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/db/ops.rs

@@ -7,14 +7,12 @@ use super::content_store::{
     all_content_ids, delete_content, ensure_content_store, read_content, write_content,
 };
 use super::shadow_write::{PIPELINE_DB, PipelineWriteMsg};
-use super::yaml_legacy::parse_front_matter;
 
 /// Typed metadata for a pipeline item write.
 ///
-/// Replaces the prior YAML-parsing write path (story 864): callers now pass
-/// metadata explicitly instead of round-tripping it through a serialized
-/// front-matter blob.  Every field is `Option`-typed; `None` means
-/// "leave unchanged" on update, "use the default" on insert.
+/// Story 929: callers pass metadata explicitly — no YAML parsing.  Every
+/// field is `Option`-typed; `None` means "leave unchanged" on update,
+/// "use the default" on insert.
 #[derive(Default, Clone, Debug)]
 pub struct ItemMeta {
     pub name: Option<String>,
@@ -33,26 +31,6 @@ impl ItemMeta {
             ..Self::default()
         }
     }
-
-    /// Parse YAML front-matter from a content string into typed metadata.
-    ///
-    /// This is an explicit caller-side conversion — the write path itself
-    /// no longer parses YAML.  Use this when the caller has a raw content
-    /// string with front-matter and wants the metadata to flow into the
-    /// CRDT.  Returns `Self::default()` if parsing fails or there is no
-    /// front-matter present.
-    pub fn from_yaml(content: &str) -> Self {
-        match parse_front_matter(content) {
-            Ok(m) => Self {
-                name: m.name,
-                agent: m.agent,
-                retry_count: m.retry_count.map(|r| r as i64),
-                blocked: m.blocked,
-                depends_on: m.depends_on,
-            },
-            Err(_) => Self::default(),
-        }
-    }
 }
 
 /// Write a pipeline item from in-memory content (no filesystem access).