feat(backend): Add Celery worker infrastructure with task stubs

- Add Celery app configuration with Redis broker/backend
- Add task modules: agent, workflow, cost, git, sync
- Add task stubs for:
  - Agent execution (spawn, heartbeat, terminate)
  - Workflow orchestration (start sprint, checkpoint, code review)
  - Cost tracking (record usage, calculate, generate report)
  - Git operations (clone, commit, push, sync)
  - External sync (import issues, export updates)
- Add task tests directory structure
- Configure for production-ready Celery setup

Implements #18

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/app/tasks/__init__.py

@@ -0,0 +1,23 @@
+# app/tasks/__init__.py
+"""
+Celery background tasks for Syndarix.
+
+This package contains all Celery tasks organized by domain:
+
+Modules:
+    agent: Agent execution tasks (run_agent_step, spawn_agent, terminate_agent)
+    git: Git operation tasks (clone, commit, branch, push, PR)
+    sync: Issue synchronization tasks (incremental/full sync, webhooks)
+    workflow: Workflow state management tasks
+    cost: Cost tracking and budget monitoring tasks
+"""
+
+from app.tasks import agent, cost, git, sync, workflow
+
+__all__ = [
+    "agent",
+    "cost",
+    "git",
+    "sync",
+    "workflow",
+]

backend/app/tasks/agent.py

@@ -0,0 +1,150 @@
+# app/tasks/agent.py
+"""
+Agent execution tasks for Syndarix.
+
+These tasks handle the lifecycle of AI agent instances:
+- Spawning new agent instances from agent types
+- Executing agent steps (LLM calls, tool execution)
+- Terminating agent instances
+
+Tasks are routed to the 'agent' queue for dedicated processing.
+"""
+
+import logging
+from typing import Any
+
+from app.celery_app import celery_app
+
+logger = logging.getLogger(__name__)
+
+
+@celery_app.task(bind=True, name="app.tasks.agent.run_agent_step")
+def run_agent_step(
+    self,
+    agent_instance_id: str,
+    context: dict[str, Any],
+) -> dict[str, Any]:
+    """
+    Execute a single step of an agent's workflow.
+
+    This task performs one iteration of the agent loop:
+    1. Load agent instance state
+    2. Call LLM with context and available tools
+    3. Execute tool calls if any
+    4. Update agent state
+    5. Return result for next step or completion
+
+    Args:
+        agent_instance_id: UUID of the agent instance
+        context: Current execution context including:
+            - messages: Conversation history
+            - tools: Available tool definitions
+            - state: Agent state data
+            - metadata: Project/task metadata
+
+    Returns:
+        dict with status and agent_instance_id
+    """
+    logger.info(
+        f"Running agent step for instance {agent_instance_id} with context keys: {list(context.keys())}"
+    )
+
+    # TODO: Implement actual agent step execution
+    # This will involve:
