runcard 0.1.1

//! The read models: the seven card kinds folded into tables in the same file as the log.
//!
//! # Why the fold is here and not in Teal
//!
//! eventsdb's projection contract is that applying an event and moving the consumer's
//! cursor happen inside **one** transaction — which is only expressible if the fold writes
//! through the transaction the log is being read on. That transaction is a Rust value with
//! a lifetime; there is no way to hand it to Lua and no way to let a Lua error unwind
//! through it. So the fold is mechanism, and it sits beside the append it mirrors.
//!
//! What stays policy is everything above the tables: which of them a query touches, what a
//! card may be filtered on, how a refusal is worded. `src/cardbox/find.tl` is that half,
//! and it reaches these tables through the store's read-only SQL hatch.
//!
//! # The name is the version
//!
//! [`CardsProjection::NAME`] is `cards_v4`, and the suffix is the migration convention
//! rather than decoration: a projection's name **is** the primary key of its checkpoint,
//! so a shape change old rows cannot be carried into is done by renaming the projection.
//! The new name has no checkpoint, so it starts at the beginning of the log and folds all
//! of it, and nothing has to reason about which of the old rows were still right.
//! `rebuild()` on the same name is the other route — empty and replay — which is what a
//! changed fold over unchanged tables wants.
//!
//! `cards_v1` was this model without the two alias kinds and without `cb_aliases` /
//! `cb_alias_log`; `cards_v2` was it without `cards_pruned`, so a database folded by that
//! build holds rows for cards a journal event has since removed; `cards_v3` was it before
//! a card carried `params`, a `model` and a run identity in `cb_cards`, a `source` on each
//! eval, and tags in `cb_tags`. [`crate::Store::open`] carries a database written under
//! any retired name forward; what it does and what it cannot do is documented there.
//!
//! Where this departs from the textbook (Marten's "build the new model beside the old one
//! and switch when it has caught up"): the two versions here share the `cb_*` table names,
//! so the old model does not survive the migration. There is nothing to serve it to. This
//! store is one process that opens the file, folds and answers; a window in which two read
//! models are both live is a thing a service needs and a library embedded in its only
//! reader does not.
//!
//! # The `cb_` prefix
//!
//! Every table here is `cb_`-prefixed because it shares a file with eventsdb's own —
//! `events`, `stream_seq`, `checkpoints`, `retention`, `exports`. Those names are reserved:
//! the transaction handed to `apply` refuses writes to them (and refuses creating anything
//! that would shadow one), so a collision is not a silent overwrite. The prefix is what
//! keeps the refusal from ever being the thing that tells us.

use eventsdb::sqlite::Projection;
use eventsdb::sqlite::rusqlite::{self, OptionalExtension, Transaction};
use eventsdb::{Error, Result};
use serde_json::Value as Json;

/// The stream prefix a card's events live under: `card-<id>`.
pub const STREAM_PREFIX: &str = "card-";

/// The stream prefix an alias's events live under: `alias-<name>`.
pub const ALIAS_PREFIX: &str = "alias-";

/// The one stream the prune journal lives on.
///
/// Not a prefix and not per card: it is the log of every removal there has been, in order,
/// and it is the one stream retention never takes — which is what makes it the pointer
/// event the removed history leaves behind. What went, when, why, and where the export
/// that vouched for it is.
pub const PRUNE_STREAM: &str = "prune";

/// The read model over a card's seven kinds and an alias's two.
///
/// Stateless apart from the name it answers to: everything it knows is in the tables,
/// which is what makes a rebuild a replay rather than a reconstruction of anything held
/// here.
pub struct CardsProjection {
    name: String,
}

impl Default for CardsProjection {
    fn default() -> Self {
        CardsProjection::new()
    }
}

impl CardsProjection {
    /// The consumer name, and so the identity of the cursor. See the module doc for what
    /// the `_v4` is for.
    pub const NAME: &'static str = "cards_v4";

    /// The projection this build folds under.
    pub fn new() -> CardsProjection {
        CardsProjection {
            name: CardsProjection::NAME.to_string(),
        }
    }

    /// The same fold under some other cursor.
    ///
    /// Only the migration test, and only to write a database whose checkpoint is under a
    /// name this build has retired — which is the one thing about an older store that
    /// `Store::open` has to handle and that nothing else can produce in-process. The
    /// tables it creates are this version's, so what the test reproduces is the *cursor*
    /// of the old build and not its schema; the rest of the old schema is a subset of
    /// this one, so `init` on the way in would have added the difference anyway.
    #[cfg(test)]
    pub fn under(name: &str) -> CardsProjection {
        CardsProjection {
            name: name.to_string(),
        }
    }

