recall_echo/graph/

gc.rs

//! Garbage collection for the knowledge graph.
//!
//! Sweep order: stale relationships → dead relationships → orphaned entities →
//! spent episodes → delete. Dry-run by default. Pipeline-linked entities are
//! protected, and so is anything a surviving record cites as its source.

use std::collections::HashSet;

use chrono::{DateTime, Utc};
use surrealdb::Surreal;

use super::confidence::{self, Provenance};
use super::crud;
use super::error::GraphError;
use super::store::Db;
use super::types::{Entity, Relationship};

/// Default age, in days, before a never-retrieved episode may be collected.
///
/// Two confidence half-lives: an episode nothing has read in half a year, and
/// which no surviving entity or edge cites, is storage rather than memory.
pub const DEFAULT_EPISODE_MAX_AGE_DAYS: u64 = 180;

/// Configuration for garbage collection thresholds.
#[derive(Debug, Clone)]
pub struct GcConfig {
    /// Days since valid_from before a low-confidence relationship is considered stale.
    pub stale_days: u64,
    /// Confidence threshold for stale relationships (below this = candidate).
    pub stale_confidence: f64,
    /// Confidence threshold for dead relationships (below this + age check = dead).
    pub dead_confidence: f64,
    /// Minimum age in days for dead relationship pruning.
    pub dead_min_age_days: u64,
    /// If true, also sweep episodes. Off by default: the relationship sweep
    /// predates episode collection and must keep behaving as it did.
    pub collect_episodes: bool,
    /// Days since an episode's timestamp before it may be collected.
    pub episode_max_age_days: u64,
    /// If true, only report — don't delete anything.
    pub dry_run: bool,
    /// If true, never GC entities linked to pipeline documents.
    pub protect_pipeline: bool,
}

impl Default for GcConfig {
    fn default() -> Self {
        Self {
            stale_days: 30,
            stale_confidence: 0.5,
            dead_confidence: 0.2,
            dead_min_age_days: 14,
            collect_episodes: false,
            episode_max_age_days: DEFAULT_EPISODE_MAX_AGE_DAYS,
            dry_run: true,
            protect_pipeline: true,
        }
    }
}

/// A single GC action with reason.
#[derive(Debug, Clone)]
pub struct GcAction {
    pub target_id: String,
    pub target_name: String,
    pub kind: GcActionKind,
    pub reason: String,
}

/// What kind of thing is being collected.
#[derive(Debug, Clone, PartialEq)]
pub enum GcActionKind {
    StaleRelationship,
    DeadRelationship,
    OrphanedEntity,
    SpentEpisode,
}

impl std::fmt::Display for GcActionKind {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::StaleRelationship => write!(f, "stale_relationship"),
            Self::DeadRelationship => write!(f, "dead_relationship"),
            Self::OrphanedEntity => write!(f, "orphaned_entity"),
            Self::SpentEpisode => write!(f, "spent_episode"),
        }
    }
}

/// Report from a GC run.
#[derive(Debug, Clone, Default)]
pub struct GcReport {
    pub entities_scanned: u64,
    pub relationships_scanned: u64,
    pub episodes_scanned: u64,
    pub stale_relationships: u64,
    pub dead_relationships: u64,
    pub orphaned_entities: u64,
    pub spent_episodes: u64,
    pub total_removed: u64,
    pub dry_run: bool,
    pub actions: Vec<GcAction>,
    pub errors: Vec<String>,
}

/// Run garbage collection on the graph.
pub async fn run_gc(db: &Surreal<Db>, config: &GcConfig) -> Result<GcReport, GraphError> {
    let now = Utc::now();
    let mut report = GcReport {
        dry_run: config.dry_run,
        ..Default::default()
    };

    // Load all relationships and entities
    let all_rels = crud::list_all_relationships(db).await?;
    let all_entities = crud::list_entities(db, None).await?;
    report.relationships_scanned = all_rels.len() as u64;
    report.entities_scanned = all_entities.len() as u64;

    // Phase 1: Stale relationship decay
    let stale_ids = phase_stale_relationships(&all_rels, config, &now, &mut report);

    // Phase 2: Dead relationship pruning
    let dead_ids = phase_dead_relationships(&all_rels, config, &now, &stale_ids, &mut report);

