feat: Assignment service (v2) (#12320)

## Linear Link

 
## Description

This PR introduces a new robust auto-assignment system for conversations
in Chatwoot. The system replaces the existing round-robin assignment
with a more sophisticated service-based architecture that supports
multiple assignment strategies, rate limiting, and Enterprise features
like capacity-based assignment and balanced distribution.

## Type of change

- [ ] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- Unit test cases
- Test conversations getting assigned on status change to open
- Test the job directly via rails console

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds a new service-based auto-assignment system with scheduled jobs,
rate limiting, enterprise capacity/balanced selection, and wiring via
inbox/handler; includes Redis helpers and comprehensive tests.
> 
> - **Auto-assignment v2 (core services)**:
> - Add `AutoAssignment::AssignmentService` with bulk assignment,
configurable conversation priority, RR selection, and per-agent rate
limiting via `AutoAssignment::RateLimiter`.
>   - Add `AutoAssignment::RoundRobinSelector` for agent selection.
> - **Jobs & scheduling**:
> - Add `AutoAssignment::AssignmentJob` (per-inbox bulk assign;
env-based limit) and `AutoAssignment::PeriodicAssignmentJob` (batch over
accounts/inboxes).
> - Schedule periodic run in `config/schedule.yml`
(`periodic_assignment_job`).
> - **Model/concerns wiring**:
> - Include `InboxAgentAvailability` in `Inbox`; add
`Inbox#auto_assignment_v2_enabled?`.
> - Update `AutoAssignmentHandler` to trigger v2 job when
`auto_assignment_v2_enabled?`, else fallback to legacy.
> - **Enterprise extensions**:
> - Add `Enterprise::InboxAgentAvailability` (capacity-aware filtering)
and `Enterprise::Concerns::Inbox` association `inbox_capacity_limits`.
> - Extend service via `Enterprise::AutoAssignment::AssignmentService`
(policy-driven config, capacity filtering, exclusion rules) and add
selectors/services: `BalancedSelector`, `CapacityService`.
> - **Infrastructure**:
> - Enhance `Redis::Alfred` with `expire`, key scan/count, and extended
ZSET helpers (`zadd`, `zcount`, `zcard`, `zrangebyscore`).
> - **Tests**:
> - Add specs for jobs, core service, rate limiter, RR selector, and
enterprise features (capacity, balanced selection, exclusions).
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
0ebe187c8aea73765b0122a44b18d6f465c2477f. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

lib/redis/alfred.rb

@@ -35,6 +35,25 @@ module Redis::Alfred
       $alfred.with { |conn| conn.exists?(key) }
     end
 
+    # set expiry on a key in seconds
+    def expire(key, seconds)
+      $alfred.with { |conn| conn.expire(key, seconds) }
+    end
+
+    # scan keys matching a pattern
+    def scan_each(match: nil, count: 100, &)
+      $alfred.with do |conn|
+        conn.scan_each(match: match, count: count, &)
+      end
+    end
+
+    # count keys matching a pattern
+    def keys_count(pattern)
+      count = 0
+      scan_each(match: pattern) { count += 1 }
+      count
+    end
+
     # list operations
 
     def llen(key)
@@ -81,8 +100,15 @@ module Redis::Alfred
     # sorted set operations
 
     # add score and value for a key
-    def zadd(key, score, value)
-      $alfred.with { |conn| conn.zadd(key, score, value) }
+    # Modern Redis syntax: zadd(key, [[score, member], ...])
+    def zadd(key, score, value = nil)
+      if value.nil? && score.is_a?(Array)
+        # New syntax: score is actually an array of [score, member] pairs
+        $alfred.with { |conn| conn.zadd(key, score) }
+      else
+        # Support old syntax for backward compatibility
+        $alfred.with { |conn| conn.zadd(key, [[score, value]]) }
+      end
     end
 
     # get score of a value for key
@@ -90,9 +116,22 @@ module Redis::Alfred
       $alfred.with { |conn| conn.zscore(key, value) }
     end
 
+    # count members in a sorted set with scores within the given range
+    def zcount(key, min_score, max_score)
+      $alfred.with { |conn| conn.zcount(key, min_score, max_score) }
+    end
+
+    # get the number of members in a sorted set
+    def zcard(key)
+      $alfred.with { |conn| conn.zcard(key) }
+    end
+
     # get values by score
-    def zrangebyscore(key, range_start, range_end)
-      $alfred.with { |conn| conn.zrangebyscore(key, range_start, range_end) }
+    def zrangebyscore(key, range_start, range_end, with_scores: false, limit: nil)
+      options = {}
+      options[:with_scores] = with_scores if with_scores
+      options[:limit] = limit if limit
+      $alfred.with { |conn| conn.zrangebyscore(key, range_start, range_end, **options) }
     end
 
     # remove values by score

lib/redis/redis_keys.rb

@@ -42,4 +42,9 @@ module Redis::RedisKeys
   SLACK_MESSAGE_MUTEX = 'SLACK_MESSAGE_LOCK::%<conversation_id>s::%<reference_id>s'.freeze
   EMAIL_MESSAGE_MUTEX = 'EMAIL_CHANNEL_LOCK::%<inbox_id>s'.freeze
   CRM_PROCESS_MUTEX = 'CRM_PROCESS_MUTEX::%<hook_id>s'.freeze
+
+  ## Auto Assignment Keys
+  # Track conversation assignments to agents for rate limiting
+  ASSIGNMENT_KEY = 'ASSIGNMENT::%<inbox_id>d::AGENT::%<agent_id>d::CONVERSATION::%<conversation_id>d'.freeze
+  ASSIGNMENT_KEY_PATTERN = 'ASSIGNMENT::%<inbox_id>d::AGENT::%<agent_id>d::*'.freeze
 end