brokk-mj-controller 2.23.2

use super::*;
use rusqlite::OpenFlags;

const COMPATIBILITY_METADATA_VERSION: i64 = 30;

pub(super) struct SchemaState {
    pub(super) revision: i64,
    minimum_compatible: Option<i64>,
}

impl SchemaState {
    pub(super) fn ensure_supported(&self) -> Result<()> {
        self.ensure_supported_by(SCHEMA_VERSION)
    }

    fn ensure_supported_by(&self, supported: i64) -> Result<()> {
        let reason = if self.revision < supported {
            StoreSchemaMismatchReason::NeedsMigration
        } else if let Some(minimum_compatible) = self.minimum_compatible {
            if minimum_compatible <= supported {
                return Ok(());
            }
            StoreSchemaMismatchReason::Incompatible { minimum_compatible }
        } else {
            StoreSchemaMismatchReason::InvalidCompatibilityMetadata
        };
        Err(StoreSchemaMismatch {
            found: self.revision,
            supported,
            reason,
        }
        .into())
    }
}

/// The revision, ledger, and compatibility floor must describe one snapshot.
/// A missing floor is only legitimate before compatibility was introduced.
pub(super) fn read_schema_state(connection: &Connection) -> Result<SchemaState> {
    let snapshot = connection
        .unchecked_transaction()
        .context("start database compatibility snapshot")?;
    let revision: i64 = snapshot
        .query_row("PRAGMA user_version", [], |row| row.get(0))
        .context("read database migration revision")?;
    let minimum_compatible = if revision >= COMPATIBILITY_METADATA_VERSION {
        let invalid = || StoreSchemaMismatch {
            found: revision,
            supported: SCHEMA_VERSION,
            reason: StoreSchemaMismatchReason::InvalidCompatibilityMetadata,
        };
        let (count, singleton, floor, recorded): (i64, Option<i64>, Option<i64>, Option<i64>) =
            snapshot
                .query_row(
                    "SELECT count(*), min(singleton), min(minimum_compatible_version),
                    (SELECT max(version) FROM schema_migrations)
             FROM schema_compatibility",
                    [],
                    |row| Ok((row.get(0)?, row.get(1)?, row.get(2)?, row.get(3)?)),
                )
                .map_err(|error| {
                    // Missing tables/columns and invalid field types are
                    // structural. Busy, I/O, and interruption errors are not
                    // evidence of an incompatible migration.
                    let structural = match &error {
                        rusqlite::Error::SqliteFailure(code, _) => {
                            code.code == rusqlite::ErrorCode::Unknown
                        }
                        _ => true,
                    };
                    let error = anyhow::Error::new(error);
                    if structural {
                        error.context(invalid())
                    } else {
                        error.context("read database compatibility metadata")
                    }
                })?;
        if count != 1
            || singleton != Some(1)
            || recorded != Some(revision)
            || !floor
                .is_some_and(|floor| (COMPATIBILITY_METADATA_VERSION..=revision).contains(&floor))
        {
            return Err(invalid().into());
        }
        floor
    } else {
        None
    };
    snapshot
        .commit()
        .context("finish database compatibility snapshot")?;
    Ok(SchemaState {
        revision,
        minimum_compatible,
    })
}

pub fn database_path() -> PathBuf {
    data_dir().join("mj.sqlite3")
}

/// Verify that this client can read the daemon's store without creating or
/// migrating it. Startup must pass this gate before handing out a connection,
/// even when an older daemon happens to speak the same wire protocol.
pub fn check_read_compatibility() -> Result<()> {
    open_reader_strict(&database_path()).map(drop)
}

/// A writer-capable connection whose transactions take the WAL write lock at
/// `BEGIN`, where the busy handler applies. A DEFERRED transaction that has
/// already read cannot wait: SQLite only calls the busy handler when the
/// connection holds no transaction, so the upgrade to a write returns
/// `SQLITE_BUSY` at once (issue 1117).
pub(super) fn open_writer(path: &Path) -> Result<Connection> {
    let mut connection = open_writable(path)?;
    connection.set_transaction_behavior(rusqlite::TransactionBehavior::Immediate);
    Ok(connection)
}

fn open_writable(path: &Path) -> Result<Connection> {
    if let Some(parent) = path.parent() {
        fs::create_dir_all(parent)
            .with_context(|| format!("create Mjolnir data directory {}", parent.display()))?;
    }
    let connection = Connection::open(path)
        .with_context(|| format!("open Mjolnir database {}", path.display()))?;
    connection.busy_timeout(Duration::from_secs(5))?;
    connection.execute_batch(
        "PRAGMA foreign_keys = ON;
         PRAGMA journal_mode = WAL;
         PRAGMA synchronous = FULL;",
    )?;
    verify_schema_once(path, &connection)?;
    committed::observe_connection(&connection, path)?;
    Ok(connection)
}

pub(super) fn open(path: &Path) -> Result<Connection> {
    open_writer(path)
}

/// Open an existing database without permitting schema or data mutation.
/// Client processes use this path so an accidental write fails locally
/// instead of competing with the daemon's writer.
#[cfg(not(test))]
pub(super) fn open_reader(path: &Path) -> Result<Connection> {
    open_reader_strict(path)
}

#[cfg(test)]
pub(super) fn open_reader(path: &Path) -> Result<Connection> {
    // Path-taking database helpers are migration fixtures in unit tests: they
    // intentionally open old or not-yet-created schemas. Production query
    // entry points compile against the strict reader above. The connection is
    // writable but keeps SQLite's DEFERRED default, so a fixture read does not
    // take the write lock.
    open_writable(path)
}

#[cfg_attr(test, allow(dead_code))]
fn open_reader_strict(path: &Path) -> Result<Connection> {
    let connection = Connection::open_with_flags(
        path,
        OpenFlags::SQLITE_OPEN_READ_ONLY | OpenFlags::SQLITE_OPEN_NO_MUTEX,
    )
    .with_context(|| format!("open Mjolnir database read-only {}", path.display()))?;
    connection.busy_timeout(Duration::from_secs(5))?;
    connection.execute_batch(
        "PRAGMA foreign_keys = ON;
         PRAGMA query_only = ON;",
    )?;
    read_schema_state(&connection)?.ensure_supported()?;
    Ok(connection)
}

/// Databases this process has already migrated. A controller owns its store
/// exclusively (`ControllerStoreGuard`), so a schema verified once stays
/// verified and later connections skip the migration probes entirely.
fn verified_schemas() -> &'static Mutex<HashSet<PathBuf>> {
    static VERIFIED: OnceLock<Mutex<HashSet<PathBuf>>> = OnceLock::new();
    VERIFIED.get_or_init(|| Mutex::new(HashSet::new()))
}

