Implement unified Atom model for multi-source abstraction

- Create internal/models/atom.go with Atom struct and enums
- Add mapper functions for Task, Card, Note, and Meal types
- Normalize priority scales (1-4) and assign brand colors
- Update Phase 2 plan with Atom architecture as Step 1
- Document architectural decision in SESSION_STATE.md

This abstraction enables consistent handling, sorting, and rendering
of items from Trello, Todoist, Obsidian, and PlanToEat sources.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

3 files changed, 261 insertions, 1 deletions

diff --git a/PHASE_2_SURGICAL_PLAN.md b/PHASE_2_SURGICAL_PLAN.md
new file mode 100644
index 0000000..dbac3a6
--- /dev/null
+++ b/PHASE_2_SURGICAL_PLAN.md
@@ -0,0 +1,114 @@
+# Phase 2: The Productivity OS (Interactive & Refined)
+
+This phase transforms the dashboard into a primary interface with write capabilities, smart sorting, and a refined "Glassmorphism" UI.
+
+## 1. The Unified Atom Model
+**Status:** [ ] Pending
+
+```text
+Define `models.Atom` to abstract over Trello, Todoist, Obsidian, and PlanToEat.
+Implement mapper functions.
+
+1.  **Model:** Create `internal/models/atom.go` with:
+    - AtomSource enum (trello, todoist, obsidian, plantoeat)
+    - AtomType enum (task, note, meal)
+    - Atom struct with normalized fields (ID, Title, Description, DueDate, Priority, etc.)
+    - UI helper fields (SourceIcon, ColorClass)
+    - Raw field for preserving original data
+2.  **Mappers:** Implement converter functions:
+    - TaskToAtom(Task) -> Atom
+    - CardToAtom(Card) -> Atom
+    - NoteToAtom(Note) -> Atom
+    - MealToAtom(Meal) -> Atom
+3.  **Priority Mapping:** Normalize priority scales to 1-4 (Low to Urgent)
+4.  **Color Mapping:** Assign brand colors (Trello=Blue, Todoist=Red, Obsidian=Purple, PlanToEat=Green)
+```
+
+## 2. Information Architecture: The 4-Tab Split
+**Status:** [ ] Pending
+
+```text
+Refactor the frontend and router to support 4 distinct tabs.
+
+1.  **Templates:** Update `web/templates/index.html` navigation to:
+    - Tasks (Todoist + Due Trello)
+    - Planning (Trello Boards)
+    - Notes (Obsidian)
+    - Meals (PlanToEat)
+2.  **Handlers:** Create/Update handlers in `internal/handlers/tabs.go` (new file):
+    - `HandleTasksTab`: Aggregates Todoist + Trello cards with due dates.
+    - `HandlePlanningTab`: Returns Trello boards (excluding cards shown in Tasks?).
+    - `HandleMealsTab`: Returns PlanToEat data.
+3.  **Router:** Register new routes `/tabs/tasks`, `/tabs/planning`, `/tabs/meals`.
+```
+
+## 3. Trello: Smart Sorting & Logic
+**Status:** [ ] Pending
+
+```text
+Enhance Trello sorting in `internal/api/trello.go` and `internal/store/sqlite.go`.
+
+1.  **Backend:** Update `GetBoardsWithCards` to sort by:
+    - Primary: Has active cards?
+    - Secondary: Newest card modification date (requires parsing Trello ID hex timestamp).
+    - Tertiary: Number of cards.
+2.  **Store:** Update SQL query in `GetBoards` to reflect this sort order.
+```
+
+## 4. Todoist: "Due First" Sorting
+**Status:** [ ] Pending
+
+```text
+Ensure Todoist tasks are sorted by urgency.
+
+1.  **Store:** Edit `internal/store/sqlite.go` -> `GetTasks`.