+    # 1. Loading agent instance from database
+    # 2. Calling LLM provider (via litellm or anthropic SDK)
+    # 3. Processing tool calls through MCP servers
+    # 4. Updating agent state in database
+    # 5. Scheduling next step if needed
+
+    return {
+        "status": "pending",
+        "agent_instance_id": agent_instance_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.agent.spawn_agent")
+def spawn_agent(
+    self,
+    agent_type_id: str,
+    project_id: str,
+    initial_context: dict[str, Any],
+) -> dict[str, Any]:
+    """
+    Spawn a new agent instance from an agent type.
+
+    This task creates a new agent instance:
+    1. Load agent type configuration (model, expertise, personality)
+    2. Create agent instance record in database
+    3. Initialize agent state with project context
+    4. Start first agent step
+
+    Args:
+        agent_type_id: UUID of the agent type template
+        project_id: UUID of the project this agent will work on
+        initial_context: Starting context including:
+            - goal: High-level objective
+            - constraints: Any limitations or requirements
+            - assigned_issues: Issues to work on
+            - autonomy_level: FULL_CONTROL, MILESTONE, or AUTONOMOUS
+
+    Returns:
+        dict with status, agent_type_id, and project_id
+    """
+    logger.info(
+        f"Spawning agent of type {agent_type_id} for project {project_id}"
+    )
+
+    # TODO: Implement agent spawning
+    # This will involve:
+    # 1. Loading agent type from database
+    # 2. Creating agent instance record
+    # 3. Setting up MCP tool access
+    # 4. Initializing agent state
+    # 5. Kicking off first step
+
+    return {
+        "status": "spawned",
+        "agent_type_id": agent_type_id,
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.agent.terminate_agent")
+def terminate_agent(
+    self,
+    agent_instance_id: str,
+    reason: str,
+) -> dict[str, Any]:
+    """
+    Terminate an agent instance.
+
+    This task gracefully shuts down an agent:
+    1. Mark agent instance as terminated
+    2. Save final state for audit
+    3. Release any held resources
+    4. Notify relevant subscribers
+
+    Args:
+        agent_instance_id: UUID of the agent instance
+        reason: Reason for termination (completion, error, manual, budget)
+
+    Returns:
+        dict with status and agent_instance_id
+    """
+    logger.info(
+        f"Terminating agent instance {agent_instance_id} with reason: {reason}"
+    )
+
+    # TODO: Implement agent termination
+    # This will involve:
+    # 1. Loading agent instance
+    # 2. Updating status to terminated
+    # 3. Saving termination reason
+    # 4. Cleaning up any pending tasks
+    # 5. Sending termination event
+
+    return {
+        "status": "terminated",
+        "agent_instance_id": agent_instance_id,
+    }

