M5: Replace streak logic with Adherence Rate + Tracking Consistency

[Sturmi77]

Context

M5 was originally planned with streak-based habit tracking. This conflicts with the new core promise "No gamification, ever — you track your habits, not how often you open the app".

Streaks are gamification by definition: they punish interruptions, create artificial urgency, and optimize for app opens rather than genuine user value.

Decision

Streaks in M5 are replaced entirely by three non-gamification alternatives:

1. Adherence Rate (primary KPI)

Instead of "12-day sport streak", show: "Sport: 71% of the last 4 weeks"

• Honest, does not break on a single missed day
• No guilt-trip framing
• Formula: count(days_with_tag) / total_days_in_window * 100
• Configurable window: 7 / 14 / 28 / 90 days

2. Calendar Heatmap (visual representation)

• Reuse existing M2 tag-frequency heatmap component
• No number, no "you failed" moment
• Visual frequency display only
• GitHub-contribution-graph style but without any streak counter

3. Correlation Contribution Score (long-term value)

• Show how strongly a habit contributes to insight quality: "Sport is your strongest mood predictor (r=0.72)"
• Pulled from M3/M8 insight engine output
• The real reason why consistent tracking matters — no artificial motivation needed

Impact on M2 Entry-Streak Widget

The M2 entry-streak widget is already implemented. It should be relabeled (not removed):

• Old: "Streak: 12 days" (gamification framing)
• New: "Tracking consistency: 12 of last 14 days" (neutral, data-quality framing)
• Rationale: this is directly linked to the confidence scale from the insight engine — more consistent data = better insights. That is the honest reason to keep tracking.

Acceptance Criteria

• No streak counter anywhere in the habits UI
• Adherence Rate shown as primary habit KPI (configurable window: 7/14/28/90 days)
• Calendar heatmap reused from M2 for habit frequency visualization
• Correlation Contribution Score shown per habit (requires M3 insight engine data)
• M2 Entry-Streak widget relabeled to "Tracking consistency: X of last Y days"
• No badge, points, or reward system of any kind
• Habit language remains neutral: build / reduce, never good / bad
• No "you failed" or "streak broken" messaging in any UI state
• Quality-Gate: Code-Quality-Review + Security-Audit passed

References

• Core promise: "No gamification, ever — you track your habits, not how often you open the app"
• ADR-0012: M2/M5 streak semantics (to be updated)
• M3 Insight Engine (correlation contribution data source)
• M2 Entry-Streak widget (relabeling only, no schema change)

[Sturmi77]

M3 reconciliation note (2026-05-12): this remains intentionally outside the M3 implementation scope. It is the M5 habit redesign track. M3 will provide correlation/insight data that M5 can later consume, but this issue should not block M3 closure.