Implement Phase B: Crash Recovery

Add startup integrity checks, corruption recovery, CAS size limits,
graceful shutdown orchestration, and a task supervisor — turning 5
previously-RED resilience tests GREEN and adding 5 new tests.

- CAS: pre-check size limit in put(), add StoreFull error variant
- CAS: sled corruption recovery in open() (retry then recreate)
- SQLite: open_with_integrity_check() via PRAGMA integrity_check(1)
- tantivy: open_with_recovery() deletes and rebuilds corrupt index
- CLI: CancellationToken-based ordered shutdown sequence
- Core: TaskSupervisor with spawn_supervised/spawn_critical + backoff
- Tests: replace 4 todo!() stubs, add 5 new shutdown/supervisor tests

musicfs/crates/musicfs-search/src/index.rs

@@ -6,7 +6,7 @@ use tantivy::collector::TopDocs;
 use tantivy::query::{BooleanQuery, FuzzyTermQuery, Occur, Query, QueryParser};
 use tantivy::schema::{Field, Schema, Value, STORED, TEXT, INDEXED};
 use tantivy::{Index, IndexReader, IndexWriter, ReloadPolicy, TantivyDocument, Term};
-use tracing::{debug, info};
+use tracing::{debug, info, warn};
 
 const SCHEMA_VERSION: u32 = 1;
 
@@ -95,6 +95,28 @@ impl SearchIndex {
         })
     }
 
+    pub fn open_with_recovery(index_path: &Path) -> Result<Self, SearchError> {
+        match Self::open(index_path) {
+            Ok(index) => {
+                let docs = index.reader.searcher().num_docs();
+                info!(docs, "Search index opened successfully");
+                Ok(index)
+            }
+            Err(e) => {
+                warn!(
+                    error = %e,
+                    path = ?index_path,
+                    "Search index corrupted, rebuilding from scratch"
+                );
+                if index_path.exists() {
+                    std::fs::remove_dir_all(index_path)
+                        .map_err(SearchError::Io)?;
+                }
+                Self::open(index_path)
+            }
+        }
+    }
+
     pub fn index_file(&self, file: &FileMeta) -> Result<(), SearchError> {
         let mut doc = TantivyDocument::new();