    /// The kinds these streams carry. Naming them is not only a filter: it is what lets
    /// the runner read through the `(kind, position)` index instead of walking the whole
    /// log, and it is the reason `apply` may treat an unknown kind as a bug.
    pub const KINDS: [&'static str; 10] = [
        "card_opened",
        "samples_appended",
        "eval_recorded",
        "checkpoint_saved",
        "card_closed",
        "tag_set",
        "tag_unset",
        "alias_bound",
        "alias_released",
        "cards_pruned",
    ];
}

/// The tables, and the indexes the three questions `find` actually asks need: which cards
/// are in this pkg, which are in this state, which are the newest, and who descends from
/// this one.
///
/// `cb_aliases` is the *current* binding, one row per name, and `cb_alias_log` is every
/// binding there has been. The first is a fold that forgets — a rebind overwrites the row,
/// a release deletes it — and the second is the fold that does not, which is what makes
/// "what did this alias point at in March" a question with an answer. Neither is the
/// authority: `alias-<name>` in the log is, and both of these are replayed out of it.
///
/// `cb_cards` carries `stats` and `cost` twice — once as the JSON that was written, once
/// flattened into columns. The JSON is what `get` hands back unchanged, so a card reads the
/// same whatever a run chose to put in there; the columns are what a `WHERE mean_score >
/// 0.5` compares without `json_extract` on every row. A key the writer left out is NULL,
/// and NULL compares false, which is the answer a filter on a card that never recorded a
/// score should give.
///
/// `params_json` is the same arrangement for what a run was *given*: the JSON as the open
/// wrote it, for `get`, and beside it the four scalars the open put in its `meta` —
/// `model`, `trace_id`, `work_url`, `fingerprint` — as columns, because those are what a
/// reader asks by ("every card of this model", "the run that trace belongs to") and what a
/// fingerprint is for is being compared. Anything else inside `params` is reached with
/// `json_extract`, which is what `find`'s `params.<path>` clauses expand to; a key that
/// turns out to be asked for on every query is promoted to a column the way these four
/// were, under a new projection name.
///
/// `cb_tags` is the one table here keyed by something a writer chose: a tag is a label a
/// person or a schedule puts on a card after the fact, and the set of keys is nobody's to
/// declare in advance. The current value is one row per `(card, key)` that `tag_set`
/// overwrites and `tag_unset` deletes; the history is the card's stream.
const CREATE: &str = "\
CREATE TABLE IF NOT EXISTS cb_cards (
    id               TEXT PRIMARY KEY,
    pkg              TEXT,
    scenario         TEXT,
    source           TEXT,
    created_by       TEXT,
    note             TEXT,
    model            TEXT,
    trace_id         TEXT,
    work_url         TEXT,
    fingerprint      TEXT,
    params_json      TEXT,
    state            TEXT NOT NULL,
    opened_ms        INTEGER,
    closed_ms        INTEGER,
    opened_position  INTEGER,
    error            TEXT,
    stats_json       TEXT,
    cost_json        TEXT,
    mean_score       REAL,
    n                INTEGER,
    pass_rate        REAL,
    passed           INTEGER,
    elapsed_ms       INTEGER,
    llm_calls        INTEGER,
    sample_batches   INTEGER NOT NULL DEFAULT 0,
    sample_rows      INTEGER NOT NULL DEFAULT 0,
    eval_count       INTEGER NOT NULL DEFAULT 0,
    checkpoint_count INTEGER NOT NULL DEFAULT 0
);
CREATE INDEX IF NOT EXISTS cb_cards_pkg       ON cb_cards (pkg);
CREATE INDEX IF NOT EXISTS cb_cards_state     ON cb_cards (state);
CREATE INDEX IF NOT EXISTS cb_cards_opened_ms ON cb_cards (opened_ms);
CREATE INDEX IF NOT EXISTS cb_cards_model     ON cb_cards (model);
CREATE INDEX IF NOT EXISTS cb_cards_trace     ON cb_cards (trace_id);
CREATE INDEX IF NOT EXISTS cb_cards_print     ON cb_cards (fingerprint);

CREATE TABLE IF NOT EXISTS cb_samples (
    card_id   TEXT    NOT NULL,
    seq       INTEGER NOT NULL,
    n         INTEGER,
    rows_json TEXT,
    blob      TEXT,
    size      INTEGER,
    epoch_ms  INTEGER,
    PRIMARY KEY (card_id, seq)
);