backend/app/tasks/cost.py

@@ -0,0 +1,201 @@
+# app/tasks/cost.py
+"""
+Cost tracking and budget management tasks for Syndarix.
+
+These tasks implement multi-layered cost tracking per ADR-012:
+- Per-agent token usage tracking
+- Project budget monitoring
+- Daily cost aggregation
+- Budget threshold alerts
+- Cost reporting
+
+Costs are tracked in real-time in Redis for speed,
+then aggregated to PostgreSQL for durability.
+"""
+
+import logging
+from typing import Any
+
+from app.celery_app import celery_app
+
+logger = logging.getLogger(__name__)
+
+
+@celery_app.task(bind=True, name="app.tasks.cost.aggregate_daily_costs")
+def aggregate_daily_costs(self) -> dict[str, Any]:
+    """
+    Aggregate daily costs from Redis to PostgreSQL.
+
+    This periodic task (runs daily):
+    1. Read accumulated costs from Redis
+    2. Aggregate by project, agent, and model
+    3. Store in PostgreSQL cost_records table
+    4. Clear Redis counters for new day
+
+    Returns:
+        dict with status
+    """
+    logger.info("Starting daily cost aggregation")
+
+    # TODO: Implement cost aggregation
+    # This will involve:
+    # 1. Fetching cost data from Redis
+    # 2. Grouping by project_id, agent_id, model
+    # 3. Inserting into PostgreSQL cost tables
+    # 4. Resetting Redis counters
+
+    return {
+        "status": "pending",
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.cost.check_budget_thresholds")
+def check_budget_thresholds(
+    self,
+    project_id: str,
+) -> dict[str, Any]:
+    """
+    Check if a project has exceeded budget thresholds.
+
+    This task checks budget limits:
+    1. Get current spend from Redis counters
+    2. Compare against project budget limits
+    3. Send alerts if thresholds exceeded
+    4. Pause agents if hard limit reached
+
+    Args:
+        project_id: UUID of the project
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(f"Checking budget thresholds for project {project_id}")
+
+    # TODO: Implement budget checking
+    # This will involve:
+    # 1. Loading project budget configuration
+    # 2. Getting current spend from Redis
+    # 3. Comparing against soft/hard limits
+    # 4. Sending alerts or pausing agents
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.cost.record_llm_usage")
+def record_llm_usage(
+    self,
+    agent_id: str,
+    project_id: str,
+    model: str,
+    prompt_tokens: int,
+    completion_tokens: int,
+    cost_usd: float,
+) -> dict[str, Any]:
+    """
+    Record LLM usage from an agent call.
+
+    This task tracks each LLM API call:
+    1. Increment Redis counters for real-time tracking
+    2. Store raw usage event for audit
+    3. Trigger budget check if threshold approaching
+
+    Args:
+        agent_id: UUID of the agent instance
+        project_id: UUID of the project
+        model: Model identifier (e.g., claude-opus-4-5-20251101)
+        prompt_tokens: Number of input tokens
+        completion_tokens: Number of output tokens
+        cost_usd: Calculated cost in USD
+
+    Returns:
+        dict with status, agent_id, project_id, and cost_usd
+    """
+    logger.debug(
+        f"Recording LLM usage for model {model}: "
+        f"{prompt_tokens} prompt + {completion_tokens} completion tokens = ${cost_usd}"
+    )
+
+    # TODO: Implement usage recording
+    # This will involve:
+    # 1. Incrementing Redis counters
+    # 2. Storing usage event
+    # 3. Checking if near budget threshold
+
+    return {
+        "status": "pending",
+        "agent_id": agent_id,
+        "project_id": project_id,
+        "cost_usd": cost_usd,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.cost.generate_cost_report")
+def generate_cost_report(
+    self,
+    project_id: str,
+    start_date: str,
+    end_date: str,
+) -> dict[str, Any]:
+    """
+    Generate a cost report for a project.
+
+    This task creates a detailed cost breakdown:
+    1. Query cost records for date range
+    2. Group by agent, model, and day
+    3. Calculate totals and trends
+    4. Format report for display
+
+    Args:
+        project_id: UUID of the project
+        start_date: Report start date (YYYY-MM-DD)
+        end_date: Report end date (YYYY-MM-DD)
+
+    Returns:
+        dict with status, project_id, and date range
+    """
+    logger.info(
+        f"Generating cost report for project {project_id} from {start_date} to {end_date}"
+    )
+
+    # TODO: Implement report generation
+    # This will involve:
+    # 1. Querying PostgreSQL for cost records
+    # 2. Aggregating by various dimensions
+    # 3. Calculating totals and averages
+    # 4. Formatting report data
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+        "start_date": start_date,
+        "end_date": end_date,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.cost.reset_daily_budget_counters")
+def reset_daily_budget_counters(self) -> dict[str, Any]:
+    """
+    Reset daily budget counters in Redis.
+
+    This periodic task (runs daily at midnight UTC):
+    1. Archive current day's counters
+    2. Reset all daily budget counters
+    3. Prepare for new day's tracking
+
+    Returns:
+        dict with status
+    """
+    logger.info("Resetting daily budget counters")
+
+    # TODO: Implement counter reset
+    # This will involve:
+    # 1. Getting all daily counter keys from Redis
+    # 2. Archiving current values
+    # 3. Resetting counters to zero
+
+    return {
+        "status": "pending",
+    }

