"""Full-text / trigram / CJK message search and FTS maintenance for SessionDB.

Mixin contract: this is a plain mixin class consumed by
``hermes_state.SessionDB``. It defines no ``__init__`` and no state of its
own; methods access the host's attributes (``self._conn``, ``self.db_path``,
``self._execute_write`` and other SessionDB methods) established by
``SessionDB.__init__``. It must never import hermes_state (cycle) — shared
module-level constants live in hermes_state_common.
"""

import logging
import json
import os
import re
import sqlite3
import time
from typing import Any, Callable, Collection, Dict, List, Optional, Tuple

from agent.skill_commands import describe_skill_invocation
from hermes_state_common import (
    FTS_CJK_STALE_KEY,
    FTS_SQL,
    FTS_STORAGE_VERSION,
    FTS_TRIGRAM_SQL,
    MAX_FTS5_QUERY_CHARS,
    SCHEMA_VERSION,
    _FTS_CJK_TRIGGERS,
)

# Moved methods logged under the "hermes_state" logger before the split;
# keep that logger identity so log filtering/capture behavior is unchanged.
logger = logging.getLogger("hermes_state")


class SessionSearchMixin:
    """See module docstring — mixin for SessionDB (Search cluster)."""

    _SEARCH_MESSAGE_RESULT_FIELDS = (
        "id",
        "session_id",
        "role",
        "snippet",
        "timestamp",
        "tool_name",
        "source",
        "model",
        "session_started",
        "context",
    )

    @classmethod
    def _search_message_fields(
        cls, fields: Optional[Collection[str]]
    ) -> Optional[Tuple[str, ...]]:
        """Validate and canonically order an optional result projection."""
        if fields is None:
            return None
        if isinstance(fields, str):
            raise TypeError("search fields must be a collection of field names, not a string")
        requested = set(fields)
        unknown = requested.difference(cls._SEARCH_MESSAGE_RESULT_FIELDS)
        if unknown:
            raise ValueError(f"unknown search result field(s): {', '.join(sorted(unknown))}")
        return tuple(
            field for field in cls._SEARCH_MESSAGE_RESULT_FIELDS if field in requested
        )

    def _try_incremental_merge_fts(self) -> None:
        """Run one bounded FTS5 merge pass without failing the completed write."""
        if not self._fts_enabled:
            return
        try:
            self._merge_fts_incrementally(
                max_pages=self._FTS_MERGE_MAX_PAGES_PER_INDEX
            )
        except sqlite3.Error as exc:
            # Routine maintenance is best effort, but unexpected SQLite errors
            # must remain visible instead of being silently mistaken for an
            # optional missing index.
            logger.warning("FTS incremental merge failed: %s", exc)

    def fts_rebuild_status(self) -> Optional[Dict[str, Any]]:
        """Return deferred-rebuild progress, or None when no rebuild pending.

        Shape: {"pending": True, "total": <rows at drop time>,
        "indexed": <rows backfilled>, "percent": <0-100 int>}.
        Consumed by search_messages() notes and by status surfaces
        (dashboard/desktop can poll this to render a progress indicator).

        Reads state_meta directly via _read_ctx instead of calling
        get_meta() (which takes self._lock) so search_messages doesn't
        block on the writer lock when checking rebuild status.
        """
        with self._read_ctx() as conn:
            row = conn.execute(
                "SELECT key, value FROM state_meta WHERE key IN (?, ?)",
                ("fts_rebuild_high_water", "fts_rebuild_progress"),
            ).fetchall()
        meta = {r["key"]: r["value"] for r in row}
        high_water = meta.get("fts_rebuild_high_water")
        if high_water is None:
            return None
        progress = int(meta.get("fts_rebuild_progress") or 0)
        total = int(high_water)
        if total <= 0:
            return None
        pct = min(100, int(100 * progress / total))
        return {"pending": True, "total": total, "indexed": progress, "percent": pct}

    def _fts_rebuild_finish(self) -> None:
        """Finalize the deferred rebuild: boundary sweep + clear markers.

        The sweep is cheap insurance against any write that slipped through
        the migration-boundary instant (between high_water capture and
        trigger activation): re-index any row near the boundary that the
        index is missing. docsize has one row per indexed doc, so the
        anti-join is exact and runs on a narrow id range.