    // Collect all relationship IDs to delete
    let mut rel_ids_to_delete: Vec<String> = Vec::new();
    rel_ids_to_delete.extend(stale_ids);
    rel_ids_to_delete.extend(dead_ids);

    // Phase 3: Orphaned entity removal (must account for relationships being removed)
    let orphan_ids =
        phase_orphaned_entities(db, &all_entities, config, &rel_ids_to_delete, &mut report).await?;

    // Phase 4: Spent episodes (must account for everything above being removed:
    // an episode is evidence only for records that survive the sweep)
    let pending = Pending {
        relationships: &rel_ids_to_delete,
        entities: &orphan_ids,
    };
    let episode_ids = phase_spent_episodes(db, config, &now, &pending, &mut report).await?;

    // Phase 5: Execute deletions
    if !config.dry_run {
        for rel_id in &rel_ids_to_delete {
            if let Err(e) = crud::delete_relationship(db, rel_id).await {
                report
                    .errors
                    .push(format!("Failed to delete relationship {rel_id}: {e}"));
            } else {
                report.total_removed += 1;
            }
        }

        for entity_id in &orphan_ids {
            if let Err(e) = crud::delete_entity(db, entity_id).await {
                report
                    .errors
                    .push(format!("Failed to delete entity {entity_id}: {e}"));
            } else {
                report.total_removed += 1;
            }
        }

        for episode_id in &episode_ids {
            if let Err(e) = crud::delete_episode(db, episode_id).await {
                report
                    .errors
                    .push(format!("Failed to delete episode {episode_id}: {e}"));
            } else {
                report.total_removed += 1;
            }
        }
    } else {
        report.total_removed =
            (rel_ids_to_delete.len() + orphan_ids.len() + episode_ids.len()) as u64;
    }

    Ok(report)
}

/// Records this sweep has already decided to remove. Episode collection reads
/// it so that "cited by a surviving record" means what it says.
struct Pending<'a> {
    relationships: &'a [String],
    entities: &'a [String],
}

/// Phase 1: Find relationships older than stale_days with effective confidence below stale_confidence.
/// Uses temporal decay — effective confidence accounts for time since last reinforcement.
/// Only considers active relationships (valid_until is None).
fn phase_stale_relationships(
    rels: &[Relationship],
    config: &GcConfig,
    now: &DateTime<Utc>,
    report: &mut GcReport,
) -> Vec<String> {
    let mut stale_ids = Vec::new();

    for rel in rels {
        // Skip already-superseded relationships
        if rel.valid_until.is_some() {
            continue;
        }

        // Compute effective confidence with temporal decay
        let effective = confidence::effective_confidence(
            rel.confidence,
            rel.last_reinforced.as_ref(),
            &rel.valid_from,
            now,
        );

        // Check effective confidence threshold
        if effective >= config.stale_confidence {
            continue;
        }

        // Check age
        let age_days = match parse_datetime(&rel.valid_from) {
            Some(dt) => (*now - dt).num_days(),
            None => continue,
        };

        if age_days < config.stale_days as i64 {
            continue;
        }

        let id = rel.id_string();
        let description = rel.description.as_deref().unwrap_or("(no description)");
        report.actions.push(GcAction {
            target_id: id.clone(),
            target_name: format!(
                "{} --[{}]--> {}",
                value_to_short_id(&rel.from_id),
                rel.rel_type,
                value_to_short_id(&rel.to_id)
            ),
            kind: GcActionKind::StaleRelationship,
            reason: format!(
                "effective_confidence {:.2} (stored {:.2}) < {:.2}, age {} days > {}, desc: {}",
                effective,
                rel.confidence,
                config.stale_confidence,
                age_days,
                config.stale_days,
                description
            ),
        });
        stale_ids.push(id);
        report.stale_relationships += 1;
    }

    stale_ids
}

/// Phase 2: Find very low effective confidence relationships older than dead_min_age_days.
/// Uses temporal decay. Excludes relationships already caught in phase 1.
fn phase_dead_relationships(
    rels: &[Relationship],
    config: &GcConfig,
    now: &DateTime<Utc>,
    already_caught: &[String],
    report: &mut GcReport,
) -> Vec<String> {
    let mut dead_ids = Vec::new();

    for rel in rels {
        let id = rel.id_string();

        // Skip if already caught in phase 1
        if already_caught.contains(&id) {
            continue;
        }

