lean_ctx/core/

memory_lifecycle.rs

//! Memory Lifecycle Management — consolidation, decay, compaction, archival.
//!
//! Runs automatically on knowledge stores to keep memory healthy:
//! - Confidence decay over time
//! - Semantic consolidation of similar facts
//! - Compaction when limits are exceeded
//! - Archival of old/unused facts

use chrono::{DateTime, Duration, Utc};
use serde::{Deserialize, Serialize};
use std::path::PathBuf;

use super::knowledge::KnowledgeFact;

const DEFAULT_DECAY_RATE: f32 = 0.01;
const DEFAULT_MAX_FACTS: usize = 1000;
const LOW_CONFIDENCE_THRESHOLD: f32 = 0.3;
const STALE_DAYS: i64 = 30;
/// Bound archive-dir disk growth. The reader (`rehydrate_from_archives`) only ever
/// consults the newest `KNOWLEDGE_REHYDRATE_MAX_ARCHIVES` (= 4) files, so any value
/// well above that prunes only already-unreachable files.
const MAX_ARCHIVE_FILES: usize = 16;

/// Spacing/testing effect: how strongly each prior retrieval lengthens memory
/// stability. 0.5 ⇒ ~10 retrievals make a fact roughly 6× more durable.
const SPACING_GAIN: f32 = 0.5;
/// Floor on derived stability (days) so even a heavily down-voted fact decays
/// smoothly rather than collapsing in a single pass.
const MIN_STABILITY_DAYS: f32 = 1.0;
/// Confidence never decays below this — archival happens elsewhere, decay never
/// hard-deletes.
const CONFIDENCE_FLOOR: f32 = 0.05;
/// Default characteristic memory stability (days) for the Ebbinghaus curve.
pub const DEFAULT_BASE_STABILITY_DAYS: f32 = 90.0;

/// Which forgetting curve drives confidence decay (#1).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum ForgettingModel {
    /// Exponential retention `R = exp(-Δt / S)` with spacing-boosted stability
    /// `S` (Ebbinghaus forgetting curve + SM-2 spacing). Deterministic, the
    /// default: durable memories fade gracefully, rehearsed ones persist.
    #[default]
    Ebbinghaus,
    /// Legacy linear subtraction, kept for reproducibility / explicit opt-out.
    Linear,
}

impl ForgettingModel {
    pub fn parse(s: &str) -> Self {
        match s.trim().to_lowercase().as_str() {
            "linear" => Self::Linear,
            _ => Self::Ebbinghaus,
        }
    }

    pub fn as_str(self) -> &'static str {
        match self {
            Self::Ebbinghaus => "ebbinghaus",
            Self::Linear => "linear",
        }
    }
}

#[derive(Debug, Clone)]
pub struct LifecycleConfig {
    pub decay_rate_per_day: f32,
    pub max_facts: usize,
    pub low_confidence_threshold: f32,
    pub stale_days: i64,
    pub consolidation_similarity: f32,
    /// Forgetting curve (#1). Defaults to Ebbinghaus.
    pub forgetting_model: ForgettingModel,
    /// Characteristic stability (days) for the Ebbinghaus curve before spacing
    /// and feedback modulation.
    pub base_stability_days: f32,
    /// When true, scale stability by the fact's archetype so structural *evidence*
    /// (architecture/dependency/…) decays slower than *inference* (#802/cognition).
    /// Default false keeps the baseline tuning byte-for-byte.
    pub archetype_aware_decay: bool,
}

impl Default for LifecycleConfig {
    fn default() -> Self {
        Self {
            decay_rate_per_day: DEFAULT_DECAY_RATE,
            max_facts: DEFAULT_MAX_FACTS,
            low_confidence_threshold: LOW_CONFIDENCE_THRESHOLD,
            stale_days: STALE_DAYS,
            consolidation_similarity: 0.85,
            forgetting_model: ForgettingModel::default(),
            base_stability_days: DEFAULT_BASE_STABILITY_DAYS,
            archetype_aware_decay: false,
        }
    }
}