backend/app/tasks/git.py

@@ -0,0 +1,225 @@
+# app/tasks/git.py
+"""
+Git operation tasks for Syndarix.
+
+These tasks handle Git operations for projects:
+- Cloning repositories
+- Creating branches
+- Committing changes
+- Pushing to remotes
+- Creating pull requests
+
+Tasks are routed to the 'git' queue for dedicated processing.
+All operations are scoped by project_id for multi-tenancy.
+"""
+
+import logging
+from typing import Any
+
+from app.celery_app import celery_app
+
+logger = logging.getLogger(__name__)
+
+
+@celery_app.task(bind=True, name="app.tasks.git.clone_repository")
+def clone_repository(
+    self,
+    project_id: str,
+    repo_url: str,
+    branch: str = "main",
+) -> dict[str, Any]:
+    """
+    Clone a repository for a project.
+
+    This task clones a Git repository to the project workspace:
+    1. Prepare workspace directory
+    2. Clone repository with credentials
+    3. Checkout specified branch
+    4. Update project metadata
+
+    Args:
+        project_id: UUID of the project
+        repo_url: Git repository URL (HTTPS or SSH)
+        branch: Branch to checkout (default: main)
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(
+        f"Cloning repository {repo_url} for project {project_id} on branch {branch}"
+    )
+
+    # TODO: Implement repository cloning
+    # This will involve:
+    # 1. Getting project credentials from secrets store
+    # 2. Creating workspace directory
+    # 3. Running git clone with proper auth
+    # 4. Checking out the target branch
+    # 5. Updating project record with clone status
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.git.commit_changes")
+def commit_changes(
+    self,
+    project_id: str,
+    message: str,
+    files: list[str] | None = None,
+) -> dict[str, Any]:
+    """
+    Commit changes in a project repository.
+
+    This task creates a Git commit:
+    1. Stage specified files (or all if None)
+    2. Create commit with message
+    3. Update commit history record
+
+    Args:
+        project_id: UUID of the project
+        message: Commit message (follows conventional commits)
+        files: List of files to stage, or None for all staged
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(
+        f"Committing changes for project {project_id}: {message}"
+    )
+
+    # TODO: Implement commit operation
+    # This will involve:
+    # 1. Loading project workspace path
+    # 2. Running git add for specified files
+    # 3. Running git commit with message
+    # 4. Recording commit hash in database
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.git.create_branch")
+def create_branch(
+    self,
+    project_id: str,
+    branch_name: str,
+    from_ref: str = "HEAD",
+) -> dict[str, Any]:
+    """
+    Create a new branch in a project repository.
+
+    This task creates a Git branch:
+    1. Checkout from reference
+    2. Create new branch
+    3. Update branch tracking
+
+    Args:
+        project_id: UUID of the project
+        branch_name: Name of the new branch (e.g., feature/123-description)
+        from_ref: Reference to branch from (default: HEAD)
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(
+        f"Creating branch {branch_name} from {from_ref} for project {project_id}"
+    )
+
+    # TODO: Implement branch creation
+    # This will involve:
+    # 1. Loading project workspace
+    # 2. Running git checkout -b from_ref
+    # 3. Recording branch in database
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.git.create_pull_request")
+def create_pull_request(
+    self,
+    project_id: str,
+    title: str,
+    body: str,
+    head_branch: str,
+    base_branch: str = "main",
+) -> dict[str, Any]:
+    """
+    Create a pull request for a project.
+
+    This task creates a PR on the external Git provider:
+    1. Push branch if needed
+    2. Create PR via API (Gitea, GitHub, GitLab)
+    3. Store PR reference
+
+    Args:
+        project_id: UUID of the project
+        title: PR title
+        body: PR description (markdown)
+        head_branch: Branch with changes
+        base_branch: Target branch (default: main)
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(
+        f"Creating PR '{title}' from {head_branch} to {base_branch} for project {project_id}"
+    )
+
+    # TODO: Implement PR creation
+    # This will involve:
+    # 1. Loading project and Git provider config
+    # 2. Ensuring head_branch is pushed
+    # 3. Calling provider API to create PR
+    # 4. Storing PR URL and number
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.git.push_changes")
+def push_changes(
+    self,
+    project_id: str,
+    branch: str,
+    force: bool = False,
+) -> dict[str, Any]:
+    """
+    Push changes to remote repository.
+
+    This task pushes commits to the remote:
+    1. Verify authentication
+    2. Push branch to remote
+    3. Handle push failures
+
+    Args:
+        project_id: UUID of the project
+        branch: Branch to push
+        force: Whether to force push (use with caution)
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(
+        f"Pushing branch {branch} for project {project_id} (force={force})"
+    )
+
+    # TODO: Implement push operation
+    # This will involve:
+    # 1. Loading project credentials
+    # 2. Running git push (with --force if specified)
+    # 3. Handling authentication and conflicts
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }

