v0: stdlib-only Discourse client — categories/topics/posts + raw passthrough

Covers the MOPAC briefing/report surface (Redmine 495 Part A): category
list/create (create needs the admin-scoped key; current key 403s, typed
as ErrForbidden), topic create/list/latest/get, post create/update/get,
current-user identity probe, and a Do() JSON passthrough so unmodeled
endpoints need no client release. Key is env/constructor-only, never a
flag, never logged; errors classify via errors.Is. Fake-server unit
tests + containerized end-to-end smoke (redaction sweep included); live
reads verified against community.turnsys.com.

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

topics.go

@@ -0,0 +1,137 @@
+// Topics: create (POST /posts.json — Discourse creates topics by posting
+// the first post with a title), list per category (GET /c/<...>.json) and
+// latest (GET /latest.json), fetch one (GET /t/<id>.json).
+package discourse
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+// TopicSummary is one row of a topic list.
+type TopicSummary struct {
+	ID         int    `json:"id"`
+	Title      string `json:"title"`
+	Slug       string `json:"slug"`
+	CategoryID int    `json:"category_id"`
+	PostsCount int    `json:"posts_count"`
+	CreatedAt  string `json:"created_at"`
+	UpdatedAt  string `json:"updated_at"`
+	Closed     bool   `json:"closed"`
+	Archived   bool   `json:"archived"`
+}
+
+// Topic is the full topic payload (GET /t/<id>.json); posts live under
+// PostStream.Posts.
+type Topic struct {
+	ID         int    `json:"id"`
+	Title      string `json:"title"`
+	Slug       string `json:"slug"`
+	CategoryID int    `json:"category_id"`
+	CreatedAt  string `json:"created_at"`
+	Closed     bool   `json:"closed"`
+	Archived  bool   `json:"archived"`
+	PostStream struct {
+		Posts []Post `json:"posts"`
+	} `json:"post_stream"`
+}
+
+// CreateTopicRequest creates a topic: title + markdown body + category.
+type CreateTopicRequest struct {
+	Title    string   `json:"title"`
+	Raw      string   `json:"raw"`
+	Category int      `json:"category"`
+	Tags     []string `json:"tags,omitempty"`
+}
+
+// CreateTopicResult is the POST /posts.json response for a topic
+// creation: the first post's id plus the new topic's id and slug.
+type CreateTopicResult struct {
+	PostID    int    `json:"id"`
+	TopicID   int    `json:"topic_id"`
+	TopicSlug string `json:"topic_slug"`
+}
+
+// URL renders the topic's canonical URL on this instance.
+func (r CreateTopicResult) URL(baseURL string) string {
+	if r.TopicID == 0 {
+		return ""
+	}
+	slug := r.TopicSlug
+	if slug == "" {
+		slug = "topic"
+	}
+	return strings.TrimSuffix(baseURL, "/") + "/t/" + slug + "/" + fmt.Sprint(r.TopicID)
+}
+
+// CreateTopic posts a new topic into the category and returns its ids.
+func (c *Client) CreateTopic(ctx context.Context, req CreateTopicRequest) (*CreateTopicResult, error) {
+	if strings.TrimSpace(req.Title) == "" {
+		return nil, fmt.Errorf("%w: topic title is required", ErrInvalidRequest)
+	}
+	if req.Category == 0 {
+		return nil, fmt.Errorf("%w: topic category id is required", ErrInvalidRequest)
+	}
+	var out CreateTopicResult
+	if err := c.Post(ctx, "/posts.json", req, &out); err != nil {
+		return nil, err
+	}
+	if out.TopicID == 0 {
+		return nil, fmt.Errorf("%w: topic created but response carries no topic_id", ErrMalformedResponse)
+	}
+	return &out, nil
+}
+
+// ListTopics returns the topic list of a category, addressed by id
+// (GET /c/<id>.json) or slug (GET /c/<slug>.json). Pass slug="" with id>0
+// or id=0 with a slug.
+func (c *Client) ListTopics(ctx context.Context, id int, slug string) ([]TopicSummary, error) {
+	if id == 0 && slug == "" {
+		return nil, fmt.Errorf("%w: category id or slug is required", ErrInvalidRequest)
+	}
+	var path string
+	if id > 0 {
+		if slug != "" {
+			path = "/c/" + quotePathSegment(slug) + "/" + fmt.Sprint(id) + ".json"
+		} else {
+			path = "/c/" + fmt.Sprint(id) + ".json"
+		}
+	} else {
+		path = "/c/" + quotePathSegment(slug) + ".json"
+	}
+	var payload struct {
+		TopicList struct {
+			Topics []TopicSummary `json:"topics"`
+		} `json:"topic_list"`
+	}
+	if err := c.Get(ctx, path, &payload); err != nil {
+		return nil, err
+	}
+	return payload.TopicList.Topics, nil
+}
+
+// LatestTopics returns the instance's latest topic list (GET /latest.json).
+func (c *Client) LatestTopics(ctx context.Context) ([]TopicSummary, error) {
+	var payload struct {
+		TopicList struct {
+			Topics []TopicSummary `json:"topics"`
+		} `json:"topic_list"`
+	}
+	if err := c.Get(ctx, "/latest.json", &payload); err != nil {
+		return nil, err
+	}
+	return payload.TopicList.Topics, nil
+}
+
+// GetTopic fetches one topic by id, posts included.
+func (c *Client) GetTopic(ctx context.Context, id int) (*Topic, error) {
+	if id <= 0 {
+		return nil, fmt.Errorf("%w: topic id must be > 0", ErrInvalidRequest)
+	}
+	var topic Topic
+	if err := c.Get(ctx, "/t/"+fmt.Sprint(id)+".json", &topic); err != nil {
+		return nil, err
+	}
+	return &topic, nil
+}