CREATE TABLE IF NOT EXISTS cb_evals (
    card_id   TEXT    NOT NULL,
    seq       INTEGER NOT NULL,
    source    TEXT,
    data_json TEXT,
    epoch_ms  INTEGER,
    PRIMARY KEY (card_id, seq)
);

CREATE TABLE IF NOT EXISTS cb_tags (
    card_id  TEXT NOT NULL,
    key      TEXT NOT NULL,
    value    TEXT NOT NULL,
    set_ms   INTEGER,
    PRIMARY KEY (card_id, key)
);
CREATE INDEX IF NOT EXISTS cb_tags_key ON cb_tags (key, value);

CREATE TABLE IF NOT EXISTS cb_checkpoints (
    card_id  TEXT    NOT NULL,
    seq      INTEGER NOT NULL,
    blob     TEXT,
    size     INTEGER,
    format   TEXT,
    note     TEXT,
    epoch_ms INTEGER,
    PRIMARY KEY (card_id, seq)
);

CREATE TABLE IF NOT EXISTS cb_lineage (
    child  TEXT NOT NULL,
    parent TEXT NOT NULL,
    PRIMARY KEY (child, parent)
);
CREATE INDEX IF NOT EXISTS cb_lineage_parent ON cb_lineage (parent);

CREATE TABLE IF NOT EXISTS cb_blobs (
    hash TEXT PRIMARY KEY,
    size INTEGER,
    refs INTEGER NOT NULL DEFAULT 0
);

CREATE TABLE IF NOT EXISTS cb_aliases (
    name     TEXT PRIMARY KEY,
    card_id  TEXT NOT NULL,
    pkg      TEXT,
    bound_ms INTEGER,
    note     TEXT
);
CREATE INDEX IF NOT EXISTS cb_aliases_card ON cb_aliases (card_id);

CREATE TABLE IF NOT EXISTS cb_alias_log (
    name     TEXT    NOT NULL,
    seq      INTEGER NOT NULL,
    kind     TEXT    NOT NULL,
    card_id  TEXT,
    epoch_ms INTEGER,
    note     TEXT,
    PRIMARY KEY (name, seq)
);
";

/// What `reset` undoes. Dropping a table takes its indexes with it, so they are not listed.
const DROP: &str = "\
DROP TABLE IF EXISTS cb_cards;
DROP TABLE IF EXISTS cb_samples;
DROP TABLE IF EXISTS cb_evals;
DROP TABLE IF EXISTS cb_tags;
DROP TABLE IF EXISTS cb_checkpoints;
DROP TABLE IF EXISTS cb_lineage;
DROP TABLE IF EXISTS cb_blobs;
DROP TABLE IF EXISTS cb_aliases;
DROP TABLE IF EXISTS cb_alias_log;
";

impl Projection for CardsProjection {
    fn name(&self) -> &str {
        &self.name
    }

    fn kinds(&self) -> Option<Vec<String>> {
        Some(
            CardsProjection::KINDS
                .iter()
                .map(|k| k.to_string())
                .collect(),
        )
    }

    /// Create the tables — after dropping them, when the ones there predate this shape.
    ///
    /// `CREATE TABLE IF NOT EXISTS` leaves an existing table as it is, so a `cb_cards`
    /// written by an older build has no `params_json`, and the `CREATE INDEX` on `model`
    /// that follows would fail on every open — which is what `cardbox version` did on a
    /// store a `cards_v3` build had created. The tables are a fold of the log and nothing
    /// else, so an outdated one is dropped and folded again; [`crate::Store::open`] runs
    /// the rebuild, having asked [`shape_outdated`] the same question before this ran.
    fn init(&mut self, tx: &Transaction<'_>) -> Result<()> {
        if shape_outdated(tx)? {
            tx.execute_batch(DROP).map_err(storage)?;
        }
        tx.execute_batch(CREATE).map_err(storage)
    }

    fn reset(&mut self, tx: &Transaction<'_>) -> Result<()> {
        tx.execute_batch(DROP).map_err(storage)
    }