+2.  **Query:** Update ORDER BY clause:
+    - `CASE WHEN due_date IS NULL THEN 1 ELSE 0 END` (Due dates first)
+    - `due_date ASC` (Earliest first)
+    - `priority DESC` (High priority next)
+```
+
+## 5. Obsidian: Search & Categorization
+**Status:** [ ] Pending
+
+```text
+Enhance Obsidian to support search and categorization.
+
+1.  **Backend:** Edit `internal/api/obsidian.go`.
+    - Add `SearchNotes(query string)`.
+    - Add logic to group notes by tags (e.g., #planning, #task, #meal).
+2.  **Frontend:** Add a Search Bar to the Notes tab.
+    - HTMX trigger: `hx-get="/tabs/notes/search" hx-trigger="keyup changed delay:500ms"`.
+```
+
+## 6. Visual Overhaul: "Muted Landscape"
+**Status:** [ ] Pending
+
+```text
+Apply the new visual design.
+
+1.  **CSS:** Update Tailwind config for "muted" palette.
+2.  **Layout:** Add a full-screen background image container.
+3.  **Components:** Update cards to use `bg-white/80 backdrop-blur-md` (Glassmorphism).
+```
+
+## 7. Write Operations (The "Primary Interface" Goal)
+**Status:** [ ] Pending
+
+```text
+Implement the interactive features.
+
+1.  **Trello:** Implement `UpdateCard` (Archive) and "Mark Complete" button.
+2.  **Obsidian:** Implement `CreateNote` (Quick Capture) and "New Note" form.
+```
+
+## 8. Mobile PWA
+**Status:** [ ] Pending
+
+```text
+Make it installable.
+
+1.  Create `web/static/manifest.json`.
+2.  Add icons.
+3.  Link manifest in `index.html`.
+```
diff --git a/SESSION_STATE.md b/SESSION_STATE.md
index f4b76f0..e3a498e 100644
--- a/SESSION_STATE.md
+++ b/SESSION_STATE.md
@@ -32,6 +32,13 @@ Frontend modernization with tabs, HTMX, and Tailwind build pipeline complete.
   - Empty boards now pushed to bottom, active boards at top
   - **Commit:** 9ef5b7f "Sort Trello boards with active boards first"
 - **Frontend Modernization:** Complete UI overhaul with tabs, HTMX, and Tailwind build pipeline
+  - **Commit:** 06c7485 "Modernize frontend with tabs, HTMX, and Tailwind build pipeline"
+- **Unified Atom Model:** Created abstraction layer for all data sources
+  - internal/models/atom.go: New Atom struct with AtomSource and AtomType enums
+  - Mapper functions: TaskToAtom, CardToAtom, NoteToAtom, MealToAtom
+  - Priority normalization (1-4 scale), brand color mapping (Trello=Blue, Todoist=Red, Obsidian=Purple, PlanToEat=Green)
+  - Preserves raw data for future write operations
+  - All tests passing after implementation
   - **Build Pipeline:** npm + PostCSS + Tailwind configuration (replaced CDN)
     - package.json, tailwind.config.js, postcss.config.js, Makefile
     - Custom design system with brand colors (Trello, Todoist, Obsidian, PlanToEat)
@@ -72,9 +79,13 @@ Frontend modernization with tabs, HTMX, and Tailwind build pipeline complete.
 - **Decision:** Compiled Tailwind over CDN for 99% smaller CSS and custom design tokens.
 - **Decision:** Template partials for HTMX-friendly swap targets and reusability.
 - **Decision:** Native `<details>` element for empty board collapsible (no JS required).
+- **Decision:** Unified Atom Model - Abstract all data sources (Trello, Todoist, Obsidian, PlanToEat) into a single `models.Atom` type for consistent handling, sorting, and rendering across the UI.
 