        The trigram half of the sweep is gated on ``self._trigram_available``
        for the same reason ``fts_rebuild_step()`` gates its backfill INSERT:
        when the SQLite build has no trigram tokenizer (or the table was
        never created), an unconditional INSERT raises ``no such table``
        and aborts the whole rebuild — taking ``optimize_fts_storage()``
        down with it.
        """
        include_trigram = self._trigram_available

        def _do(conn):
            hw_row = conn.execute(
                "SELECT value FROM state_meta WHERE key = 'fts_rebuild_high_water'"
            ).fetchone()
            if hw_row is not None:
                hw = int(hw_row[0])
                # Sweep a generous window around the boundary.
                lo, hi = hw - 1000, hw + 1000
                conn.execute(
                    "INSERT INTO messages_fts(rowid, content, tool_name, tool_calls) "
                    "SELECT m.id, m.content, m.tool_name, m.tool_calls "
                    "FROM messages m "
                    "WHERE m.id > ? AND m.id <= ? "
                    "AND NOT EXISTS (SELECT 1 FROM messages_fts_docsize d WHERE d.id = m.id)",
                    (lo, hi),
                )
                if include_trigram:
                    conn.execute(
                        "INSERT INTO messages_fts_trigram(rowid, content, tool_name, tool_calls) "
                        "SELECT m.id, m.content, m.tool_name, m.tool_calls "
                        "FROM messages m "
                        "WHERE m.id > ? AND m.id <= ? AND m.role <> 'tool' "
                        "AND NOT EXISTS (SELECT 1 FROM messages_fts_trigram_docsize d WHERE d.id = m.id)",
                        (lo, hi),
                    )
            conn.execute(
                "DELETE FROM state_meta WHERE key IN "
                "('fts_rebuild_high_water', 'fts_rebuild_progress')"
            )
        self._execute_write(_do)
        logger.info("Deferred FTS rebuild complete — all messages indexed.")

    def _fts_teardown_trash_step(self) -> bool:
        """Tear down one chunk of a demoted v22 FTS shadow table.

        The trash tables are PLAIN tables (their vtable parent was demoted
        away during the migration), so chunked DELETE + final DROP involve
        no FTS5 machinery at all. Returns True while teardown work remains.
        """
        with self._lock:
            trash = [
                r[0] for r in self._conn.execute(
                    "SELECT name FROM sqlite_master WHERE type = 'table' "
                    "AND name LIKE ? ESCAPE '\\'",
                    (self._FTS_TRASH_PREFIX.replace("_", "\\_") + "%",),
                ).fetchall()
            ]
        if not trash:
            return False

        tbl = trash[0]

        def _do(conn):
            pk_cols = [
                r[1] for r in conn.execute(f"PRAGMA table_info({tbl})")
                if r[5] > 0
            ]
            key = ", ".join(pk_cols) if pk_cols else "rowid"
            cur = conn.execute(
                f"DELETE FROM {tbl} WHERE ({key}) IN "
                f"(SELECT {key} FROM {tbl} LIMIT {self._FTS_REBUILD_CHUNK_ROWS})"
            )
            if cur.rowcount == 0:
                # Empty — the DROP is cheap now.
                conn.execute(f"DROP TABLE IF EXISTS {tbl}")
                logger.info("Old FTS shadow table %s torn down.", tbl)
            return True  # re-check: more trash tables / chunks may remain

        try:
            return bool(self._execute_write(_do))
        except sqlite3.OperationalError as exc:
            logger.debug("FTS trash teardown chunk failed (will retry): %s", exc)
            return True

    def fts_rebuild_step(self) -> bool:
        """Backfill one chunk of the deferred FTS rebuild.

        Returns True when more work remains, False when the rebuild is
        complete (or none is pending). Safe to call from any process at any
        time; chunks are claimed atomically inside the write transaction, so
        concurrent callers interleave instead of duplicating rows.
        """
        if not self._fts_enabled:
            return False
        high_water_raw = self.get_meta("fts_rebuild_high_water")
        if high_water_raw is None:
            return False
        high_water = int(high_water_raw)
        include_trigram = self._trigram_available
        chunk = self._FTS_REBUILD_CHUNK_ROWS

        def _do(conn):
            # Re-read progress inside the write transaction (BEGIN IMMEDIATE
            # is already held by _execute_write) — this is the claim: two
            # workers can't read the same progress value concurrently.
            row = conn.execute(
                "SELECT value FROM state_meta WHERE key = 'fts_rebuild_progress'"
            ).fetchone()
            if row is None:
                return False  # finished (or cleared) by another process
            progress = int(row[0])
            if progress >= high_water:
                return False

            # The chunk upper bound is an id, not a row count, so gaps from
            # deleted rows don't shrink chunks below the claimed range.
            upper = min(progress + chunk, high_water)
            conn.execute(
                "INSERT INTO messages_fts(rowid, content, tool_name, tool_calls) "
                "SELECT id, content, tool_name, tool_calls FROM messages "
                "WHERE id > ? AND id <= ?",
                (progress, upper),
            )
            if include_trigram:
                conn.execute(
                    "INSERT INTO messages_fts_trigram"
                    "(rowid, content, tool_name, tool_calls) "
                    "SELECT id, content, tool_name, tool_calls FROM messages "
                    "WHERE id > ? AND id <= ? AND role <> 'tool'",
                    (progress, upper),
                )
            # Publish progress in the same transaction as the rows it
            # covers — crash-atomic: either both land or neither does.
            conn.execute(
                "UPDATE state_meta SET value = ? "
                "WHERE key = 'fts_rebuild_progress'",
                (str(upper),),
            )
            return upper < high_water

