Curation v2 step 2: Claude Opus 5 editor, the Brief, per-provider budgets

- AnthropicBackend (Messages API, cached system block, output_config.effort,
  server-side fallbacks, refusal surfaced as an error); Llms { bulk, editor }
  with editor_or_bulk(); PriceTable-based UsageMeter per provider.
- [anthropic], [editorial], deepseek.max_concurrent_requests and
  curation.max_article_count config; startup logs resolved providers.
- Budget day is the UTC date of started_at, preloaded from
  runs.provider_costs_json; finish_run writes provider_costs_json and
  config_json. Stage A batches run concurrently with per-batch budget checks.
- Editor prompt with one-line "why" per pick; no minimum lineup size;
  --max-articles is a ceiling; top-up branch deleted; why stored on picks and
  issue_articles.why and rendered in chapters and In this issue.
- Summaries on the editor client (3k-token input, concurrency 4, bulk then
  excerpt fallback); "The Brief" replaces From the Editor; section intros gone.
- Colophon carries per-provider costs and models.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A1rCLQeKBgnBo3oTgHuTMe

src/epub/fixtures.rs

@@ -86,6 +86,7 @@ pub fn issue() -> Issue {
         section: "Top Stories".into(),
         position: 0,
         is_lead: true,
+        why: Some("The systems story with enough operational detail to matter".into()),
         summary: Some("What it argues, and why it is worth the time.".into()),
         llm: None,
         discussion: Some(discussion(1, 1001)),
@@ -95,12 +96,11 @@ pub fn issue() -> Issue {
         section: "Niche Corner".into(),
         position: 0,
         is_lead: false,
+        why: Some("A small-scene delight outside the usual technical orbit".into()),
         summary: None,
         llm: None,
         discussion: None,
     };
-    let mut section_intros = BTreeMap::new();
-    section_intros.insert("Top Stories".to_string(), "The day in brief.".to_string());
     let mut summaries = BTreeMap::new();
     summaries.insert(2, "A short abstract for the second piece.".to_string());
 
@@ -122,7 +122,6 @@ pub fn issue() -> Issue {
         },
         editorial: Editorial {
             front_page_html: "<p>Two stories today, both worth your coffee.</p>".into(),
-            section_intros,
             summaries,
         },
         world_briefing: Some(WorldBriefing {
@@ -141,7 +140,15 @@ pub fn issue() -> Issue {
             }],
         }),
         colophon: Colophon {
-            model: "deepseek-v4-flash".into(),
+            provider_costs: BTreeMap::from([
+                ("deepseek".into(), 0.0231),
+                ("anthropic".into(), 0.05),
+            ]),
+            models: Models {
+                bulk: "deepseek-v4-flash".into(),
+                editor: "claude-opus-5".into(),
+                summaries: "claude-opus-5".into(),
+            },
             entries_fetched: 431,
             feeds_seen: 92,
             candidates: 120,