backend/app/tasks/sync.py

@@ -0,0 +1,198 @@
+# app/tasks/sync.py
+"""
+Issue synchronization tasks for Syndarix.
+
+These tasks handle bidirectional issue synchronization:
+- Incremental sync (polling for recent changes)
+- Full reconciliation (daily comprehensive sync)
+- Webhook event processing
+- Pushing local changes to external trackers
+
+Tasks are routed to the 'sync' queue for dedicated processing.
+Per ADR-011, sync follows a master/replica model with configurable direction.
+"""
+
+import logging
+from typing import Any
+
+from app.celery_app import celery_app
+
+logger = logging.getLogger(__name__)
+
+
+@celery_app.task(bind=True, name="app.tasks.sync.sync_issues_incremental")
+def sync_issues_incremental(self) -> dict[str, Any]:
+    """
+    Perform incremental issue synchronization across all projects.
+
+    This periodic task (runs every 5 minutes):
+    1. Query each project's external tracker for recent changes
+    2. Compare with local issue cache
+    3. Apply updates to local database
+    4. Handle conflicts based on sync direction config
+
+    Returns:
+        dict with status and type
+    """
+    logger.info("Starting incremental issue sync across all projects")
+
+    # TODO: Implement incremental sync
+    # This will involve:
+    # 1. Loading all active projects with sync enabled
+    # 2. For each project, querying external tracker since last_sync_at
+    # 3. Upserting issues into local database
+    # 4. Updating last_sync_at timestamp
+
+    return {
+        "status": "pending",
+        "type": "incremental",
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.sync.sync_issues_full")
+def sync_issues_full(self) -> dict[str, Any]:
+    """
+    Perform full issue reconciliation across all projects.
+
+    This periodic task (runs daily):
+    1. Fetch all issues from external trackers
+    2. Compare with local database
+    3. Handle orphaned issues
+    4. Resolve any drift between systems
+
+    Returns:
+        dict with status and type
+    """
+    logger.info("Starting full issue reconciliation across all projects")
+
+    # TODO: Implement full sync
+    # This will involve:
+    # 1. Loading all active projects
+    # 2. Fetching complete issue lists from external trackers
+    # 3. Comparing with local database
+    # 4. Handling deletes and orphans
+    # 5. Resolving conflicts based on sync config
+
+    return {
+        "status": "pending",
+        "type": "full",
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.sync.process_webhook_event")
+def process_webhook_event(
+    self,
+    provider: str,
+    event_type: str,
+    payload: dict[str, Any],
+) -> dict[str, Any]:
+    """
+    Process a webhook event from an external Git provider.
+
+    This task handles real-time updates from:
+    - Gitea: issue.created, issue.updated, pull_request.*, etc.
+    - GitHub: issues, pull_request, push, etc.
+    - GitLab: issue events, merge request events, etc.
+
+    Args:
+        provider: Git provider name (gitea, github, gitlab)
+        event_type: Event type from provider
+        payload: Raw webhook payload
+
+    Returns:
+        dict with status, provider, and event_type
+    """
+    logger.info(f"Processing webhook event from {provider}: {event_type}")
+
+    # TODO: Implement webhook processing
+    # This will involve:
+    # 1. Validating webhook signature
+    # 2. Parsing provider-specific payload
+    # 3. Mapping to internal event format
+    # 4. Updating local database
+    # 5. Triggering any dependent workflows
+
+    return {
+        "status": "pending",
+        "provider": provider,
+        "event_type": event_type,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.sync.sync_project_issues")
+def sync_project_issues(
+    self,
+    project_id: str,
+    full: bool = False,
+) -> dict[str, Any]:
+    """
+    Synchronize issues for a specific project.
+
+    This task can be triggered manually or by webhooks:
+    1. Connect to project's external tracker
+    2. Fetch issues (incremental or full)
+    3. Update local database
+
+    Args:
+        project_id: UUID of the project
+        full: Whether to do full sync or incremental
+
+    Returns:
+        dict with status and project_id
+    """
+    logger.info(
+        f"Syncing issues for project {project_id} (full={full})"
+    )
+
+    # TODO: Implement project-specific sync
+    # This will involve:
+    # 1. Loading project configuration
+    # 2. Connecting to external tracker
+    # 3. Fetching issues based on full flag
+    # 4. Upserting to database
+
+    return {
+        "status": "pending",
+        "project_id": project_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.sync.push_issue_to_external")
+def push_issue_to_external(
+    self,
+    project_id: str,
+    issue_id: str,
+    operation: str,
+) -> dict[str, Any]:
+    """
+    Push a local issue change to the external tracker.
+
+    This task handles outbound sync when Syndarix is the master:
+    - create: Create new issue in external tracker
+    - update: Update existing issue
+    - close: Close issue in external tracker
+
+    Args:
+        project_id: UUID of the project
+        issue_id: UUID of the local issue
+        operation: Operation type (create, update, close)
+
+    Returns:
+        dict with status, issue_id, and operation
+    """
+    logger.info(
+        f"Pushing {operation} for issue {issue_id} in project {project_id}"
+    )
+
+    # TODO: Implement outbound sync
+    # This will involve:
+    # 1. Loading issue and project config
+    # 2. Mapping to external tracker format
+    # 3. Calling provider API
+    # 4. Updating external_id mapping
+
+    return {
+        "status": "pending",
+        "issue_id": issue_id,
+        "operation": operation,
+    }