#[derive(Debug, Default)]
pub struct LifecycleReport {
    pub decayed_count: usize,
    pub consolidated_count: usize,
    pub archived_count: usize,
    pub compacted_count: usize,
    pub remaining_facts: usize,
}

pub fn apply_confidence_decay(facts: &mut [KnowledgeFact], config: &LifecycleConfig) -> usize {
    let now = Utc::now();
    let mut count = 0;

    for fact in facts.iter_mut() {
        if !fact.is_current() {
            continue;
        }

        if let Some(valid_until) = fact.valid_until
            && valid_until < now
            && fact.confidence > 0.1
        {
            fact.confidence = 0.1;
            count += 1;
            continue;
        }

        let days_since_confirmed = now.signed_duration_since(fact.last_confirmed).num_days() as f32;
        if days_since_confirmed <= 0.0 {
            continue;
        }
        let days_since_retrieved = fact
            .last_retrieved
            .map_or(3650.0, |t| now.signed_duration_since(t).num_days() as f32);
        let retrieval_count = fact.retrieval_count as f32;
        let net_feedback = i64::from(fact.feedback_up) - i64::from(fact.feedback_down);

        // Archetype-aware stability (opt-in): structural evidence is more durable
        // than inference. Off by default → identical to the prior baseline.
        let base_stability = if config.archetype_aware_decay {
            config.base_stability_days * fact.archetype.stability_multiplier()
        } else {
            config.base_stability_days
        };

        let new_confidence = match config.forgetting_model {
            ForgettingModel::Ebbinghaus => ebbinghaus_confidence(
                fact.confidence,
                days_since_confirmed,
                days_since_retrieved,
                retrieval_count,
                net_feedback,
                base_stability,
            ),
            ForgettingModel::Linear => linear_confidence(
                fact.confidence,
                days_since_confirmed,
                days_since_retrieved,
                retrieval_count,
                net_feedback,
                config.decay_rate_per_day,
            ),
        };
        if (new_confidence - fact.confidence).abs() > 0.001 {
            fact.confidence = new_confidence;
            count += 1;
        }
    }

    if count > 0 && config.forgetting_model == ForgettingModel::Ebbinghaus {
        crate::core::introspect::tick("power_law_decay");
    }
    count
}

/// Ebbinghaus retention `R = exp(-Δt / S)` (#1). Stability `S` grows with the
/// spacing effect (each prior retrieval) and net feedback; `Δt` is time since
/// the memory was last reinforced (confirmed *or* retrieved). Multiplicative so
/// confidence approaches the floor smoothly and never overshoots. Deterministic.
fn ebbinghaus_confidence(
    confidence: f32,
    days_since_confirmed: f32,
    days_since_retrieved: f32,
    retrieval_count: f32,
    net_feedback: i64,
    base_stability_days: f32,
) -> f32 {
    let elapsed = days_since_confirmed.min(days_since_retrieved).max(0.0);
    let spacing = 1.0 + SPACING_GAIN * retrieval_count;
    let feedback_mult = match net_feedback.cmp(&0) {
        std::cmp::Ordering::Greater => 1.0 + (net_feedback as f32).ln_1p(),
        std::cmp::Ordering::Less => 1.0 / (1.0 + (net_feedback.unsigned_abs() as f32).ln_1p()),
        std::cmp::Ordering::Equal => 1.0,
    };
    let stability = (base_stability_days * spacing * feedback_mult).max(MIN_STABILITY_DAYS);
    let retention = (-(f64::from(elapsed)) / f64::from(stability)).exp() as f32;
    (confidence * retention).max(CONFIDENCE_FLOOR)
}

/// Legacy linear subtraction, preserved verbatim for `forgetting_model = linear`.
/// FadeMem-inspired: protect frequently/recently retrieved facts; feedback
/// steers retention. Deterministic, local-only.
fn linear_confidence(
    confidence: f32,
    days_since_confirmed: f32,
    days_since_retrieved: f32,
    retrieval_count: f32,
    net_feedback: i64,
    decay_rate_per_day: f32,
) -> f32 {
    let freq_protect = 1.0 / (1.0 + retrieval_count.ln_1p());
    let recency_protect = (1.0 - (days_since_retrieved / 30.0).min(1.0)).max(0.0);
    let protect = (freq_protect * (1.0 - 0.5 * recency_protect)).max(0.05);
    let feedback_factor = match net_feedback.cmp(&0) {
        std::cmp::Ordering::Greater => 1.0 / (1.0 + (net_feedback as f32).ln_1p()),
        std::cmp::Ordering::Less => (1.0 + (net_feedback.unsigned_abs() as f32).ln_1p()).min(4.0),
        std::cmp::Ordering::Equal => 1.0,
    };
    let decay = decay_rate_per_day * days_since_confirmed * protect * feedback_factor;
    (confidence - decay).max(CONFIDENCE_FLOOR)
}

