feat(933): add item_type + epic CRDT registers + migrate epic mechanism

Replaces the YAML-only `type: epic` / `epic: <id>` front-matter fields with
typed CRDT registers on PipelineItemCrdt. The epic-mechanism MCP tools
(`tool_list_epics`, `tool_show_epic`), the epic-context injection in agent
spawn, and the type-classifier helpers (`item_type_from_id`, `is_bug_item`,
`is_refactor_item`) now all read from the CRDT.

Schema:
- PipelineItemCrdt: `item_type: LwwRegisterCrdt<String>` and
  `epic: LwwRegisterCrdt<String>` registers.
- WorkItem: typed `item_type()` and `epic()` accessors returning `Option<&str>`.
- crdt_state::set_item_type(story_id, Option<&str>) and
  crdt_state::set_epic(story_id, Option<&str>) typed setters.

Write paths populate the new registers:
- create_story_file / create_bug_file / create_spike_file /
  create_refactor_file / create_epic_file — each calls set_item_type after
  write_story_content.
- tool_update_story intercepts `epic` and `type` fields and routes them to
  the typed setters (same pattern as qa / depends_on).

Read paths migrated off yaml_legacy:
- http/mcp/story_tools/epic.rs: tool_list_epics + tool_show_epic.
- agents/lifecycle.rs::item_type_from_id (numeric-only IDs).
- agents/pool/start/spawn.rs epic-context injection.
- http/workflow/bug_ops/bug.rs::is_bug_item, refactor.rs::is_refactor_item.
- http/workflow/pipeline.rs::load_pipeline_state — review_hold/qa/epic_id
  all come from the CRDT now; only merge_failure is still YAML (sweep in
  929 stage 10).

All `yaml_residue(...)` wraps for item_type / epic are removed; the
remaining residue marker doc no longer references 933.

cargo fmt --check, clippy --all-targets -- -D warnings, and the 2857-test
suite all pass.

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

server/src/http/mcp/story_tools/epic.rs

@@ -4,10 +4,6 @@
 //! and refactors. They are not pipeline-driven but provide authoritative context
 //! injected into agent prompts for all member work items.
 
-// Epic mechanism (item_type, epic link) has no CRDT register yet — story 933.
-// parse_front_matter calls here are wrapped in `yaml_residue` so they're
-// grep-findable until 933 lands.
-use crate::db::yaml_legacy::{parse_front_matter, yaml_residue};
 use crate::http::context::AppContext;
 use crate::http::workflow::create_epic_file;
 use serde_json::{Value, json};
@@ -53,7 +49,7 @@ pub(crate) fn tool_list_epics(_ctx: &AppContext) -> Result<String, String> {
 
     let all_items = crate::pipeline_state::read_all_typed();
 
-    // Collect epics: items with type == "epic".
+    // Collect epics: items with item_type == "epic" in the CRDT register.
     let mut epics: Vec<(String, String)> = Vec::new(); // (id, name)
     // Collect member items: map from epic_id → list of (story_id, is_done).
     let mut members: std::collections::HashMap<String, Vec<(String, bool)>> =
@@ -61,23 +57,18 @@ pub(crate) fn tool_list_epics(_ctx: &AppContext) -> Result<String, String> {
 
     for item in &all_items {
         let sid = &item.story_id.0;
-        let content = match crate::db::read_content(sid) {
-            Some(c) => c,
-            None => continue,
-        };
-        let meta = match yaml_residue(parse_front_matter(&content)) {
-            Ok(m) => m,
-            Err(_) => continue,
+        let Some(view) = crate::crdt_state::read_item(sid) else {
+            continue;
         };
 
-        if meta.item_type.as_deref() == Some("epic") {
+        if view.item_type() == Some("epic") {
             epics.push((sid.clone(), item.name.clone()));
         }
 
-        if let Some(epic_id) = meta.epic {
+        if let Some(epic_id) = view.epic() {
             let is_done = matches!(item.stage, Stage::Done { .. });
             members
-                .entry(epic_id)
+                .entry(epic_id.to_string())
                 .or_default()
                 .push((sid.clone(), is_done));
         }
@@ -116,13 +107,13 @@ pub(crate) fn tool_show_epic(args: &Value, _ctx: &AppContext) -> Result<String,
     let content = crate::db::read_content(epic_id)
         .ok_or_else(|| format!("Epic '{epic_id}' not found in content store"))?;
 
-    let meta = yaml_residue(parse_front_matter(&content))
-        .map_err(|e| format!("Failed to parse epic front matter: {e}"))?;
+    let epic_view = crate::crdt_state::read_item(epic_id)
+        .ok_or_else(|| format!("Epic '{epic_id}' not found in CRDT"))?;
 
-    if meta.item_type.as_deref() != Some("epic") {
+    if epic_view.item_type() != Some("epic") {
         return Err(format!(
-            "'{epic_id}' is not an epic (type: {:?})",
-            meta.item_type
+            "'{epic_id}' is not an epic (item_type: {:?})",
+            epic_view.item_type()
         ));
     }
 
