 	}
+	// Drift status is not persisted, so replayed pre-crash segments credit to
+	// unclassified (driftStatus is driftIdle here). Totals in Buckets are exact;
+	// only the on/off split degrades — honest, never falsely on-task.
 	for _, e := range events {
 		c.applyEvent(time.UnixMilli(e.AtUnixMillis), snapFromEvent(e))
 	}