/// Stable cache identity for a database. The file itself may not exist yet, so
/// the canonicalized parent directory carries the identity.
fn schema_cache_key(path: &Path) -> PathBuf {
    let Some(parent) = path
        .parent()
        .filter(|parent| !parent.as_os_str().is_empty())
    else {
        return path.to_owned();
    };
    match (fs::canonicalize(parent), path.file_name()) {
        (Ok(canonical), Some(name)) => canonical.join(name),
        _ => path.to_owned(),
    }
}

/// Run the migration ladder the first time this process opens a database.
/// Later opens confirm compatibility without repeating schema repairs. A
/// database behind this build is migrated again, so a recreated file under a
/// reused path still converges. Compatible future stores are never repaired.
fn verify_schema_once(path: &Path, connection: &Connection) -> Result<()> {
    let key = schema_cache_key(path);
    let mut verified = verified_schemas()
        .lock()
        .unwrap_or_else(PoisonError::into_inner);
    let state = read_schema_state(connection)?;
    if state.revision > SCHEMA_VERSION
        || (state.revision == SCHEMA_VERSION && verified.contains(&key))
    {
        // An older build must never run its repairs against a newer schema.
        return state.ensure_supported();
    }
    // Holding the lock across the ladder keeps two first opens of the same
    // database from running the additive migration steps against each other.
    migrate_schema(connection)?;
    read_schema_state(connection)?.ensure_supported()?;
    verified.insert(key);
    Ok(())
}

/// Forget that this process verified a database's schema. Only tests need it:
/// they simulate a store written by an older build by editing the schema of a
/// database this process has already opened, which no controller can do.
#[cfg(test)]
pub(super) fn forget_verified_schema(path: &Path) {
    verified_schemas()
        .lock()
        .unwrap_or_else(PoisonError::into_inner)
        .remove(&schema_cache_key(path));
}

/// New stores start at the revision Mjolnir 2.7.2 shipped. Existing stores
/// retain the complete migration path, even when users skip many releases.
const BASELINE_SCHEMA_VERSION: i64 = 33;

/// The compatibility floor a baseline store records. Migration 32 (ZCode) was
/// the last breaking change before the baseline.
const BASELINE_MINIMUM_COMPATIBLE_VERSION: i64 = 32;

fn migrate_schema(connection: &Connection) -> Result<()> {
    let state = read_schema_state(connection)?;
    let version = state.revision;
    if version > SCHEMA_VERSION {
        return state.ensure_supported();
    }
    if version == 0 {
        create_baseline_schema(connection)?;
    } else if version < BASELINE_SCHEMA_VERSION {
        super::legacy_schema::migrate_to_baseline(connection)
            .context("upgrade historical database schema")?;
    }
    // Compatible: adds one table. Older readers ignore it and treat read-write
    // mounts as copy-on-write, a behaviour difference rather than lost data.
    // Older writers rewrite `session_mounts` but never touch this table, so its
    // rows survive their updates; a row only applies while a mount with the same
    // source and destination is still not read-only, so an older build that
    // makes the mount read-only or removes it keeps that choice. The
    // compatibility floor stays where it is.
    if version < 34 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             CREATE TABLE IF NOT EXISTS session_mount_access (
                 session_id TEXT NOT NULL REFERENCES sessions(session_id) ON DELETE CASCADE,
                 source BLOB NOT NULL,
                 destination BLOB NOT NULL,
                 access TEXT NOT NULL CHECK(access IN ('rw')),
                 PRIMARY KEY(session_id, destination)
             ) STRICT;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (34, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 34;
             COMMIT;",
        )?;
    }
    // Compatible: adds one nullable column. Older readers ignore it, and the
    // older writer's session upsert lists columns explicitly, so it preserves
    // the value. An older executable launching such a session uses the shared
    // `/workspace` instead of the recorded per-session path, which is a
    // behaviour difference, not data loss. The compatibility floor stays where
    // it is.
    if version < 35 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             ALTER TABLE sessions ADD COLUMN container_workspace TEXT;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (35, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 35;
             COMMIT;",
        )?;
    }
    // Compatible: adds one nullable column. Older readers ignore it, and the
    // older writer's session upsert lists columns explicitly, so it preserves
    // the value. An older executable launching such a session runs it without
    // the mbx build cache, which is a behaviour difference, not data loss. The
    // compatibility floor stays where it is.
    if version < 36 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             ALTER TABLE sessions ADD COLUMN build_cache_json TEXT;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (36, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 36;
             COMMIT;",
        )?;
    }
    // Compatible: adds one nullable column to `session_targets`. Only a
    // container sub-agent child row ever carries a value, and older builds
    // could never start such a child, so an older update that rewrites the row
    // without the column loses nothing usable. Older readers ignore it. The
    // compatibility floor stays where it is.
    if version < 37 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             ALTER TABLE session_targets ADD COLUMN borrowed_from TEXT;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (37, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 37;
             COMMIT;",
        )?;
    }
    // Compatible: adds one table holding the dashboard's conversation pane
    // arrangement per workspace. Older readers never select from it and older
    // writers never touch it, so their updates leave its rows intact; a
    // workspace deleted by an older build still removes them through the
    // foreign key. Losing the table only means the conversation area opens as
    // a single pane. The compatibility floor stays where it is.
    if version < 38 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             CREATE TABLE IF NOT EXISTS workspace_layouts (
                 workspace_id TEXT PRIMARY KEY REFERENCES workspaces(workspace_id) ON DELETE CASCADE,
                 layout TEXT NOT NULL
             ) STRICT;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (38, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 38;
             COMMIT;",
        )?;
    }
    // Breaking: persisted input_required API events can now omit the structured
    // request. Older readers require it and fail to deserialize the event log;
    // the shared read/write compatibility floor must advance with the revision.
    if version < 39 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             UPDATE schema_compatibility SET minimum_compatible_version = 39 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (39, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 39;
             COMMIT;",
        )?;
    }
    // Breaking: native child projections and relay observations must be preserved
    // by every reader/writer; older builds cannot interpret their lifecycle.
    if version < 40 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             CREATE TABLE native_agents (
                 owner TEXT NOT NULL REFERENCES sessions(session_id) ON DELETE CASCADE,
                 child TEXT NOT NULL,
                 staging INTEGER NOT NULL CHECK(staging IN (0,1)),
                 body TEXT NOT NULL CHECK(json_valid(body)),
                 PRIMARY KEY(owner, child, staging)
             ) STRICT;
             CREATE TABLE native_agent_transcript (
                 owner TEXT NOT NULL,
                 child TEXT NOT NULL,
                 staging INTEGER NOT NULL,
                 stable_id TEXT NOT NULL,
                 position INTEGER NOT NULL,
                 body TEXT NOT NULL CHECK(json_valid(body)),
                 PRIMARY KEY(owner, child, staging, stable_id),
                 FOREIGN KEY(owner, child, staging) REFERENCES native_agents(owner, child, staging)
                     ON DELETE CASCADE ON UPDATE CASCADE
             ) STRICT;
             CREATE INDEX native_agent_transcript_position ON native_agent_transcript(owner, child, staging, position);
             CREATE TABLE native_agent_replay (
                 owner TEXT PRIMARY KEY REFERENCES sessions(session_id) ON DELETE CASCADE
             ) STRICT;
             UPDATE schema_compatibility SET minimum_compatible_version = 40 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (40, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 40;
             COMMIT;",
        )?;
    }
    // Breaking: clear-context relay commands/outcomes are persisted in event
    // JSON. Older readers cannot decode them or honor the context boundary.
    if version < 41 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             UPDATE schema_compatibility SET minimum_compatible_version = 41 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (41, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 41;
             COMMIT;",
        )?;
    }

