zeph_subagent/

transcript.rs

// SPDX-FileCopyrightText: 2026 Andrei G <bug-ops>
// SPDX-License-Identifier: MIT OR Apache-2.0

//! JSONL-based transcript persistence for sub-agent conversations.
//!
//! Each sub-agent session writes a `<task_id>.jsonl` file of [`TranscriptEntry`] lines
//! and a companion `<task_id>.meta.json` sidecar with [`TranscriptMeta`].
//!
//! Files are created with `0o600` permissions on Unix to prevent other users from
//! reading conversation history.
//!
//! The [`sweep_old_transcripts`] function prunes the oldest `.jsonl` files when a
//! configurable maximum count is exceeded.

use std::fs::{self, File};
use std::io::{self, BufRead, BufReader, Write as _};
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};

use serde::{Deserialize, Serialize};
use zeph_llm::provider::Message;

use super::error::SubAgentError;
use super::state::SubAgentState;

/// A single entry in a JSONL transcript file.
///
/// Each line in `<task_id>.jsonl` deserializes to a `TranscriptEntry`.
/// Entries are written in append order; `seq` is a monotonically increasing counter
/// within a single session.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TranscriptEntry {
    /// Zero-based sequence number within the session.
    pub seq: u32,
    /// ISO 8601 UTC timestamp at the time of writing (e.g. `"2026-04-09T12:00:00Z"`).
    pub timestamp: String,
    /// The LLM message that was appended at this sequence position.
    pub message: Message,
}

/// Sidecar metadata for a transcript, written as `<agent_id>.meta.json`.
///
/// The sidecar is written twice: once at spawn time with `status: Submitted` and
/// again at collection time with the final terminal state and `finished_at`.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TranscriptMeta {
    /// UUID of this sub-agent session.
    pub agent_id: String,
    /// Runtime agent name (same as `def_name` for non-resumed sessions).
    pub agent_name: String,
    /// Name of the [`SubAgentDef`][crate::SubAgentDef] that was used.
    pub def_name: String,
    /// Terminal lifecycle state recorded at collection time.
    pub status: SubAgentState,
    /// ISO 8601 UTC timestamp when the session was spawned.
    pub started_at: String,
    /// ISO 8601 UTC timestamp when the session finished, if known.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub finished_at: Option<String>,
    /// ID of the original agent session this was resumed from.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub resumed_from: Option<String>,
    /// Number of LLM turns consumed by the session.
    pub turns_used: u32,
    /// MCP tool names available when this session was spawned.
    ///
    /// Persisted so that a resumed session can restore the same tool name annotations
    /// in its system prompt without re-connecting MCP servers.
    #[serde(default)]
    pub mcp_tool_names: Vec<String>,
}

/// Appends [`TranscriptEntry`] lines to a JSONL transcript file.
///
/// The file handle is kept open for the writer's lifetime to avoid
/// race conditions from repeated open/close cycles. The handle is wrapped in
/// `Arc<Mutex<File>>` so the writer can be cheaply cloned and passed to
/// `tokio::task::spawn_blocking` for non-blocking appends.
///
/// # Examples
///
/// ```rust,no_run
/// use std::path::Path;
/// use zeph_subagent::transcript::TranscriptWriter;
///
/// let writer = TranscriptWriter::new(Path::new("/tmp/session.jsonl")).unwrap();
/// // writer.append(seq, &message) to persist each message.
/// ```
#[derive(Clone)]
pub struct TranscriptWriter {
    file: Arc<Mutex<File>>,
}

impl TranscriptWriter {
    /// Create (or open) a JSONL transcript file in append mode.
    ///
    /// Creates parent directories if they do not already exist.
    ///
    /// # Errors
    ///
    /// Returns `io::Error` if the directory cannot be created or the file cannot be opened.
    pub fn new(path: &Path) -> io::Result<Self> {
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent)?;
        }
        let file = zeph_common::fs_secure::append_private(path)?;
        Ok(Self {
            file: Arc::new(Mutex::new(file)),
        })
    }

