fix: replace bash_tasks.rs with generic mcp_loose_ends scanner

- hive-ag3nt: remove bash_tasks.rs entirely; add mcp_loose_ends.rs that
  scans harness/mcp-loose-ends/*.json generically (no bash knowledge)
- hive-bash-mcp: daemon writes mcp-loose-ends/bash.json on every task
  state transition (pending/running/done/interrupted/timed_out)
- get_loose_ends: reads mcp_loose_ends::collect() instead of bash-specific code
- implements the generic mechanism from #1162

hive-ag3nt/src/mcp_loose_ends.rs

@@ -0,0 +1,50 @@
+//! Generic scanner for MCP loose-end summary files.
+//!
+//! External MCP daemons (hive-bash-mcp, hive-matrix-mcp, etc.) write
+//! JSON files to `$HYPERHIVE_HARNESS_DIR/mcp-loose-ends/<name>.json`.
+//! Each file contains a JSON array of plain-text summary strings.
+//!
+//! The harness reads all files in this directory in `get_loose_ends` to
+//! surface active background work from any MCP without hardcoding
+//! per-MCP knowledge here.
+
+use std::path::PathBuf;
+
+fn loose_ends_dir() -> PathBuf {
+    let base = if let Some(p) = std::env::var_os("HYPERHIVE_HARNESS_DIR") {
+        PathBuf::from(p)
+    } else {
+        let state = std::env::var("HYPERHIVE_STATE_DIR").unwrap_or_default();
+        let state_path = PathBuf::from(&state);
+        state_path
+            .parent()
+            .map(|p| p.join("harness"))
+            .unwrap_or_else(|| PathBuf::from(state))
+    };
+    base.join("mcp-loose-ends")
+}
+
+/// Collect all loose-end summary strings published by external MCP daemons.
+/// Each string is a single line suitable for inclusion in `get_loose_ends`
+/// output. Returns an empty vec if the directory doesn't exist or is empty.
+#[must_use]
+pub fn collect() -> Vec<String> {
+    let Ok(rd) = std::fs::read_dir(loose_ends_dir()) else {
+        return Vec::new();
+    };
+    let mut out = Vec::new();
+    for entry in rd.flatten() {
+        let path = entry.path();
+        if path.extension().and_then(|e| e.to_str()) != Some("json") {
+            continue;
+        }
+        let Ok(content) = std::fs::read_to_string(&path) else {
+            continue;
+        };
+        let Ok(items) = serde_json::from_str::<Vec<String>>(&content) else {
+            continue;
+        };
+        out.extend(items);
+    }
+    out
+}