fix: extract datetime from slot selection ID before booking

scheduledAt was passed as raw "slot:{id}:{datetime}" — platform rejected
it. Added extract_datetime expression to pull the ISO datetime from the
third segment. Updated flow JSON with SetVariableBlock after slot input.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/messaging/flow/default-flows/appointment-booking.json

@@ -21,7 +21,8 @@
         { "id": "v13", "name": "docListResult", "type": "object" },
         { "id": "v14", "name": "slotListResult", "type": "object" },
         { "id": "v15", "name": "aiGreeting", "type": "string" },
-        { "id": "v16", "name": "reason", "type": "string" }
+        { "id": "v16", "name": "reason", "type": "string" },
+        { "id": "v17", "name": "scheduledDateTime", "type": "string" }
     ],
     "groups": [
         {
@@ -189,6 +190,13 @@
                     "type": "input",
                     "inputType": "any",
                     "variableId": "selectedSlot"
+                },
+                {
+                    "id": "b17a",
+                    "type": "set_variable",
+                    "variableId": "scheduledDateTime",
+                    "value": "selectedSlot",
+                    "expression": "extract_datetime"
                 }
             ]
         },
@@ -253,7 +261,7 @@
                         "phoneNumber": "{{_phone}}",
                         "department": "{{selectedDepartmentTitle}}",
                         "doctorName": "{{selectedDoctor_title}}",
-                        "scheduledAt": "{{selectedSlot}}",
+                        "scheduledAt": "{{scheduledDateTime}}",
                         "reason": "{{reason}}"
                     },
                     "outputVariableId": "bookingResult"
@@ -312,7 +320,7 @@
         { "id": "e6", "from": { "blockId": "b13", "conditionId": "c4" }, "to": { "groupId": "g4a" } },
         { "id": "e7", "from": { "blockId": "b14" }, "to": { "groupId": "g5" } },
         { "id": "e8", "from": { "blockId": "b15" }, "to": { "groupId": "g5" } },
-        { "id": "e9", "from": { "blockId": "b17" }, "to": { "groupId": "g6" } },
+        { "id": "e9", "from": { "blockId": "b17a" }, "to": { "groupId": "g6" } },
         { "id": "e10", "from": { "blockId": "b19" }, "to": { "groupId": "g7" } },
         { "id": "e11", "from": { "blockId": "b22", "conditionId": "c5" }, "to": { "groupId": "g8" } },
         { "id": "e12", "from": { "blockId": "b22", "conditionId": "c6" }, "to": { "groupId": "g9" } }

src/messaging/flow/flow-types.ts

@@ -81,7 +81,7 @@ export type SetVariableBlock = {
     type: 'set_variable';
     variableId: string;
     value: string;
-    expression?: 'extract_id' | 'date_tomorrow' | 'date_day_after';
+    expression?: 'extract_id' | 'extract_datetime' | 'date_tomorrow' | 'date_day_after';
 };
 
 export type ToolCallBlock = {

src/messaging/flow/flow-variable.service.ts

@@ -25,10 +25,16 @@ export class FlowVariableService {
     evaluateExpression(expression: string, value: string, variables: Record<string, any>): any {
         switch (expression) {
             case 'extract_id': {
-                // Extract UUID from "doc:{uuid}:{name}" or "dept:{name}" or "slot:{id}:{datetime}"
+                // Extract second segment: "doc:{uuid}:{name}" → uuid, "dept:{name}" → name
                 const parts = value.split(':');
                 return parts.length >= 2 ? parts[1] : value;
             }
+            case 'extract_datetime': {
+                // Extract datetime from "slot:{doctorId}:{datetime}" → "2026-04-21T14:00:00"
+                const parts = value.split(':');
+                // Rejoin from index 2 onwards (datetime contains colons: 2026-04-21T14:00:00)
+                return parts.length >= 3 ? parts.slice(2).join(':') : value;
+            }
             case 'date_tomorrow': {
                 const d = new Date(Date.now() + 86400000);
                 return d.toISOString().split('T')[0];