    /// Append a single message as a JSON line and flush immediately.
    ///
    /// Serialization is done on the caller's thread; the blocking write and flush
    /// are offloaded to `tokio::task::spawn_blocking` so the Tokio executor is not stalled.
    ///
    /// # Errors
    ///
    /// Returns `io::Error` on serialization, write failure, lock poison, or thread-pool panic.
    pub async fn append(&self, seq: u32, message: &Message) -> io::Result<()> {
        let entry = TranscriptEntry {
            seq,
            timestamp: utc_now(),
            message: message.clone(),
        };
        let line = serde_json::to_string(&entry)
            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        let file = Arc::clone(&self.file);
        tokio::task::spawn_blocking(move || {
            let mut guard = file
                .lock()
                .map_err(|_| io::Error::other("transcript writer lock poisoned"))?;
            guard.write_all(line.as_bytes())?;
            guard.write_all(b"\n")?;
            guard.flush()
        })
        .await
        .map_err(|e| io::Error::other(format!("spawn_blocking panicked: {e}")))?
    }

    /// Write the meta sidecar file for an agent.
    ///
    /// # Errors
    ///
    /// Returns `io::Error` on serialization or write failure.
    pub fn write_meta(dir: &Path, agent_id: &str, meta: &TranscriptMeta) -> io::Result<()> {
        let path = dir.join(format!("{agent_id}.meta.json"));
        let content = serde_json::to_string_pretty(meta)
            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        zeph_common::fs_secure::write_private(&path, content.as_bytes())
    }

    /// Async variant of [`write_meta`][Self::write_meta] that offloads the blocking FS write
    /// to a `spawn_blocking` thread so the Tokio executor is not stalled.
    ///
    /// # Errors
    ///
    /// Returns `io::Error` on serialization, write failure, or thread-pool panic.
    pub async fn write_meta_async(
        dir: &Path,
        agent_id: &str,
        meta: &TranscriptMeta,
    ) -> io::Result<()> {
        let path = dir.join(format!("{agent_id}.meta.json"));
        let content = serde_json::to_string_pretty(meta)
            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        let bytes = content.into_bytes();
        tokio::task::spawn_blocking(move || zeph_common::fs_secure::write_private(&path, &bytes))
            .await
            .map_err(|e| io::Error::other(format!("spawn_blocking panicked: {e}")))?
    }
}

/// Reads and reconstructs message history from JSONL transcript files.
///
/// `TranscriptReader` is a zero-size marker type with only associated functions.
/// Use [`TranscriptReader::load`] to reconstruct a message history from a `.jsonl` file,
/// [`TranscriptReader::load_meta`] to read the companion `.meta.json` sidecar, and
/// [`TranscriptReader::find_by_prefix`] to resolve a short ID prefix to a full UUID.
pub struct TranscriptReader;

impl TranscriptReader {
    /// Load all messages from a JSONL transcript file.
    ///
    /// Malformed lines are skipped with a warning. An empty or missing file
    /// returns an empty `Vec`. If the file does not exist at all but a matching
    /// `.meta.json` sidecar exists, returns `SubAgentError::Transcript` with a
    /// clear message so the caller knows the data is gone rather than silently
    /// degrading to a fresh start.
    ///
    /// # Errors
    ///
    /// Returns [`SubAgentError::Transcript`] on unrecoverable I/O failures, or
    /// when the transcript file is missing but meta exists (data-loss guard).
    pub fn load(path: &Path) -> Result<Vec<Message>, SubAgentError> {
        Self::load_impl(path, false)
    }

