feat: increase activity monitor half-life to 72 hours (3 days)

Changed JUPYTERHUB_ACTIVITYMON_HALF_LIFE default from 48h to 72h
for more stable activity scores. Activity from 3 days ago now has
50% weight, better suited for users with irregular schedules.

Updated: Dockerfile, custom_handlers.py, activity_sampler.py,
settings_dictionary.yml, README.md, docs/activity-tracking-methodology.md

.claude/JOURNAL.md

@@ -249,3 +249,6 @@ This journal tracks substantive work on documents, diagrams, and documentation c
 
 82. **Task - Simplify Activity column header**: Removed retention period from column title<br>
     **Result**: Changed Activity column header from "Activity (7 days)" to just "Activity" in activity.html
+
+83. **Task - Activity monitor half-life to 72h (3 days)**: Extended decay half-life for smoother scoring<br>
+    **Result**: Updated JUPYTERHUB_ACTIVITYMON_HALF_LIFE default from 48h to 72h across Dockerfile, custom_handlers.py, activity_sampler.py, settings_dictionary.yml, README.md, and docs/activity-tracking-methodology.md. With 72h half-life, activity from 3 days ago has 50% weight, providing more stable activity scores for users with irregular schedules

README.md

@@ -392,7 +392,7 @@ services:
     environment:
       - JUPYTERHUB_ACTIVITYMON_SAMPLE_INTERVAL=600   # 10 minutes (default) - how often to record samples
       - JUPYTERHUB_ACTIVITYMON_RETENTION_DAYS=7      # 7 days (default) - how long to keep samples
-      - JUPYTERHUB_ACTIVITYMON_HALF_LIFE=48          # 48 hours (default) - decay half-life for scoring
+      - JUPYTERHUB_ACTIVITYMON_HALF_LIFE=72          # 72 hours / 3 days (default) - decay half-life for scoring
       - JUPYTERHUB_ACTIVITYMON_INACTIVE_AFTER=60     # 60 minutes (default) - threshold for inactive status
 ```
 

docs/activity-tracking-methodology.md

@@ -7,7 +7,7 @@ Our current approach uses **exponential decay scoring**:
 - Each sample marked active/inactive based on `last_activity` within threshold
 - Score calculated as weighted ratio: `weighted_active / weighted_total`
 - Weight formula: `weight = exp(-λ × age_hours)` where `λ = ln(2) / half_life`
-- Default half-life: 24 hours (activity from yesterday worth 50%)
+- Default half-life: 72 hours / 3 days (activity from 3 days ago worth 50%)
 
 ## Industry Approaches
 
@@ -157,14 +157,13 @@ Our current implementation is actually well-designed for the use case:
 |--------|------------------------|
 | Sampling | Every 10 min (configurable) |
 | Active threshold | 60 min since last_activity |
-| Decay | 24-hour half-life |
+| Decay | 72-hour (3-day) half-life |
 | Score range | 0-100% |
 | Visualization | 5-segment bar with color coding |
 
 **Suggested improvements:**
 1. Add tooltip showing actual score percentage
-2. Consider longer half-life (48-72h) for less frequent users
-3. Document what the score represents
+2. Document what the score represents
 
 ### Option B: Hybrid Daily + Decay
 
@@ -205,8 +204,8 @@ Weekly score = sum of daily points / 7
    - Option: Relative to user's own historical average
 
 2. **How fast should old activity decay?**
-   - Current: 24-hour half-life (aggressive decay)
-   - Alternative: 72-hour half-life (more stable)
+   - Current: 72-hour / 3-day half-life (balanced decay)
+   - Alternative: 24-hour half-life (aggressive decay)
    - Alternative: 7-day half-life (weekly trend)
 
 3. **Should weekends count differently?**

services/jupyterhub/Dockerfile.jupyterhub

@@ -90,7 +90,7 @@ ENV JUPYTERHUB_IDLE_CULLER_MAX_EXTENSION=24
 # Activity monitor
 ENV JUPYTERHUB_ACTIVITYMON_SAMPLE_INTERVAL=600
 ENV JUPYTERHUB_ACTIVITYMON_RETENTION_DAYS=7
-ENV JUPYTERHUB_ACTIVITYMON_HALF_LIFE=48
+ENV JUPYTERHUB_ACTIVITYMON_HALF_LIFE=72
 ENV JUPYTERHUB_ACTIVITYMON_INACTIVE_AFTER=60
 ENV JUPYTERHUB_ACTIVITYMON_RESOURCES_UPDATE_INTERVAL=10
 ENV JUPYTERHUB_ACTIVITYMON_VOLUMES_UPDATE_INTERVAL=3600

services/jupyterhub/conf/bin/activity_sampler.py

@@ -14,7 +14,7 @@ Environment Variables:
     JUPYTERHUB_API_URL: Hub API URL (provided by JupyterHub)
     JUPYTERHUB_ACTIVITYMON_SAMPLE_INTERVAL: Sampling interval in seconds (default: 600)
     JUPYTERHUB_ACTIVITYMON_RETENTION_DAYS: Days to retain samples (default: 7)
-    JUPYTERHUB_ACTIVITYMON_HALF_LIFE: Score decay half-life in hours (default: 48)
+    JUPYTERHUB_ACTIVITYMON_HALF_LIFE: Score decay half-life in hours (default: 72)
     JUPYTERHUB_ACTIVITYMON_INACTIVE_AFTER: Minutes before marking inactive (default: 60)
 """
 
@@ -71,7 +71,7 @@ class ActivitySamplerService:
         # Sampling configuration
         self.sample_interval = int(os.environ.get('JUPYTERHUB_ACTIVITYMON_SAMPLE_INTERVAL', 600))
         self.retention_days = int(os.environ.get('JUPYTERHUB_ACTIVITYMON_RETENTION_DAYS', 7))
-        self.half_life_hours = int(os.environ.get('JUPYTERHUB_ACTIVITYMON_HALF_LIFE', 48))
+        self.half_life_hours = int(os.environ.get('JUPYTERHUB_ACTIVITYMON_HALF_LIFE', 72))
         self.inactive_after_minutes = int(os.environ.get('JUPYTERHUB_ACTIVITYMON_INACTIVE_AFTER', 60))
 
         # Database

services/jupyterhub/conf/bin/custom_handlers.py

@@ -94,7 +94,7 @@ class ActivityMonitor:
 
     # Default configuration
     DEFAULT_RETENTION_DAYS = 7       # 7 days
-    DEFAULT_HALF_LIFE = 48           # 48 hours
+    DEFAULT_HALF_LIFE = 72           # 72 hours (3 days)
     DEFAULT_INACTIVE_AFTER = 60      # 60 minutes
     DEFAULT_ACTIVITY_UPDATE_INTERVAL = 600  # 10 minutes
 

services/jupyterhub/conf/settings_dictionary.yml

@@ -87,7 +87,7 @@ Activity Monitor:
 
   - name: JUPYTERHUB_ACTIVITYMON_HALF_LIFE
     description: Decay half-life in hours (1-168)
-    default: "48"
+    default: "72"
 
   - name: JUPYTERHUB_ACTIVITYMON_INACTIVE_AFTER
     description: Minutes until user considered inactive (1-1440)