    // Breaking: older layout writers discard Browse identity and pin badges.
    if version < 42 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             UPDATE schema_compatibility SET minimum_compatible_version = 42 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (42, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 42;
             COMMIT;",
        )?;
    }

    // Breaking: durable steering commands/observations and native availability
    // cannot be interpreted or preserved by older readers and writers.
    if version < 43 {
        connection.execute_batch("BEGIN IMMEDIATE;
            UPDATE schema_compatibility SET minimum_compatible_version = 43 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (43, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 43;
            COMMIT;")?;
    }

    // Breaking: new quota recovery commands in stored relay JSON cannot be
    // read or preserved by older binaries, even though the cache is additive.
    if version < 44 {
        connection.execute_batch("BEGIN IMMEDIATE;
            CREATE TABLE quota_reset_cache (identity TEXT PRIMARY KEY, body TEXT NOT NULL);
            UPDATE schema_compatibility SET minimum_compatible_version = 44 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (44, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 44;
            COMMIT;")?;
    }

    // Compatible: adds one nullable column. Older readers ignore it, and the
    // older writer's session upsert lists columns explicitly, so it preserves
    // the value. An older executable relaunching such a session starts it at
    // HEAD or the remote default branch instead of the recorded revision,
    // which is a behaviour difference, not data loss. The compatibility floor
    // stays where it is.
    if version < 45 {
        // The column is added only when it is absent, the way migration 34
        // creates its table only when absent: a store rolled back to an older
        // revision still carries the column, and a second ALTER would refuse.
        let add_column =
            match super::legacy_schema::table_has_column(connection, "sessions", "launch_base")? {
                true => "",
                false => "ALTER TABLE sessions ADD COLUMN launch_base TEXT;",
            };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (45, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 45;
             COMMIT;"
        ))?;
    }

    // Breaking: older writers can replace a target without updating its saved
    // connection, leaving access metadata attached to the wrong resource.
    // Refuse both older readers and writers before they operate that target.
    if version < 46 {
        let add_column = if super::legacy_schema::table_has_column(
            connection,
            "sessions",
            "target_runtime_json",
        )? {
            ""
        } else {
            "ALTER TABLE sessions ADD COLUMN target_runtime_json TEXT;"
        };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             UPDATE schema_compatibility SET minimum_compatible_version = 46 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (46, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 46;
             COMMIT;"
        ))?;
    }

    // Breaking: the managed checkout JSON can now describe an independent
    // clone. Older readers reject its `kind`, and older writers cannot safely
    // retain that clone's unpublished commits during lifecycle cleanup.
    if version < 47 {
        let add_branch =
            if super::legacy_schema::table_has_column(connection, "sessions", "launch_branch")? {
                ""
            } else {
                "ALTER TABLE sessions ADD COLUMN launch_branch TEXT;"
            };
        let add_publication = if super::legacy_schema::table_has_column(
            connection,
            "sessions",
            "publication_json",
        )? {
            ""
        } else {
            "ALTER TABLE sessions ADD COLUMN publication_json TEXT;"
        };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_branch}
             {add_publication}
             UPDATE schema_compatibility SET minimum_compatible_version = 47 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (47, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 47;
             COMMIT;",
        ))?;
    }

    // Breaking: stored relay JSON can now hold the steering-returned outcome,
    // and stored active-turn JSON the prompt a steer continued, which older
    // readers reject and older writers would drop.
    if version < 48 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             UPDATE schema_compatibility SET minimum_compatible_version = 48 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (48, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 48;
             COMMIT;",
        )?;
    }

    // Breaking: a sub-agent record can now say its child has the `handback`
    // tool, and older readers refuse the unknown field. The reports themselves
    // live in their own table, because a full state save rewrites every
    // sub-agent record from whatever copy the saving controller holds.
    if version < 49 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             CREATE TABLE IF NOT EXISTS subagent_handbacks (
                 child_session_id TEXT PRIMARY KEY,
                 handback_command_id TEXT,
                 handback_message TEXT,
                 handback_recorded_at_ms INTEGER,
                 reminder_command_id TEXT,
                 reminder_for_command_id TEXT,
                 reminder_sent_at_ms INTEGER,
                 reminder_failed_for_command_id TEXT
             );
             UPDATE schema_compatibility SET minimum_compatible_version = 49 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (49, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 49;
             COMMIT;",
        )?;
    }

    // Compatible: a new nullable column that only this build reads. Older
    // readers ignore it, and older writers name their columns, so an update
    // from one keeps it.
    if version < 50 {
        let add_column = if super::legacy_schema::table_has_column(
            connection,
            "subagent_handbacks",
            "awaited_ordinal",
        )? {
            ""
        } else {
            "ALTER TABLE subagent_handbacks ADD COLUMN awaited_ordinal INTEGER;"
        };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (50, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 50;
             COMMIT;"
        ))?;
    }

    // Compatible: the directory on the parent's target where a child writes
    // the details its report points to. A nullable column only this build
    // reads, like `awaited_ordinal`.
    if version < 51 {
        let add_column = if super::legacy_schema::table_has_column(
            connection,
            "subagent_handbacks",
            "report_dir",
        )? {
            ""
        } else {
            "ALTER TABLE subagent_handbacks ADD COLUMN report_dir TEXT;"
        };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (51, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 51;
             COMMIT;"
        ))?;
    }