pub fn consolidate_similar(facts: &mut Vec<KnowledgeFact>, similarity_threshold: f32) -> usize {
    let mut to_remove: std::collections::HashSet<usize> = std::collections::HashSet::new();

    let mut category_groups: std::collections::HashMap<String, Vec<usize>> =
        std::collections::HashMap::new();
    for (i, f) in facts.iter().enumerate() {
        if f.is_current() {
            category_groups
                .entry(f.category.clone())
                .or_default()
                .push(i);
        }
    }

    for indices in category_groups.values() {
        for (pos_a, &i) in indices.iter().enumerate() {
            if to_remove.contains(&i) {
                continue;
            }
            for &j in &indices[pos_a + 1..] {
                if to_remove.contains(&j) {
                    continue;
                }
                let sim = word_similarity(&facts[i].value, &facts[j].value);
                if sim >= similarity_threshold {
                    if facts[i].confidence >= facts[j].confidence {
                        facts[i].confirmation_count += facts[j].confirmation_count;
                        if facts[j].last_confirmed > facts[i].last_confirmed {
                            facts[i].last_confirmed = facts[j].last_confirmed;
                        }
                        to_remove.insert(j);
                    } else {
                        facts[j].confirmation_count += facts[i].confirmation_count;
                        if facts[i].last_confirmed > facts[j].last_confirmed {
                            facts[j].last_confirmed = facts[i].last_confirmed;
                        }
                        to_remove.insert(i);
                        break;
                    }
                }
            }
        }
    }

    let count = to_remove.len();
    let mut sorted: Vec<usize> = to_remove.into_iter().collect();
    sorted.sort_unstable();
    for idx in sorted.into_iter().rev() {
        facts.remove(idx);
    }

    count
}

pub fn compact(
    facts: &mut Vec<KnowledgeFact>,
    config: &LifecycleConfig,
) -> (usize, Vec<KnowledgeFact>) {
    let mut archived: Vec<KnowledgeFact> = Vec::new();
    let now = Utc::now();
    let stale_threshold = now - Duration::days(config.stale_days);

    let mut to_archive: Vec<usize> = Vec::new();

    for (i, fact) in facts.iter().enumerate() {
        let recently_retrieved = fact
            .last_retrieved
            .is_some_and(|t| now.signed_duration_since(t).num_days() < 14);
        let frequently_retrieved = fact.retrieval_count >= 5;

        if fact.confidence < config.low_confidence_threshold {
            to_archive.push(i);
            continue;
        }

        if fact.last_confirmed < stale_threshold
            && fact.confirmation_count <= 1
            && fact.confidence < 0.5
            && !recently_retrieved
            && !frequently_retrieved
        {
            to_archive.push(i);
        }
    }

    to_archive.sort_unstable();
    to_archive.dedup();
    let count = to_archive.len();

    for idx in to_archive.into_iter().rev() {
        archived.push(facts.remove(idx));
    }

    if facts.len() > config.max_facts {
        facts.sort_by(|a, b| {
            b.confidence
                .partial_cmp(&a.confidence)
                .unwrap_or(std::cmp::Ordering::Equal)
        });
        let excess: Vec<KnowledgeFact> = facts.drain(config.max_facts..).collect();
        archived.extend(excess);
    }

    (count, archived)
}

pub fn run_lifecycle(facts: &mut Vec<KnowledgeFact>, config: &LifecycleConfig) -> LifecycleReport {
    let decayed = apply_confidence_decay(facts, config);
    let consolidated = consolidate_similar(facts, config.consolidation_similarity);
    let (compacted, archived) = compact(facts, config);

    if !archived.is_empty() {
        let _ = archive_facts(&archived);
    }

    LifecycleReport {
        decayed_count: decayed,
        consolidated_count: consolidated,
        archived_count: archived.len(),
        compacted_count: compacted,
        remaining_facts: facts.len(),
    }
}

#[derive(Debug, Serialize, Deserialize)]
struct ArchivedFacts {
    pub archived_at: DateTime<Utc>,
    pub facts: Vec<KnowledgeFact>,
}

fn archive_facts(facts: &[KnowledgeFact]) -> Result<(), String> {
    let dir = crate::core::data_dir::lean_ctx_data_dir()?
        .join("memory")
        .join("archive");
    std::fs::create_dir_all(&dir).map_err(|e| format!("{e}"))?;