@@ -131,15 +122,10 @@ pub(crate) fn tool_show_epic(args: &Value, _ctx: &AppContext) -> Result<String,
     let mut member_items: Vec<Value> = Vec::new();
     for item in &all_items {
         let sid = &item.story_id.0;
-        let member_content = match crate::db::read_content(sid) {
-            Some(c) => c,
-            None => continue,
+        let Some(member_view) = crate::crdt_state::read_item(sid) else {
+            continue;
         };
-        let member_meta = match yaml_residue(parse_front_matter(&member_content)) {
-            Ok(m) => m,
-            Err(_) => continue,
-        };
-        if member_meta.epic.as_deref() == Some(epic_id) {
+        if member_view.epic() == Some(epic_id) {
             let stage_name = match &item.stage {
                 Stage::Upcoming | Stage::Backlog => "backlog",
                 Stage::Coding => "current",
@@ -164,7 +150,7 @@ pub(crate) fn tool_show_epic(args: &Value, _ctx: &AppContext) -> Result<String,
 
     serde_json::to_string_pretty(&json!({
         "epic_id": epic_id,
-        "name": meta.name,
+        "name": epic_view.name(),
         "content": content,
         "members": member_items,
         "rollup": format!("{done}/{total} done"),
@@ -242,34 +228,36 @@ mod tests {
 
     #[test]
     fn tool_list_epics_shows_member_rollup() {
+        crate::crdt_state::init_for_test();
         crate::db::ensure_content_store();
 
-        // Write a fake epic.
+        // Write a fake epic with the typed CRDT registers (story 933).
         crate::db::write_item_with_content(
             "9990_epic_rollup",
             "1_backlog",
-            "---\ntype: epic\nname: \"Rollup Epic\"\n---\n\n## Goal\n\nTest\n",
-            crate::db::ItemMeta::from_yaml(
-                "---\ntype: epic\nname: \"Rollup Epic\"\n---\n\n## Goal\n\nTest\n",
-            ),
+            "# Rollup Epic\n\n## Goal\n\nTest\n",
+            crate::db::ItemMeta::named("Rollup Epic"),
         );
+        crate::crdt_state::set_item_type("9990_epic_rollup", Some("epic"));
+
         // Write two member items: one done, one current.
         crate::db::write_item_with_content(
             "9991_story_member_done",
             "5_done",
-            "---\ntype: story\nname: \"Done Member\"\nepic: \"9990_epic_rollup\"\n---\n",
-            crate::db::ItemMeta::from_yaml(
-                "---\ntype: story\nname: \"Done Member\"\nepic: \"9990_epic_rollup\"\n---\n",
-            ),
+            "# Done Member\n",
+            crate::db::ItemMeta::named("Done Member"),
         );
+        crate::crdt_state::set_item_type("9991_story_member_done", Some("story"));
+        crate::crdt_state::set_epic("9991_story_member_done", Some("9990_epic_rollup"));
+
         crate::db::write_item_with_content(
             "9992_story_member_current",
             "2_current",
-            "---\ntype: story\nname: \"Current Member\"\nepic: \"9990_epic_rollup\"\n---\n",
-            crate::db::ItemMeta::from_yaml(
-                "---\ntype: story\nname: \"Current Member\"\nepic: \"9990_epic_rollup\"\n---\n",
-            ),
+            "# Current Member\n",
+            crate::db::ItemMeta::named("Current Member"),
         );
+        crate::crdt_state::set_item_type("9992_story_member_current", Some("story"));
+        crate::crdt_state::set_epic("9992_story_member_current", Some("9990_epic_rollup"));
 
         let tmp = tempfile::tempdir().unwrap();
         let ctx = crate::http::test_helpers::test_ctx(tmp.path());

server/src/http/mcp/story_tools/story/update.rs

@@ -40,6 +40,17 @@ pub(crate) fn tool_update_story(args: &Value, ctx: &AppContext) -> Result<String
         crate::crdt_state::set_qa_mode(story_id, mode);
     }
 
+    // Story 933: intercept `epic` and `type` fields — route to typed CRDT
+    // registers so the auto-assigner / epic-rollup tools see the change.
+    if let Some(epic_val) = front_matter.remove("epic") {
+        let epic_id = epic_val.as_str().filter(|s| !s.is_empty());
+        crate::crdt_state::set_epic(story_id, epic_id);
+    }
+    if let Some(type_val) = front_matter.remove("type") {
+        let item_type = type_val.as_str().filter(|s| !s.is_empty());
+        crate::crdt_state::set_item_type(story_id, item_type);
+    }
+
     // Route `depends_on` to the typed CRDT register and remove it from the
     // front-matter map so it is NOT written back to the YAML content store.
     // This matches the `qa` field pattern: CRDT is the single source of truth.