    /// One event, folded.
    ///
    /// The card's id comes from the **stream name** rather than from `meta`: the stream is
    /// what the store's own decisions fold over, so it is the identity the invariants are
    /// already stated in terms of, and a `meta` that disagreed with it would describe a
    /// card that no `append_if` was ever protecting. An event of one of these kinds on a
    /// stream that is not a card's is a bug in whatever wrote it, and is reported rather
    /// than skipped.
    ///
    /// An unknown kind is likewise an error. `kinds()` is what the runner filters on, so
    /// one arriving here means the filter and this match have drifted apart, and a fold
    /// that quietly ignored it would leave a read model missing rows with nothing saying so.
    /// **Yes — and only because every removal announces itself first.**
    ///
    /// The default is `false`, and for an accumulating model the default is the right
    /// answer: `sample_rows`, `eval_count` and `cb_blobs.refs` are running totals, and a
    /// replay over a log missing part of its input produces a smaller number with nothing
    /// about it saying so. What makes this model different is the shape of the only
    /// removal it allows.
    ///
    /// A prune is `retain(Plan::Streams, ..)` over whole `card-<id>` streams, and a
    /// `cards_pruned` event on [`PRUNE_STREAM`] is appended **before** it — that stream is
    /// never itself retained, so the journal survives what it describes. On a rebuild the
    /// pruned cards' events are gone, so no row is ever created for them and no counter
    /// ever incremented; the journal event then replays over an absent card and
    /// [`purge`] returns without touching anything. The totals come out the same as they
    /// were, because the events that would have moved them and the event that moved them
    /// back are both absent.
    ///
    /// That is the whole of the claim, and it is narrow on purpose: it holds for a
    /// removal of whole card streams that a journal event announced, and it would not
    /// hold for a bare [`eventsdb::sqlite::Plan::Before`] or `OlderThan` over this log.
    /// Neither is reachable — [`crate::Store`] exposes `retain_streams` and nothing else.
    fn tolerates_truncation(&self) -> bool {
        true
    }

    fn apply(&mut self, tx: &Transaction<'_>, event: &eventsdb::Recorded) -> Result<()> {
        let kind = event.kind();
        let seq = event.seq() as i64;
        let position = event.position.get() as i64;
        let epoch_ms = num(event.event.get("epoch_ms")).unwrap_or(0);
        let meta = event.event.get("meta");
        let data = event.event.get("data");

        // Two stream shapes, so the kind picks the prefix before anything is stripped: an
        // `alias_bound` is on `alias-<name>` and a `card_opened` on `card-<id>`, and
        // asking either name to yield the other's identity is how a fold would quietly
        // file an alias under a card.
        match kind {
            "card_opened" => opened(
                tx,
                card_id(&event.stream, kind)?,
                epoch_ms,
                position,
                meta,
                data,
            ),
            "samples_appended" => samples(tx, card_id(&event.stream, kind)?, seq, epoch_ms, data),
            "eval_recorded" => eval(tx, card_id(&event.stream, kind)?, seq, epoch_ms, meta, data),
            "tag_set" => tag_set(tx, card_id(&event.stream, kind)?, epoch_ms, meta),
            "tag_unset" => tag_unset(tx, card_id(&event.stream, kind)?, meta),
            "checkpoint_saved" => {
                checkpoint(tx, card_id(&event.stream, kind)?, seq, epoch_ms, data)
            }
            "card_closed" => closed(tx, card_id(&event.stream, kind)?, epoch_ms, meta, data),
            "alias_bound" => bound(
                tx,
                alias_name(&event.stream, kind)?,
                seq,
                epoch_ms,
                meta,
                data,
            ),
            "alias_released" => released(
                tx,
                alias_name(&event.stream, kind)?,
                seq,
                epoch_ms,
                meta,
                data,
            ),
            "cards_pruned" => {
                on_prune_stream(&event.stream, kind)?;
                pruned(tx, data)
            }
            other => Err(Error::storage(format!(
                "the {} projection was handed a {other:?} event, which is not one of the \
                 kinds it asked for ({})",
                self.name,
                CardsProjection::KINDS.join(", ")
            ))),
        }
    }
}

/// One column per table that a build before this shape did not have. A table that
/// exists without it was written by that build.
///
/// `cb_cards.params_json` arrived with `cards_v4`, and so did `cb_evals.source`; a table
/// added whole (`cb_tags`) needs no entry, `CREATE TABLE IF NOT EXISTS` adds it.
pub const SHAPE_MARKS: [(&str, &str); 2] = [("cb_cards", "params_json"), ("cb_evals", "source")];

/// The SQL that asks whether `table` carries `column`, for the hatch and for `init`.
pub fn shape_probe(table: &str) -> String {
    format!("PRAGMA table_info({table})")
}

/// Whether the `cb_*` tables in this database predate [`SHAPE_MARKS`].
///
/// Read inside the transaction `init` runs in, so the drop that follows a `true` and the
/// create after it are one change.
pub fn shape_outdated(tx: &Transaction<'_>) -> Result<bool> {
    for (table, column) in SHAPE_MARKS {
        let mut stmt = tx.prepare(&shape_probe(table)).map_err(storage)?;
        let names = stmt
            .query_map([], |row| row.get::<_, String>(1))
            .map_err(storage)?
            .collect::<rusqlite::Result<Vec<String>>>()
            .map_err(storage)?;
        if !names.is_empty() && !names.iter().any(|n| n == column) {
            return Ok(true);
        }
    }
    Ok(false)
}

