dupehell_core/

schema.rs

// DupeHell -- MIT License
//
// Synthetic multi-domain dataset generator for record linkage benchmarking.
// No liability for misuse.

use std::collections::HashMap;
use std::path::Path;

use crate::pipeline::PipelineConfig;

#[derive(serde::Deserialize)]
pub struct DomainSchema {
    pub entities: Vec<EntitySchema>,
    pub hn_types: Vec<HnSchema>,
}

fn default_entity_weight() -> f64 {
    1.0
}

/// Infer an entity's identifier column: prefer `{entity_name}_id`, then
/// `id`, then the first column ending in `_id`.
fn infer_identifier_col(entity: &EntitySchema) -> Option<String> {
    let entity_id_name = format!("{}_id", entity.name);
    let col_names: Vec<&str> = entity
        .columns
        .iter()
        .filter_map(|c| c.get("name").and_then(|v| v.as_str()))
        .collect();
    if col_names.contains(&entity_id_name.as_str()) {
        Some(entity_id_name)
    } else if col_names.contains(&"id") {
        Some("id".to_string())
    } else {
        col_names
            .iter()
            .find(|n| n.ends_with("_id"))
            .map(|n| (*n).to_string())
    }
}

#[derive(serde::Deserialize)]
pub struct EntitySchema {
    pub name: String,
    pub columns: Vec<serde_json::Value>,
    #[serde(default)]
    pub fk_remaps: Vec<serde_json::Value>,
    /// Relative population size of this entity within the domain, used to
    /// split `total_unique` identities across entities (`build_pipeline_config`).
    /// Defaults to `1.0` (every entity gets an equal share) when a schema
    /// doesn't set it — every schema written before this field existed keeps
    /// behaving exactly as before. Set explicit weights when entities aren't
    /// realistically equal in population (e.g. aviation: far more
    /// `passenger` identities than `airline` ones) — see `docs/` or ask
    /// before picking numbers for a domain you don't know well; a wrong
    /// weight is as misleading as the uniform default, just in the other
    /// direction.
    #[serde(default = "default_entity_weight")]
    pub weight: f64,
}

#[derive(serde::Deserialize)]
pub struct HnSchema {
    pub entity_type: String,
    pub config_json: String,
}

#[derive(Debug, Clone)]
struct DifficultySettings {
    singleton: f64,
    doublet: f64,
    /// Noise types active for this difficulty, weighted equally. Curated
    /// explicitly per level (rather than derived from a truncated,
    /// order-dependent countdown) so that "broad" noise types — `typo` and
    /// `visual`, which both corrupt name+address+phone+company on the same
    /// record at once (see `pipeline::noise_type_targets_column`) — never
    /// end up a *larger* share of the mix at a lower difficulty than at a
    /// higher one. A prior countdown-weight scheme caused exactly that:
    /// medium (4 active types) put 70% of its noise budget on typo+visual,
    /// vs. only ~42% for hell (8 active types), making medium duplicates
    /// *more* likely to have every strong matching field wiped out at once
    /// than hell duplicates, despite medium being meant as the easier tier.
    noise_types: &'static [&'static str],
    /// Number of *independent* noise passes applied to each duplicate copy
    /// (see `pipeline::run_pipeline`'s dup-generation loop). Each additional
    /// pass draws its own noise_type from `noise_types` and applies it on
    /// top of the previous pass's result.
    ///
    /// This is the actual difficulty lever between tiers with different
    /// `noise_types.len()` — not the category list itself. Each entry's
    /// per-pass weight is `1 / noise_types.len()` (`build_pipeline_config`
    /// below), so adding categories to make a tier "harder" *dilutes* every
    /// existing category's weight, including whichever one happens to guard
    /// a domain's single most reliable linkage column — a tier with more
    /// categories active can paradoxically end up *easier* on some schemas
    /// (measured: a "hard" tier here, folded into hell, kept coming out
    /// easier than "hell" on several domains despite having fewer
    /// categories; then a hand-picked category weighted twice fixed 2 of 6
    /// domains tested but not the rest, since the dominant reliable column
    /// isn't always the same category across schemas). Passes sidestep this
    /// entirely: the probability a given column is touched at least once
    /// across `P` independent passes is `1 - (1 - p)^P` where `p` is its
    /// single-pass weight — strictly increasing in `P` regardless of how
    /// small `p` is, so more passes can never make a tier easier the way
    /// more categories can. `difficulty::estimate_difficulty` models this
    /// exact same formula.
    passes: usize,
}