    // Sub-second suffix avoids same-second filename collisions that would otherwise
    // silently overwrite a prior archive written in the same wall-clock second.
    let now = Utc::now();
    let suffix = now.timestamp_subsec_nanos() % 1_000_000;
    let filename = format!("archive-{}-{suffix:06}.json", now.format("%Y%m%d-%H%M%S"));
    let archive = ArchivedFacts {
        archived_at: now,
        facts: facts.to_vec(),
    };
    let json = serde_json::to_string_pretty(&archive).map_err(|e| format!("{e}"))?;
    std::fs::write(dir.join(filename), json).map_err(|e| format!("{e}"))?;

    // Prune to the newest MAX_ARCHIVE_FILES; list_archives() is already sorted ascending
    // (lexical == chronological for the zero-padded timestamp prefix). Best-effort: a
    // prune failure must not fail the archive write itself.
    let archives = list_archives();
    if archives.len() > MAX_ARCHIVE_FILES {
        for old in &archives[..archives.len() - MAX_ARCHIVE_FILES] {
            let _ = std::fs::remove_file(old);
        }
    }
    Ok(())
}

pub fn restore_archive(archive_path: &str) -> Result<Vec<KnowledgeFact>, String> {
    let data = std::fs::read_to_string(archive_path).map_err(|e| format!("{e}"))?;
    let archive: ArchivedFacts = serde_json::from_str(&data).map_err(|e| format!("{e}"))?;
    Ok(archive.facts)
}

pub fn list_archives() -> Vec<PathBuf> {
    let dir = match crate::core::data_dir::lean_ctx_data_dir() {
        Ok(d) => d.join("memory").join("archive"),
        Err(_) => return Vec::new(),
    };

    if !dir.exists() {
        return Vec::new();
    }

    let mut archives: Vec<PathBuf> = std::fs::read_dir(&dir)
        .into_iter()
        .flatten()
        .flatten()
        .filter(|e| e.path().extension().is_some_and(|ext| ext == "json"))
        .map(|e| e.path())
        .collect();

    archives.sort();
    archives
}

fn word_similarity(a: &str, b: &str) -> f32 {
    let a_lower = a.to_lowercase();
    let b_lower = b.to_lowercase();
    let a_words: std::collections::HashSet<&str> = a_lower.split_whitespace().collect();
    let b_words: std::collections::HashSet<&str> = b_lower.split_whitespace().collect();

    if a_words.is_empty() && b_words.is_empty() {
        return 1.0;
    }

    let intersection = a_words.intersection(&b_words).count();
    let union = a_words.union(&b_words).count();

    if union == 0 {
        return 0.0;
    }

    intersection as f32 / union as f32
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::core::knowledge::KnowledgeArchetype;

    fn make_fact(category: &str, key: &str, value: &str, confidence: f32) -> KnowledgeFact {
        KnowledgeFact {
            category: category.to_string(),
            key: key.to_string(),
            value: value.to_string(),
            source_session: "s1".to_string(),
            confidence,
            created_at: Utc::now(),
            last_confirmed: Utc::now(),
            retrieval_count: 0,
            last_retrieved: None,
            valid_from: Some(Utc::now()),
            valid_until: None,
            supersedes: None,
            confirmation_count: 1,
            feedback_up: 0,
            feedback_down: 0,
            last_feedback: None,
            privacy: crate::core::memory_boundary::FactPrivacy::default(),
            sensitivity: crate::core::sensitivity::SensitivityLevel::default(),
            imported_from: None,
            archetype: KnowledgeArchetype::default(),
            fidelity: None,
            revision_count: 0,
        }
    }

    fn make_old_fact(
        category: &str,
        key: &str,
        value: &str,
        confidence: f32,
        days_old: i64,
    ) -> KnowledgeFact {
        let past = Utc::now() - Duration::days(days_old);
        KnowledgeFact {
            category: category.to_string(),
            key: key.to_string(),
            value: value.to_string(),
            source_session: "s1".to_string(),
            confidence,
            created_at: past,
            last_confirmed: past,
            retrieval_count: 0,
            last_retrieved: None,
            valid_from: Some(past),
            valid_until: None,
            supersedes: None,
            confirmation_count: 1,
            feedback_up: 0,
            feedback_down: 0,
            last_feedback: None,
            privacy: crate::core::memory_boundary::FactPrivacy::default(),
            sensitivity: crate::core::sensitivity::SensitivityLevel::default(),
            imported_from: None,
            archetype: KnowledgeArchetype::default(),
            fidelity: None,
            revision_count: 0,
        }
    }