    /// Load all messages from a JSONL transcript file, failing closed on the first skipped line.
    ///
    /// Unlike [`load`][Self::load], which tolerates an unreadable or malformed line by skipping
    /// it with a warning and returning the surviving entries as `Ok`, `load_strict` returns
    /// `SubAgentError::Transcript` the moment any line would be skipped. Callers that must be
    /// able to distinguish a genuinely complete trace from a partial one — e.g. tool-call
    /// grounding, where a silently dropped `ToolUse` entry would misrepresent a partial read as
    /// an authoritative "no tool ran" trace — should use this instead of [`load`][Self::load].
    ///
    /// # Errors
    ///
    /// Returns [`SubAgentError::Transcript`] if any line is unreadable or fails to parse, or if
    /// the file is missing but a meta sidecar exists (data-loss guard, same as
    /// [`load`][Self::load]).
    pub fn load_strict(path: &Path) -> Result<Vec<Message>, SubAgentError> {
        Self::load_impl(path, true)
    }

    fn load_impl(path: &Path, strict: bool) -> Result<Vec<Message>, SubAgentError> {
        let file = match File::open(path) {
            Ok(f) => f,
            Err(e) if e.kind() == io::ErrorKind::NotFound => {
                // Check if a meta sidecar exists — if so, data has been lost.
                // Build meta path from the file stem (e.g. "abc" from "abc.jsonl")
                // so it is consistent with write_meta which uses format!("{agent_id}.meta.json").
                let meta_path =
                    if let (Some(parent), Some(stem)) = (path.parent(), path.file_stem()) {
                        parent.join(format!("{}.meta.json", stem.to_string_lossy()))
                    } else {
                        path.with_extension("meta.json")
                    };
                if meta_path.exists() {
                    return Err(SubAgentError::Transcript(format!(
                        "transcript file '{}' is missing but meta sidecar exists — \
                         transcript data may have been deleted",
                        path.display()
                    )));
                }
                return Ok(vec![]);
            }
            Err(e) => {
                return Err(SubAgentError::Transcript(format!(
                    "failed to open transcript '{}': {e}",
                    path.display()
                )));
            }
        };

        let reader = BufReader::new(file);
        let mut messages = Vec::new();
        for (line_no, line_result) in reader.lines().enumerate() {
            let line = match line_result {
                Ok(l) => l,
                Err(e) => {
                    if strict {
                        return Err(SubAgentError::Transcript(format!(
                            "failed to read transcript '{}' line {}: {e}",
                            path.display(),
                            line_no + 1
                        )));
                    }
                    tracing::warn!(
                        path = %path.display(),
                        line = line_no + 1,
                        error = %e,
                        "failed to read transcript line — skipping"
                    );
                    continue;
                }
            };
            let trimmed = line.trim();
            if trimmed.is_empty() {
                continue;
            }
            match serde_json::from_str::<TranscriptEntry>(trimmed) {
                Ok(entry) => messages.push(entry.message),
                Err(e) => {
                    if strict {
                        return Err(SubAgentError::Transcript(format!(
                            "malformed transcript entry in '{}' line {}: {e}",
                            path.display(),
                            line_no + 1
                        )));
                    }
                    tracing::warn!(
                        path = %path.display(),
                        line = line_no + 1,
                        error = %e,
                        "malformed transcript entry — skipping"
                    );
                }
            }
        }
        Ok(messages)
    }

    /// Load the meta sidecar for an agent.
    ///
    /// # Errors
    ///
    /// Returns [`SubAgentError::NotFound`] if the file does not exist,
    /// [`SubAgentError::Transcript`] on parse failure.
    pub fn load_meta(dir: &Path, agent_id: &str) -> Result<TranscriptMeta, SubAgentError> {
        let path = dir.join(format!("{agent_id}.meta.json"));
        let content = fs::read_to_string(&path).map_err(|e| {
            if e.kind() == io::ErrorKind::NotFound {
                SubAgentError::NotFound(agent_id.to_owned())
            } else {
                SubAgentError::Transcript(format!("failed to read meta '{}': {e}", path.display()))
            }
        })?;
        serde_json::from_str(&content).map_err(|e| {
            SubAgentError::Transcript(format!("failed to parse meta '{}': {e}", path.display()))
        })
    }