/// `card-<id>` → `<id>`.
fn card_id<'a>(stream: &'a str, kind: &str) -> Result<&'a str> {
    stream.strip_prefix(STREAM_PREFIX).ok_or_else(|| {
        Error::storage(format!(
            "a {kind:?} event is on stream {stream:?}, which is not a card's: \
             a card's stream is {STREAM_PREFIX}<id>"
        ))
    })
}

/// `alias-<name>` → `<name>`.
///
/// The alias's name comes from the stream for the same reason a card's id does: the
/// stream is what the store's decision folds over, so it is the identity the invariant is
/// already stated in terms of. A `meta.name` that disagreed with it would name a
/// reservation nobody was holding.
fn alias_name<'a>(stream: &'a str, kind: &str) -> Result<&'a str> {
    stream.strip_prefix(ALIAS_PREFIX).ok_or_else(|| {
        Error::storage(format!(
            "a {kind:?} event is on stream {stream:?}, which is not an alias's: \
             an alias's stream is {ALIAS_PREFIX}<name>"
        ))
    })
}

/// The row a card starts as.
///
/// `ON CONFLICT DO NOTHING`: a stream carries one `card_opened` because `append_if`'s
/// `unwritten` decision is what `cards.open` writes under, and only a raw `store:append`
/// could produce a second. If one is there anyway, the first open stays the card's opening
/// — the alternative is an error that would refuse every later read of the whole model,
/// including the rebuild that would be the way out of it.
fn opened(
    tx: &Transaction<'_>,
    id: &str,
    epoch_ms: i64,
    position: i64,
    meta: Option<&Json>,
    data: Option<&Json>,
) -> Result<()> {
    let params = data.and_then(|d| d.get("params"));
    tx.execute(
        "INSERT INTO cb_cards (id, pkg, scenario, source, created_by, note,
                               model, trace_id, work_url, fingerprint, params_json,
                               state, opened_ms, opened_position)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, 'open', ?12, ?13)
         ON CONFLICT (id) DO NOTHING",
        rusqlite::params![
            id,
            text(meta, "pkg"),
            text(meta, "scenario"),
            text(meta, "source"),
            text(meta, "created_by"),
            text(data, "note"),
            text(meta, "model"),
            text(meta, "trace_id"),
            text(meta, "work_url"),
            text(meta, "fingerprint"),
            params.map(Json::to_string),
            epoch_ms,
            position,
        ],
    )
    .map_err(storage)?;

    // `data.parents` is an array when a run named one and an empty *object* when it named
    // none — Lua cannot tell `{}` from `[]`, and the host resolves that in the one
    // direction that round-trips a cleared record. `as_array` answering `None` for the
    // object is therefore the same answer as an empty list, which is what this wants.
    let parents = data.and_then(|d| d.get("parents")).and_then(Json::as_array);
    for parent in parents.into_iter().flatten() {
        let Some(parent) = parent.as_str() else {
            continue;
        };
        tx.execute(
            "INSERT INTO cb_lineage (child, parent) VALUES (?1, ?2)
             ON CONFLICT (child, parent) DO NOTHING",
            rusqlite::params![id, parent],
        )
        .map_err(storage)?;
    }
    Ok(())
}

fn samples(
    tx: &Transaction<'_>,
    id: &str,
    seq: i64,
    epoch_ms: i64,
    data: Option<&Json>,
) -> Result<()> {
    let n = num(data.and_then(|d| d.get("n")));
    let rows = data
        .and_then(|d| d.get("rows"))
        .map(|rows| rows.to_string());
    let blob = text(data, "blob");
    let size = num(data.and_then(|d| d.get("size")));
    tx.execute(
        "INSERT INTO cb_samples (card_id, seq, n, rows_json, blob, size, epoch_ms)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7)
         ON CONFLICT (card_id, seq) DO NOTHING",
        rusqlite::params![id, seq, n, rows, blob.as_deref(), size, epoch_ms],
    )
    .map_err(storage)?;
    tx.execute(
        "UPDATE cb_cards SET sample_batches = sample_batches + 1,
                             sample_rows = sample_rows + ?2
         WHERE id = ?1",
        rusqlite::params![id, n.unwrap_or(0)],
    )
    .map_err(storage)?;
    if let Some(hash) = blob {
        reference_blob(tx, &hash, size)?;
    }
    Ok(())
}