        // Compute effective confidence with temporal decay
        let effective = confidence::effective_confidence(
            rel.confidence,
            rel.last_reinforced.as_ref(),
            &rel.valid_from,
            now,
        );

        // Check effective confidence threshold (lower bar than stale)
        if effective >= config.dead_confidence {
            continue;
        }

        // Check minimum age
        let age_days = match parse_datetime(&rel.valid_from) {
            Some(dt) => (*now - dt).num_days(),
            None => continue,
        };

        if age_days < config.dead_min_age_days as i64 {
            continue;
        }

        let description = rel.description.as_deref().unwrap_or("(no description)");
        report.actions.push(GcAction {
            target_id: id.clone(),
            target_name: format!(
                "{} --[{}]--> {}",
                value_to_short_id(&rel.from_id),
                rel.rel_type,
                value_to_short_id(&rel.to_id)
            ),
            kind: GcActionKind::DeadRelationship,
            reason: format!(
                "effective_confidence {:.2} (stored {:.2}) < {:.2}, age {} days > {}, desc: {}",
                effective,
                rel.confidence,
                config.dead_confidence,
                age_days,
                config.dead_min_age_days,
                description
            ),
        });
        dead_ids.push(id);
        report.dead_relationships += 1;
    }

    dead_ids
}

/// Phase 3: Find entities with zero relationships (accounting for pending deletions),
/// zero access_count, and no pipeline linkage.
async fn phase_orphaned_entities(
    db: &Surreal<Db>,
    entities: &[Entity],
    config: &GcConfig,
    pending_rel_deletions: &[String],
    report: &mut GcReport,
) -> Result<Vec<String>, GraphError> {
    let mut orphan_ids = Vec::new();

    for entity in entities {
        // Skip entities that have been accessed
        if entity.access_count > 0 {
            continue;
        }

        // Skip pipeline-linked entities if protection is on
        if config.protect_pipeline && is_pipeline_entity(entity) {
            continue;
        }

        // Count current relationships
        let entity_id = entity.id_string();
        let current_rels = crud::count_relationships(db, &entity_id).await?;

        // Count how many of those relationships are being deleted
        // (we need to check the actual relationship IDs touching this entity)
        let rels_being_deleted =
            count_pending_deletions_for_entity(db, &entity_id, pending_rel_deletions).await?;

        let remaining = current_rels.saturating_sub(rels_being_deleted);

        if remaining > 0 {
            continue;
        }

        report.actions.push(GcAction {
            target_id: entity_id.clone(),
            target_name: format!("{} ({})", entity.name, entity.entity_type),
            kind: GcActionKind::OrphanedEntity,
            reason: format!(
                "zero relationships after pruning, access_count={}",
                entity.access_count
            ),
        });
        orphan_ids.push(entity_id);
        report.orphaned_entities += 1;
    }

    Ok(orphan_ids)
}

/// Count how many of the pending relationship deletions affect a given entity.
async fn count_pending_deletions_for_entity(
    db: &Surreal<Db>,
    entity_id: &str,
    pending_deletions: &[String],
) -> Result<u64, GraphError> {
    if pending_deletions.is_empty() {
        return Ok(0);
    }

    // Get all relationships for this entity and check overlap with pending deletions
    let mut response = db
        .query(
            r#"SELECT id FROM relates_to
               WHERE in = type::record($id) OR out = type::record($id)"#,
        )
        .bind(("id", entity_id.to_string()))
        .await?;

    #[derive(serde::Deserialize)]
    struct IdRow {
        id: serde_json::Value,
    }

    let rows: Vec<IdRow> = super::deserialize_take(&mut response, 0)?;
    let count = rows
        .iter()
        .filter(|r| {
            let id_str = match &r.id {
                serde_json::Value::String(s) => s.clone(),
                other => other.to_string(),
            };
            pending_deletions.contains(&id_str)
        })
        .count();

    Ok(count as u64)
}

// ── Episodes ─────────────────────────────────────────────────────────
//
// Episodes are the raw text a session left behind. The graph does not link
// them to entities or edges directly; the one linkage the schema has is by
// session: entities and relationships extracted from a session carry its id
// in `source`. So "evidence for a surviving record" is exactly "some record
// that survives this sweep cites my session as its source", and an episode is
// collectable only when it is old, never retrieved, self-authored, and cited
// by nothing.

