Feature: Agentic AI Productivity Assistant for Smart Task Management

### Summary

Introduce an **Agentic AI assistant** into TaskNexus that can help users manage their tasks proactively. Instead of only adding, completing, or deleting tasks, the AI will be able to:

* Suggest priorities based on deadlines & workload.
* Automatically categorize tasks (work, personal, urgent).
* Recommend time blocks or schedules.
* Generate insights like “You’re most productive on mornings, schedule hard tasks then.”
* Auto-detect overdue tasks and propose re-scheduling.

This makes TaskNexus not just a **task tracker** but a **personal productivity coach**.

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### Problem / Motivation

Currently, TaskNexus functions as a **reactive task manager** — users must manually add, update, and prioritize tasks. But modern productivity tools increasingly include AI-driven assistance to help users avoid overwhelm.

Adding an **agentic AI** layer will enable:

* Smarter planning (not just storing tasks).
* Personalized recommendations.
* Adaptive workflows (AI learns from usage patterns).

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### Proposed Solution

* **Backend**

* Add an `ai-agent-service` that integrates with Supabase tasks.
* Endpoints:

* `/api/agent/prioritize` → Returns ranked task list.
* `/api/agent/schedule` → Suggests a time-block schedule.
* `/api/agent/insights` → Provides weekly insights.
* **Frontend**

* New “Smart Assistant” tab in the bottom nav.
* Inline “AI Suggest” button in Task Add/Edit modal.
* Daily productivity digest notification (via Expo push).

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### Architecture (Mermaid)

```mermaid
flowchart TD
User[User Tasks & Data] --> AgentPlanner[AI Agent Planner]
AgentPlanner --> Prioritizer[Task Prioritizer]
AgentPlanner --> Categorizer[Auto Categorizer]
AgentPlanner --> Scheduler[Smart Scheduler]
AgentPlanner --> InsightGen[Weekly Insights Generator]
Prioritizer --> Supabase[(Supabase DB)]
Categorizer --> Supabase
Scheduler --> Supabase
InsightGen --> Supabase
Supabase --> Results[AI Recommendations]
Results --> User
```

* **Agent Planner**: Decides which analysis to run.
* **Prioritizer**: Orders tasks by urgency, importance, and context.
* **Categorizer**: Auto-assigns tags/categories.
* **Scheduler**: Suggests calendar-friendly blocks.
* **Insight Generator**: Produces weekly productivity reports.

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### Acceptance Criteria

* [ ] Users can tap **“Smart Assistant”** to see prioritized tasks.
* [ ] AI can suggest due dates or rescheduling for overdue tasks.
* [ ] Weekly insights include patterns (e.g., completion rates, time-of-day trends).
* [ ] Tasks get auto-categorized (e.g., Work, Personal, Urgent).
* [ ] Push notification reminders can be AI-generated.

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### Benefits

* Makes TaskNexus a **proactive productivity tool** instead of just a static tracker.
* Improves **task completion rates** with better prioritization.
* Provides **personalized insights** for continuous productivity growth.
* Differentiates TaskNexus from basic to-do apps.

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