const DIFFICULTY_MAP: [(&str, DifficultySettings); 3] = [
    (
        "light",
        DifficultySettings {
            singleton: 0.50,
            doublet: 0.30,
            noise_types: &["names", "dates"],
            passes: 1,
        },
    ),
    (
        "medium",
        DifficultySettings {
            singleton: 0.30,
            doublet: 0.40,
            noise_types: &["typo", "names", "dates", "identifiers"],
            // 3 passes: a column protected by exactly one of medium's 4
            // equally-weighted categories (weight 1/4 -- e.g. a pure date
            // column, only matched by "dates", not by "typo"'s broader
            // predicate) is diluted well below light's worst case (2
            // categories, weight 1/2). At passes=1 this let medium come out
            // *easier* than light on 19/40 domains (found via
            // scripts/validate_all_domains.py). 1 - (1 - 1/4)^3 ≈ 0.578 >
            // light's single-pass 0.5, closing the gap for any category
            // medium shares with light regardless of which column ends up
            // being a given domain's escape hatch. Re-validated across all
            // 40 domains with the same script after this change.
            passes: 3,
        },
    ),
    (
        "hell",
        DifficultySettings {
            singleton: 0.10,
            doublet: 0.20,
            // `typo_aggressive` corrupts more of each string than plain
            // `typo` (same target columns, more damage per hit — see
            // `noise::typos`), and `unicode_pollution` gets its own bucket
            // (rather than only ever showing up as one of `visual`'s five
            // random sub-choices).
            noise_types: &[
                "typo_aggressive",
                "visual",
                "unicode_pollution",
                "names",
                "dates",
                "identifiers",
                "addresses",
                "companies",
                "extra",
            ],
            // 8 passes: medium was bumped from 1 to 3 passes to fix its own
            // dilution against light (see the comment on medium's `passes`
            // above), which raised medium's worst-case single-category
            // touch probability to 1-(1-1/4)^3 ≈ 0.578. With 9
            // equally-weighted categories (weight 1/9 each), hell needs
            // 1-(1-1/9)^passes >= 0.578 to stay at least as hard as medium
            // on any column protected by only one category -- solving gives
            // passes >= 7.33, rounded up to 8 (1-(1-1/9)^8 ≈ 0.617).
            // Re-validated across all 40 domains via
            // scripts/validate_all_domains.py (0 crashes, 0 monotonicity
            // violations) after this change.
            passes: 8,
        },
    ),
];

pub fn default_singleton_master_fraction(difficulty: &str) -> f64 {
    difficulty_settings(difficulty).singleton
}

fn difficulty_settings(difficulty: &str) -> DifficultySettings {
    DIFFICULTY_MAP
        .iter()
        .find(|(name, _)| *name == difficulty)
        .map(|(_, s)| s.clone())
        .unwrap_or_else(|| DIFFICULTY_MAP[1].1.clone())
}

/// Generate a domain-unique run ID based on the current Unix timestamp (hex).
pub fn chrono_now() -> String {
    let start = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .unwrap_or_default();
    format!("{:x}", start.as_secs())
}