/// The scan projection for an episode: everything the sweep judges on, and
/// nothing it does not — no content, no embedding.
#[derive(Debug, Clone, serde::Deserialize)]
struct EpisodeRow {
    id: serde_json::Value,
    session_id: String,
    timestamp: serde_json::Value,
    #[serde(default)]
    log_number: Option<i64>,
    #[serde(default)]
    provenance: Option<String>,
    #[serde(default, deserialize_with = "super::util::count_or_zero")]
    access_count: i64,
}

impl EpisodeRow {
    fn id_string(&self) -> String {
        value_to_record_id(&self.id)
    }

    /// Who authored this episode; absent and unrecognised resolve to `self`.
    fn provenance(&self) -> Provenance {
        Provenance::from_stored(self.provenance.as_deref())
    }

    /// How this episode reads in a GC report.
    fn label(&self) -> String {
        match self.log_number {
            Some(n) => format!("{} (log {n:03})", self.session_id),
            None => self.session_id.clone(),
        }
    }
}

/// Phase 4: find episodes nothing needs any more.
async fn phase_spent_episodes(
    db: &Surreal<Db>,
    config: &GcConfig,
    now: &DateTime<Utc>,
    pending: &Pending<'_>,
    report: &mut GcReport,
) -> Result<Vec<String>, GraphError> {
    if !config.collect_episodes {
        return Ok(Vec::new());
    }

    let episodes = load_episode_rows(db).await?;
    report.episodes_scanned = episodes.len() as u64;

    let cited = cited_session_ids(db, pending).await?;
    let mut spent_ids = Vec::new();

    for episode in &episodes {
        let Some(reason) = episode_prune_reason(episode, &cited, config, now) else {
            continue;
        };

        report.actions.push(GcAction {
            target_id: episode.id_string(),
            target_name: episode.label(),
            kind: GcActionKind::SpentEpisode,
            reason,
        });
        spent_ids.push(episode.id_string());
        report.spent_episodes += 1;
    }

    Ok(spent_ids)
}

/// Why this episode is collectable, or `None` if it is not.
///
/// All four conditions must hold, and the order is cheapest-first:
/// never retrieved, self-authored, cited by no surviving record, older than
/// the configured age. An unparseable timestamp keeps the episode.
fn episode_prune_reason(
    episode: &EpisodeRow,
    cited_sessions: &HashSet<String>,
    config: &GcConfig,
    now: &DateTime<Utc>,
) -> Option<String> {
    if episode.access_count > 0 {
        return None;
    }
    if episode.provenance() != Provenance::SelfGenerated {
        return None;
    }
    if cited_sessions.contains(&episode.session_id) {
        return None;
    }

    let age_days = (*now - parse_datetime(&episode.timestamp)?).num_days();
    if age_days < config.episode_max_age_days as i64 {
        return None;
    }

    Some(format!(
        "age {age_days} days > {}, never retrieved, provenance self, session {} cited by nothing",
        config.episode_max_age_days, episode.session_id
    ))
}

/// Load every episode's judgeable fields.
async fn load_episode_rows(db: &Surreal<Db>) -> Result<Vec<EpisodeRow>, GraphError> {
    let mut response = db
        .query(
            "SELECT id, session_id, timestamp, log_number, provenance, access_count FROM episode",
        )
        .await?;

    super::deserialize_take(&mut response, 0)
}

/// Session ids cited as `source` by records that survive this sweep.
async fn cited_session_ids(
    db: &Surreal<Db>,
    pending: &Pending<'_>,
) -> Result<HashSet<String>, GraphError> {
    #[derive(serde::Deserialize)]
    struct SourceRow {
        id: serde_json::Value,
        source: Option<String>,
    }

    let mut cited = HashSet::new();

    for (table, doomed) in [
        ("relates_to", pending.relationships),
        ("entity", pending.entities),
    ] {
        let query = format!("SELECT id, source FROM {table} WHERE source IS NOT NONE");
        let mut response = db.query(&query).await?;
        let rows: Vec<SourceRow> = super::deserialize_take(&mut response, 0)?;

        for row in rows {
            if doomed.contains(&value_to_record_id(&row.id)) {
                continue;
            }
            if let Some(source) = row.source {
                cited.insert(source);
            }
        }
    }

    Ok(cited)
}

/// Check if an entity is linked to a pipeline document.
fn is_pipeline_entity(entity: &Entity) -> bool {
    // Check source field
    if let Some(ref source) = entity.source {
        if source.starts_with("pipeline:") {
            return true;
        }
    }