backend/app/tasks/workflow.py

@@ -0,0 +1,213 @@
+# app/tasks/workflow.py
+"""
+Workflow state management tasks for Syndarix.
+
+These tasks manage workflow execution and state transitions:
+- Sprint workflows (planning -> implementation -> review -> done)
+- Story workflows (todo -> in_progress -> review -> done)
+- Approval checkpoints for autonomy levels
+- Stale workflow recovery
+
+Per ADR-007 and ADR-010, workflow state is durable in PostgreSQL
+with defined state transitions.
+"""
+
+import logging
+from typing import Any
+
+from app.celery_app import celery_app
+
+logger = logging.getLogger(__name__)
+
+
+@celery_app.task(bind=True, name="app.tasks.workflow.recover_stale_workflows")
+def recover_stale_workflows(self) -> dict[str, Any]:
+    """
+    Recover workflows that have become stale.
+
+    This periodic task (runs every 5 minutes):
+    1. Find workflows stuck in intermediate states
+    2. Check for timed-out agent operations
+    3. Retry or escalate based on configuration
+    4. Notify relevant users if needed
+
+    Returns:
+        dict with status and recovered count
+    """
+    logger.info("Checking for stale workflows to recover")
+
+    # TODO: Implement stale workflow recovery
+    # This will involve:
+    # 1. Querying for workflows with last_updated > threshold
+    # 2. Checking if associated agents are still running
+    # 3. Retrying or resetting stuck workflows
+    # 4. Sending notifications for manual intervention
+
+    return {
+        "status": "pending",
+        "recovered": 0,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.workflow.execute_workflow_step")
+def execute_workflow_step(
+    self,
+    workflow_id: str,
+    transition: str,
+) -> dict[str, Any]:
+    """
+    Execute a state transition for a workflow.
+
+    This task applies a transition to a workflow:
+    1. Validate transition is allowed from current state
+    2. Execute any pre-transition hooks
+    3. Update workflow state
+    4. Execute any post-transition hooks
+    5. Trigger follow-up tasks
+
+    Args:
+        workflow_id: UUID of the workflow
+        transition: Transition to execute (start, approve, reject, etc.)
+
+    Returns:
+        dict with status, workflow_id, and transition
+    """
+    logger.info(
+        f"Executing transition '{transition}' for workflow {workflow_id}"
+    )
+
+    # TODO: Implement workflow transition
+    # This will involve:
+    # 1. Loading workflow from database
+    # 2. Validating transition from current state
+    # 3. Running pre-transition hooks
+    # 4. Updating state in database
+    # 5. Running post-transition hooks
+    # 6. Scheduling follow-up tasks
+
+    return {
+        "status": "pending",
+        "workflow_id": workflow_id,
+        "transition": transition,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.workflow.handle_approval_response")
+def handle_approval_response(
+    self,
+    workflow_id: str,
+    approved: bool,
+    comment: str | None = None,
+) -> dict[str, Any]:
+    """
+    Handle a user approval response for a workflow checkpoint.