/// Deterministic run ID derived from generation parameters, so the same
/// (domain, size, seed, difficulty, hard_neg_ratio, singleton_master_fraction,
/// locale) always produces the same output filename regardless of output
/// format (IPC vs Parquet) or how many times it's run — and, just as
/// important, a *different* filename whenever any of these parameters
/// differ, since they all affect the generated data. `singleton_master_fraction`
/// and `locale` were missing from this list until this was flagged as a bug
/// (BUGS.md C14/C15): two runs differing only in `--singleton-master-fraction`
/// or `--locale` produced the exact same filename, so the second run silently
/// overwrote the first's output.
#[allow(clippy::too_many_arguments)]
pub fn deterministic_run_id(
    domain: &str,
    size: usize,
    seed: u64,
    difficulty: &str,
    hard_neg_ratio: f64,
    singleton_master_fraction: f64,
    locale: &str,
    only_entity: Option<&str>,
    chunk_size: Option<usize>,
) -> String {
    use std::hash::{Hash, Hasher};
    let mut hasher = std::collections::hash_map::DefaultHasher::new();
    domain.hash(&mut hasher);
    size.hash(&mut hasher);
    seed.hash(&mut hasher);
    difficulty.hash(&mut hasher);
    hard_neg_ratio.to_bits().hash(&mut hasher);
    singleton_master_fraction.to_bits().hash(&mut hasher);
    locale.hash(&mut hasher);
    // BUGS.md C14/C15: every parameter that changes the output must be
    // hashed in, or two runs differing only in this one collide on the same
    // filename and silently overwrite each other.
    only_entity.unwrap_or("").hash(&mut hasher);
    // `--chunk-size` doesn't change the final dataset's *content* (chunked
    // and non-chunked runs of the same total size are meant to be
    // equivalent data, modulo per-chunk RNG independence) but it DOES
    // change the sequence of per-chunk seeds actually used internally
    // (`seed + chunk_idx` per chunk vs a single unbroken `seed`), so two
    // runs with the same total size/seed but a different chunking must
    // never collide on the same output filename.
    chunk_size.unwrap_or(0).hash(&mut hasher);
    format!("{}_{:x}", domain, hasher.finish())
}

/// Load and parse a domain schema JSON file.
///
/// On failure, the error message includes the path attempted and a hint listing
/// available domains found in the same directory.
pub fn load_schema(domain: &str, schemas_dir: &Path) -> Result<DomainSchema, String> {
    let path = schemas_dir.join(format!("{domain}.json"));
    // Case-sensitive exact match against the actual schema file names, so
    // "KYC" is rejected the same way on every OS — on a case-insensitive
    // filesystem (Windows), `read_to_string` alone would silently succeed
    // for "KYC" via the "kyc.json" file, producing a different run hash
    // than "kyc" for what the user intended to be the same domain.
    let available = available_domain_names(schemas_dir);
    if !available.iter().any(|d| d == domain) {
        let hint = if available.is_empty() {
            "no schemas found".to_string()
        } else {
            available.join(", ")
        };
        return Err(format!(
            "schema file not found for domain '{domain}' at {path:?}. \
             Available domains ({hint})"
        ));
    }
    let data =
        std::fs::read_to_string(&path).map_err(|e| format!("cannot read schema {path:?}: {e}"))?;
    serde_json::from_str(&data).map_err(|e| format!("cannot parse schema {domain}.json: {e}"))
}

/// List available domain names (without .json extension) in a directory.
fn available_domain_names(dir: &Path) -> Vec<String> {
    match std::fs::read_dir(dir) {
        Ok(entries) => entries
            .filter_map(|e| e.ok())
            .filter(|e| {
                e.path()
                    .extension()
                    .map(|ext| ext == "json")
                    .unwrap_or(false)
            })
            .filter_map(|e| {
                e.path()
                    .file_stem()
                    .map(|s| s.to_string_lossy().to_string())
            })
            .collect(),
        Err(_) => Vec::new(),
    }
}