/// One assessment of a card. `meta.source` says who made it — `code`, `llm_judge` or
/// `human` — and is a column because "every human verdict on this pkg" is a question.
fn eval(
    tx: &Transaction<'_>,
    id: &str,
    seq: i64,
    epoch_ms: i64,
    meta: Option<&Json>,
    data: Option<&Json>,
) -> Result<()> {
    tx.execute(
        "INSERT INTO cb_evals (card_id, seq, source, data_json, epoch_ms)
         VALUES (?1, ?2, ?3, ?4, ?5)
         ON CONFLICT (card_id, seq) DO NOTHING",
        rusqlite::params![
            id,
            seq,
            text(meta, "source"),
            data.map(Json::to_string),
            epoch_ms
        ],
    )
    .map_err(storage)?;
    tx.execute(
        "UPDATE cb_cards SET eval_count = eval_count + 1 WHERE id = ?1",
        rusqlite::params![id],
    )
    .map_err(storage)?;
    Ok(())
}

fn checkpoint(
    tx: &Transaction<'_>,
    id: &str,
    seq: i64,
    epoch_ms: i64,
    data: Option<&Json>,
) -> Result<()> {
    let blob = text(data, "blob");
    let size = num(data.and_then(|d| d.get("size")));
    tx.execute(
        "INSERT INTO cb_checkpoints (card_id, seq, blob, size, format, note, epoch_ms)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7)
         ON CONFLICT (card_id, seq) DO NOTHING",
        rusqlite::params![
            id,
            seq,
            blob.as_deref(),
            size,
            text(data, "format"),
            text(data, "note"),
            epoch_ms,
        ],
    )
    .map_err(storage)?;
    tx.execute(
        "UPDATE cb_cards SET checkpoint_count = checkpoint_count + 1 WHERE id = ?1",
        rusqlite::params![id],
    )
    .map_err(storage)?;
    if let Some(hash) = blob {
        reference_blob(tx, &hash, size)?;
    }
    Ok(())
}

/// A label on a card. Last write wins: the row is the current value, and what it replaced
/// is on the stream. A `tag_set` without a key or a value is a write that went around
/// `cards.tag`, and is reported rather than filed as a row with nothing in it.
fn tag_set(tx: &Transaction<'_>, id: &str, epoch_ms: i64, meta: Option<&Json>) -> Result<()> {
    let (Some(key), Some(value)) = (text(meta, "key"), text(meta, "value")) else {
        return Err(Error::storage(format!(
            "a tag_set on {STREAM_PREFIX}{id} carries no meta.key and meta.value"
        )));
    };
    tx.execute(
        "INSERT INTO cb_tags (card_id, key, value, set_ms) VALUES (?1, ?2, ?3, ?4)
         ON CONFLICT (card_id, key) DO UPDATE SET value = excluded.value,
                                                  set_ms = excluded.set_ms",
        rusqlite::params![id, key, value, epoch_ms],
    )
    .map_err(storage)?;
    Ok(())
}

/// The label is gone. Unsetting a key that was never set is nothing to do, not an error:
/// the event says the card does not carry the key, and it does not.
fn tag_unset(tx: &Transaction<'_>, id: &str, meta: Option<&Json>) -> Result<()> {
    let Some(key) = text(meta, "key") else {
        return Err(Error::storage(format!(
            "a tag_unset on {STREAM_PREFIX}{id} carries no meta.key"
        )));
    };
    tx.execute(
        "DELETE FROM cb_tags WHERE card_id = ?1 AND key = ?2",
        rusqlite::params![id, key],
    )
    .map_err(storage)?;
    Ok(())
}

/// How a card ends: the state, the JSON as written, and the handful of numbers flattened
/// out of it so a filter can compare them.
fn closed(
    tx: &Transaction<'_>,
    id: &str,
    epoch_ms: i64,
    meta: Option<&Json>,
    data: Option<&Json>,
) -> Result<()> {
    let state = match text(meta, "outcome").as_deref() {
        Some("ok") => "closed_ok",
        _ => "closed_failed",
    };
    let stats = data.and_then(|d| d.get("stats"));
    let cost = data.and_then(|d| d.get("cost"));
    tx.execute(
        "UPDATE cb_cards SET state = ?2, closed_ms = ?3, error = ?4,
                             stats_json = ?5, cost_json = ?6,
                             mean_score = ?7, n = ?8, pass_rate = ?9, passed = ?10,
                             elapsed_ms = ?11, llm_calls = ?12
         WHERE id = ?1",
        rusqlite::params![
            id,
            state,
            epoch_ms,
            text(data, "error"),
            stats.map(Json::to_string),
            cost.map(Json::to_string),
            real(stats.and_then(|s| s.get("mean_score"))),
            num(stats.and_then(|s| s.get("n"))),
            real(stats.and_then(|s| s.get("pass_rate"))),
            num(stats.and_then(|s| s.get("passed"))),
            num(cost.and_then(|c| c.get("elapsed_ms"))),
            num(cost.and_then(|c| c.get("llm_calls"))),
        ],
    )
    .map_err(storage)?;
    Ok(())
}

