[Bug] Worker recovery can leave NUL-prefixed JSONL records that session loading silently drops

[sankks11]

Affected area

Session persistence and daemon worker recovery in packages/coding-agent.

What happened

A byte-level audit of 25 top-level session journals found eight malformed records across seven journals. Seven decoded to prime-agent.worker_recovery records and one decoded to a session_state record after removing only the leading NUL bytes.

The prefix distribution was:

• five records with 177 leading NUL bytes
• two records with 178 leading NUL bytes
• one record with 354 leading NUL bytes

After that prefix, each line was otherwise valid UTF-8 JSON. The prefix widths also matched nearby persisted-line widths, which makes a rewrite/append offset race plausible, but I do not yet have a deterministic writer reproduction and am not claiming that mechanism as proven.

Current loading in appendEntryFromBuffer() catches parse failures and skips these rows without a diagnostic. That can hide a recovery disclosure or session-state transition from replay. Strict JSONL readers fail on the same data.

Artifact-level check

This detects the observed shape without printing journal contents:

from pathlib import Path
import json

for path in Path.home().joinpath(".prime/agent/sessions").glob("*.jsonl"):
    with path.open("rb") as journal:
        for line_number, raw in enumerate(journal, 1):
            try:
                json.loads(raw.decode("utf-8"))
                continue
            except (UnicodeDecodeError, json.JSONDecodeError):
                pass

            repaired = raw.lstrip(b"\0")
            if repaired == raw:
                continue
            json.loads(repaired.decode("utf-8"))
            print(path.name, line_number, len(raw) - len(repaired))

I have not attached the affected journals because they contain private session data.

Expected behavior

• Every persisted JSONL record starts with a valid JSON byte, including during worker recovery.
• Recovery/rewrite and append operations cannot overlap at stale offsets.
• A malformed record produces a visible diagnostic rather than being silently discarded.
• If a NUL-prefixed row can be safely recognized and recovered, replay should preserve it with a warning.

Environment

The latest observed artifact was on Linux with Node.js 24. The currently installed CLI reports 0.8.1, but the journals do not persist enough application-version provenance to bind every historical write to an exact release.