feat(dev-workflow): Add intelligent backend selection based on task complexity

## Changes

### Core Improvements
1. **Flexible Task Count**: Remove 2-5 hard limit, use natural functional boundaries (typically 2-8)
2. **Complexity-Based Routing**: Tasks rated as simple/medium/complex based on functional requirements
3. **Intelligent Backend Selection**: Orchestrator auto-selects backend based on complexity
   - Simple/Medium → claude (fast, cost-effective)
   - Complex → codex (deep reasoning)
   - UI → gemini (enforced)

### Modified Files
- `dev-workflow/agents/dev-plan-generator.md`:
  - Add complexity field to task template
  - Add comprehensive complexity assessment guide
  - Update quality checks to include complexity validation
  - Remove artificial task count limits

- `dev-workflow/commands/dev.md`:
  - Add backend selection logic in Step 4
  - Update task breakdown to include complexity ratings
  - Add detailed examples for each backend type
  - Update quality standards

- `dev-workflow/README.md`:
  - Update documentation to reflect intelligent backend selection
  - Add complexity-based routing explanation
  - Update examples with complexity ratings

## Architecture
- No changes to codeagent-wrapper (all logic in orchestrator)
- Backward compatible (existing workflows continue to work)
- Complexity evaluation based on functional requirements, NOT code volume

## Benefits
- Better resource utilization (use claude for most tasks, codex for complex ones)
- Cost optimization (avoid using expensive codex for simple tasks)
- Flexibility (no artificial limits on task count)
- Clear complexity rationale for each task

Generated with swe-agent-bot

Co-Authored-By: swe-agent-bot <agent@swe-agent.ai>

dev-workflow/README.md

@@ -15,7 +15,7 @@ codeagent analysis (plan mode + UI auto-detection)
   ↓
 dev-plan-generator (create dev doc)
   ↓
-codeagent concurrent development (2–5 tasks, backend split)
+codeagent concurrent development (intelligent backend selection)
   ↓
 codeagent testing & verification (≥90% coverage)
   ↓
@@ -31,7 +31,7 @@ Done (generate summary)
 
 ### 2. codeagent Analysis & UI Detection
 - Call codeagent to analyze the request in plan mode style
-- Extract: core functions, technical points, task list (2–5 items)
+- Extract: core functions, technical points, task list with complexity ratings
 - UI auto-detection: needs UI work when task involves style assets (.css, .scss, styled-components, CSS modules, tailwindcss) OR frontend component files (.tsx, .jsx, .vue); output yes/no plus evidence
 
 ### 3. Generate Dev Doc
@@ -42,9 +42,11 @@ Done (generate summary)
 
 ### 4. Concurrent Development
 - Work from the task list in dev-plan.md
-- Use codeagent per task with explicit backend selection:
-  - Backend/API/DB tasks → `--backend codex` (default)
-  - UI/style/component tasks → `--backend gemini` (enforced)
+- Use codeagent per task with intelligent backend selection:
+  - Simple/Medium tasks → `--backend claude` (fast, cost-effective)
+  - Complex tasks → `--backend codex` (deep reasoning)
+  - UI tasks → `--backend gemini` (enforced)
+- Backend selected automatically based on task complexity rating
 - Independent tasks → run in parallel
 - Conflicting tasks → run serially
 
@@ -80,14 +82,17 @@ Only one file—minimal and clear.
 
 ### Tools
 - **AskUserQuestion**: interactive requirement clarification
-- **codeagent skill**: analysis, development, testing; supports `--backend` for codex (default) or gemini (UI)
-- **dev-plan-generator agent**: generate dev doc (subagent via Task tool, saves context)
+- **codeagent skill**: analysis, development, testing; supports `--backend` for claude/codex/gemini
+- **dev-plan-generator agent**: generate dev doc with complexity ratings (subagent via Task tool, saves context)
 