/// Build a `PipelineConfig` from CLI / Python parameters and a parsed schema.
///
/// Validates `size >= 10`, distributes singleton/doublet/triplet records
/// across entities, and assigns noise weights per difficulty setting.
#[allow(clippy::too_many_arguments)]
pub fn build_pipeline_config(
    domain: &str,
    size: usize,
    seed: u64,
    difficulty: &str,
    hard_neg_ratio: f64,
    singleton_master_fraction: f64,
    schema: &DomainSchema,
    run_id: &str,
    output_format: &str,
    graph_enabled: bool,
    graph_format: &str,
    only_entity: Option<&str>,
) -> Result<PipelineConfig, String> {
    if size < 10 {
        return Err(format!("size must be >= 10, got {size}"));
    }
    if schema.entities.is_empty() {
        return Err(format!("schema for domain '{domain}' has no entities"));
    }
    if !(0.0..=1.0).contains(&singleton_master_fraction) {
        return Err(format!(
            "singleton_master_fraction must be in [0.0, 1.0], got {singleton_master_fraction}"
        ));
    }
    if let Some(target) = only_entity
        && !schema.entities.iter().any(|e| e.name == target)
    {
        let available: Vec<&str> = schema.entities.iter().map(|e| e.name.as_str()).collect();
        return Err(format!(
            "only_entity '{target}' not found in domain '{domain}'; available entities: {}",
            available.join(", ")
        ));
    }
    let ds = difficulty_settings(difficulty);
    let total = size;

    let n_singleton = (total as f64 * singleton_master_fraction) as usize;
    let n_doublet_float = total as f64 * ds.doublet;
    let mut n_doublet = n_doublet_float as usize;
    if !n_doublet.is_multiple_of(2) {
        n_doublet -= 1;
    }
    if n_singleton + n_doublet > total {
        return Err(format!(
            "singleton_master_fraction {singleton_master_fraction} leaves no room for this \
             difficulty's doublet share ({:.2}); reduce singleton_master_fraction",
            ds.doublet
        ));
    }
    let mut n_triplet = total - n_singleton - n_doublet;
    let r = n_triplet % 3;
    if r != 0 {
        n_triplet -= r;
    }
    let total_unique = n_singleton + n_doublet / 2 + n_triplet / 3;
    let n_duplicates = total.max(total_unique) - total_unique;

    // `--only-entity`: the weight-based split below runs over this entity
    // alone, so `total_unique`/`n_duplicates` land on it entirely instead of
    // being shared out — no separate "recompute the ratio" step needed.
    // Entities it FK-references get a small identifier-only pool appended
    // after the main loop (see `pool_only` below); every other entity in
    // the domain is simply absent from `entity_plans`.
    let active_entities: Vec<&EntitySchema> = match only_entity {
        Some(target) => schema
            .entities
            .iter()
            .filter(|e| e.name == target)
            .collect(),
        None => schema.entities.iter().collect(),
    };

    let total_ratio: f64 = active_entities.iter().map(|e| e.weight).sum::<f64>();
    let raw_floats: Vec<(&str, f64)> = active_entities
        .iter()
        .map(|e| {
            (
                e.name.as_str(),
                total_unique as f64 * e.weight / total_ratio,
            )
        })
        .collect();

    let mut floor_map: HashMap<&str, usize> = HashMap::new();
    for (name, r) in &raw_floats {
        floor_map.insert(name, r.max(2.0) as usize);
    }
    let floor_sum: usize = floor_map.values().sum();
    let need = total_unique.max(floor_sum) - floor_sum;
    if need > 0 {
        let mut remainders: Vec<(&str, f64)> = raw_floats
            .iter()
            .map(|(n, r)| (*n, r - r.floor()))
            .collect();
        remainders.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal));
        for (name, _) in remainders.iter().take(need) {
            *floor_map.get_mut(name).unwrap_or(&mut 0) += 1;
        }
    }

