wip(929): stage 10 sweep — production callsites move to CRDT, yaml_legacy shrinks

After 932 (review_hold register) and 933 (item_type + epic registers), the
remaining production yaml_legacy callers all had typed CRDT equivalents.
Migrated:

- agents/lifecycle.rs:
  - transition_to_merge_failure writes to MergeJob.error CRDT entry instead
    of YAML body. The legacy `merge_failure: "..."` front-matter write is gone.
  - reject_story_from_qa inlines the QA-rejection notes append; no longer
    needs yaml_legacy::write_rejection_notes_to_content.
  - fields_to_clear_transform helper deleted along with all five callers —
    blocked/retry_count/merge_failure are typed CRDT fields now, so clearing
    the equivalent YAML keys is redundant.

- http/workflow/pipeline.rs:
  - load_pipeline_state reads merge_failure from MergeJob.error (mirrors
    status_tools.rs).
  - validate_story_dirs checks the typed CRDT `name` register instead of
    parsing YAML front matter.

- http/mcp/status_tools.rs: review_hold reads the typed CRDT register
  (yaml_residue wrap was the last one in this file).
- http/mcp/story_tools/criteria.rs: story_name reads from CRDT.
- service/agents/mod.rs::get_work_item_content: name/agent come from CRDT.
- service/notifications/io/mod.rs::read_story_name: same.
- http/workflow/bug_ops/{bug,refactor}.rs: name-fallback paths drop YAML
  parsing in favour of the CRDT-derived item.name.

Dead helpers removed from db/yaml_legacy.rs:
  yaml_residue, write_merge_failure_in_content, write_rejection_notes_to_content,
  clear_front_matter_field_in_content, write_review_hold_in_content,
  clear_front_matter_field, write_review_hold (the last four shipped in 932).
Remaining surface: FrontMatter / StoryMetadata structs, parse_front_matter,
set_front_matter_field — kept for `coverage_baseline` writes via
test_results.rs and the generic update_story front_matter escape hatch.

Test fixtures rewritten to seed the CRDT register instead of relying on
YAML parsing during write_item_with_content:
- has_review_hold_returns_* tests
- item_type_from_id_uses_crdt_register_for_numeric_ids
- tool_list_epics_shows_member_rollup
- get_work_item_content (both copies — http/agents + service/agents)
- validate_story_dirs_missing_name_in_crdt
- server_side_merge_*_sets_merge_failure (assert MergeJob.error, not YAML)

cargo fmt --check, clippy --all-targets -- -D warnings, and the
2856-test suite all pass.

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

server/src/http/workflow/pipeline.rs

@@ -1,7 +1,6 @@
 //! Pipeline state — types and loading functions for the story pipeline.
 
 use crate::agents::AgentStatus;
-use crate::db::yaml_legacy::parse_front_matter;
 use crate::http::context::AppContext;
 use serde::Serialize;
 use std::collections::HashMap;
@@ -96,15 +95,13 @@ pub fn load_pipeline_state(ctx: &AppContext) -> Result<PipelineState, String> {
         let agent = agent_map.get(sid).cloned();
 
         // Stories 929/932/933: review_hold, qa_mode, epic_id come from typed
-        // CRDT registers. merge_failure remains in YAML for now (tracked by
-        // 929 stage 10's sweep).
+        // CRDT registers. merge_failure detail lives on the MergeJob CRDT
+        // entry (same as status_tools.rs).
         let view = crate::crdt_state::read_item(sid);
         let review_hold = view.as_ref().map(|v| v.review_hold()).filter(|b| *b);
         let qa = view.as_ref().and_then(|v| v.qa_mode().map(str::to_string));
         let epic_id = view.as_ref().and_then(|v| v.epic().map(str::to_string));
-        let merge_failure = crate::db::read_content(sid)
-            .and_then(|c| parse_front_matter(&c).ok())
-            .and_then(|meta| meta.merge_failure);
+        let merge_failure = crate::crdt_state::read_merge_job(sid).and_then(|j| j.error);
 
         let story = UpcomingStory {
             story_id: sid.clone(),
@@ -252,7 +249,10 @@ pub fn load_upcoming_stories(_ctx: &AppContext) -> Result<Vec<UpcomingStory>, St
     Ok(stories)
 }
 
-/// Validate story front matter for all backlog and current items.
+/// Validate stories for all backlog and current items.
+///
+/// Story 929: validation reads the typed CRDT `name` register; the legacy YAML
+/// front-matter parse is gone.
 pub fn validate_story_dirs(_root: &Path) -> Result<Vec<StoryValidationResult>, String> {
     use crate::pipeline_state::Stage;
 
@@ -260,44 +260,26 @@ pub fn validate_story_dirs(_root: &Path) -> Result<Vec<StoryValidationResult>, S
 
     let typed_items = crate::pipeline_state::read_all_typed();
     for item in typed_items {
-        // Only validate backlog and current items (matching the old behaviour).
         if !matches!(item.stage, Stage::Backlog | Stage::Coding) {
             continue;
         }
         let story_id = item.story_id.0.clone();
+        let name = crate::crdt_state::read_item(&story_id)
+            .and_then(|v| v.name().map(str::to_string))
+            .filter(|s| !s.is_empty());
 
-        match crate::db::read_content(&story_id) {
-            Some(contents) => match parse_front_matter(&contents) {
-                Ok(meta) => {
-                    let mut errors = Vec::new();
-                    if meta.name.is_none() {
-                        errors.push("Missing 'name' field".to_string());
-                    }
-                    if errors.is_empty() {
-                        results.push(StoryValidationResult {
-                            story_id,
-                            valid: true,
-                            error: None,
-                        });
-                    } else {
-                        results.push(StoryValidationResult {
-                            story_id,
-                            valid: false,
-                            error: Some(errors.join("; ")),
-                        });
-                    }
-                }
-                Err(e) => results.push(StoryValidationResult {
-                    story_id,
-                    valid: false,
-                    error: Some(e.to_string()),
-                }),
-            },
-            None => results.push(StoryValidationResult {
+        if name.is_some() {
+            results.push(StoryValidationResult {
+                story_id,
+                valid: true,
+                error: None,
+            });
+        } else {
+            results.push(StoryValidationResult {
                 story_id,
                 valid: false,
-                error: Some("No content found in content store".to_string()),
-            }),
+                error: Some("Missing 'name' field".to_string()),
+            });
         }
     }
 
@@ -581,13 +563,15 @@ mod tests {
     }
 
     #[test]
-    fn validate_story_dirs_missing_front_matter() {
+    fn validate_story_dirs_missing_name_in_crdt() {
+        crate::crdt_state::init_for_test();
         crate::db::ensure_content_store();
+        // Item exists in CRDT but with no name register set.
         crate::db::write_item_with_content(
             "9875_story_no_fm",
             "2_current",
             "# No front matter\n",
-            crate::db::ItemMeta::from_yaml("# No front matter\n"),
+            crate::db::ItemMeta::default(),
         );
 
         let tmp = tempfile::tempdir().unwrap();
@@ -597,7 +581,7 @@ mod tests {
             .find(|r| r.story_id == "9875_story_no_fm")
             .unwrap();
         assert!(!r.valid);
-        assert_eq!(r.error.as_deref(), Some("Missing front matter"));
+        assert_eq!(r.error.as_deref(), Some("Missing 'name' field"));
     }
 
     #[test]