    /// Find the full agent ID by scanning `dir` for `.meta.json` files whose names
    /// start with `prefix`.
    ///
    /// # Errors
    ///
    /// Returns [`SubAgentError::NotFound`] if no match is found,
    /// [`SubAgentError::AmbiguousId`] if multiple matches are found,
    /// [`SubAgentError::Transcript`] on I/O failure.
    pub fn find_by_prefix(dir: &Path, prefix: &str) -> Result<String, SubAgentError> {
        let entries = fs::read_dir(dir).map_err(|e| {
            SubAgentError::Transcript(format!(
                "failed to read transcript dir '{}': {e}",
                dir.display()
            ))
        })?;

        let mut matches: Vec<String> = Vec::new();
        for entry in entries {
            let entry = entry
                .map_err(|e| SubAgentError::Transcript(format!("failed to read dir entry: {e}")))?;
            let name = entry.file_name();
            let name_str = name.to_string_lossy();
            if let Some(agent_id) = name_str.strip_suffix(".meta.json")
                && agent_id.starts_with(prefix)
            {
                matches.push(agent_id.to_owned());
            }
        }

        match matches.len() {
            0 => Err(SubAgentError::NotFound(prefix.to_owned())),
            1 => Ok(matches.remove(0)),
            n => Err(SubAgentError::AmbiguousId(prefix.to_owned(), n)),
        }
    }
}

/// Delete the oldest `.jsonl` files in `dir` when the count exceeds `max_files`.
///
/// Files are sorted by modification time (oldest first). Returns the number of
/// files deleted.
///
/// # Errors
///
/// Returns `io::Error` if the directory cannot be read or a file cannot be deleted.
pub fn sweep_old_transcripts(dir: &Path, max_files: usize) -> io::Result<usize> {
    if max_files == 0 {
        return Ok(0);
    }

    // Create the directory if it does not exist yet (first run).
    if !dir.exists() {
        fs::create_dir_all(dir)?;
        return Ok(0);
    }

    let mut jsonl_files: Vec<(PathBuf, std::time::SystemTime)> = Vec::new();
    for entry in fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) == Some("jsonl") {
            let mtime = entry
                .metadata()
                .and_then(|m| m.modified())
                .unwrap_or(std::time::SystemTime::UNIX_EPOCH);
            jsonl_files.push((path, mtime));
        }
    }

    if jsonl_files.len() <= max_files {
        return Ok(0);
    }

    // Sort oldest first.
    jsonl_files.sort_by_key(|(_, mtime)| *mtime);

    let to_delete = jsonl_files.len() - max_files;
    let mut deleted = 0;
    for (path, _) in jsonl_files.into_iter().take(to_delete) {
        // Also remove the companion .meta.json sidecar if present.
        let meta = path.with_extension("meta.json");
        if meta.exists() {
            let _ = fs::remove_file(&meta);
        }
        fs::remove_file(&path)?;
        deleted += 1;
    }
    Ok(deleted)
}

/// Returns the current UTC time as an ISO 8601 string (`"YYYY-MM-DDTHH:MM:SSZ"`).
#[must_use]
pub(crate) fn utc_now() -> String {
    // Use SystemTime for a zero-dependency ISO 8601 timestamp.
    // Format: 2026-03-05T00:18:16Z
    let secs = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs();
    let (y, mo, d, h, mi, s) = epoch_to_parts(secs);
    format!("{y:04}-{mo:02}-{d:02}T{h:02}:{mi:02}:{s:02}Z")
}

/// Convert Unix epoch seconds to (year, month, day, hour, minute, second).
///
/// Uses the proleptic Gregorian calendar algorithm (Fliegel-Van Flandern variant).
/// All values are u64 throughout to avoid truncating casts; the caller knows values
/// fit in u32 for the ranges used (years 1970–2554, seconds/minutes/hours/days).
fn epoch_to_parts(epoch: u64) -> (u32, u32, u32, u32, u32, u32) {
    let sec = epoch % 60;
    let epoch = epoch / 60;
    let min = epoch % 60;
    let epoch = epoch / 60;
    let hour = epoch % 24;
    let days = epoch / 24;

    // Days since 1970-01-01 → civil calendar (Gregorian).
    let z = days + 719_468;
    let era = z / 146_097;
    let doe = z - era * 146_097;
    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
    let year = yoe + era * 400;
    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
    let mp = (5 * doy + 2) / 153;
    let day = doy - (153 * mp + 2) / 5 + 1;
    let month = if mp < 10 { mp + 3 } else { mp - 9 };
    let year = if month <= 2 { year + 1 } else { year };