    let dup_ratios: Vec<(&str, f64)> = active_entities
        .iter()
        .map(|e| {
            (
                e.name.as_str(),
                *floor_map.get(e.name.as_str()).unwrap_or(&2) as f64 / total_unique as f64,
            )
        })
        .collect();
    let mut dup_floor: HashMap<&str, usize> = HashMap::new();
    for (name, r) in &dup_ratios {
        dup_floor.insert(name, (n_duplicates as f64 * r) as usize);
    }
    let dup_sum: usize = dup_floor.values().sum();
    let dup_need = n_duplicates.max(dup_sum) - dup_sum;
    if dup_need > 0 {
        let mut remainders: Vec<(&str, f64)> = dup_ratios
            .iter()
            .map(|(n, r)| (*n, r - r.floor()))
            .collect();
        remainders.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal));
        for (name, _) in remainders.iter().take(dup_need) {
            *dup_floor.get_mut(name).unwrap_or(&mut 0) += 1;
        }
    }

    let noise_count = ds.noise_types.len();
    let noise_weights: Vec<f64> = vec![1.0 / noise_count as f64; noise_count];

    let mut entity_plans = Vec::new();
    for entity in &active_entities {
        let n_base = *floor_map.get(entity.name.as_str()).unwrap_or(&2);
        let n_dup = *dup_floor.get(entity.name.as_str()).unwrap_or(&0);

        let mut noise_entries = Vec::new();
        if n_dup > 0 {
            let mut counts: Vec<usize> = noise_weights
                .iter()
                .map(|w| (w * n_dup as f64) as usize)
                .collect();
            let count_sum: usize = counts.iter().sum();
            if count_sum < n_dup {
                *counts.last_mut().unwrap_or(&mut 0) += n_dup - count_sum;
            }
            for (i, noise_type) in ds.noise_types.iter().enumerate() {
                if counts[i] == 0 {
                    continue;
                }
                noise_entries.push(serde_json::json!({
                    "noise_type": noise_type,
                    "columns": [],
                    "count": counts[i],
                }));
            }
        }

        let identifier_col = infer_identifier_col(entity);

        let columns_json = serde_json::to_string(&entity.columns)
            .map_err(|e| format!("serialize columns: {e}"))?;

        entity_plans.push(serde_json::json!({
            "name": entity.name,
            "n_base": n_base,
            "n_dup": n_dup,
            "identifier_col": identifier_col,
            "columns_json": columns_json,
            "noise_types": noise_entries,
            "fk_remaps": entity.fk_remaps,
        }));
    }

    // `--only-entity`: entities the target directly references via
    // `fk_remaps` still need to exist enough to give it something plausible
    // to point at, without paying for a full-size, fully-noised generation
    // of an entity the run never writes. Generate just an identifier pool,
    // capped at `FK_POOL_CAP` (same cap the FK-remap sampler itself already
    // enforces, so a larger pool would never be consulted anyway).
    if let Some(target) = only_entity {
        let target_schema = schema
            .entities
            .iter()
            .find(|e| e.name == target)
            .expect("only_entity validated to exist above");
        let mut pool_target_names: Vec<&str> = target_schema
            .fk_remaps
            .iter()
            .filter_map(|r| r.get("target_entity").and_then(|v| v.as_str()))
            .filter(|&t| t != target)
            .collect();
        pool_target_names.sort_unstable();
        pool_target_names.dedup();

        let pool_n = crate::pipeline::FK_POOL_CAP.min(total_unique.max(2));
        for name in pool_target_names {
            let Some(entity) = schema.entities.iter().find(|e| e.name == name) else {
                continue;
            };
            let identifier_col = infer_identifier_col(entity);
            let columns_json = serde_json::to_string(&entity.columns)
                .map_err(|e| format!("serialize columns: {e}"))?;
            entity_plans.push(serde_json::json!({
                "name": entity.name,
                "n_base": pool_n,
                "n_dup": 0,
                "identifier_col": identifier_col,
                "columns_json": columns_json,
                "noise_types": [],
                "fk_remaps": entity.fk_remaps,
                "pool_only": true,
            }));
        }
    }