    // Check attributes for pipeline_stage
    if let Some(ref attrs) = entity.attributes {
        if attrs.get("pipeline_stage").is_some() {
            return true;
        }
    }

    false
}

use super::util::parse_datetime;

/// Extract a short ID from a record ID value (e.g. "entity:abc" → "abc").
fn value_to_short_id(val: &serde_json::Value) -> String {
    match val {
        serde_json::Value::String(s) => s.split(':').next_back().unwrap_or(s).to_string(),
        other => other.to_string(),
    }
}

/// Render a record ID value whole (e.g. "entity:abc"), as deletion needs it.
fn value_to_record_id(val: &serde_json::Value) -> String {
    match val {
        serde_json::Value::String(s) => s.clone(),
        other => other.to_string(),
    }
}

/// Get stats-only report without computing deletion candidates.
/// Uses effective confidence (with temporal decay) for threshold counts.
pub async fn stats_only(db: &Surreal<Db>) -> Result<GcStatsReport, GraphError> {
    let now = Utc::now();
    let all_rels = crud::list_all_relationships(db).await?;
    let all_entities = crud::list_entities(db, None).await?;

    let pipeline_entities = all_entities
        .iter()
        .filter(|e| is_pipeline_entity(e))
        .count();

    let zero_access_entities = all_entities.iter().filter(|e| e.access_count == 0).count();

    let low_confidence_rels = all_rels
        .iter()
        .filter(|r| {
            confidence::effective_confidence(
                r.confidence,
                r.last_reinforced.as_ref(),
                &r.valid_from,
                &now,
            ) < 0.5
        })
        .count();

    let very_low_confidence_rels = all_rels
        .iter()
        .filter(|r| {
            confidence::effective_confidence(
                r.confidence,
                r.last_reinforced.as_ref(),
                &r.valid_from,
                &now,
            ) < 0.2
        })
        .count();

    let superseded_rels = all_rels.iter().filter(|r| r.valid_until.is_some()).count();

    Ok(GcStatsReport {
        total_entities: all_entities.len() as u64,
        total_relationships: all_rels.len() as u64,
        pipeline_entities: pipeline_entities as u64,
        zero_access_entities: zero_access_entities as u64,
        low_confidence_rels: low_confidence_rels as u64,
        very_low_confidence_rels: very_low_confidence_rels as u64,
        superseded_rels: superseded_rels as u64,
    })
}

/// Health stats without running GC.
#[derive(Debug, Clone)]
pub struct GcStatsReport {
    pub total_entities: u64,
    pub total_relationships: u64,
    pub pipeline_entities: u64,
    pub zero_access_entities: u64,
    /// Count of relationships with effective (decayed) confidence < 0.5
    pub low_confidence_rels: u64,
    /// Count of relationships with effective (decayed) confidence < 0.2
    pub very_low_confidence_rels: u64,
    pub superseded_rels: u64,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_gc_config_defaults() {
        let config = GcConfig::default();
        assert_eq!(config.stale_days, 30);
        assert_eq!(config.stale_confidence, 0.5);
        assert_eq!(config.dead_confidence, 0.2);
        assert_eq!(config.dead_min_age_days, 14);
        assert!(config.dry_run);
        assert!(config.protect_pipeline);
    }

    #[test]
    fn test_parse_datetime_iso() {
        let val = serde_json::Value::String("2024-01-15T10:30:00Z".to_string());
        let dt = parse_datetime(&val);
        assert!(dt.is_some());
    }

    #[test]
    fn test_parse_datetime_invalid() {
        let val = serde_json::Value::String("not-a-date".to_string());
        let dt = parse_datetime(&val);
        assert!(dt.is_none());
    }

    #[test]
    fn test_parse_datetime_non_string() {
        let val = serde_json::Value::Number(serde_json::Number::from(12345));
        let dt = parse_datetime(&val);
        assert!(dt.is_none());
    }

    #[test]
    fn test_value_to_short_id() {
        let val = serde_json::Value::String("entity:abc123".to_string());
        assert_eq!(value_to_short_id(&val), "abc123");
    }

    #[test]
    fn test_value_to_short_id_no_colon() {
        let val = serde_json::Value::String("abc123".to_string());
        assert_eq!(value_to_short_id(&val), "abc123");
    }