    // All values are in range for u32 for any timestamp in [1970, 2554].
    #[allow(clippy::cast_possible_truncation)]
    (
        year as u32,
        month as u32,
        day as u32,
        hour as u32,
        min as u32,
        sec as u32,
    )
}

#[cfg(test)]
mod tests {
    use std::assert_matches;
    use zeph_llm::provider::{Message, MessageMetadata, Role};

    use super::*;

    fn test_message(role: Role, content: &str) -> Message {
        Message {
            role,
            content: content.to_owned(),
            parts: vec![],
            metadata: MessageMetadata::default(),
        }
    }

    fn test_meta(agent_id: &str) -> TranscriptMeta {
        TranscriptMeta {
            agent_id: agent_id.to_owned(),
            agent_name: "bot".to_owned(),
            def_name: "bot".to_owned(),
            status: SubAgentState::Completed,
            started_at: "2026-01-01T00:00:00Z".to_owned(),
            finished_at: Some("2026-01-01T00:01:00Z".to_owned()),
            resumed_from: None,
            turns_used: 2,
            mcp_tool_names: Vec::new(),
        }
    }

    #[tokio::test]
    async fn writer_reader_roundtrip() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("test.jsonl");

        let msg1 = test_message(Role::User, "hello");
        let msg2 = test_message(Role::Assistant, "world");

        let writer = TranscriptWriter::new(&path).unwrap();
        writer.append(0, &msg1).await.unwrap();
        writer.append(1, &msg2).await.unwrap();
        drop(writer);

        let messages = TranscriptReader::load(&path).unwrap();
        assert_eq!(messages.len(), 2);
        assert_eq!(messages[0].content, "hello");
        assert_eq!(messages[1].content, "world");
    }

    #[test]
    fn load_missing_file_no_meta_returns_empty() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("ghost.jsonl");
        let messages = TranscriptReader::load(&path).unwrap();
        assert!(messages.is_empty());
    }

    #[test]
    fn load_missing_file_with_meta_returns_error() {
        let dir = tempfile::tempdir().unwrap();
        let meta_path = dir.path().join("ghost.meta.json");
        std::fs::write(&meta_path, "{}").unwrap();
        let jsonl_path = dir.path().join("ghost.jsonl");
        let err = TranscriptReader::load(&jsonl_path).unwrap_err();
        assert_matches!(err, SubAgentError::Transcript(_));
    }

    #[test]
    fn load_skips_malformed_lines() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("mixed.jsonl");

        let good = test_message(Role::User, "good");
        let entry = TranscriptEntry {
            seq: 0,
            timestamp: "2026-01-01T00:00:00Z".to_owned(),
            message: good.clone(),
        };
        let good_line = serde_json::to_string(&entry).unwrap();
        let content = format!("{good_line}\nnot valid json\n{good_line}\n");
        std::fs::write(&path, &content).unwrap();

        let messages = TranscriptReader::load(&path).unwrap();
        assert_eq!(messages.len(), 2);
    }

    #[test]
    fn load_strict_fails_on_first_malformed_line() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("mixed.jsonl");

        let good = test_message(Role::User, "good");
        let entry = TranscriptEntry {
            seq: 0,
            timestamp: "2026-01-01T00:00:00Z".to_owned(),
            message: good.clone(),
        };
        let good_line = serde_json::to_string(&entry).unwrap();
        // A torn/malformed line sits between two well-formed entries — simulates a sub-agent
        // canceled/killed mid-write.
        let content = format!("{good_line}\nnot valid json\n{good_line}\n");
        std::fs::write(&path, &content).unwrap();

        let err = TranscriptReader::load_strict(&path).unwrap_err();
        assert_matches!(err, SubAgentError::Transcript(_));

        // The lenient reader still tolerates the same file, proving the two variants diverge
        // only in this failure mode.
        let messages = TranscriptReader::load(&path).unwrap();
        assert_eq!(messages.len(), 2);
    }

