history: show DELETED marker on tombstone entries

cmd_history was silently hiding the deleted flag, making it
impossible to tell from the output that a node had been deleted.
This masked the kernel-patterns deletion — looked like the node
existed in the log but wouldn't load.

Also adds merge-logs and diag-key diagnostic binaries, and makes
Node::to_capnp public for use by external tools.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

poc-memory/src/bin/diag-key.rs

@@ -0,0 +1,45 @@
+// Diagnostic: dump all entries matching a key pattern from a capnp log
+use std::io::BufReader;
+use std::fs;
+use capnp::{message, serialize};
+use poc_memory::memory_capnp;
+use poc_memory::store::Node;
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+    if args.len() != 3 {
+        eprintln!("usage: diag-key <nodes.capnp> <key-substring>");
+        std::process::exit(1);
+    }
+    let path = &args[1];
+    let pattern = &args[2];
+
+    let file = fs::File::open(path).unwrap();
+    let mut reader = BufReader::new(file);
+    let mut entry_num = 0u64;
+    let mut matches = 0u64;
+
+    while let Ok(msg) = serialize::read_message(&mut reader, message::ReaderOptions::new()) {
+        let log = msg.get_root::<memory_capnp::node_log::Reader>().unwrap();
+        for node_reader in log.get_nodes().unwrap() {
+            entry_num += 1;
+            let node = Node::from_capnp_migrate(node_reader).unwrap();
+
+            // Exact substring match, but exclude keys with trailing chars
+            // (e.g. "kernel-patterns-foo") unless pattern itself has the dash
+            if node.key == *pattern || (node.key.contains(pattern) && !node.key.contains(&format!("{}-", pattern))) {
+                matches += 1;
+                println!("Entry #{}: key={:?} (len={})", entry_num, node.key, node.key.len());
+                println!("  key bytes: {:02x?}", node.key.as_bytes());
+                println!("  uuid: {:02x?}", node.uuid);
+                println!("  version: {}", node.version);
+                println!("  deleted: {}", node.deleted);
+                println!("  timestamp: {}", node.timestamp);
+                println!("  content len: {}", node.content.len());
+                println!("  provenance: {}", node.provenance);
+                println!();
+            }
+        }
+    }
+    eprintln!("Scanned {} entries, {} matches for {:?}", entry_num, matches, pattern);
+}