    #[test]
    fn test_is_pipeline_entity_by_source() {
        let entity = Entity {
            id: serde_json::Value::String("entity:test".to_string()),
            name: "Test".to_string(),
            entity_type: super::super::types::EntityType::Thread,
            abstract_text: "test".to_string(),
            overview: "test".to_string(),
            content: None,
            attributes: None,
            embedding: None,
            mutable: true,
            access_count: 0,
            utility_score: 0.5,
            utility_updates: 0,
            created_at: serde_json::Value::String("2024-01-01T00:00:00Z".to_string()),
            updated_at: serde_json::Value::String("2024-01-01T00:00:00Z".to_string()),
            source: Some("pipeline:learning".to_string()),
        };
        assert!(is_pipeline_entity(&entity));
    }

    #[test]
    fn test_is_pipeline_entity_by_attributes() {
        let entity = Entity {
            id: serde_json::Value::String("entity:test".to_string()),
            name: "Test".to_string(),
            entity_type: super::super::types::EntityType::Concept,
            abstract_text: "test".to_string(),
            overview: "test".to_string(),
            content: None,
            attributes: Some(serde_json::json!({"pipeline_stage": "thoughts"})),
            embedding: None,
            mutable: true,
            access_count: 0,
            utility_score: 0.5,
            utility_updates: 0,
            created_at: serde_json::Value::String("2024-01-01T00:00:00Z".to_string()),
            updated_at: serde_json::Value::String("2024-01-01T00:00:00Z".to_string()),
            source: None,
        };
        assert!(is_pipeline_entity(&entity));
    }

    #[test]
    fn test_is_not_pipeline_entity() {
        let entity = Entity {
            id: serde_json::Value::String("entity:test".to_string()),
            name: "Test".to_string(),
            entity_type: super::super::types::EntityType::Tool,
            abstract_text: "test".to_string(),
            overview: "test".to_string(),
            content: None,
            attributes: None,
            embedding: None,
            mutable: true,
            access_count: 0,
            utility_score: 0.5,
            utility_updates: 0,
            created_at: serde_json::Value::String("2024-01-01T00:00:00Z".to_string()),
            updated_at: serde_json::Value::String("2024-01-01T00:00:00Z".to_string()),
            source: Some("llm:ingest".to_string()),
        };
        assert!(!is_pipeline_entity(&entity));
    }

    #[test]
    fn test_phase_stale_relationships() {
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(45)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:abc".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: Some("test rel".to_string()),
            valid_from: serde_json::Value::String(old_date),
            valid_until: None,
            confidence: 0.3,
            alpha: Some(3.0),
            beta: Some(7.0),
            self_reinforcements: Some(0),
            last_reinforced: None,
            source: Some("ingest".to_string()),
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let stale = phase_stale_relationships(&rels, &config, &now, &mut report);

        assert_eq!(stale.len(), 1);
        assert_eq!(report.stale_relationships, 1);
    }

    #[test]
    fn test_phase_stale_skips_high_confidence() {
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(45)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:abc".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: None,
            valid_from: serde_json::Value::String(old_date),
            valid_until: None,
            confidence: 0.8,
            alpha: Some(8.0),
            beta: Some(2.0),
            self_reinforcements: Some(0),
            last_reinforced: None,
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let stale = phase_stale_relationships(&rels, &config, &now, &mut report);

        assert!(stale.is_empty());
    }

    #[test]
    fn test_phase_stale_skips_young() {
        let now = Utc::now();
        let recent_date = (now - chrono::Duration::days(5)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:abc".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: None,
            valid_from: serde_json::Value::String(recent_date),
            valid_until: None,
            confidence: 0.3,
            alpha: Some(3.0),
            beta: Some(7.0),
            self_reinforcements: Some(0),
            last_reinforced: None,
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let stale = phase_stale_relationships(&rels, &config, &now, &mut report);

        assert!(stale.is_empty());
    }

    #[test]
    fn test_phase_stale_skips_superseded() {
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(45)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:abc".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: None,
            valid_from: serde_json::Value::String(old_date.clone()),
            valid_until: Some(serde_json::Value::String(old_date)),
            confidence: 0.3,
            alpha: Some(3.0),
            beta: Some(7.0),
            self_reinforcements: Some(0),
            last_reinforced: None,
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let stale = phase_stale_relationships(&rels, &config, &now, &mut report);

        assert!(stale.is_empty());
    }

    #[test]
    fn test_phase_dead_relationships() {
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(20)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:dead1".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: None,
            valid_from: serde_json::Value::String(old_date),
            valid_until: None,
            confidence: 0.1,
            alpha: Some(1.0),
            beta: Some(9.0),
            self_reinforcements: Some(0),
            last_reinforced: None,
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let already_caught = vec![];
        let dead = phase_dead_relationships(&rels, &config, &now, &already_caught, &mut report);

        assert_eq!(dead.len(), 1);
        assert_eq!(report.dead_relationships, 1);
    }

