fix(server): trigger agent on reply in thread where agent already participated

When a member replies in a member-started thread without @mentioning the
assigned agent, the on_comment trigger was suppressed — even if the agent
had already replied in that thread. This meant the common flow of
"member posts → agent replies → member follows up" would not re-trigger
the agent on the follow-up.

Add HasAgentRepliedInThread SQL query and check it in isReplyToMemberThread
so that agent participation in a thread is treated as an ongoing conversation.

server/cmd/server/comment_trigger_integration_test.go

@@ -241,6 +241,20 @@ func TestCommentTriggerOnComment(t *testing.T) {
 		}
 	})
 
+	t.Run("reply to member thread after agent replied triggers agent", func(t *testing.T) {
+		clearTasks(t, issueID)
+		// Member starts a thread (top-level comment).
+		threadID := postComment(t, issueID, "Please fix this bug", nil)
+		clearTasks(t, issueID)
+		// Agent replies in the thread.
+		postCommentAsAgent(t, issueID, "Working on it, found the root cause.", agentID, strPtr(threadID))
+		// Member follows up in the same thread without @mentioning the agent.
+		postComment(t, issueID, "Great, please also check the edge case", strPtr(threadID))
+		if n := countPendingTasks(t, issueID); n != 1 {
+			t.Errorf("expected 1 pending task (agent participated in thread), got %d", n)
+		}
+	})
+
 	t.Run("reply to member thread mentioning assignee triggers agent", func(t *testing.T) {
 		clearTasks(t, issueID)
 		// Member starts a thread.

server/internal/handler/comment.go

@@ -262,7 +262,7 @@ func (h *Handler) CreateComment(w http.ResponseWriter, r *http.Request) {
 	// assignee — the user is continuing a member-to-member conversation.
 	if authorType == "member" && h.shouldEnqueueOnComment(r.Context(), issue) &&
 		!h.commentMentionsOthersButNotAssignee(comment.Content, issue) &&
-		!h.isReplyToMemberThread(parentComment, comment.Content, issue) {
+		!h.isReplyToMemberThread(r.Context(), parentComment, comment.Content, issue) {
 		// Resolve thread root: if the comment is a reply, agent should reply
 		// to the thread root (matching frontend behavior where all replies
 		// in a thread share the same top-level parent).
@@ -325,7 +325,9 @@ func (h *Handler) commentMentionsOthersButNotAssignee(content string, issue db.I
 // in the reply, still triggers on_comment as expected.
 // If the parent (thread root) itself @mentions the assignee, the thread is
 // considered a conversation with the agent, so replies are allowed to trigger.
-func (h *Handler) isReplyToMemberThread(parent *db.Comment, content string, issue db.Issue) bool {
+// If the assigned agent has already replied in the thread, the member is
+// conversing with the agent, so replies are allowed to trigger.
+func (h *Handler) isReplyToMemberThread(ctx context.Context, parent *db.Comment, content string, issue db.Issue) bool {
 	if parent == nil {
 		return false // Not a reply — normal top-level comment
 	}
@@ -333,7 +335,8 @@ func (h *Handler) isReplyToMemberThread(parent *db.Comment, content string, issu
 		return false // Thread started by an agent — allow trigger
 	}
 	// Thread was started by a member. Suppress on_comment unless the reply
-	// or the parent explicitly @mentions the assignee agent.
+	// or the parent explicitly @mentions the assignee agent, or the agent
+	// has already participated in this thread.
 	if !issue.AssigneeID.Valid {
 		return true // No assignee to mention
 	}
@@ -351,7 +354,18 @@ func (h *Handler) isReplyToMemberThread(parent *db.Comment, content string, issu
 			return false // Assignee mentioned in thread root — allow trigger
 		}
 	}
-	return true // Reply to member thread without mentioning agent — suppress
+	// Check if the assigned agent has already replied in this thread —
+	// if so, the member is continuing a conversation with the agent.
+	if h.Queries != nil {
+		hasReplied, err := h.Queries.HasAgentRepliedInThread(ctx, db.HasAgentRepliedInThreadParams{
+			ParentID: parent.ID,
+			AgentID:  issue.AssigneeID,
+		})
+		if err == nil && hasReplied {
+			return false // Agent participated in thread — allow trigger
+		}
+	}
+	return true // Reply to member thread without agent participation — suppress
 }
 
 // enqueueMentionedAgentTasks parses @agent mentions from comment content and

server/internal/handler/trigger_test.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"context"
 	"fmt"
 	"testing"
 
@@ -205,7 +206,7 @@ func TestIsReplyToMemberThread(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got := h.isReplyToMemberThread(tt.parent, tt.content, issue)
+			got := h.isReplyToMemberThread(context.Background(), tt.parent, tt.content, issue)
 			if got != tt.want {
 				t.Errorf("isReplyToMemberThread() = %v, want %v", got, tt.want)
 			}
@@ -233,7 +234,7 @@ func TestOnCommentTriggerDecision(t *testing.T) {
 	//   !commentMentionsOthersButNotAssignee && !isReplyToMemberThread
 	shouldTrigger := func(parent *db.Comment, content string) bool {
 		return !h.commentMentionsOthersButNotAssignee(content, issue) &&
-			!h.isReplyToMemberThread(parent, content, issue)
+			!h.isReplyToMemberThread(context.Background(), parent, content, issue)
 	}
 
 	tests := []struct {

server/pkg/db/generated/comment.sql.go

@@ -153,6 +153,26 @@ func (q *Queries) HasAgentCommentedSince(ctx context.Context, arg HasAgentCommen
 	return commented, err
 }
 
+const hasAgentRepliedInThread = `-- name: HasAgentRepliedInThread :one
+SELECT count(*) > 0 AS has_replied FROM comment
+WHERE parent_id = $1 AND author_type = 'agent' AND author_id = $2
+`
+
+type HasAgentRepliedInThreadParams struct {
+	ParentID pgtype.UUID `json:"parent_id"`
+	AgentID  pgtype.UUID `json:"agent_id"`
+}
+
+// Returns true if the given agent has posted a reply in the thread rooted at
+// the specified parent comment. Used to detect agent participation in a
+// member-started thread so that follow-up member replies still trigger the agent.
+func (q *Queries) HasAgentRepliedInThread(ctx context.Context, arg HasAgentRepliedInThreadParams) (bool, error) {
+	row := q.db.QueryRow(ctx, hasAgentRepliedInThread, arg.ParentID, arg.AgentID)
+	var has_replied bool
+	err := row.Scan(&has_replied)
+	return has_replied, err
+}
+
 const listComments = `-- name: ListComments :many
 SELECT id, issue_id, author_type, author_id, content, type, created_at, updated_at, parent_id, workspace_id FROM comment
 WHERE issue_id = $1 AND workspace_id = $2

server/pkg/db/queries/comment.sql

@@ -53,5 +53,12 @@ SELECT EXISTS (
       AND created_at >= @since
 ) AS commented;
 
+-- name: HasAgentRepliedInThread :one
+-- Returns true if the given agent has posted a reply in the thread rooted at
+-- the specified parent comment. Used to detect agent participation in a
+-- member-started thread so that follow-up member replies still trigger the agent.
+SELECT count(*) > 0 AS has_replied FROM comment
+WHERE parent_id = @parent_id AND author_type = 'agent' AND author_id = @agent_id;
+
 -- name: DeleteComment :exec
 DELETE FROM comment WHERE id = $1;