 ## 📋 Next Steps
-1. **Future:** Consider Phase 2 features (write operations, user management).
+1. **Phase 2 Step 2:** Implement 4-Tab Split (Tasks, Planning, Notes, Meals) using the Atom model.
+2. **Phase 2 Step 3:** Trello smart sorting (activity-based, modification date).
+3. **Phase 2 Step 4:** Todoist "due first" sorting.
+4. **Phase 2 Remaining:** Search, visual overhaul, write operations, PWA.
 
 ## ⚠️ Known Blockers / Debt
 - None currently.
diff --git a/internal/models/atom.go b/internal/models/atom.go
new file mode 100644
index 0000000..47695d9
--- /dev/null
+++ b/internal/models/atom.go
@@ -0,0 +1,135 @@
+package models
+
+import "time"
+
+type AtomSource string
+
+const (
+	SourceTrello   AtomSource = "trello"
+	SourceTodoist  AtomSource = "todoist"
+	SourceObsidian AtomSource = "obsidian"
+	SourceMeal     AtomSource = "plantoeat"
+)
+
+type AtomType string
+
+const (
+	TypeTask AtomType = "task"
+	TypeNote AtomType = "note"
+	TypeMeal AtomType = "meal"
+)
+
+// Atom represents a unified unit of work or information
+type Atom struct {
+	ID          string
+	Title       string
+	Description string
+	Source      AtomSource
+	Type        AtomType
+
+	// Metadata
+	URL       string
+	DueDate   *time.Time
+	CreatedAt time.Time
+
+	Priority int // Normalized: 1 (Low) to 4 (Urgent)
+
+	// UI Helpers (to be populated by mappers)
+	SourceIcon string // e.g., "trello-icon.svg" or emoji
+	ColorClass string // e.g., "border-blue-500"
+
+	// Original Data (for write operations)
+	Raw interface{}
+}
+
+// TaskToAtom converts a Todoist Task to an Atom
+func TaskToAtom(t Task) Atom {
+	// Todoist priority: 1 (normal) to 4 (urgent)
+	// Keep as-is since it already matches our 1-4 scale
+	priority := t.Priority
+	if priority < 1 {
+		priority = 1
+	}
+	if priority > 4 {
+		priority = 4
+	}
+
+	return Atom{
+		ID:          t.ID,
+		Title:       t.Content,
+		Description: t.Description,
+		Source:      SourceTodoist,
+		Type:        TypeTask,
+		URL:         t.URL,
+		DueDate:     t.DueDate,
+		CreatedAt:   t.CreatedAt,
+		Priority:    priority,
+		SourceIcon:  "✓", // Checkmark emoji for tasks
+		ColorClass:  "border-red-500",
+		Raw:         t,
+	}
+}
+
+// CardToAtom converts a Trello Card to an Atom
+func CardToAtom(c Card) Atom {
+	// Trello doesn't have explicit priority, default to medium (2)
+	// Can be enhanced later with label-based priority detection
+	priority := 2
+
+	return Atom{
+		ID:          c.ID,
+		Title:       c.Name,
+		Description: c.ListName, // Use list name as description
+		Source:      SourceTrello,
+		Type:        TypeTask,
+		URL:         c.URL,
+		DueDate:     c.DueDate,
+		CreatedAt:   time.Time{}, // Trello ID contains timestamp, can be parsed later
+		Priority:    priority,
+		SourceIcon:  "📋", // Clipboard emoji for boards
+		ColorClass:  "border-blue-500",
+		Raw:         c,
+	}
+}
+
+// NoteToAtom converts an Obsidian Note to an Atom
+func NoteToAtom(n Note) Atom {
+	// Notes don't have priority, default to low (1)
+	priority := 1
+
+	return Atom{
+		ID:          n.Path, // Use path as unique ID
+		Title:       n.Title,
+		Description: n.Content,
+		Source:      SourceObsidian,
+		Type:        TypeNote,
+		URL:         "",     // Obsidian notes don't have URLs
+		DueDate:     nil,    // Notes typically don't have due dates
+		CreatedAt:   n.Modified, // Use modified time as created time
+		Priority:    priority,
+		SourceIcon:  "📝", // Memo emoji for notes
+		ColorClass:  "border-purple-500",
+		Raw:         n,
+	}
+}
+
+// MealToAtom converts a PlanToEat Meal to an Atom
+func MealToAtom(m Meal) Atom {
+	// Meals don't have priority, default to low (1)
+	priority := 1
+
+	return Atom{
+		ID:          m.ID,
+		Title:       m.RecipeName,
+		Description: m.MealType, // breakfast, lunch, dinner
+		Source:      SourceMeal,
+		Type:        TypeMeal,
+		URL:         m.RecipeURL,
+		DueDate:     &m.Date, // Meal date is effectively the "due date"
+		CreatedAt:   time.Time{},
+		Priority:    priority,
+		SourceIcon:  "🍽️", // Fork and knife emoji for meals
+		ColorClass:  "border-green-500",
+		Raw:         m,
+	}
+}