    #[test]
    fn load_strict_succeeds_on_intact_file() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("clean.jsonl");

        let good = test_message(Role::User, "good");
        let entry = TranscriptEntry {
            seq: 0,
            timestamp: "2026-01-01T00:00:00Z".to_owned(),
            message: good,
        };
        let good_line = serde_json::to_string(&entry).unwrap();
        std::fs::write(&path, format!("{good_line}\n")).unwrap();

        let messages = TranscriptReader::load_strict(&path).unwrap();
        assert_eq!(messages.len(), 1);
    }

    #[test]
    fn load_strict_missing_file_no_meta_returns_empty() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("ghost.jsonl");
        let messages = TranscriptReader::load_strict(&path).unwrap();
        assert!(messages.is_empty());
    }

    #[test]
    fn meta_roundtrip() {
        let dir = tempfile::tempdir().unwrap();
        let meta = test_meta("abc-123");
        TranscriptWriter::write_meta(dir.path(), "abc-123", &meta).unwrap();
        let loaded = TranscriptReader::load_meta(dir.path(), "abc-123").unwrap();
        assert_eq!(loaded.agent_id, "abc-123");
        assert_eq!(loaded.turns_used, 2);
    }

    #[test]
    fn meta_not_found_returns_not_found_error() {
        let dir = tempfile::tempdir().unwrap();
        let err = TranscriptReader::load_meta(dir.path(), "ghost").unwrap_err();
        assert_matches!(err, SubAgentError::NotFound(_));
    }

    #[test]
    fn find_by_prefix_exact() {
        let dir = tempfile::tempdir().unwrap();
        let meta = test_meta("abcdef01-0000-0000-0000-000000000000");
        TranscriptWriter::write_meta(dir.path(), "abcdef01-0000-0000-0000-000000000000", &meta)
            .unwrap();
        let id =
            TranscriptReader::find_by_prefix(dir.path(), "abcdef01-0000-0000-0000-000000000000")
                .unwrap();
        assert_eq!(id, "abcdef01-0000-0000-0000-000000000000");
    }

    #[test]
    fn find_by_prefix_short_prefix() {
        let dir = tempfile::tempdir().unwrap();
        let meta = test_meta("deadbeef-0000-0000-0000-000000000000");
        TranscriptWriter::write_meta(dir.path(), "deadbeef-0000-0000-0000-000000000000", &meta)
            .unwrap();
        let id = TranscriptReader::find_by_prefix(dir.path(), "deadbeef").unwrap();
        assert_eq!(id, "deadbeef-0000-0000-0000-000000000000");
    }

    #[test]
    fn find_by_prefix_not_found() {
        let dir = tempfile::tempdir().unwrap();
        let err = TranscriptReader::find_by_prefix(dir.path(), "xxxxxxxx").unwrap_err();
        assert_matches!(err, SubAgentError::NotFound(_));
    }

    #[test]
    fn find_by_prefix_ambiguous() {
        let dir = tempfile::tempdir().unwrap();
        TranscriptWriter::write_meta(dir.path(), "aabb0001-x", &test_meta("aabb0001-x")).unwrap();
        TranscriptWriter::write_meta(dir.path(), "aabb0002-y", &test_meta("aabb0002-y")).unwrap();
        let err = TranscriptReader::find_by_prefix(dir.path(), "aabb").unwrap_err();
        assert_matches!(err, SubAgentError::AmbiguousId(_, 2));
    }

    #[test]
    fn sweep_old_transcripts_removes_oldest() {
        let dir = tempfile::tempdir().unwrap();

        for i in 0..5u32 {
            let path = dir.path().join(format!("file{i:02}.jsonl"));
            std::fs::write(&path, b"").unwrap();
            // Vary mtime by touching the file — not reliable without explicit mtime set,
            // but tempdir files get sequential syscall timestamps in practice.
            // We set the mtime explicitly via filetime crate... but we have no filetime dep.
            // Instead we just verify count is correct.
        }

        let deleted = sweep_old_transcripts(dir.path(), 3).unwrap();
        assert_eq!(deleted, 2);

        let remaining: Vec<_> = std::fs::read_dir(dir.path())
            .unwrap()
            .filter_map(std::result::Result::ok)
            .filter(|e| e.path().extension().and_then(|x| x.to_str()) == Some("jsonl"))
            .collect();
        assert_eq!(remaining.len(), 3);
    }