    // Compatible: adds one table that only this build reads. It lists the
    // sub-agents a parent's suspend stopped until the parent's model has been
    // told. It is not a column of `sessions` because a full state save
    // rewrites every session row from whatever copy the saving controller
    // holds, which could drop the list or bring back one already delivered.
    // Rows go with their parent's session row.
    if version < 52 {
        connection.execute_batch(
            "BEGIN IMMEDIATE;
             CREATE TABLE IF NOT EXISTS stopped_subagents (
                 parent_session_id TEXT NOT NULL
                     REFERENCES sessions(session_id) ON DELETE CASCADE,
                 child_session_id TEXT NOT NULL,
                 record_json TEXT NOT NULL CHECK(json_valid(record_json)),
                 PRIMARY KEY(parent_session_id, child_session_id)
             ) STRICT;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (52, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 52;
             COMMIT;",
        )?;
    }

    // Breaking: a sub-agent whose turn ended can be stored as `parked`. The
    // `sessions.state` constraint has to be rebuilt to admit it, and an older
    // reader panics on a state it does not know, so the floor rises with the
    // revision.
    if version < 53 {
        migrate_parked_session_state(connection)?;
    }

    // Breaking: older daemons cannot enforce exact checkout preparation on
    // admitted sessions, so they must not recover or provision these records.
    if version < 54 {
        let add_column =
            if super::legacy_schema::table_has_column(connection, "sessions", "checkout_json")? {
                ""
            } else {
                "ALTER TABLE sessions ADD COLUMN checkout_json TEXT;"
            };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             UPDATE schema_compatibility SET minimum_compatible_version = 54 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (54, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 54;
             COMMIT;"
        ))?;
    }

    // Breaking: older daemons cannot enforce the runtime constraint or read
    // the new runtime receipt stored in relay/API events.
    if version < 55 {
        let add_column = if super::legacy_schema::table_has_column(
            connection,
            "sessions",
            "expected_runtime_identity",
        )? {
            ""
        } else {
            "ALTER TABLE sessions ADD COLUMN expected_runtime_identity TEXT;"
        };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             UPDATE schema_compatibility SET minimum_compatible_version = 55 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (55, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 55;
             COMMIT;"
        ))?;
    }

    // Breaking: older readers/writers cannot honor None or fixed model/effort.
    if version < 56 {
        let add_column = if super::legacy_schema::table_has_column(
            connection,
            "sessions",
            "subagents",
        )? {
            ""
        } else {
            "ALTER TABLE sessions ADD COLUMN subagents TEXT CHECK(subagents IS NULL OR json_valid(subagents));"
        };
        connection.execute_batch(&format!(
            "BEGIN IMMEDIATE;
             {add_column}
             UPDATE sessions SET subagents = CASE WHEN mjolnir_subagents = 1
                 THEN '{{\"mode\":\"all_models\"}}' ELSE '{{\"mode\":\"native\"}}' END WHERE subagents IS NULL AND mjolnir_subagents IS NOT NULL;
             CREATE TABLE IF NOT EXISTS subagent_preference (singleton INTEGER PRIMARY KEY CHECK(singleton = 1), policy TEXT NOT NULL CHECK(json_valid(policy)));
             UPDATE schema_compatibility SET minimum_compatible_version = 56 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at) VALUES (56, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
             PRAGMA user_version = 56;
             COMMIT;"
        ))?;
    }

    // Breaking: typed event bodies cannot be decoded by older readers, and
    // pending checkpoint identities must survive every writer's transitions.
    if version < 57 {
        let tx = connection.unchecked_transaction()?;
        tx.execute_batch("DROP TRIGGER IF EXISTS api_session_error_updated;
            DROP TRIGGER IF EXISTS api_session_error_inserted;
            CREATE TABLE IF NOT EXISTS checkpoint_operations (
                session_id TEXT PRIMARY KEY REFERENCES sessions(session_id) ON DELETE CASCADE,
                command_id TEXT NOT NULL UNIQUE,
                related_command_ids TEXT NOT NULL DEFAULT '[]' CHECK(json_valid(related_command_ids))
            ) STRICT;")?;
        super::events::migrate_event_outcomes(&tx)?;
        tx.execute_batch("UPDATE schema_compatibility SET minimum_compatible_version = 57 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (57, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 57;")?;
        tx.commit()?;
    }

    // Breaking: relay assessment observations and seeded-context commands are
    // persisted as JSON that older readers cannot decode or preserve.
    if version < 58 {
        connection.execute_batch("BEGIN IMMEDIATE;
            UPDATE schema_compatibility SET minimum_compatible_version = 58 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (58, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 58;
            COMMIT;")?;
    }

    // Breaking: an older daemon cannot resume acknowledged startup delivery
    // and may instead restore or resend its prompt with a different identity.
    if version < 59 {
        connection.execute_batch("BEGIN IMMEDIATE;
            CREATE TABLE IF NOT EXISTS startup_steps (
                sequence INTEGER PRIMARY KEY AUTOINCREMENT,
                session_id TEXT NOT NULL,
                group_id TEXT,
                command_id TEXT NOT NULL UNIQUE,
                step_json TEXT NOT NULL,
                phase TEXT NOT NULL DEFAULT 'pending'
                    CHECK (phase IN ('pending', 'delivering', 'accepted', 'cancelling', 'rejecting', 'done', 'failed', 'dismissed')),
                error TEXT,
                accepted_ordinal INTEGER
            ) STRICT;
            CREATE INDEX IF NOT EXISTS startup_steps_session_sequence
                ON startup_steps(session_id, sequence);
            CREATE INDEX IF NOT EXISTS startup_steps_group_sequence
                ON startup_steps(group_id, sequence) WHERE group_id IS NOT NULL;
            CREATE INDEX IF NOT EXISTS startup_steps_pending
                ON startup_steps(session_id, sequence)
                WHERE phase IN ('pending', 'delivering', 'accepted', 'cancelling', 'rejecting');
            UPDATE schema_compatibility SET minimum_compatible_version = 59 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (59, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 59;
            COMMIT;")?;
    }
    // Breaking: older dispatchers would resolve a prepared request's target
    // again instead of honoring its persisted effect identity and outcome.
    if version < 60 {
        connection.execute_batch("BEGIN IMMEDIATE;
            CREATE TABLE IF NOT EXISTS delegation_effects (
                parent_session_id TEXT NOT NULL,
                request_id TEXT NOT NULL,
                phase TEXT NOT NULL,
                prepared_json TEXT,
                result_json TEXT,
                receipt_pending INTEGER NOT NULL DEFAULT 0,
                PRIMARY KEY(parent_session_id, request_id)
            ) STRICT;
            CREATE INDEX IF NOT EXISTS delegation_effects_receipt_cleanup
                ON delegation_effects(parent_session_id, request_id) WHERE receipt_pending = 1;
            UPDATE schema_compatibility SET minimum_compatible_version = 60 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (60, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 60;
            COMMIT;")?;
    }
    // Breaking: older review hosts clear active reviews on startup and cannot
    // reconstruct or preserve the durable orchestration and effect outbox.
    if version < 61 {
        let add_column = if super::legacy_schema::table_has_column(
            connection,
            "turn_review_state",
            "orchestration",
        )? {
            ""
        } else {
            "ALTER TABLE turn_review_state ADD COLUMN orchestration TEXT;"
        };
        connection.execute_batch(&format!("BEGIN IMMEDIATE;
            {add_column}
            UPDATE schema_compatibility SET minimum_compatible_version = 61 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (61, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 61;
            COMMIT;"))?;
    }
    // Breaking: older recovery cannot distinguish an accepted worker swap
    // awaiting readiness from a worker that should be recreated or abandoned.
    if version < 62 {
        connection.execute_batch("BEGIN IMMEDIATE;
            CREATE TABLE IF NOT EXISTS worker_restart_intents (
                session_id TEXT PRIMARY KEY REFERENCES sessions(session_id) ON DELETE CASCADE,
                operation_id TEXT NOT NULL,
                target_json TEXT NOT NULL,
                desired_build TEXT NOT NULL,
                phase TEXT NOT NULL CHECK(phase IN ('prepared', 'swapping', 'awaiting_readiness'))
            ) STRICT;
            UPDATE schema_compatibility SET minimum_compatible_version = 62 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (62, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 62;
            COMMIT;")?;
    }

