feat(934): typed Stage enum replaces directory-string state model

The state machine's `Stage` enum becomes the source of truth for pipeline
state. Six stages of work land together:

  1. Clean wire vocabulary (`coding`, `merge`, `merge_failure`, ...) replaces
     legacy directory-style strings (`2_current`, `4_merge`, ...) on the wire.
     `Stage::from_dir` accepted both during deployment; new writes always
     emit the clean form via `stage_dir_name`. Lexicographic `dir >= "5_done"`
     checks in lifecycle.rs become typed `matches!` checks since the new
     vocabulary doesn't sort in pipeline order.
  2. `crdt_state::write_item` takes typed `&Stage`, serialising via
     `stage_dir_name` at the CRDT boundary. `#[cfg(test)] write_item_str`
     parses legacy strings for test fixtures.
  3. `WorkItem::stage()` returns typed `crdt_state::Stage`; `stage_str()`
     is gone from the public API. Projection dispatches on the typed enum.
  4. `frozen` becomes an orthogonal CRDT register. `Stage::Frozen` and
     `PipelineEvent::Freeze`/`Unfreeze` are removed; `transition_to_frozen`/
     `unfrozen` set the flag directly without touching the stage register.
  5. Watcher sweep and `tool_update_story`'s `blocked` setter route through
     `apply_transition` so the typed transition table validates every
     stage change. `update_story` gains a `frozen` field for symmetry.
  6. One-shot startup migration rewrites pre-934 directory-style stage
     registers (and sets `frozen=true` on items previously at `7_frozen`).
     `Stage::from_dir` drops legacy aliases. The db boundary keeps a small
     normaliser so callers with legacy strings (MCP, tests) still work.

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

server/src/chat/commands/backlog.rs

@@ -71,6 +71,7 @@ mod tests {
             stage,
             depends_on: Vec::new(),
             retry_count: 0,
+            frozen: false,
         }
     }
 
@@ -81,6 +82,7 @@ mod tests {
             stage,
             depends_on: deps.iter().map(|n| StoryId(n.to_string())).collect(),
             retry_count: 0,
+            frozen: false,
         }
     }
 

server/src/chat/commands/freeze.rs

@@ -205,7 +205,7 @@ mod tests {
             .expect("read_typed should succeed")
             .expect("item should be present");
         assert!(
-            item.stage.is_frozen(),
+            item.is_frozen(),
             "stage should be Frozen after freeze: {:?}",
             item.stage
         );

server/src/chat/commands/status/tests.rs

@@ -13,6 +13,7 @@ fn make_item(id: &str, name: &str, stage: Stage) -> PipelineItem {
         stage,
         depends_on: Vec::new(),
         retry_count: 0,
+        frozen: false,
     }
 }
 
@@ -24,6 +25,7 @@ fn make_item_with_deps(id: &str, name: &str, stage: Stage, deps: Vec<u32>) -> Pi
         stage,
         depends_on: deps.iter().map(|n| StoryId(n.to_string())).collect(),
         retry_count: 0,
+        frozen: false,
     }
 }
 

server/src/chat/commands/unblock.rs

@@ -205,7 +205,7 @@ mod tests {
         );
         // Seed the story in the CRDT in 2_blocked stage so the typed
         // Blocked → Coding transition fires and clears `blocked` properly.
-        crate::crdt_state::write_item(
+        crate::crdt_state::write_item_str(
             "9903_story_stuck",
             "2_blocked",
             Some("Stuck Story"),
@@ -273,7 +273,7 @@ mod tests {
         );
         // Seed CRDT registers: blocked=true, retry_count=5, with a name so the
         // response can echo it back instead of falling through to the raw id.
-        crate::crdt_state::write_item(
+        crate::crdt_state::write_item_str(
             story_id,
             stage,
             Some("Stuck Story"),

server/src/chat/lookup.rs

@@ -33,18 +33,14 @@ pub(crate) fn find_story_by_number(
     if let Some(items) = crate::crdt_state::read_all_items() {
         for item in items {
             if item.story_id().split('_').next().unwrap_or("") == number {
+                let stage_dir = item.stage().as_dir().to_string();
                 let path = project_root
                     .join(".huskies")
                     .join("work")
-                    .join(item.stage_str())
+                    .join(&stage_dir)
                     .join(format!("{}.md", item.story_id()));
                 let content = crate::db::read_content(item.story_id());
-                return Some((
-                    item.story_id().to_string(),
-                    item.stage_str().to_string(),
-                    path,
-                    content,
-                ));
+                return Some((item.story_id().to_string(), stage_dir, path, content));
             }
         }
     }
@@ -58,8 +54,8 @@ pub(crate) fn find_story_by_number(
             continue;
         }
         let stage_dir = crate::crdt_state::read_item(&id)
-            .map(|v| v.stage_str().to_string())
-            .unwrap_or_else(|| "1_backlog".to_string());
+            .map(|v| v.stage().as_dir().to_string())
+            .unwrap_or_else(|| "backlog".to_string());
         let path = project_root
             .join(".huskies")
             .join("work")

server/src/chat/transport/matrix/assign.rs

@@ -313,7 +313,7 @@ mod tests {
             None,
         );
         // Seed CRDT so set_agent can write to the item.
-        crate::crdt_state::write_item(
+        crate::crdt_state::write_item_str(
             "9972_story_test",
             "1_backlog",
             Some("Test Feature"),
@@ -369,7 +369,7 @@ mod tests {
             "---\nname: Small Story\n---\n",
             None,
         );
-        crate::crdt_state::write_item(
+        crate::crdt_state::write_item_str(
             "9973_story_small",
             "1_backlog",
             Some("Small Story"),
@@ -420,7 +420,7 @@ mod tests {
             "---\nname: Existing\nagent: coder-sonnet\n---\n",
             None,
         );
-        crate::crdt_state::write_item(
+        crate::crdt_state::write_item_str(
             "9974_story_existing",
             "1_backlog",
             Some("Existing"),

server/src/chat/transport/matrix/delete.rs

@@ -112,7 +112,6 @@ fn stage_display_name(stage: &str) -> &str {
         Some(Stage::Done { .. }) => "done",
         Some(Stage::Archived { .. }) => "archived",
         Some(Stage::MergeFailure { .. }) => "merge-failure",
-        Some(Stage::Frozen { .. }) => "frozen",
         None => stage,
     }
 }
@@ -239,7 +238,7 @@ mod tests {
         let story_number = "9977";
 
         // Seed in CRDT.
-        crate::crdt_state::write_item(
+        crate::crdt_state::write_item_str(
             story_id,
             "1_backlog",
             Some("CRDT Tombstone Check"),