-## UI Auto-Detection & Backend Routing
-- **UI detection standard**: style files (.css, .scss, styled-components, CSS modules, tailwindcss) OR frontend component code (.tsx, .jsx, .vue) trigger `needs_ui: true`
-- **Flow impact**: Step 2 auto-detects UI work; Step 3 appends a separate UI task in `dev-plan.md` when detected
-- **Backend split**: backend/API tasks use codex backend (default); UI tasks force gemini backend
-- **Implementation**: Orchestrator invokes codeagent skill with appropriate backend parameter per task type
+## Intelligent Backend Selection
+- **Complexity-based routing**: Tasks are rated as simple/medium/complex based on functional requirements (NOT code volume)
+  - Simple: Follows existing patterns, deterministic logic → claude
+  - Medium: Requires design decisions, multiple scenarios → claude
+  - Complex: Architecture design, algorithms, deep domain knowledge → codex
+  - UI: Style/component work → gemini (enforced)
+- **Flow impact**: Step 2 analyzes complexity; Step 3 includes complexity ratings in dev-plan.md; Step 4 auto-selects backend
+- **Implementation**: Orchestrator reads complexity field and invokes codeagent skill with appropriate backend parameter
 
 ## Key Features
 
@@ -102,9 +107,9 @@ Only one file—minimal and clear.
 - Steps are straightforward
 
 ### ✅ Concurrency
-- 2–5 tasks in parallel
+- Tasks split based on natural functional boundaries
 - Auto-detect dependencies and conflicts
-- codeagent executes independently
+- codeagent executes independently with optimal backend
 
 ### ✅ Quality Assurance
 - Enforces 90% coverage
@@ -126,18 +131,18 @@ A: Yes, use JWT token
 # Step 2: codeagent analysis
 Output:
 - Core: email/password login + JWT auth
-- Task 1: Backend API
-- Task 2: Password hashing
-- Task 3: Frontend form
+- Task 1: Backend API (complexity: medium)
+- Task 2: Password hashing (complexity: simple)
+- Task 3: Frontend form (complexity: simple)
 UI detection: needs_ui = true (tailwindcss classes in frontend form)
 