    // Hard negatives are per-entity (`HnSchema::entity_type`) — under
    // `--only-entity` only the target's own hard-negative types apply; the
    // rest belong to entities this run no longer writes.
    let active_hn_types: Vec<&HnSchema> = schema
        .hn_types
        .iter()
        .filter(|hn| only_entity.is_none_or(|t| hn.entity_type == t))
        .collect();

    // Scaled off `n_duplicates` (which itself scales with the tier's
    // singleton/doublet fractions — light ~0.28*size, medium ~0.40*size,
    // hell ~0.57*size) rather than off raw `size`. A flat `size`-based count
    // makes `total_guaranteed_fp` roughly constant across tiers while
    // `total_true_pairs` grows a lot with difficulty, which mechanically
    // inflates `precision_max` for higher tiers regardless of how much
    // noise they actually inject — enough to invert `light <= medium` on
    // some schemas (e.g. aviation, where light/medium f1_max came out
    // 0.828/0.833). The 0.125 constant keeps medium's hard-neg volume
    // matching the old flat formula (0.40 * 0.125 = 0.05), so
    // `hard_neg_ratio`'s documented "~1.5% of size at default 0.3" still
    // holds at medium; light gets proportionally fewer, hell more.
    let n_hard_neg = (n_duplicates as f64 * hard_neg_ratio * 0.125) as usize;
    let hn_per_type = n_hard_neg / active_hn_types.len().max(1);
    let hard_neg_types: Vec<serde_json::Value> = active_hn_types
        .iter()
        .map(|hn| {
            serde_json::json!({
                "entity_type": hn.entity_type,
                "config_json": hn.config_json,
                "count": hn_per_type,
            })
        })
        .collect();

    let config = serde_json::json!({
        "domain": domain,
        "size": size,
        "seed": seed,
        "difficulty": difficulty,
        "output_format": output_format,
        "run_id": run_id,
        "entity_plans": entity_plans,
        "hard_neg_types": hard_neg_types,
        "hard_neg_ratio": hard_neg_ratio,
        "noise_passes": ds.passes,
        "graph_enabled": graph_enabled,
        "graph_format": graph_format,
    });

    serde_json::from_value(config).map_err(|e| format!("build PipelineConfig: {e}"))
}

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

    fn schemas_dir() -> std::path::PathBuf {
        std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("schemas")
    }

    fn kyc_schema() -> DomainSchema {
        load_schema("kyc", &schemas_dir()).expect("load kyc.json")
    }

    fn aviation_schema() -> DomainSchema {
        load_schema("aviation", &schemas_dir()).expect("load aviation.json")
    }

    #[test]
    fn test_load_schema_known_domain() {
        let schema = kyc_schema();
        assert_eq!(schema.entities.len(), 2);
        assert!(schema.entities.iter().any(|e| e.name == "natural_person"));
        assert!(!schema.hn_types.is_empty());
    }

    #[test]
    fn test_load_schema_unknown_domain_lists_available() {
        let err = load_schema("not-a-real-domain", &schemas_dir())
            .err()
            .unwrap();
        assert!(err.contains("not-a-real-domain"));
        assert!(err.contains("kyc"));
    }

    #[test]
    fn test_load_schema_case_sensitive() {
        // Windows filesystems are case-insensitive; load_schema must still
        // reject "KYC" so run hashes stay consistent across OSes.
        let err = load_schema("KYC", &schemas_dir()).err().unwrap();
        assert!(err.contains("KYC"));
    }