    // Breaking: older delegation executors do not fence delayed lifecycle
    // effects against the durable incarnation they originally selected.
    if version < 63 {
        connection.execute_batch("BEGIN IMMEDIATE;
            CREATE TABLE IF NOT EXISTS session_incarnations (
                session_id TEXT PRIMARY KEY REFERENCES sessions(session_id) ON DELETE CASCADE,
                identity TEXT NOT NULL
            ) STRICT;
            INSERT OR IGNORE INTO session_incarnations(session_id, identity)
                SELECT session_id, lower(hex(randomblob(16))) FROM sessions;
            CREATE TRIGGER IF NOT EXISTS session_incarnation_insert
                AFTER INSERT ON sessions BEGIN
                    INSERT INTO session_incarnations(session_id, identity)
                    VALUES(NEW.session_id, lower(hex(randomblob(16))));
                END;
            CREATE TRIGGER IF NOT EXISTS session_incarnation_resume
                AFTER UPDATE OF state ON sessions
                WHEN (NEW.state = 'provisioning' AND OLD.state <> 'provisioning')
                  OR (NEW.state = 'running' AND OLD.state IN
                      ('stopped', 'parked', 'error', 'lost', 'destroyed-with-data-loss'))
                BEGIN
                    UPDATE session_incarnations SET identity = lower(hex(randomblob(16)))
                    WHERE session_id = NEW.session_id;
                END;
            UPDATE schema_compatibility SET minimum_compatible_version = 63 WHERE singleton = 1;
            INSERT INTO schema_migrations(version, applied_at) VALUES (63, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
            PRAGMA user_version = 63;
            COMMIT;")?;
    }

    let recorded: Option<i64> =
        connection.query_row("SELECT max(version) FROM schema_migrations", [], |row| {
            row.get(0)
        })?;
    if recorded != Some(SCHEMA_VERSION) {
        bail!(
            "Mjolnir database migration ledger {:?} does not match schema {}",
            recorded,
            SCHEMA_VERSION
        );
    }
    Ok(())
}

/// Migration 53: rebuild `sessions` so its `state` constraint admits
/// `'parked'`. SQLite cannot alter a CHECK constraint, so the table is copied
/// into one declared with the new constraint, the way migration 32
/// (`migrate_zcode_harness_kind`) did. The table's own stored definition is
/// edited, so every column later migrations added is kept as it is. A store
/// whose constraint already admits the value is only stamped.
fn migrate_parked_session_state(connection: &Connection) -> Result<()> {
    const BEFORE: &str = "'stopped','lost',";
    const AFTER: &str = "'stopped','parked','lost',";
    connection.execute_batch("PRAGMA foreign_keys = OFF;")?;
    let migration = (|| -> Result<()> {
        let transaction = connection.unchecked_transaction()?;
        let sql: String = transaction.query_row(
            "SELECT sql FROM sqlite_schema WHERE type='table' AND name='sessions'",
            [],
            |row| row.get(0),
        )?;
        let (_, definition) = sql
            .split_once('(')
            .context("missing sessions table definition")?;
        if !definition.contains(AFTER) {
            ensure!(
                definition.matches(BEFORE).count() == 1,
                "unexpected sessions state constraint"
            );
            let definition = definition.replace(BEFORE, AFTER);
            let objects: Vec<String> = transaction
                .prepare(
                    "SELECT sql FROM sqlite_schema WHERE tbl_name='sessions'
                     AND type IN ('index','trigger') AND sql IS NOT NULL",
                )?
                .query_map([], |row| row.get(0))?
                .collect::<rusqlite::Result<_>>()?;
            transaction.execute_batch(&format!(
                "CREATE TABLE sessions_parked_v53 ({definition};
                 INSERT INTO sessions_parked_v53 SELECT * FROM sessions;
                 DROP TABLE sessions;
                 ALTER TABLE sessions_parked_v53 RENAME TO sessions;"
            ))?;
            for object in objects {
                transaction.execute_batch(&object)?;
            }
            ensure!(
                !transaction
                    .prepare("PRAGMA foreign_key_check")?
                    .exists([])?,
                "foreign key violation in the parked-state migration"
            );
        }
        transaction.execute_batch(
            "UPDATE schema_compatibility SET minimum_compatible_version = 53
                 WHERE singleton = 1;
             INSERT INTO schema_migrations(version, applied_at)
                 VALUES (53, strftime('%Y-%m-%dT%H:%M:%fZ','now'));
             PRAGMA user_version = 53;",
        )?;
        transaction.commit()?;
        Ok(())
    })();
    let restored = connection.execute_batch("PRAGMA foreign_keys = ON;");
    migration.context("migrate the sessions state constraint for parked sub-agents")?;
    restored.context("restore foreign key enforcement after the parked-state migration")?;
    Ok(())
}

