Add read_file skill, session persistence, and update script

- New read_file skill: paginated file reading with line ranges,
  path restricted to /workspace, binary detection, directory listing
- Session persistence via SQLite + FTS5: conversation history survives
  agent restarts, last N messages restored into deque on boot,
  auto-prune to 1000 messages
- Update truncation hint to reference read_file instead of run_command
- New scripts/update.sh for patching rootfs + rebuilding snapshot

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agent/sessions.py

@@ -0,0 +1,87 @@
+"""Session persistence — SQLite + FTS5 for conversation history."""
+
+import sqlite3
+import threading
+import time
+
+
+def log(msg):
+    print(f"[sessions] {msg}", flush=True)
+
+
+def set_logger(fn):
+    global log
+    log = fn
+
+
+_write_lock = threading.Lock()
+
+
+def init_db(db_path):
+    """Create/open the session database. Returns a connection."""
+    conn = sqlite3.connect(db_path, check_same_thread=False)
+    conn.execute("PRAGMA journal_mode=WAL")
+    conn.execute("""
+        CREATE TABLE IF NOT EXISTS messages (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            ts REAL NOT NULL,
+            nick TEXT NOT NULL,
+            channel TEXT NOT NULL,
+            text TEXT NOT NULL,
+            full_text TEXT
+        )
+    """)
+    conn.execute("""
+        CREATE INDEX IF NOT EXISTS idx_messages_channel_ts
+        ON messages(channel, ts)
+    """)
+    # FTS5 virtual table for full-text search
+    conn.execute("""
+        CREATE VIRTUAL TABLE IF NOT EXISTS messages_fts
+        USING fts5(text, content=messages, content_rowid=id)
+    """)
+    conn.commit()
+    _prune(conn)
+    log(f"Session DB ready: {db_path}")
+    return conn
+
+
+def save_message(conn, nick, channel, text, full_text=None):
+    """Persist a message to the session database."""
+    with _write_lock:
+        cur = conn.execute(
+            "INSERT INTO messages (ts, nick, channel, text, full_text) VALUES (?, ?, ?, ?, ?)",
+            (time.time(), nick, channel, text, full_text),
+        )
+        conn.execute(
+            "INSERT INTO messages_fts(rowid, text) VALUES (?, ?)",
+            (cur.lastrowid, text),
+        )
+        conn.commit()
+
+
+def load_recent(conn, limit=20):
+    """Load the last N messages for boot recovery.
+    Returns list of {"nick", "text", "channel"} dicts in chronological order."""
+    rows = conn.execute(
+        "SELECT nick, text, channel FROM messages ORDER BY id DESC LIMIT ?",
+        (limit,),
+    ).fetchall()
+    return [{"nick": r[0], "text": r[1], "channel": r[2]} for r in reversed(rows)]
+
+
+def _prune(conn, keep=1000):
+    """Delete old messages beyond the last `keep`. Runs once at init."""
+    count = conn.execute("SELECT COUNT(*) FROM messages").fetchone()[0]
+    if count <= keep:
+        return
+    deleted = count - keep
+    conn.execute("""
+        DELETE FROM messages WHERE id NOT IN (
+            SELECT id FROM messages ORDER BY id DESC LIMIT ?
+        )
+    """, (keep,))
+    # Rebuild FTS index after bulk delete
+    conn.execute("INSERT INTO messages_fts(messages_fts) VALUES('rebuild')")
+    conn.commit()
+    log(f"Pruned {deleted} old messages (kept {keep})")