feat(929): delete db/yaml_legacy.rs entirely — CRDT is the sole source of truth

Final 929 sweep: every YAML-shaped helper is gone. No production code
parses or writes YAML front matter anywhere.

Surface removed:
- db/yaml_legacy.rs (FrontMatter/StoryMetadata structs, parse_front_matter,
  set_front_matter_field, yaml_residue marker) — file deleted.
- ItemMeta::from_yaml — deleted; callers pass typed ItemMeta::named(...) or
  ItemMeta::default() and use typed CRDT setters (set_depends_on,
  set_blocked, set_retry_count, set_agent, set_qa_mode, set_review_hold,
  set_item_type, set_epic, set_mergemaster_attempted) for the rest.
- write_coverage_baseline_to_story_file + read_coverage_percent_from_json —
  the coverage_baseline YAML field was write-only (nothing read it back);
  removed along with its caller in agent_tools/lifecycle.rs.
- update_story_in_file's generic `front_matter` HashMap parameter —
  tool_update_story now intercepts every known field name and routes it
  to a typed CRDT setter; unknown keys are rejected with an explicit error
  pointing at the typed setters. The function only takes user_story /
  description sections now.
- All 117 ItemMeta::from_yaml callsites migrated. Where tests previously
  passed a YAML-shaped content blob and relied on the helper to extract
  name/depends_on/blocked/agent/qa, they now pass:
    write_item_with_content(id, stage, content, ItemMeta::named("Foo"))
    crate::crdt_state::set_depends_on(id, &[...])    // when needed
    crate::crdt_state::set_blocked(id, true)         // when needed
    crate::crdt_state::set_agent(id, Some("..."))    // when needed
- write_story_content + write_story_file (test helper) now take an
  explicit `name: Option<&str>` instead of parsing it from content.
- db::ops::move_item_stage stopped re-parsing YAML on every stage
  transition; metadata is read straight from the CRDT view when mirroring
  the row into SQLite.

New CRDT setters added for symmetry:
- crdt_state::set_name (mirrors set_agent — explicit name updates).

cargo fmt --check, clippy --all-targets -- -D warnings, and the
2830-test suite all pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/crdt_state/write/item.rs

@@ -128,6 +128,29 @@ pub fn set_mergemaster_attempted(story_id: &str, value: bool) -> bool {
     true
 }
 
+/// Set the `name` field for a pipeline item by its story ID.
+///
+/// `Some(name)` writes the human-readable name into the CRDT register.
+/// `None` clears the register by writing an empty string.
+///
+/// Returns `true` if the item was found and the write was performed.
+pub fn set_name(story_id: &str, name: Option<&str>) -> bool {
+    let Some(state_mutex) = get_crdt() else {
+        return false;
+    };
+    let Ok(mut state) = state_mutex.lock() else {
+        return false;
+    };
+    let Some(&idx) = state.index.get(story_id) else {
+        return false;
+    };
+    let value = name.unwrap_or("").to_string();
+    apply_and_persist(&mut state, |s| {
+        s.crdt.doc.items[idx].name.set(value.clone())
+    });
+    true
+}
+
 /// Set the `agent` field for a pipeline item by its story ID.
 ///
 /// `Some(name)` writes the agent name into the CRDT register.

server/src/crdt_state/write/mod.rs

@@ -11,6 +11,6 @@ mod tests;
 
 pub use item::{
     bump_retry_count, set_agent, set_blocked, set_depends_on, set_epic, set_item_type,
-    set_mergemaster_attempted, set_qa_mode, set_retry_count, set_review_hold, write_item,
+    set_mergemaster_attempted, set_name, set_qa_mode, set_retry_count, set_review_hold, write_item,
 };
 pub use migrations::{migrate_names_from_slugs, migrate_story_ids_to_numeric, name_from_story_id};