    #[test]
    fn test_build_pipeline_config_basic() {
        let schema = kyc_schema();
        let config = build_pipeline_config(
            "kyc", 1000, 42, "medium", 0.1, 0.3, &schema, "kyc_test", "parquet", false, "parquet",
            None,
        )
        .expect("build config");
        assert_eq!(config.domain, "kyc");
        assert_eq!(config.size, 1000);
        assert_eq!(config.entity_plans.len(), 2);
        // Every entity must get at least the floor of 2 base records.
        assert!(config.entity_plans.iter().all(|p| p.n_base >= 2));
        assert!(!config.hard_neg_types.is_empty());
    }

    #[test]
    fn test_build_pipeline_config_rejects_size_below_10() {
        let schema = kyc_schema();
        let err = build_pipeline_config(
            "kyc", 5, 42, "medium", 0.1, 0.3, &schema, "kyc_test", "parquet", false, "parquet",
            None,
        )
        .unwrap_err();
        assert!(err.contains("size must be >= 10"));
    }

    #[test]
    fn test_build_pipeline_config_rejects_invalid_singleton_fraction() {
        let schema = kyc_schema();
        let err = build_pipeline_config(
            "kyc", 1000, 42, "medium", 0.1, 1.5, &schema, "kyc_test", "parquet", false, "parquet",
            None,
        )
        .unwrap_err();
        assert!(err.contains("singleton_master_fraction"));
    }

    #[test]
    fn test_build_pipeline_config_deterministic() {
        let schema = kyc_schema();
        let build = || {
            build_pipeline_config(
                "kyc", 1000, 42, "hell", 0.1, 0.2, &schema, "kyc_test", "parquet", false,
                "parquet", None,
            )
            .expect("build config")
        };
        let a = build();
        let b = build();
        assert_eq!(a.entity_plans.len(), b.entity_plans.len());
        for (pa, pb) in a.entity_plans.iter().zip(b.entity_plans.iter()) {
            assert_eq!(pa.n_base, pb.n_base);
            assert_eq!(pa.noise_types.len(), pb.noise_types.len());
        }
    }

    /// No-FK case (BUGS.md-style regression target, kyc's two entities
    /// aren't FK-linked): `only_entity` should produce exactly one entity
    /// plan, sized to the full `size`, with no pool-only entities appended.
    #[test]
    fn test_build_pipeline_config_only_entity_no_fk() {
        let schema = kyc_schema();
        let config = build_pipeline_config(
            "kyc",
            1000,
            42,
            "medium",
            0.1,
            0.3,
            &schema,
            "kyc_test",
            "parquet",
            false,
            "parquet",
            Some("natural_person"),
        )
        .expect("build config");
        assert_eq!(config.entity_plans.len(), 1);
        let plan = &config.entity_plans[0];
        assert_eq!(plan.name, "natural_person");
        assert!(!plan.pool_only);
        // With only one active entity, all of `total_unique` (there's no
        // weight split to share it with `legal_entity`) lands on it —
        // comfortably more than the usual weight-shared slice would be.
        assert!(plan.n_base > 100);
        assert!(
            config
                .hard_neg_types
                .iter()
                .all(|hn| hn.entity_type == "natural_person")
        );
    }

    /// FK case: aviation's `passenger` entity has no direct `fk_remaps` of
    /// its own (verified against `schemas/aviation.json`), so `only_entity`
    /// on it should still produce a single plan and no pool-only entities.
    /// `flight`, which DOES reference `airline`/`aircraft`, is the case
    /// that appends pool-only plans — covered by asserting the mechanism
    /// generically below via `aircraft` (references `airline`).
    #[test]
    fn test_build_pipeline_config_only_entity_with_fk_pool() {
        let schema = aviation_schema();
        let config = build_pipeline_config(
            "aviation",
            10_000,
            42,
            "medium",
            0.1,
            0.3,
            &schema,
            "aviation_test",
            "parquet",
            false,
            "parquet",
            Some("aircraft"),
        )
        .expect("build config");
        // aircraft (target, written) + airline (pool-only, FK target).
        assert_eq!(config.entity_plans.len(), 2);
        let target = config
            .entity_plans
            .iter()
            .find(|p| p.name == "aircraft")
            .expect("aircraft plan present");
        assert!(!target.pool_only);
        assert!(target.n_base > 1_000);
        let pool = config
            .entity_plans
            .iter()
            .find(|p| p.name == "airline")
            .expect("airline pool-only plan present");
        assert!(pool.pool_only);
        assert!(pool.noise_types.is_empty());
        // Pool-only entity is capped, not sized to the full run.
        assert!(pool.n_base <= crate::pipeline::FK_POOL_CAP);
    }