/// An alias now points here.
///
/// The current binding is one row that the rebind overwrites, because "what does this
/// name mean" has one answer and a table with two rows for it would need a reader to know
/// which. What the overwrite would lose goes to `cb_alias_log` first, which keeps every
/// one of them.
fn bound(
    tx: &Transaction<'_>,
    name: &str,
    seq: i64,
    epoch_ms: i64,
    meta: Option<&Json>,
    data: Option<&Json>,
) -> Result<()> {
    let card_id = text(meta, "card_id");
    let note = text(data, "note");
    alias_logged(
        tx,
        name,
        seq,
        "alias_bound",
        card_id.as_deref(),
        epoch_ms,
        note.as_deref(),
    )?;
    // An `alias_bound` with no `card_id` is a binding to nothing, which the store cannot
    // write: `bind_alias` reads the card before the append and puts its id in the meta.
    // One arriving here anyway is reported rather than filed as a row pointing nowhere.
    let Some(card_id) = card_id else {
        return Err(Error::storage(format!(
            "an alias_bound on {ALIAS_PREFIX}{name} carries no meta.card_id, \
             so it binds the name to nothing"
        )));
    };
    tx.execute(
        "INSERT INTO cb_aliases (name, card_id, pkg, bound_ms, note) VALUES (?1, ?2, ?3, ?4, ?5)
         ON CONFLICT (name) DO UPDATE SET card_id = excluded.card_id, pkg = excluded.pkg,
                                          bound_ms = excluded.bound_ms, note = excluded.note",
        rusqlite::params![name, card_id, text(meta, "pkg"), epoch_ms, note],
    )
    .map_err(storage)?;
    Ok(())
}

/// The name points at nothing again. The row goes; the history does not.
fn released(
    tx: &Transaction<'_>,
    name: &str,
    seq: i64,
    epoch_ms: i64,
    meta: Option<&Json>,
    data: Option<&Json>,
) -> Result<()> {
    alias_logged(
        tx,
        name,
        seq,
        "alias_released",
        text(meta, "card_id").as_deref(),
        epoch_ms,
        text(data, "note").as_deref(),
    )?;
    tx.execute(
        "DELETE FROM cb_aliases WHERE name = ?1",
        rusqlite::params![name],
    )
    .map_err(storage)?;
    Ok(())
}

/// One line of an alias's history, keyed by the seq it has on its own stream.
fn alias_logged(
    tx: &Transaction<'_>,
    name: &str,
    seq: i64,
    kind: &str,
    card_id: Option<&str>,
    epoch_ms: i64,
    note: Option<&str>,
) -> Result<()> {
    tx.execute(
        "INSERT INTO cb_alias_log (name, seq, kind, card_id, epoch_ms, note)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6)
         ON CONFLICT (name, seq) DO NOTHING",
        rusqlite::params![name, seq, kind, card_id, epoch_ms, note],
    )
    .map_err(storage)?;
    Ok(())
}

/// The journal event's stream has to be the journal's.
///
/// The other two identities in this fold are read *out of* the stream name; this one is
/// checked against a constant, because a `cards_pruned` is about a set of cards named in
/// its own data and the stream carries no identity at all. One anywhere else is a write
/// that went around [`crate::Store::retain_streams`].
fn on_prune_stream(stream: &str, kind: &str) -> Result<()> {
    if stream == PRUNE_STREAM {
        return Ok(());
    }
    Err(Error::storage(format!(
        "a {kind:?} event is on stream {stream:?}: the prune journal is the one stream \
         {PRUNE_STREAM:?}"
    )))
}

/// Cards have gone. Take them out of every table that holds one.
///
/// `data.cards` is the list; anything that is not a string in it is skipped rather than
/// refused, on the same reading `opened` gives a malformed `parents`.
fn pruned(tx: &Transaction<'_>, data: Option<&Json>) -> Result<()> {
    let cards = data.and_then(|d| d.get("cards")).and_then(Json::as_array);
    for card in cards.into_iter().flatten() {
        if let Some(id) = card.as_str() {
            purge(tx, id)?;
        }
    }
    Ok(())
}