/// Create an empty store at the baseline revision in one immediate transaction.
/// The revision is read again under the write lock, so a second process that
/// raced to create the same store finds it already created.
fn create_baseline_schema(connection: &Connection) -> Result<()> {
    connection.execute_batch("BEGIN IMMEDIATE;")?;
    let created = (|| -> Result<()> {
        let version: i64 = connection.query_row("PRAGMA user_version", [], |row| row.get(0))?;
        if version != 0 {
            return Ok(());
        }
        connection.execute_batch(include_str!("baseline.sql"))?;
        connection.execute(
            "INSERT INTO schema_compatibility(singleton, minimum_compatible_version) VALUES (1, ?1)",
            [BASELINE_MINIMUM_COMPATIBLE_VERSION],
        )?;
        connection.execute(
            "INSERT INTO schema_migrations(version, applied_at)
             VALUES (?1, strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))",
            [BASELINE_SCHEMA_VERSION],
        )?;
        connection.pragma_update(None, "user_version", BASELINE_SCHEMA_VERSION)?;
        Ok(())
    })();
    match created {
        Ok(()) => connection
            .execute_batch("COMMIT;")
            .context("commit baseline database schema"),
        Err(error) => {
            if let Err(rollback) = connection.execute_batch("ROLLBACK;") {
                tracing::warn!(%rollback, "could not roll back a failed baseline schema");
            }
            Err(error.context("create baseline database schema"))
        }
    }
}

#[cfg(test)]
pub(super) fn advance_test_schema(path: &Path, revision: i64, minimum_compatible: i64) {
    let connection = Connection::open(path).unwrap();
    let transaction = connection.unchecked_transaction().unwrap();
    transaction
        .execute(
            "UPDATE schema_compatibility SET minimum_compatible_version = ?1",
            [minimum_compatible],
        )
        .unwrap();
    transaction
        .execute(
            "INSERT INTO schema_migrations(version, applied_at) VALUES (?1, 'test')",
            [revision],
        )
        .unwrap();
    transaction
        .pragma_update(None, "user_version", revision)
        .unwrap();
    transaction.commit().unwrap();
    forget_verified_schema(path);
}

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

    #[test]
    fn every_historical_revision_upgrades_directly_and_preserves_user_data() {
        for revision in 1..SCHEMA_VERSION {
            let directory = tempfile::tempdir().unwrap();
            let path = directory.path().join("mj.sqlite3");
            let connection = Connection::open(&path).unwrap();
            connection
                .execute_batch(include_str!("legacy_v1.sql"))
                .unwrap();
            connection.execute_batch(
                "INSERT INTO session_contexts VALUES ('old-session', 'project', '2026-01-01T00:00:00Z');
                 INSERT INTO sessions(session_id, title, harness_kind, last_profile,
                     target_template_id, state, updated_at, native_session_id)
                     VALUES ('old-session', 'Keep my work', 'codex', 'codex', 'local', 'error',
                         '2026-01-01T00:00:00Z', 'native-original');
                 INSERT INTO prompt_history(session_id, event_sequence, submitted_at, text)
                     VALUES ('old-session', 1, '2026-01-01T00:00:00Z', 'Keep my prompt');"
            ).unwrap();
            // Interrupt at each historical transaction boundary. Closing the
            // connection rolls back the interrupted step, exactly as a killed
            // updater would. Reopening must resume without manual cleanup.
            connection
                .execute_batch(&format!(
                    "CREATE TRIGGER stop_at_revision BEFORE INSERT ON schema_migrations
                 WHEN NEW.version > {revision}
                 BEGIN SELECT RAISE(ABORT, 'fixture migration boundary'); END;"
                ))
                .unwrap();
            if revision < BASELINE_SCHEMA_VERSION {
                assert!(super::super::legacy_schema::migrate_to_baseline(&connection).is_err());
            } else {
                super::super::legacy_schema::migrate_to_baseline(&connection).unwrap();
                assert!(migrate_schema(&connection).is_err());
            }
            drop(connection);
            let connection = Connection::open(&path).unwrap();
            let found: i64 = connection
                .query_row("PRAGMA user_version", [], |row| row.get(0))
                .unwrap();
            assert_eq!(found, revision);
            connection
                .execute_batch("DROP TRIGGER stop_at_revision")
                .unwrap();
            drop(connection);

            let writer =
                open_writer(&path).unwrap_or_else(|error| panic!("revision {revision}: {error:#}"));
            assert_eq!(read_schema_state(&writer).unwrap().revision, SCHEMA_VERSION);
            assert_eq!(
                writer
                    .query_row("PRAGMA integrity_check", [], |row| row.get::<_, String>(0))
                    .unwrap(),
                "ok"
            );
            assert!(
                !writer
                    .prepare("PRAGMA foreign_key_check")
                    .unwrap()
                    .exists([])
                    .unwrap()
            );
            drop(writer);
            let reader = open_reader_strict(&path).unwrap();
            let prompt: String = reader
                .query_row("SELECT text FROM prompt_history", [], |row| row.get(0))
                .unwrap();
            assert_eq!(prompt, "Keep my prompt");
            let state = load_state_from(&path).unwrap();
            assert_eq!(state.sessions["old-session"].title, "Keep my work");
            assert_eq!(
                state.sessions["old-session"].native_session_id.as_deref(),
                Some("native-original")
            );
            drop(reader);
            // A fresh writer process must not apply any migration twice.
            forget_verified_schema(&path);
            drop(open_writer(&path).unwrap());
        }
    }

    /// The oldest executable revision that can still read and write a store at
    /// `SCHEMA_VERSION`. Migration 62 requires durable worker-swap recovery.
    const MINIMUM_COMPATIBLE_VERSION: i64 = 63;

    /// Rewrites a store's recorded schema version the way another build's
    /// migration ladder would, and forgets that this process verified it.
    fn stamp_schema_version(path: &Path, version: i64) {
        if version > SCHEMA_VERSION {
            advance_test_schema(path, version, version);
            return;
        }
        let connection = Connection::open(path).unwrap();
        connection
            .execute_batch(&format!("PRAGMA user_version = {version};"))
            .unwrap();
        connection
            .execute(
                "DELETE FROM schema_migrations WHERE version > ?1",
                [version],
            )
            .unwrap();
        if version == 30 {
            connection
                .execute(
                    "UPDATE schema_compatibility SET minimum_compatible_version = 30 WHERE singleton = 1",
                    [],
                )
                .unwrap();
        }
        drop(connection);
        forget_verified_schema(path);
    }