    #[test]
    fn test_build_pipeline_config_only_entity_unknown_name() {
        let schema = kyc_schema();
        let err = build_pipeline_config(
            "kyc",
            1000,
            42,
            "medium",
            0.1,
            0.3,
            &schema,
            "kyc_test",
            "parquet",
            false,
            "parquet",
            Some("not_a_real_entity"),
        )
        .unwrap_err();
        assert!(err.contains("not_a_real_entity"));
        assert!(err.contains("natural_person"));
    }

    #[test]
    fn test_deterministic_run_id_stable_and_sensitive() {
        let a = deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, None);
        let b = deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, None);
        assert_eq!(a, b);
        let c = deterministic_run_id("kyc", 1000, 43, "medium", 0.1, 0.3, "en", None, None);
        assert_ne!(a, c);
    }

    /// Regression: BUGS.md C14/C15 — `singleton_master_fraction` and
    /// `locale` weren't hashed into the run ID, so two runs differing only
    /// in one of these parameters (but producing genuinely different data)
    /// got the exact same output filename, silently overwriting each other.
    #[test]
    fn test_deterministic_run_id_sensitive_to_singleton_fraction_and_locale() {
        let base = deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, None);
        let diff_fraction =
            deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.5, "en", None, None);
        let diff_locale =
            deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "fr", None, None);
        assert_ne!(base, diff_fraction);
        assert_ne!(base, diff_locale);
        assert_ne!(diff_fraction, diff_locale);
    }

    /// Regression guard for the `only_entity` hash input added alongside
    /// `--only-entity`: two runs differing only in which entity is targeted
    /// must not collide on the same run id (same class of bug as C14/C15).
    #[test]
    fn test_deterministic_run_id_sensitive_to_only_entity() {
        let base = deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, None);
        let only_a = deterministic_run_id(
            "kyc",
            1000,
            42,
            "medium",
            0.1,
            0.3,
            "en",
            Some("natural_person"),
            None,
        );
        let only_b = deterministic_run_id(
            "kyc",
            1000,
            42,
            "medium",
            0.1,
            0.3,
            "en",
            Some("legal_entity"),
            None,
        );
        assert_ne!(base, only_a);
        assert_ne!(base, only_b);
        assert_ne!(only_a, only_b);
    }

    /// Regression guard for the `chunk_size` hash input added alongside
    /// `--chunk-size`: two runs with the same total size but a different
    /// chunking must not collide on the same run id, since the per-chunk
    /// seed sequence actually used internally differs (same class of bug
    /// as C14/C15).
    #[test]
    fn test_deterministic_run_id_sensitive_to_chunk_size() {
        let base = deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, None);
        let chunked_a =
            deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, Some(500));
        let chunked_b =
            deterministic_run_id("kyc", 1000, 42, "medium", 0.1, 0.3, "en", None, Some(250));
        assert_ne!(base, chunked_a);
        assert_ne!(base, chunked_b);
        assert_ne!(chunked_a, chunked_b);
    }

    #[test]
    fn test_default_singleton_master_fraction_known_and_unknown() {
        assert_eq!(default_singleton_master_fraction("light"), 0.50);
        assert_eq!(default_singleton_master_fraction("hell"), 0.10);
        // Unknown difficulty falls back to "medium".
        assert_eq!(
            default_singleton_master_fraction("bogus"),
            default_singleton_master_fraction("medium")
        );
    }
}