    #[test]
    fn decay_reduces_confidence() {
        let config = LifecycleConfig::default();
        let mut facts = vec![make_old_fact("arch", "db", "PostgreSQL", 0.9, 10)];

        let count = apply_confidence_decay(&mut facts, &config);
        assert_eq!(count, 1);
        assert!(facts[0].confidence < 0.9);
        assert!(facts[0].confidence > 0.7);
    }

    #[test]
    fn archetype_aware_decay_protects_evidence() {
        // Opt-in: structural evidence (Architecture) decays slower than inference
        // (Preference). Off (default), archetype is ignored and both decay alike.
        let mut evidence = make_old_fact("arch", "db", "PostgreSQL", 0.9, 30);
        evidence.archetype = KnowledgeArchetype::Architecture;
        let mut inference = make_old_fact("pref", "style", "tabs", 0.9, 30);
        inference.archetype = KnowledgeArchetype::Preference;

        let off = LifecycleConfig::default();
        let mut a = vec![evidence.clone(), inference.clone()];
        apply_confidence_decay(&mut a, &off);
        assert!(
            (a[0].confidence - a[1].confidence).abs() < 1e-6,
            "flag off → archetype ignored, equal decay"
        );

        let on = LifecycleConfig {
            archetype_aware_decay: true,
            ..Default::default()
        };
        let mut b = vec![evidence, inference];
        apply_confidence_decay(&mut b, &on);
        assert!(
            b[0].confidence > b[1].confidence,
            "evidence {} should outlast inference {}",
            b[0].confidence,
            b[1].confidence
        );
    }

    #[test]
    fn decay_skips_recent_facts() {
        let config = LifecycleConfig::default();
        let mut facts = vec![make_fact("arch", "db", "PostgreSQL", 0.9)];

        let count = apply_confidence_decay(&mut facts, &config);
        assert_eq!(count, 0);
    }

    #[test]
    fn feedback_steers_decay_keep_vs_forget() {
        let config = LifecycleConfig::default();
        let mut praised = make_old_fact("arch", "loved", "keep me", 0.9, 10);
        praised.feedback_up = 5;
        let mut panned = make_old_fact("arch", "hated", "forget me", 0.9, 10);
        panned.feedback_down = 5;
        let neutral = make_old_fact("arch", "meh", "neutral", 0.9, 10);

        let mut facts = vec![praised, panned, neutral];
        apply_confidence_decay(&mut facts, &config);

        let (praised_c, panned_c, neutral_c) = (
            facts[0].confidence,
            facts[1].confidence,
            facts[2].confidence,
        );

        // Reward bridge: up-voted retains more than neutral, neutral more than down-voted.
        assert!(
            praised_c > neutral_c,
            "praised {praised_c} should outlast neutral {neutral_c}"
        );
        assert!(
            neutral_c > panned_c,
            "neutral {neutral_c} should outlast panned {panned_c}"
        );
        // Even a heavily down-voted fact only fades toward the floor — never hard-deleted.
        assert!(panned_c >= 0.05);
    }

    #[test]
    fn spacing_effect_protects_frequently_retrieved() {
        // #1: under the Ebbinghaus curve, a fact retrieved many times must decay
        // slower than an identical never-retrieved fact of the same age.
        let config = LifecycleConfig::default();
        let rarely = make_old_fact("arch", "rare", "x", 0.9, 20);
        let mut often = make_old_fact("arch", "often", "y", 0.9, 20);
        often.retrieval_count = 20;
        let mut facts = vec![rarely, often];
        apply_confidence_decay(&mut facts, &config);
        assert!(
            facts[1].confidence > facts[0].confidence,
            "spacing effect: rehearsed {} should outlast un-rehearsed {}",
            facts[1].confidence,
            facts[0].confidence
        );
    }

