fix: throttle filtered unread count rebuilds (#14980)

Reduces database pressure from filtered unread-count cache rebuilds
during high-traffic account rollouts by serving stale snapshots longer
and limiting inline saved-filter rebuild fanout.

## Closes

None

## What changed

- Increase filtered unread-count refresh throttling from 30 seconds to 5
minutes.
- Increase the stale snapshot window from 30 minutes to 1 hour.
- Reduce inline saved-filter count rebuilds per request from 10 to 3.
- Update unread-count specs to assert refresh and stale behavior through
the shared constants.

## How to test

- Enable `conversation_unread_counts` and `unread_count_for_filters` for
an account with conversation custom filters.
- Open the dashboard and verify unread-count badges still return values.
- Mutate conversations and verify stale filtered counts are served while
rebuilds are throttled, instead of repeatedly rebuilding every 30
seconds.

app/services/conversations/unread_counts.rb

@@ -2,9 +2,9 @@ module Conversations::UnreadCounts
   READY_TTL = 24.hours.to_i
   SET_TTL = 25.hours.to_i
   FILTERED_COUNT_FRESH_TTL = 5.minutes.to_i
-  FILTERED_COUNT_STALE_WINDOW = 30.minutes.to_i
+  FILTERED_COUNT_STALE_WINDOW = 1.hour.to_i
   FILTERED_COUNT_REDIS_TTL = FILTERED_COUNT_FRESH_TTL + FILTERED_COUNT_STALE_WINDOW
   FILTERED_COUNT_VERSION_TTL = SET_TTL
-  FILTERED_COUNT_MIN_REFRESH_INTERVAL = 30.seconds.to_i
-  MAX_INLINE_FILTER_BUILDS = 10
+  FILTERED_COUNT_MIN_REFRESH_INTERVAL = 5.minutes.to_i
+  MAX_INLINE_FILTER_BUILDS = 3
 end

spec/services/conversations/unread_counts/filtered_count_store_spec.rb

@@ -96,7 +96,14 @@ RSpec.describe Conversations::UnreadCounts::FilteredCountStore do
 
       described_class.bump_built_in_filter_version!(account_id: account_id, user_id: user_id)
       expect(described_class.built_in_filter_counts_state(account_id: account_id, user_id: user_id, now: built_at + 2.minutes)).to be_stale
-      expect(described_class.built_in_filter_counts_state(account_id: account_id, user_id: user_id, now: built_at + 36.minutes)).to be_expired
+      expect(
+        described_class.built_in_filter_counts_state(
+          account_id: account_id,
+          user_id: user_id,
+          now: built_at + Conversations::UnreadCounts::FILTERED_COUNT_FRESH_TTL +
+            Conversations::UnreadCounts::FILTERED_COUNT_STALE_WINDOW + 1.second
+        )
+      ).to be_expired
 
       Redis::Alfred.delete(described_class.built_in_filter_counts_key(account_id, user_id))
       expect(described_class.built_in_filter_counts_state(account_id: account_id, user_id: user_id)).to be_missing
@@ -202,8 +209,18 @@ RSpec.describe Conversations::UnreadCounts::FilteredCountStore do
       )
 
       snapshot = described_class.built_in_filter_counts(account_id: account_id, user_id: user_id)
-      expect(described_class.refresh_due?(snapshot, now: built_at + 10.seconds)).to be(false)
-      expect(described_class.refresh_due?(snapshot, now: built_at + 31.seconds)).to be(true)
+      expect(
+        described_class.refresh_due?(
+          snapshot,
+          now: built_at + Conversations::UnreadCounts::FILTERED_COUNT_MIN_REFRESH_INTERVAL - 1.second
+        )
+      ).to be(false)
+      expect(
+        described_class.refresh_due?(
+          snapshot,
+          now: built_at + Conversations::UnreadCounts::FILTERED_COUNT_MIN_REFRESH_INTERVAL + 1.second
+        )
+      ).to be(true)
 
       expect(described_class.claim_built_in_filter_refresh!(account_id: account_id, user_id: user_id)).to be(true)
       expect(described_class.claim_built_in_filter_refresh!(account_id: account_id, user_id: user_id)).to be(false)

spec/services/conversations/unread_counts/filtered_counter_spec.rb

@@ -48,10 +48,22 @@ RSpec.describe Conversations::UnreadCounts::FilteredCounter do
     create(:mention, account: account, conversation: second_mention, user: agent)
     store.bump_conversation_version!(account.id)
 
-    expect(described_class.new(account: account, user: agent, now: now + 10.seconds).perform[:mentions_count]).to eq(1)
+    expect(
+      described_class.new(
+        account: account,
+        user: agent,
+        now: now + Conversations::UnreadCounts::FILTERED_COUNT_MIN_REFRESH_INTERVAL - 1.second
+      ).perform[:mentions_count]
+    ).to eq(1)
 
     Redis::Alfred.delete(store.built_in_filter_refresh_throttle_key(account.id, agent.id))
-    expect(described_class.new(account: account, user: agent, now: now + 31.seconds).perform[:mentions_count]).to eq(2)
+    expect(
+      described_class.new(
+        account: account,
+        user: agent,
+        now: now + Conversations::UnreadCounts::FILTERED_COUNT_MIN_REFRESH_INTERVAL + 1.second
+      ).perform[:mentions_count]
+    ).to eq(2)
   end
 
   it 'returns stale built-in counts when a refresh build hits a database error' do
@@ -62,7 +74,11 @@ RSpec.describe Conversations::UnreadCounts::FilteredCounter do
 
     store.bump_conversation_version!(account.id)
     Redis::Alfred.delete(store.built_in_filter_refresh_throttle_key(account.id, agent.id))
-    failing_counter = described_class.new(account: account, user: agent, now: now + 31.seconds)
+    failing_counter = described_class.new(
+      account: account,
+      user: agent,
+      now: now + Conversations::UnreadCounts::FILTERED_COUNT_MIN_REFRESH_INTERVAL + 1.second
+    )
     allow(failing_counter).to receive(:built_in_counts_from_database).and_raise(ActiveRecord::StatementInvalid.new('statement timeout'))
 
     expect(failing_counter.perform[:mentions_count]).to eq(1)