    #[test]
    fn test_phase_dead_skips_already_caught() {
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(20)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:dead1".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: None,
            valid_from: serde_json::Value::String(old_date),
            valid_until: None,
            confidence: 0.1,
            alpha: Some(1.0),
            beta: Some(9.0),
            self_reinforcements: Some(0),
            last_reinforced: None,
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let already_caught = vec!["relates_to:dead1".to_string()];
        let dead = phase_dead_relationships(&rels, &config, &now, &already_caught, &mut report);

        assert!(dead.is_empty());
    }

    #[test]
    fn test_gc_action_kind_display() {
        assert_eq!(
            GcActionKind::StaleRelationship.to_string(),
            "stale_relationship"
        );
        assert_eq!(
            GcActionKind::DeadRelationship.to_string(),
            "dead_relationship"
        );
        assert_eq!(GcActionKind::OrphanedEntity.to_string(), "orphaned_entity");
        assert_eq!(GcActionKind::SpentEpisode.to_string(), "spent_episode");
    }

    // ── Episode collection ───────────────────────────────────────────

    /// An episode as old as `age_days`, never retrieved, self-authored — the
    /// shape that is collectable unless a test says otherwise.
    fn spent_episode(age_days: i64) -> EpisodeRow {
        EpisodeRow {
            id: serde_json::Value::String("episode:old".to_string()),
            session_id: "session-1".to_string(),
            timestamp: serde_json::Value::String(
                (Utc::now() - chrono::Duration::days(age_days)).to_rfc3339(),
            ),
            log_number: Some(7),
            provenance: Some("self".to_string()),
            access_count: 0,
        }
    }

    fn cited(sessions: &[&str]) -> HashSet<String> {
        sessions.iter().map(|s| (*s).to_string()).collect()
    }

    #[test]
    fn old_unread_self_authored_episode_is_collectable() {
        let reason = episode_prune_reason(
            &spent_episode(200),
            &HashSet::new(),
            &GcConfig::default(),
            &Utc::now(),
        );
        let reason = reason.expect("200-day-old orphan episode should be a candidate");
        assert!(reason.contains("never retrieved"), "{reason}");
        assert!(reason.contains("session session-1"), "{reason}");
    }

    #[test]
    fn young_episode_survives() {
        assert!(episode_prune_reason(
            &spent_episode(179),
            &HashSet::new(),
            &GcConfig::default(),
            &Utc::now(),
        )
        .is_none());
    }

    #[test]
    fn retrieved_episode_survives_any_age() {
        let mut episode = spent_episode(3650);
        episode.access_count = 1;

        assert!(
            episode_prune_reason(&episode, &HashSet::new(), &GcConfig::default(), &Utc::now())
                .is_none(),
            "an episode retrieval has returned is not spent"
        );
    }

    #[test]
    fn non_self_authored_episodes_survive_any_age() {
        // The human's words and ingested documents are not the agent's to
        // discard: they are the only evidence in the store that is not the
        // agent restating itself.
        for class in ["user", "external"] {
            let mut episode = spent_episode(3650);
            episode.provenance = Some(class.to_string());

            assert!(
                episode_prune_reason(&episode, &HashSet::new(), &GcConfig::default(), &Utc::now())
                    .is_none(),
                "{class}-authored episodes must survive"
            );
        }
    }

    #[test]
    fn legacy_episodes_without_provenance_are_collectable() {
        // AC7's conservative default cuts the other way here: unlabelled text
        // reads as self-authored, and self-authored text is collectable.
        let mut episode = spent_episode(200);
        episode.provenance = None;

        assert!(
            episode_prune_reason(&episode, &HashSet::new(), &GcConfig::default(), &Utc::now())
                .is_some()
        );
    }

