feat: configure acquire chat batch size (#23196)

## Summary
- add a hidden deployment config option for chat acquire batch size
(`CODER_CHAT_ACQUIRE_BATCH_SIZE` / `chat.acquireBatchSize`)
- thread the configured value into chatd startup while preserving the
existing default of `10`
- clamp the deployment value to the `int32` range before passing it into
chatd
- regenerate the API/docs/types/testdata artifacts for the new config
field

## Why
`chatd` currently acquires pending chats in batches of `10` via a
compile-time default. This change makes that batch size
operator-configurable from deployment config, so we can tune acquisition
behavior without another code change.

coderd/chatd/chatd.go

@@ -58,11 +58,11 @@ const (
 	// of 5 means recovery runs at 1/5 of the stale-after duration.
 	staleRecoveryIntervalDivisor = 5
 
-	// maxChatsPerAcquire is the maximum number of chats to
+	// DefaultMaxChatsPerAcquire is the maximum number of chats to
 	// acquire in a single processOnce call. Batching avoids
 	// waiting a full polling interval between acquisitions
 	// when many chats are pending.
-	maxChatsPerAcquire int32 = 10
+	DefaultMaxChatsPerAcquire int32 = 10
 
 	defaultSubagentInstruction = "You are running as a delegated sub-agent chat. Complete the delegated task and provide clear, concise assistant responses for the parent agent."
 )
@@ -98,6 +98,7 @@ type Server struct {
 
 	// Configuration
 	pendingChatAcquireInterval time.Duration
+	maxChatsPerAcquire         int32
 	inFlightChatStaleAfter     time.Duration
 }
 
@@ -1174,6 +1175,7 @@ type Config struct {
 	ReplicaID                  uuid.UUID
 	SubscribeFn                SubscribeFn
 	PendingChatAcquireInterval time.Duration
+	MaxChatsPerAcquire         int32
 	InFlightChatStaleAfter     time.Duration
 	AgentConn                  AgentConnFunc
 	CreateWorkspace            chattool.CreateWorkspaceFn
@@ -1199,6 +1201,11 @@ func New(cfg Config) *Server {
 		inFlightChatStaleAfter = DefaultInFlightChatStaleAfter
 	}
 
+	maxChatsPerAcquire := cfg.MaxChatsPerAcquire
+	if maxChatsPerAcquire <= 0 {
+		maxChatsPerAcquire = DefaultMaxChatsPerAcquire
+	}
+
 	workerID := cfg.ReplicaID
 	if workerID == uuid.Nil {
 		workerID = uuid.New()
@@ -1219,6 +1226,7 @@ func New(cfg Config) *Server {
 		providerAPIKeys:            cfg.ProviderAPIKeys,
 		instructionCache:           make(map[uuid.UUID]cachedInstruction),
 		pendingChatAcquireInterval: pendingChatAcquireInterval,
+		maxChatsPerAcquire:         maxChatsPerAcquire,
 		inFlightChatStaleAfter:     inFlightChatStaleAfter,
 	}
 
@@ -1272,7 +1280,7 @@ func (p *Server) processOnce(ctx context.Context) {
 	chats, err := p.db.AcquireChats(acquireCtx, database.AcquireChatsParams{
 		StartedAt: time.Now(),
 		WorkerID:  p.workerID,
-		NumChats:  maxChatsPerAcquire,
+		NumChats:  p.maxChatsPerAcquire,
 	})
 	acquireCancel()
 	if err != nil {