feat: Add phase_guard for contract phase transitions

Implement phase_guard logic in the advance_phase tool. When a contract
has phase_guard enabled, the phase transition now:

1. Asks for user confirmation before advancing
2. Allows users to request changes to phase deliverables
3. Passes feedback to the task without advancing if changes requested

Changes:
- Add phase_guard field to Contract model and CreateContractRequest
- Add PhaseTransitionRequest, PhaseFileInfo, PhaseTaskInfo structs
- Update ChangePhaseRequest with confirmed and feedback fields
- Update ContractToolRequest::AdvancePhase with confirmed/feedback
- Modify advance_phase handling in contract_chat.rs with phase_guard logic
- Update change_phase endpoint in contracts.rs with phase_guard support
- Add database migration for phase_guard column

When phase_guard=false: Phase advances immediately (current behavior)
When phase_guard=true: Returns pending_confirmation status with deliverables
If user provides feedback: Returns feedback to task, doesn't advance

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

1 files changed, 84 insertions, 2 deletions

diff --git a/makima/src/server/handlers/contract_chat.rs b/makima/src/server/handlers/contract_chat.rs
index 48dd864..29ec620 100644
--- a/makima/src/server/handlers/contract_chat.rs
+++ b/makima/src/server/handlers/contract_chat.rs
@@ -1689,7 +1689,7 @@ async fn handle_contract_request(
             }
         }
 
-        ContractToolRequest::AdvancePhase { new_phase } => {
+        ContractToolRequest::AdvancePhase { new_phase, confirmed, feedback } => {
             let contract = match repository::get_contract_for_owner(pool, contract_id, owner_id).await {
                 Ok(Some(c)) => c,
                 Ok(None) => {
@@ -1723,7 +1723,88 @@ async fn handle_contract_request(
                 };
             }
 
-            // Update phase
+            // Check if phase_guard is enabled
+            if contract.phase_guard {
+                // If user provided feedback, return it for the task to address
+                if let Some(ref user_feedback) = feedback {
+                    return ContractRequestResult {
+                        success: true,
+                        message: format!(
+                            "Phase transition to '{}' requires changes. User feedback: {}",
+                            new_phase, user_feedback
+                        ),
+                        data: Some(json!({
+                            "status": "changes_requested",
+                            "currentPhase": current_phase,
+                            "requestedPhase": new_phase,
+                            "feedback": user_feedback,
+                            "action": "Address the user feedback and try again when ready"
+                        })),
+                    };
+                }
+
+                // If not confirmed, return pending confirmation with phase deliverables
+                if !confirmed {
+                    // Get files created in this phase
+                    let phase_files = match repository::list_files_in_contract(pool, contract_id, owner_id).await {
+                        Ok(files) => files
+                            .into_iter()
+                            .filter(|f| f.contract_phase.as_deref() == Some(current_phase))
+                            .map(|f| json!({
+                                "id": f.id,
+                                "name": f.name,
+                                "description": f.description
+                            }))
+                            .collect::<Vec<_>>(),
+                        Err(_) => Vec::new(),
+                    };
+
+                    // Get tasks completed in this contract
+                    let phase_tasks = match repository::list_tasks_in_contract(pool, contract_id, owner_id).await {
+                        Ok(tasks) => tasks
+                            .into_iter()
+                            .filter(|t| t.status == "done" || t.status == "completed")
+                            .map(|t| json!({
+                                "id": t.id,
+                                "name": t.name,
+                                "status": t.status
+                            }))
+                            .collect::<Vec<_>>(),
+                        Err(_) => Vec::new(),
+                    };
+
+                    // Build deliverables summary
+                    let deliverables_summary = format!(
+                        "Phase '{}' deliverables: {} files created, {} tasks completed.",
+                        current_phase,
+                        phase_files.len(),
+                        phase_tasks.len()
+                    );
+
+                    let transition_id = uuid::Uuid::new_v4().to_string();
+
+                    return ContractRequestResult {
+                        success: true,
+                        message: format!(
+                            "Phase transition to '{}' requires user confirmation. Review the deliverables and call advance_phase again with confirmed=true to proceed, or provide feedback to request changes.",
+                            new_phase
+                        ),
+                        data: Some(json!({
+                            "status": "pending_confirmation",
+                            "transitionId": transition_id,
+                            "currentPhase": current_phase,
+                            "nextPhase": new_phase,
+                            "deliverablesSummary": deliverables_summary,
+                            "phaseFiles": phase_files,
+                            "phaseTasks": phase_tasks,
+                            "requiresConfirmation": true,
+                            "instructions": "To proceed: call advance_phase with confirmed=true. To request changes: call advance_phase with feedback='your feedback here'"
+                        })),
+                    };
+                }
+            }
+
+            // Update phase (either phase_guard is disabled, or user confirmed)
             match repository::change_contract_phase_for_owner(pool, contract_id, owner_id, &new_phase).await {
                 Ok(Some(updated)) => {
                     // Get deliverables for the new phase
@@ -1748,6 +1829,7 @@ async fn handle_contract_request(
                             current_phase, new_phase, deliverables.guidance
                         ),
                         data: Some(json!({
+                            "status": "advanced",
                             "previousPhase": current_phase,
                             "newPhase": updated.phase,
                             "phaseGuidance": deliverables.guidance,