    #[test]
    fn subagent_policy_migration_preserves_legacy_choices_and_refuses_old_writers() {
        use mj_core::subagent::SubagentPolicy;
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("subagent-policy.sqlite3");
        for id in ["all", "native", "unset"] {
            save_session_to(&path, &super::super::tests::session(id, "project")).unwrap();
        }
        let connection = Connection::open(&path).unwrap();
        connection
            .execute_batch(
                "UPDATE sessions SET mjolnir_subagents = 1 WHERE session_id = 'all';
             UPDATE sessions SET mjolnir_subagents = 0 WHERE session_id = 'native';
             ALTER TABLE sessions DROP COLUMN subagents;
             DROP TABLE subagent_preference;
             DELETE FROM schema_migrations WHERE version >= 56;
             UPDATE schema_compatibility SET minimum_compatible_version = 55;
             PRAGMA user_version = 55;",
            )
            .unwrap();
        drop(connection);
        forget_verified_schema(&path);
        let upgraded = open_writer(&path).unwrap();
        assert!(
            read_schema_state(&upgraded)
                .unwrap()
                .ensure_supported_by(55)
                .is_err()
        );
        drop(upgraded);
        let state = load_state_from(&path).unwrap();
        assert_eq!(
            state.sessions["all"].subagents,
            Some(SubagentPolicy::AllModels)
        );
        assert_eq!(
            state.sessions["native"].subagents,
            Some(SubagentPolicy::Native)
        );
        assert_eq!(state.sessions["unset"].subagents, None);
        assert_eq!(state.last_subagent_policy, SubagentPolicy::Native);
    }

    #[test]
    fn steering_migration_refuses_builds_that_cannot_read_returned_steers() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("steering-migration.sqlite3");
        let record = super::super::tests::session("steered-session", "project");
        save_session_to(&path, &record).unwrap();
        let connection = Connection::open(&path).unwrap();
        connection
            .execute_batch(
                "DELETE FROM schema_migrations WHERE version >= 48;
             UPDATE schema_compatibility SET minimum_compatible_version = 47;
             PRAGMA user_version = 47;",
            )
            .unwrap();
        drop(connection);
        forget_verified_schema(&path);
        let upgraded = open_writer(&path).unwrap();
        let schema = read_schema_state(&upgraded).unwrap();
        assert_eq!(schema.revision, SCHEMA_VERSION);
        assert_eq!(schema.minimum_compatible, Some(MINIMUM_COMPATIBLE_VERSION));
        let error = schema.ensure_supported_by(47).unwrap_err();
        assert!(matches!(
            error.downcast_ref::<StoreSchemaMismatch>().unwrap().reason,
            StoreSchemaMismatchReason::Incompatible {
                minimum_compatible: MINIMUM_COMPATIBLE_VERSION
            }
        ));
        drop(upgraded);
        assert_eq!(load_state_from(&path).unwrap().sessions[&record.id], record);
    }

    #[test]
    fn durable_target_migration_preserves_sessions_and_refuses_previous_builds() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("target-migration.sqlite3");
        let record = super::super::tests::session("preserved-session", "project");
        save_session_to(&path, &record).unwrap();
        let connection = Connection::open(&path).unwrap();
        connection
            .execute_batch(
                "ALTER TABLE sessions DROP COLUMN target_runtime_json;
             DELETE FROM schema_migrations WHERE version >= 46;
             UPDATE schema_compatibility SET minimum_compatible_version = 44;
             PRAGMA user_version = 45;",
            )
            .unwrap();
        forget_verified_schema(&path);
        let upgraded = open_writer(&path).unwrap();
        let schema = read_schema_state(&upgraded).unwrap();
        assert_eq!(schema.revision, SCHEMA_VERSION);
        assert_eq!(schema.minimum_compatible, Some(MINIMUM_COMPATIBLE_VERSION));
        let error = schema.ensure_supported_by(45).unwrap_err();
        assert!(matches!(
            error.downcast_ref::<StoreSchemaMismatch>().unwrap().reason,
            StoreSchemaMismatchReason::Incompatible {
                minimum_compatible: MINIMUM_COMPATIBLE_VERSION
            }
        ));
        drop(upgraded);
        let restored = load_state_from(&path).unwrap();
        assert_eq!(restored.sessions[&record.id], record);
    }

    #[test]
    fn native_agents_and_unstructured_input_raise_the_store_compatibility_floor() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("mj.sqlite3");
        let connection = open_writer(&path).unwrap();
        connection
            .execute_batch(
                "BEGIN IMMEDIATE;
             DROP TABLE quota_reset_cache;
             DROP TABLE native_agent_transcript;
             DROP TABLE native_agents;
             DROP TABLE native_agent_replay;
             DELETE FROM schema_migrations WHERE version >= 39;
             UPDATE schema_compatibility SET minimum_compatible_version = 32;
             PRAGMA user_version = 38;
             COMMIT;",
            )
            .unwrap();
        migrate_schema(&connection).unwrap();
        let state = read_schema_state(&connection).unwrap();
        assert_eq!(state.revision, SCHEMA_VERSION);
        assert_eq!(state.minimum_compatible, Some(MINIMUM_COMPATIBLE_VERSION));
        let event = ApiEventData::InputRequired {
            request: None,
            turn_id: Some(1),
        };
        #[derive(serde::Deserialize)]
        struct LegacyInputEvent {
            #[serde(rename = "request")]
            _request: mj_core::elicitation::ElicitationRequest,
        }
        let encoded = serde_json::to_value(&event).unwrap();
        assert!(serde_json::from_value::<LegacyInputEvent>(encoded["data"].clone()).is_err());
    }

    #[test]
    fn older_readers_and_reopened_writers_preserve_a_compatible_future_schema() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("mj.sqlite3");
        let connection = open_writer(&path).unwrap();
        connection
            .execute_batch(
                "CREATE TABLE future_feature(value TEXT NOT NULL);
                 INSERT INTO future_feature VALUES ('preserve me');",
            )
            .unwrap();
        drop(connection);
        advance_test_schema(&path, SCHEMA_VERSION + 1, SCHEMA_VERSION);

        let reader = open_reader_strict(&path).unwrap();
        assert_eq!(
            reader
                .query_row("SELECT value FROM future_feature", [], |row| row
                    .get::<_, String>(0))
                .unwrap(),
            "preserve me"
        );
        assert!(reader.execute("DELETE FROM future_feature", []).is_err());
        drop(reader);

        // A repair would recreate this deliberately removed trigger. A future
        // schema is authoritative even when it differs from our own repairs.
        let raw = Connection::open(&path).unwrap();
        raw.execute_batch("DROP TRIGGER session_contexts_workspace_update;")
            .unwrap();
        drop(raw);
        let writer = open_writer(&path).unwrap();
        assert!(!writer.query_row("SELECT EXISTS(SELECT 1 FROM sqlite_schema WHERE name = 'session_contexts_workspace_update')", [], |row| row.get::<_, bool>(0)).unwrap());
        assert_eq!(
            writer
                .query_row("SELECT value FROM future_feature", [], |row| row
                    .get::<_, String>(0))
                .unwrap(),
            "preserve me"
        );
        let state = read_schema_state(&writer).unwrap();
        assert_eq!(state.revision, SCHEMA_VERSION + 1);
        assert_eq!(state.minimum_compatible, Some(SCHEMA_VERSION));
    }

