feat(agent-task/capi): add GetSession method

Signed-off-by: Babak K. Shandiz <babakks@github.com>

pkg/cmd/agent-task/capi/sessions.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -18,6 +19,8 @@ import (
 
 var defaultSessionsPerPage = 50
 
+var ErrSessionNotFound = errors.New("not found")
+
 // session is an in-flight agent task
 type session struct {
 	ID            string    `json:"id"`
@@ -197,6 +200,45 @@ func (c *CAPIClient) ListSessionsForRepo(ctx context.Context, owner string, repo
 	return result, nil
 }
 
+// GetSession retrieves a specific agent session by ID.
+func (c *CAPIClient) GetSession(ctx context.Context, id string) (*Session, error) {
+	if id == "" {
+		return nil, fmt.Errorf("missing session ID")
+	}
+
+	url := fmt.Sprintf("%s/agents/sessions/%s", baseCAPIURL, url.PathEscape(id))
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, http.NoBody)
+	if err != nil {
+		return nil, err
+	}
+
+	res, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		if res.StatusCode == http.StatusNotFound {
+			return nil, ErrSessionNotFound
+		}
+		return nil, fmt.Errorf("failed to get session: %s", res.Status)
+	}
+
+	var rawSession session
+	if err := json.NewDecoder(res.Body).Decode(&rawSession); err != nil {
+		return nil, fmt.Errorf("failed to decode session response: %w", err)
+	}
+
+	sessions, err := c.hydrateSessionPullRequestsAndUsers([]session{rawSession})
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch session resources: %w", err)
+	}
+
+	return sessions[0], nil
+}
+
 // hydrateSessionPullRequestsAndUsers hydrates pull request and user information in sessions
 func (c *CAPIClient) hydrateSessionPullRequestsAndUsers(sessions []session) ([]*Session, error) {
 	if len(sessions) == 0 {