 # Step 3: Generate doc
-dev-plan.md generated with backend + UI tasks ✓
+dev-plan.md generated with complexity ratings ✓
 
-# Step 4-5: Concurrent development (backend codex, UI gemini)
-[task-1] Backend API (codex) → tests → 92% ✓
-[task-2] Password hashing (codex) → tests → 95% ✓
-[task-3] Frontend form (gemini) → tests → 91% ✓
+# Step 4-5: Concurrent development (intelligent backend selection)
+[task-1] Backend API (claude, medium) → tests → 92% ✓
+[task-2] Password hashing (claude, simple) → tests → 95% ✓
+[task-3] Frontend form (gemini, UI) → tests → 91% ✓
 ```
 
 ## Directory Structure

dev-workflow/agents/dev-plan-generator.md

@@ -29,6 +29,8 @@ Your output is a single file: `./.claude/specs/{feature_name}/dev-plan.md`
 
 ### Task 1: [Task Name]
 - **ID**: task-1
+- **Complexity**: [simple|medium|complex]
+- **Rationale**: [Why this complexity level? What makes it simple/complex?]
 - **Description**: [What needs to be done]
 - **File Scope**: [Directories or files involved, e.g., src/auth/**, tests/auth/]
 - **Dependencies**: [None or depends on task-x]
@@ -38,7 +40,7 @@ Your output is a single file: `./.claude/specs/{feature_name}/dev-plan.md`
 ### Task 2: [Task Name]
 ...
 
-(2-5 tasks)
+(Tasks based on natural functional boundaries, typically 2-8)
 
 ## Acceptance Criteria
 - [ ] Feature point 1
@@ -53,9 +55,13 @@ Your output is a single file: `./.claude/specs/{feature_name}/dev-plan.md`
 
 ## Generation Rules You Must Enforce
 
-1. **Task Count**: Generate 2-5 tasks (no more, no less unless the feature is extremely simple or complex)
+1. **Task Count**: Generate tasks based on natural functional boundaries (no artificial limits)
+   - Typical range: 2-8 tasks
+   - Quality over quantity: prefer fewer well-scoped tasks over excessive fragmentation
+   - Each task should be independently completable by one agent
 2. **Task Requirements**: Each task MUST include:
    - Clear ID (task-1, task-2, etc.)
+   - Complexity rating (simple/medium/complex) with rationale
    - Specific description of what needs to be done
    - Explicit file scope (directories or files affected)
    - Dependency declaration ("None" or "depends on task-x")
@@ -65,20 +71,61 @@ Your output is a single file: `./.claude/specs/{feature_name}/dev-plan.md`
 4. **Test Commands**: Must include coverage parameters (e.g., `--cov=module --cov-report=term` for pytest, `--coverage` for npm)
 5. **Coverage Threshold**: Always require ≥90% code coverage in acceptance criteria
 
+## Task Complexity Assessment
+
+**Complexity is determined by functional requirements, NOT code volume.**
+
+### Simple Tasks
+**Characteristics**:
+- Well-defined, single responsibility
+- Follows existing patterns (copy-paste-modify)
+- No architecture decisions needed
+- Deterministic logic (no edge cases)
+
+**Examples**: Add CRUD endpoint following existing pattern, update validation rules, add configuration option, simple data transformation, UI component with clear spec
+
+**Backend**: claude (fast, pattern-matching)
+
+### Medium Tasks
+**Characteristics**:
+- Requires understanding system context
+- Some design decisions (data structure, API shape)
+- Multiple scenarios/edge cases to handle
+- Integration with existing modules
+
+**Examples**: Implement authentication flow, add caching layer with invalidation logic, design REST API with proper error handling, refactor module while preserving behavior, state management with transitions
+
+**Backend**: claude (default, handles most cases)
+
+### Complex Tasks
+**Characteristics** (ANY applies):
+- **Architecture**: Requires system-level design decisions
+- **Algorithm**: Non-trivial logic (concurrency, optimization, distributed systems)
+- **Domain**: Deep business logic understanding needed
+- **Performance**: Requires profiling, optimization, trade-off analysis
+- **Risk**: High impact, affects core functionality
+
+**Examples**: Design distributed transaction mechanism, implement rate limiting with fairness guarantees, build query optimizer, design event sourcing architecture, performance bottleneck analysis & fix, security-critical feature (auth, encryption)
+
+**Backend**: codex (deep reasoning, architecture design)
+
 ## Your Workflow
 
 1. **Analyze Input**: Review the requirements description and codeagent analysis results (including `needs_ui` flag if present)
-2. **Identify Tasks**: Break down the feature into 2-5 logical, independent tasks
-3. **Determine Dependencies**: Map out which tasks depend on others (minimize dependencies)
-4. **Specify Testing**: For each task, define the exact test command and coverage requirements
-5. **Define Acceptance**: List concrete, measurable acceptance criteria including the 90% coverage requirement
-6. **Document Technical Points**: Note key technical decisions and constraints
-7. **Write File**: Use the Write tool to create `./.claude/specs/{feature_name}/dev-plan.md`
+2. **Identify Tasks**: Break down the feature into logical, independent tasks based on natural functional boundaries
+3. **Assess Complexity**: For each task, determine complexity (simple/medium/complex) based on functional requirements
+4. **Determine Dependencies**: Map out which tasks depend on others (minimize dependencies)
+5. **Specify Testing**: For each task, define the exact test command and coverage requirements
+6. **Define Acceptance**: List concrete, measurable acceptance criteria including the 90% coverage requirement
+7. **Document Technical Points**: Note key technical decisions and constraints
+8. **Write File**: Use the Write tool to create `./.claude/specs/{feature_name}/dev-plan.md`
 
 ## Quality Checks Before Writing
 
-- [ ] Task count is between 2-5
-- [ ] Every task has all 6 required fields (ID, Description, File Scope, Dependencies, Test Command, Test Focus)
+- [ ] Task count justified by functional boundaries (typically 2-8)
+- [ ] Every task has complexity rating with clear rationale
+- [ ] Complexity based on functional requirements, NOT code volume
+- [ ] Every task has all required fields (ID, Complexity, Rationale, Description, File Scope, Dependencies, Test Command, Test Focus)
 - [ ] Test commands include coverage parameters
 - [ ] Dependencies are explicitly stated
 - [ ] Acceptance criteria includes 90% coverage requirement

dev-workflow/commands/dev.md

@@ -1,5 +1,5 @@
 ---
-description: Extreme lightweight end-to-end development workflow with requirements clarification, parallel codeagent execution, and mandatory 90% test coverage
+description: Extreme lightweight end-to-end development workflow with requirements clarification, intelligent backend selection, parallel codeagent execution, and mandatory 90% test coverage
 ---
 
 
@@ -39,7 +39,7 @@ You are the /dev Workflow Orchestrator, an expert development workflow manager s
   2. **Identify Existing Patterns**: Find how similar features are implemented, reuse conventions
   3. **Evaluate Options**: When multiple approaches exist, list trade-offs (complexity, performance, security, maintainability)
   4. **Make Architectural Decisions**: Choose patterns, APIs, data models with justification
-  5. **Design Task Breakdown**: Produce 2-5 parallelizable tasks with file scope and dependencies
+  5. **Design Task Breakdown**: Produce parallelizable tasks based on natural functional boundaries with file scope and dependencies
 
   **Analysis Output Structure**:
   ```
@@ -56,7 +56,7 @@ You are the /dev Workflow Orchestrator, an expert development workflow manager s
   [API design, data models, architecture choices made]
 