    #[test]
    fn episode_cited_as_evidence_survives_any_age() {
        let episode = spent_episode(3650);

        assert!(
            episode_prune_reason(
                &episode,
                &cited(&["session-1"]),
                &GcConfig::default(),
                &Utc::now()
            )
            .is_none(),
            "an episode a surviving record cites is evidence, not garbage"
        );
        assert!(
            episode_prune_reason(
                &episode,
                &cited(&["some-other-session"]),
                &GcConfig::default(),
                &Utc::now()
            )
            .is_some(),
            "another session's citation protects nothing here"
        );
    }

    #[test]
    fn unparseable_timestamp_keeps_the_episode() {
        let mut episode = spent_episode(200);
        episode.timestamp = serde_json::Value::String("not-a-date".to_string());

        assert!(
            episode_prune_reason(&episode, &HashSet::new(), &GcConfig::default(), &Utc::now())
                .is_none(),
            "an episode whose age cannot be established is never collected"
        );
    }

    #[test]
    fn episode_age_threshold_is_configurable() {
        let config = GcConfig {
            episode_max_age_days: 30,
            ..Default::default()
        };

        assert!(
            episode_prune_reason(&spent_episode(31), &HashSet::new(), &config, &Utc::now())
                .is_some()
        );
        assert!(
            episode_prune_reason(&spent_episode(29), &HashSet::new(), &config, &Utc::now())
                .is_none()
        );
    }

    #[test]
    fn episode_labels_carry_the_log_number_when_there_is_one() {
        assert_eq!(spent_episode(1).label(), "session-1 (log 007)");

        let mut unnumbered = spent_episode(1);
        unnumbered.log_number = None;
        assert_eq!(unnumbered.label(), "session-1");
    }

    #[test]
    fn episode_collection_is_off_by_default() {
        let config = GcConfig::default();
        assert!(!config.collect_episodes, "episodes are opt-in");
        assert_eq!(config.episode_max_age_days, DEFAULT_EPISODE_MAX_AGE_DAYS);
        assert!(
            config.dry_run,
            "and the sweep still only reports by default"
        );
    }

    #[test]
    fn test_phase_stale_decay_makes_high_stored_confidence_stale() {
        // A relationship with stored confidence 0.6 (above stale threshold 0.5)
        // but last reinforced 180 days ago — decay brings effective to ~0.15
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(180)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:decayed".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: Some("decayed rel".to_string()),
            valid_from: serde_json::Value::String(old_date),
            valid_until: None,
            confidence: 0.6, // Above stale threshold!
            alpha: Some(6.0),
            beta: Some(4.0),
            self_reinforcements: Some(0),
            last_reinforced: None, // Never reinforced, so decays from valid_from
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let stale = phase_stale_relationships(&rels, &config, &now, &mut report);

        // Without decay: 0.6 >= 0.5, would NOT be caught
        // With decay: 0.6 * 0.5^(180/90) = 0.6 * 0.25 = 0.15 < 0.5, IS caught
        assert_eq!(
            stale.len(),
            1,
            "decayed relationship should be caught as stale"
        );
    }

    #[test]
    fn test_phase_stale_reinforced_prevents_decay() {
        // Same stored confidence 0.6, old valid_from, but recently reinforced
        let now = Utc::now();
        let old_date = (now - chrono::Duration::days(180)).to_rfc3339();
        let recent_reinforce = (now - chrono::Duration::days(5)).to_rfc3339();

        let rels = vec![Relationship {
            id: serde_json::Value::String("relates_to:reinforced".to_string()),
            from_id: serde_json::Value::String("entity:a".to_string()),
            to_id: serde_json::Value::String("entity:b".to_string()),
            rel_type: "CONNECTED_TO".to_string(),
            description: None,
            valid_from: serde_json::Value::String(old_date),
            valid_until: None,
            confidence: 0.6,
            alpha: Some(6.0),
            beta: Some(4.0),
            self_reinforcements: Some(0),
            last_reinforced: Some(serde_json::Value::String(recent_reinforce)),
            source: None,
        }];

        let config = GcConfig::default();
        let mut report = GcReport::default();
        let stale = phase_stale_relationships(&rels, &config, &now, &mut report);

        // Reinforced 5 days ago: effective ≈ 0.6 * 0.5^(5/90) ≈ 0.577 > 0.5
        assert!(
            stale.is_empty(),
            "recently reinforced relationship should NOT be stale"
        );
    }
}