    #[test]
    fn ebbinghaus_decay_is_deterministic() {
        // Determinism contract (#498): same input → same output, no RNG.
        let config = LifecycleConfig::default();
        let mut a = vec![make_old_fact("arch", "k", "v", 0.8, 15)];
        let mut b = a.clone();
        apply_confidence_decay(&mut a, &config);
        apply_confidence_decay(&mut b, &config);
        assert_eq!(a[0].confidence, b[0].confidence);
    }

    #[test]
    fn linear_model_still_available() {
        // Opt-out path keeps the legacy subtractive behavior.
        let config = LifecycleConfig {
            forgetting_model: ForgettingModel::Linear,
            ..Default::default()
        };
        let mut facts = vec![make_old_fact("arch", "db", "PostgreSQL", 0.9, 10)];
        let count = apply_confidence_decay(&mut facts, &config);
        assert_eq!(count, 1);
        assert!(facts[0].confidence < 0.9 && facts[0].confidence > 0.7);
    }

    #[test]
    fn forgetting_model_parses() {
        assert_eq!(ForgettingModel::parse("linear"), ForgettingModel::Linear);
        assert_eq!(
            ForgettingModel::parse("ebbinghaus"),
            ForgettingModel::Ebbinghaus
        );
        assert_eq!(
            ForgettingModel::parse("garbage"),
            ForgettingModel::Ebbinghaus
        );
    }

    #[test]
    fn consolidate_similar_facts() {
        let mut facts = vec![
            make_fact("arch", "db", "uses PostgreSQL database", 0.8),
            make_fact("arch", "db2", "uses PostgreSQL database system", 0.6),
            make_fact("ops", "deploy", "docker compose up", 0.9),
        ];

        let count = consolidate_similar(&mut facts, 0.7);
        assert!(count > 0, "Should consolidate similar facts");
        assert!(facts.len() < 3);
    }

    #[test]
    fn consolidate_keeps_different_categories() {
        let mut facts = vec![
            make_fact("arch", "db", "PostgreSQL", 0.8),
            make_fact("ops", "db", "PostgreSQL", 0.8),
        ];

        let count = consolidate_similar(&mut facts, 0.9);
        assert_eq!(count, 0, "Different categories should not consolidate");
    }

    #[test]
    fn compact_removes_low_confidence() {
        let config = LifecycleConfig::default();
        let mut facts = vec![
            make_fact("arch", "db", "PostgreSQL", 0.9),
            make_fact("arch", "cache", "Redis", 0.1),
        ];

        let (count, archived) = compact(&mut facts, &config);
        assert_eq!(count, 1);
        assert_eq!(facts.len(), 1);
        assert_eq!(archived.len(), 1);
        assert_eq!(archived[0].key, "cache");
    }

    #[test]
    fn compact_archives_stale_facts() {
        let config = LifecycleConfig::default();
        let mut facts = vec![
            make_fact("arch", "db", "PostgreSQL", 0.9),
            make_old_fact("arch", "old", "ancient thing", 0.4, 60),
        ];

        let (count, archived) = compact(&mut facts, &config);
        assert_eq!(count, 1);
        assert_eq!(archived[0].key, "old");
    }

    #[test]
    fn full_lifecycle_run() {
        let config = LifecycleConfig {
            max_facts: 5,
            ..Default::default()
        };

        let mut facts = vec![
            make_fact("arch", "db", "PostgreSQL", 0.9),
            make_fact("arch", "cache", "Redis", 0.8),
            make_old_fact("arch", "old1", "thing1", 0.2, 50),
            make_old_fact("arch", "old2", "thing2", 0.15, 60),
            make_fact("ops", "deploy", "docker compose", 0.7),
        ];

        let report = run_lifecycle(&mut facts, &config);
        assert!(report.remaining_facts <= config.max_facts);
        assert!(report.decayed_count > 0 || report.compacted_count > 0);
    }

    #[test]
    fn word_similarity_identical() {
        assert!((word_similarity("hello world", "hello world") - 1.0).abs() < 0.01);
    }

    #[test]
    fn word_similarity_partial() {
        let sim = word_similarity("uses PostgreSQL database", "PostgreSQL database system");
        assert!(sim >= 0.5, "Expected >= 0.5 but got {sim}");
        assert!(sim < 1.0);
    }

    #[test]
    fn word_similarity_different() {
        let sim = word_similarity("Redis cache", "Docker compose");
        assert!(sim < 0.1);
    }
}