    #[test]
    fn invalid_compatibility_metadata_refuses_readers_and_writers() {
        for alteration in [
            "DROP TABLE schema_compatibility",
            "DELETE FROM schema_compatibility",
            "PRAGMA ignore_check_constraints = ON; UPDATE schema_compatibility SET minimum_compatible_version = 0",
            "UPDATE schema_compatibility SET minimum_compatible_version = 99999",
            "PRAGMA ignore_check_constraints = ON; UPDATE schema_compatibility SET singleton = 2",
            "PRAGMA ignore_check_constraints = ON; INSERT INTO schema_compatibility VALUES (2, 30)",
            "DROP TABLE schema_compatibility; CREATE TABLE schema_compatibility(singleton, minimum_compatible_version); INSERT INTO schema_compatibility VALUES (1, 'invalid')",
            "DELETE FROM schema_migrations WHERE version = (SELECT max(version) FROM schema_migrations)",
        ] {
            for future in [false, true] {
                let directory = tempfile::tempdir().unwrap();
                let path = directory.path().join("mj.sqlite3");
                drop(open_writer(&path).unwrap());
                if future {
                    advance_test_schema(&path, SCHEMA_VERSION + 1, SCHEMA_VERSION);
                }
                let raw = Connection::open(&path).unwrap();
                raw.execute_batch(alteration).unwrap();
                let before: i64 = raw
                    .query_row("PRAGMA schema_version", [], |row| row.get(0))
                    .unwrap();
                // Exercise the cached path as well as a fresh writer open.
                for error in [
                    open_reader_strict(&path).unwrap_err(),
                    open_writer(&path).unwrap_err(),
                ] {
                    let mismatch = error.downcast_ref::<StoreSchemaMismatch>().unwrap();
                    assert_eq!(
                        mismatch.reason,
                        StoreSchemaMismatchReason::InvalidCompatibilityMetadata,
                        "{alteration}"
                    );
                }
                forget_verified_schema(&path);
                assert!(open_writer(&path).is_err(), "{alteration}");
                let after: i64 = raw
                    .query_row("PRAGMA schema_version", [], |row| row.get(0))
                    .unwrap();
                assert_eq!(
                    before, after,
                    "a rejected open repaired schema: {alteration}"
                );
            }
        }
    }

    #[test]
    fn a_failed_baseline_leaves_an_empty_store_that_a_retry_creates() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("mj.sqlite3");
        let connection = Connection::open(&path).unwrap();
        // A table the baseline also creates makes its batch fail part way.
        connection
            .execute_batch("CREATE TABLE workspaces(conflict TEXT)")
            .unwrap();

        let error = migrate_schema(&connection).unwrap_err();

        assert!(format!("{error:#}").contains("create baseline database schema"));
        assert!(
            connection.is_autocommit(),
            "the failed baseline left a transaction open"
        );
        assert_eq!(read_schema_state(&connection).unwrap().revision, 0);
        let tables: i64 = connection
            .query_row(
                "SELECT count(*) FROM sqlite_schema WHERE type = 'table'",
                [],
                |row| row.get(0),
            )
            .unwrap();
        assert_eq!(tables, 1, "only the conflicting table remains");

        connection.execute_batch("DROP TABLE workspaces").unwrap();
        drop(connection);
        let writer = open_writer(&path).unwrap();
        let state = read_schema_state(&writer).unwrap();
        assert_eq!(state.revision, SCHEMA_VERSION);
        assert_eq!(state.minimum_compatible, Some(MINIMUM_COMPATIBLE_VERSION));
    }

    /// A store ahead of this build cannot be fixed by starting a daemon of
    /// this build, so the reader must not say so. This is the message the
    /// incident in #24 printed twice a second for an hour.
    #[test]
    fn strict_reader_reports_a_newer_store_without_blaming_the_daemon() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("mj.sqlite3");
        drop(open_writer(&path).unwrap());
        stamp_schema_version(&path, SCHEMA_VERSION + 1);

        let error = open_reader_strict(&path).unwrap_err();

        let mismatch = error
            .chain()
            .find_map(|cause| cause.downcast_ref::<StoreSchemaMismatch>())
            .expect("the reader reports the mismatch as a typed cause");
        assert_eq!(mismatch.found, SCHEMA_VERSION + 1);
        assert_eq!(mismatch.supported, SCHEMA_VERSION);
        let message = mismatch.to_string();
        assert!(message.contains("upgrade Mjolnir"), "got {message}");
        assert!(
            !message.contains("start the Mjolnir daemon"),
            "got {message}"
        );
    }

    /// A store behind this build keeps the advice that works, verbatim, so
    /// existing log greps and runbooks keep matching.
    #[test]
    fn strict_reader_keeps_the_migrate_advice_when_the_store_is_behind() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("mj.sqlite3");
        drop(open_writer(&path).unwrap());
        let raw = Connection::open(&path).unwrap();
        raw.execute_batch(&format!(
            "UPDATE schema_compatibility SET minimum_compatible_version = {0};
             DELETE FROM schema_migrations WHERE version > {0};
             INSERT OR IGNORE INTO schema_migrations(version, applied_at) VALUES ({0}, 'test');
             PRAGMA user_version = {0};",
            SCHEMA_VERSION - 1
        ))
        .unwrap();
        drop(raw);

        let error = open_reader_strict(&path).unwrap_err();

        let mismatch = error
            .chain()
            .find_map(|cause| cause.downcast_ref::<StoreSchemaMismatch>())
            .expect("the reader reports the mismatch as a typed cause");
        assert_eq!(
            mismatch.to_string(),
            format!(
                "Mjolnir database schema {} is not the supported schema {SCHEMA_VERSION}; \
                 start the Mjolnir daemon to migrate it",
                SCHEMA_VERSION - 1
            )
        );
    }

    #[test]
    fn strict_reader_rejects_mutation() {
        let directory = tempfile::tempdir().unwrap();
        let path = directory.path().join("mj.sqlite3");
        drop(open_writer(&path).unwrap());

        let reader = open_reader_strict(&path).unwrap();
        let error = reader
            .execute("CREATE TABLE forbidden(value TEXT)", [])
            .unwrap_err();
        assert!(
            matches!(
                error.sqlite_error_code(),
                Some(rusqlite::ErrorCode::ReadOnly)
            ),
            "unexpected mutation error: {error}"
        );
    }
}