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/mod.rs

@@ -19,9 +19,6 @@ pub mod content_store;
 pub mod ops;
 /// Background shadow-write task — persists pipeline items to SQLite asynchronously.
 pub mod shadow_write;
-/// Legacy YAML helpers — used by callers reading the small set of fields not
-/// yet mirrored into the CRDT.
-pub(crate) mod yaml_legacy;
 
 pub use content_store::{all_content_ids, delete_content, read_content, write_content};
 pub use ops::{ItemMeta, delete_item, move_item_stage, next_item_number, write_item_with_content};
@@ -33,7 +30,6 @@ pub use content_store::ensure_content_store;
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::db::yaml_legacy::parse_front_matter;
     use std::fs;
 
     /// Helper: write a minimal story .md file with front matter.
@@ -104,25 +100,11 @@ mod tests {
         assert_eq!(row.0, "10_story_shadow_test");
         assert_eq!(row.1.as_deref(), Some("Shadow Test"));
         assert_eq!(row.2, "2_current");
-
-        // Verify metadata was parsed correctly from the story file.
-        let (name, _agent, retry_count, _blocked, _depends_on) =
-            match std::fs::read_to_string(&story_path) {
-                Ok(contents) => match parse_front_matter(&contents) {
-                    Ok(meta) => (
-                        meta.name,
-                        meta.agent,
-                        meta.retry_count.map(|r| r as i64),
-                        meta.blocked,
-                        meta.depends_on,
-                    ),
-                    Err(_) => (None, None, None, None, None),
-                },
-                Err(_) => (None, None, None, None, None),
-            };
-
-        assert_eq!(name.as_deref(), Some("Shadow Test"));
-        assert_eq!(retry_count, Some(2));
+        // The shadow row's name + retry_count came through from the INSERT
+        // params above; that's what the test exercises.  Story 929 dropped
+        // the redundant "re-parse the YAML body to double-check" step that
+        // used to live here.
+        let _ = story_path;
     }
 
     #[tokio::test]