    #[test]
    fn sweep_with_zero_max_does_nothing() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::write(dir.path().join("a.jsonl"), b"").unwrap();
        let deleted = sweep_old_transcripts(dir.path(), 0).unwrap();
        assert_eq!(deleted, 0);
    }

    #[test]
    fn sweep_below_max_does_nothing() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::write(dir.path().join("a.jsonl"), b"").unwrap();
        let deleted = sweep_old_transcripts(dir.path(), 50).unwrap();
        assert_eq!(deleted, 0);
    }

    #[test]
    fn utc_now_format() {
        let ts = utc_now();
        // Basic format check: 2026-03-05T00:18:16Z
        assert_eq!(ts.len(), 20);
        assert!(ts.ends_with('Z'));
        assert!(ts.contains('T'));
    }

    #[test]
    fn load_empty_file_returns_empty() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("empty.jsonl");
        std::fs::write(&path, b"").unwrap();
        let messages = TranscriptReader::load(&path).unwrap();
        assert!(messages.is_empty());
    }

    #[test]
    fn load_meta_invalid_json_returns_transcript_error() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::write(dir.path().join("bad.meta.json"), b"not json at all {{{{").unwrap();
        let err = TranscriptReader::load_meta(dir.path(), "bad").unwrap_err();
        assert_matches!(err, SubAgentError::Transcript(_));
    }

    #[test]
    fn sweep_removes_companion_meta() {
        let dir = tempfile::tempdir().unwrap();
        // Create 4 JSONL files each with a companion meta sidecar.
        for i in 0..4u32 {
            let stem = format!("file{i:02}");
            std::fs::write(dir.path().join(format!("{stem}.jsonl")), b"").unwrap();
            std::fs::write(dir.path().join(format!("{stem}.meta.json")), b"{}").unwrap();
        }
        let deleted = sweep_old_transcripts(dir.path(), 2).unwrap();
        assert_eq!(deleted, 2);
        // Companion metas for the two deleted files should also be gone.
        let meta_count = std::fs::read_dir(dir.path())
            .unwrap()
            .filter_map(std::result::Result::ok)
            .filter(|e| e.path().to_string_lossy().ends_with(".meta.json"))
            .count();
        assert_eq!(
            meta_count, 2,
            "orphaned meta sidecars should have been removed"
        );
    }

    #[test]
    fn data_loss_guard_uses_stem_based_meta_path() {
        // path.with_extension("meta.json") on "abc.jsonl" should yield "abc.meta.json"
        // which matches write_meta's format!("{agent_id}.meta.json") when agent_id == stem.
        let dir = tempfile::tempdir().unwrap();
        let agent_id = "deadbeef-0000-0000-0000-000000000000";
        // Write meta sidecar but not the JSONL file.
        std::fs::write(dir.path().join(format!("{agent_id}.meta.json")), b"{}").unwrap();
        let jsonl_path = dir.path().join(format!("{agent_id}.jsonl"));
        let err = TranscriptReader::load(&jsonl_path).unwrap_err();
        assert_matches!(err, SubAgentError::Transcript(ref m) if m.contains("missing"));
    }

    #[test]
    fn meta_roundtrip_preserves_mcp_tool_names() {
        let dir = tempfile::tempdir().unwrap();
        let agent_id = "abc-123";
        let mut meta = test_meta(agent_id);
        meta.mcp_tool_names = vec!["search".into(), "write_file".into()];
        TranscriptWriter::write_meta(dir.path(), agent_id, &meta).unwrap();
        let loaded = TranscriptReader::load_meta(dir.path(), agent_id).unwrap();
        assert_eq!(loaded.mcp_tool_names, vec!["search", "write_file"]);
    }
}