fix: image alt on HTML-only translations and on markdown that starts with a tag

Blank content means content_html is the body (no 422 for
content_html-only translations, a regression from the markdown alt fix);
any other content is handled as markdown, so a body opening with a tag
gets its inline image label and keeps its code samples.

quick-261104-xae, review WR-02.

headings_test.go

@@ -723,6 +723,86 @@ func TestSetImageAlt(t *testing.T) {
 	}
 }
 
+// TestSetImageAltBodyShapes pins the body rule of images/alt
+// (33-REVIEW-GAPFIX WR-02): a locale whose content is blank (a translation
+// that carries only content_html) gets the alt in content_html alone, and
+// any other content is read as markdown, also when it starts with a tag.
+func TestSetImageAltBodyShapes(t *testing.T) {
+	env := newPostsEnv(t)
+	editor := env.admin(t, controllers.PermissionAccessPosts, controllers.PermissionAccessOtherPosts)
+	const a = "https://cdn.example.test/a.jpg"
+	path := journalAPIPrefix + "/images/alt"
+	decode := func(rec *httptest.ResponseRecorder) []map[string]any {
+		var out struct {
+			Changes []map[string]any `json:"changes"`
+		}
+		if err := json.Unmarshal(rec.Body.Bytes(), &out); err != nil {
+			t.Fatalf("alt body %s: %v", rec.Body.String(), err)
+		}
+		return out.Changes
+	}
+
+	t.Run("a translation that holds only content_html", func(t *testing.T) {
+		post := apiPostID(t, env.expect(t, http.StatusCreated, http.MethodPost, journalAPIPrefix+"/posts", editor, map[string]any{
+			"title": "HTML translation", "content": "Intro\n\n![](" + a + ")",
+			"translations": map[string]any{"pl": map[string]any{"title": "Obrazy", "content_html": `<p><img src="` + a + `"></p>`}},
+		}))
+		changes := decode(env.expect(t, http.StatusOK, http.MethodPost, path, editor, map[string]any{
+			"changes": []any{
+				map[string]any{"post_id": post, "src": a, "alt": "Grzyb"},
+				map[string]any{"post_id": post, "locale": "pl", "src": a, "alt": "Lew"},
+			},
+		}))
+		if len(changes) != 2 || changes[1]["locale"] != "pl" || changes[1]["changed"] != true || changes[1]["old_alt"] != nil {
+			t.Fatalf("answer = %#v", changes)
+		}
+		pl := translatedAttrs(t, env, post, "pl")
+		if html, _ := pl["content_html"].(string); !strings.Contains(html, `alt="Lew"`) {
+			t.Fatalf("pl = %#v", pl)
+		}
+		if c, has := pl["content"]; has {
+			if s, _ := c.(string); strings.TrimSpace(s) != "" {
+				t.Fatalf("pl content was written: %#v", pl)
+			}
+		}
+		if got := storedPost(t, env, post).Content; got != "Intro\n\n![Grzyb]("+a+")" {
+			t.Fatalf("default content = %q", got)
+		}
+	})
+
+	t.Run("markdown that starts with a tag", func(t *testing.T) {
+		md := "<p class=\"lead\">Intro</p>\n\n![](" + a + ")\n\n```html\n<img src=\"" + a + "\">\n```\n"
+		post := apiPostID(t, env.expect(t, http.StatusCreated, http.MethodPost, journalAPIPrefix+"/posts", editor, map[string]any{"title": "Tag lead", "content": md}))
+		env.expect(t, http.StatusOK, http.MethodPost, path, editor, map[string]any{
+			"changes": []any{map[string]any{"post_id": post, "src": a, "alt": "Grzyb"}},
+		})
+		want := "<p class=\"lead\">Intro</p>\n\n![Grzyb](" + a + ")\n\n```html\n<img src=\"" + a + "\">\n```\n"
+		stored := storedPost(t, env, post)
+		if stored.Content != want || !strings.Contains(stored.ContentHTML, `alt="Grzyb"`) {
+			t.Fatalf("after the alt = %q / %q", stored.Content, stored.ContentHTML)
+		}
+		env.expect(t, http.StatusOK, http.MethodPut, fmt.Sprintf("%s/posts/%d", journalAPIPrefix, post), editor, map[string]any{"content": stored.Content})
+		if again := storedPost(t, env, post); !strings.Contains(again.ContentHTML, `alt="Grzyb"`) {
+			t.Fatalf("the next content save lost the alt: %q", again.ContentHTML)
+		}
+	})
+
+	t.Run("markdown that starts with a tag and holds the image by reference", func(t *testing.T) {
+		ref := "<p>Lead</p>\n\n![old][r]\n\n[r]: " + a + "\n"
+		post := apiPostID(t, env.expect(t, http.StatusCreated, http.MethodPost, journalAPIPrefix+"/posts", editor, map[string]any{"title": "Tag lead reference", "content": ref}))
+		before := storedPost(t, env, post)
+		rec := env.expect(t, http.StatusUnprocessableEntity, http.MethodPost, path, editor, map[string]any{
+			"changes": []any{map[string]any{"post_id": post, "src": a, "alt": "new"}},
+		})
+		if !strings.Contains(rec.Body.String(), "changes.0.src") || !strings.Contains(rec.Body.String(), "not an inline image") {
+			t.Fatalf("reference answer %s", rec.Body.String())
+		}
+		if after := storedPost(t, env, post); after.Content != before.Content || after.ContentHTML != before.ContentHTML {
+			t.Fatalf("a refused change wrote: %q / %q", after.Content, after.ContentHTML)
+		}
+	})
+}
+
 // TestBlogEditorRequestOptions (J1, UI-SPEC C28): the post and category
 // editor fields serve headingLevels and genericAnchors per form schema
 // request, following the H1 setting and the settings' generic link texts.