   ## Task Breakdown
-  [2-5 tasks with: ID, description, file scope, dependencies, test command]
+  [Tasks with: ID, complexity (simple/medium/complex), rationale, description, file scope, dependencies, test command]
 
   ## UI Determination
   needs_ui: [true/false]
@@ -82,9 +82,34 @@ You are the /dev Workflow Orchestrator, an expert development workflow manager s
   - If user chooses "Need adjustments", return to Step 1 or Step 2 based on feedback
 
 - **Step 4: Parallel Development Execution**
-  - For each task in `dev-plan.md`, invoke codeagent skill with task brief in HEREDOC format:
+
+  **Backend Selection Logic** (executed by orchestrator):
+  - For each task in `dev-plan.md`, read the `Complexity` field
+  - Resolve backend based on complexity and UI requirements:
+    ```
+    if task has UI work (from Step 2 analysis):
+      backend = "gemini"  # UI tasks always use gemini
+    elif complexity == "simple" or complexity == "medium":
+      backend = "claude"  # Most tasks use claude (fast, cost-effective)
+    elif complexity == "complex":
+      backend = "codex"   # Complex tasks use codex (deep reasoning)
+    else:
+      backend = "claude"  # Default fallback
+    ```
+
+  **Task Execution**:
+  - Invoke codeagent skill with resolved backend in HEREDOC format:
     ```bash
-    # Backend task (use codex backend - default)
+    # Example: Simple/Medium task
+    codeagent-wrapper --backend claude - <<'EOF'
+    Task: [task-id]
+    Reference: @.claude/specs/{feature_name}/dev-plan.md
+    Scope: [task file scope]
+    Test: [test command]
+    Deliverables: code + unit tests + coverage ≥90% + coverage summary
+    EOF
+
+    # Example: Complex task
     codeagent-wrapper --backend codex - <<'EOF'
     Task: [task-id]
     Reference: @.claude/specs/{feature_name}/dev-plan.md
@@ -93,7 +118,7 @@ You are the /dev Workflow Orchestrator, an expert development workflow manager s
     Deliverables: code + unit tests + coverage ≥90% + coverage summary
     EOF
 
-    # UI task (use gemini backend - enforced)
+    # Example: UI task
     codeagent-wrapper --backend gemini - <<'EOF'
     Task: [task-id]
     Reference: @.claude/specs/{feature_name}/dev-plan.md
@@ -102,7 +127,9 @@ You are the /dev Workflow Orchestrator, an expert development workflow manager s
     Deliverables: code + unit tests + coverage ≥90% + coverage summary
     EOF
     ```
+
   - Execute independent tasks concurrently; serialize conflicting ones; track coverage reports
+  - Backend is selected automatically based on task complexity, no manual intervention needed
 
 - **Step 5: Coverage Validation**
   - Validate each task’s coverage:
@@ -119,7 +146,9 @@ You are the /dev Workflow Orchestrator, an expert development workflow manager s
 
 **Quality Standards**
 - Code coverage ≥90%
-- 2-5 genuinely parallelizable tasks
+- Tasks based on natural functional boundaries (typically 2-8)
+- Each task has clear complexity rating (simple/medium/complex)
+- Backend automatically selected based on task complexity
 - Documentation must be minimal yet actionable
 - No verbose implementations; only essential code