/// One card, out of the read models.
///
/// **The first line is what makes a rebuild work.** After the retain, a pruned card has no
/// events, so a replay reaches this event with no row ever having been created — and every
/// delete below, and every `refs` decrement, would then be a second application of a purge
/// the first fold already did. So an absent card is nothing to do. Which is also the
/// honest reading of the event: it says these cards are gone, and one that is not here is.
///
/// The alias check is under that gate rather than over it for the same reason. An aliased
/// card is refused by the policy side (`cards.prune` skips it), so reaching this is a
/// journal event somebody wrote by hand, and it is a fold error — but only while the card
/// is still there to be pointed at. Once its events are gone the question no longer
/// arises, and a rebuild that raised it would be a store that cannot be rebuilt.
fn purge(tx: &Transaction<'_>, id: &str) -> Result<()> {
    let present: Option<i64> = tx
        .query_row(
            "SELECT 1 FROM cb_cards WHERE id = ?1",
            rusqlite::params![id],
            |row| row.get(0),
        )
        .optional()
        .map_err(storage)?;
    if present.is_none() {
        return Ok(());
    }

    let named: Option<String> = tx
        .query_row(
            "SELECT name FROM cb_aliases WHERE card_id = ?1 ORDER BY name LIMIT 1",
            rusqlite::params![id],
            |row| row.get(0),
        )
        .optional()
        .map_err(storage)?;
    if let Some(name) = named {
        return Err(Error::storage(format!(
            "card {id} was pruned while the alias {name:?} still points at it: a card with \
             a name is not prunable, and the name would be left pointing at nothing"
        )));
    }

    // Row by row, and `UNION ALL`, because `refs` counts references and not distinct
    // blobs: two sample batches that happened to hold the same bytes incremented it twice.
    let hashes: Vec<String> = {
        let mut stmt = tx
            .prepare(
                "SELECT blob FROM cb_samples WHERE card_id = ?1 AND blob IS NOT NULL \
                 UNION ALL \
                 SELECT blob FROM cb_checkpoints WHERE card_id = ?1 AND blob IS NOT NULL",
            )
            .map_err(storage)?;
        let rows = stmt
            .query_map(rusqlite::params![id], |row| row.get::<_, String>(0))
            .map_err(storage)?;
        rows.collect::<rusqlite::Result<Vec<String>>>()
            .map_err(storage)?
    };
    for hash in hashes {
        tx.execute(
            "UPDATE cb_blobs SET refs = refs - 1 WHERE hash = ?1",
            rusqlite::params![hash],
        )
        .map_err(storage)?;
    }

    // `cb_lineage` both ways. A pruned card that is somebody's parent is refused by the
    // policy, so the `parent` half normally matches nothing; it is here because an edge
    // naming a card that no longer exists is exactly the dangling row this whole purge is
    // for.
    for sql in [
        "DELETE FROM cb_samples WHERE card_id = ?1",
        "DELETE FROM cb_evals WHERE card_id = ?1",
        "DELETE FROM cb_tags WHERE card_id = ?1",
        "DELETE FROM cb_checkpoints WHERE card_id = ?1",
        "DELETE FROM cb_lineage WHERE child = ?1 OR parent = ?1",
        "DELETE FROM cb_cards WHERE id = ?1",
    ] {
        tx.execute(sql, rusqlite::params![id]).map_err(storage)?;
    }
    Ok(())
}

/// One more thing points at these bytes. The blob GC is the reader: a blob whose `refs`
/// reach 0 after the events naming it are gone is the only one it may remove.
fn reference_blob(tx: &Transaction<'_>, hash: &str, size: Option<i64>) -> Result<()> {
    tx.execute(
        "INSERT INTO cb_blobs (hash, size, refs) VALUES (?1, ?2, 1)
         ON CONFLICT (hash) DO UPDATE SET refs = refs + 1, size = COALESCE(excluded.size, size)",
        rusqlite::params![hash, size],
    )
    .map_err(storage)?;
    Ok(())
}

fn text(object: Option<&Json>, key: &str) -> Option<String> {
    object
        .and_then(|o| o.get(key))
        .and_then(Json::as_str)
        .map(str::to_string)
}

fn num(value: Option<&Json>) -> Option<i64> {
    value.and_then(|v| v.as_i64().or_else(|| v.as_f64().map(|f| f as i64)))
}

fn real(value: Option<&Json>) -> Option<f64> {
    value.and_then(Json::as_f64)
}

fn storage(e: rusqlite::Error) -> Error {
    Error::storage(e.to_string())
}