+
+    This task processes approval decisions:
+    1. Record approval decision with timestamp
+    2. Update workflow state accordingly
+    3. Resume or halt workflow execution
+    4. Notify relevant parties
+
+    Args:
+        workflow_id: UUID of the workflow
+        approved: Whether the checkpoint was approved
+        comment: Optional comment from approver
+
+    Returns:
+        dict with status, workflow_id, and approved flag
+    """
+    logger.info(
+        f"Handling approval response for workflow {workflow_id}: approved={approved}"
+    )
+
+    # TODO: Implement approval handling
+    # This will involve:
+    # 1. Loading workflow and approval checkpoint
+    # 2. Recording decision with user and timestamp
+    # 3. Transitioning workflow state
+    # 4. Resuming or stopping execution
+    # 5. Sending notifications
+
+    return {
+        "status": "pending",
+        "workflow_id": workflow_id,
+        "approved": approved,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.workflow.start_sprint_workflow")
+def start_sprint_workflow(
+    self,
+    project_id: str,
+    sprint_id: str,
+) -> dict[str, Any]:
+    """
+    Start a new sprint workflow.
+
+    This task initializes sprint execution:
+    1. Create sprint workflow record
+    2. Set up sprint planning phase
+    3. Spawn Product Owner agent for planning
+    4. Begin story assignment
+
+    Args:
+        project_id: UUID of the project
+        sprint_id: UUID of the sprint
+
+    Returns:
+        dict with status and sprint_id
+    """
+    logger.info(
+        f"Starting sprint workflow for sprint {sprint_id} in project {project_id}"
+    )
+
+    # TODO: Implement sprint workflow initialization
+    # This will involve:
+    # 1. Creating workflow record for sprint
+    # 2. Setting initial state to PLANNING
+    # 3. Spawning PO agent for sprint planning
+    # 4. Setting up monitoring and checkpoints
+
+    return {
+        "status": "pending",
+        "sprint_id": sprint_id,
+    }
+
+
+@celery_app.task(bind=True, name="app.tasks.workflow.start_story_workflow")
+def start_story_workflow(
+    self,
+    project_id: str,
+    story_id: str,
+) -> dict[str, Any]:
+    """
+    Start a new story workflow.
+
+    This task initializes story execution:
+    1. Create story workflow record
+    2. Spawn appropriate developer agent
+    3. Set up implementation tracking
+    4. Configure approval checkpoints based on autonomy level
+
+    Args:
+        project_id: UUID of the project
+        story_id: UUID of the story/issue
+
+    Returns:
+        dict with status and story_id
+    """
+    logger.info(
+        f"Starting story workflow for story {story_id} in project {project_id}"
+    )
+
+    # TODO: Implement story workflow initialization
+    # This will involve:
+    # 1. Creating workflow record for story
+    # 2. Determining appropriate agent type
+    # 3. Spawning developer agent
+    # 4. Setting up checkpoints based on autonomy level
+
+    return {
+        "status": "pending",
+        "story_id": story_id,
+    }