        try:
            more = self._execute_write(_do)
        except sqlite3.OperationalError as exc:
            logger.debug("FTS rebuild chunk failed (will retry): %s", exc)
            return True  # transient (lock contention) — caller retries
        if more is False:
            status = self.fts_rebuild_status()
            if status is not None and status["indexed"] >= status["total"]:
                self._fts_rebuild_finish()
            return False
        return bool(more)

    def fts_cjk_rebuild_status(self) -> Optional[Dict[str, Any]]:
        """CJK-index backfill progress, or None when none is pending."""
        with self._read_ctx() as conn:
            row = conn.execute(
                "SELECT key, value FROM state_meta WHERE key IN (?, ?)",
                ("fts_cjk_rebuild_high_water", "fts_cjk_rebuild_progress"),
            ).fetchall()
        meta = {r["key"]: r["value"] for r in row}
        high_water = meta.get("fts_cjk_rebuild_high_water")
        if high_water is None:
            return None
        progress = int(meta.get("fts_cjk_rebuild_progress") or 0)
        total = int(high_water)
        if total <= 0:
            return None
        pct = min(100, int(100 * progress / total))
        return {"pending": True, "total": total, "indexed": progress, "percent": pct}

    def fts_cjk_rebuild_step(self) -> bool:
        """Backfill one chunk of the CJK index. True while work remains."""
        if not self._fts_enabled or not self._fts_cjk_loaded:
            return False
        high_water_raw = self.get_meta("fts_cjk_rebuild_high_water")
        if high_water_raw is None:
            return False
        high_water = int(high_water_raw)
        chunk = self._FTS_REBUILD_CHUNK_ROWS

        def _do(conn):
            row = conn.execute(
                "SELECT value FROM state_meta "
                "WHERE key = 'fts_cjk_rebuild_progress'"
            ).fetchone()
            if row is None:
                return False  # finished (or cleared) by another process
            progress = int(row[0])
            if progress >= high_water:
                return False
            upper = min(progress + chunk, high_water)
            conn.execute(
                "INSERT INTO messages_fts_cjk(rowid, content, tool_name, tool_calls) "
                "SELECT id, content, tool_name, tool_calls FROM messages "
                "WHERE id > ? AND id <= ? AND role <> 'tool'",
                (progress, upper),
            )
            conn.execute(
                "UPDATE state_meta SET value = ? "
                "WHERE key = 'fts_cjk_rebuild_progress'",
                (str(upper),),
            )
            return upper < high_water

        try:
            more = self._execute_write(_do)
        except sqlite3.OperationalError as exc:
            logger.debug("CJK FTS rebuild chunk failed (will retry): %s", exc)
            return True
        if more is False:
            status = self.fts_cjk_rebuild_status()
            if status is not None and status["indexed"] >= status["total"]:
                self._fts_cjk_rebuild_finish()
            return False
        return bool(more)

    def _fts_cjk_rebuild_finish(self) -> None:
        """Boundary sweep + clear the cjk markers; index becomes servable."""
        def _do(conn):
            hw_row = conn.execute(
                "SELECT value FROM state_meta "
                "WHERE key = 'fts_cjk_rebuild_high_water'"
            ).fetchone()
            if hw_row is not None:
                hw = int(hw_row[0])
                lo, hi = hw - 1000, hw + 1000
                conn.execute(
                    "INSERT INTO messages_fts_cjk(rowid, content, tool_name, tool_calls) "
                    "SELECT m.id, m.content, m.tool_name, m.tool_calls "
                    "FROM messages m "
                    "WHERE m.id > ? AND m.id <= ? AND m.role <> 'tool' "
                    "AND NOT EXISTS (SELECT 1 FROM messages_fts_cjk_docsize d WHERE d.id = m.id)",
                    (lo, hi),
                )
            conn.execute(
                "DELETE FROM state_meta WHERE key IN "
                "('fts_cjk_rebuild_high_water', 'fts_cjk_rebuild_progress')"
            )
        self._execute_write(_do)
        self._fts_cjk_available = True
        logger.info("CJK FTS index backfill complete — serving CJK search.")

    def _fts_cjk_reset_if_stale(self) -> None:
        """Rebuild path for a stale cjk index (triggers were dropped).

        The gap's extent is unknown, so the only safe recovery is a from-
        scratch rebuild: drop the table + triggers, clear the breadcrumb,
        recreate via ``_ensure_fts_cjk_schema`` (which sets fresh backfill
        markers on a populated DB). Called from ``optimize_fts_storage`` on
        a tokenizer-capable host; no-op when not stale.
        """
        if not self._fts_cjk_loaded:
            return

        def _do(conn):
            stale = conn.execute(
                "SELECT 1 FROM state_meta WHERE key = ?",
                (FTS_CJK_STALE_KEY,),
            ).fetchone()
            if not stale:
                return False
            for trig in _FTS_CJK_TRIGGERS:
                conn.execute(f"DROP TRIGGER IF EXISTS {trig}")
            conn.execute("DROP TABLE IF EXISTS messages_fts_cjk")
            conn.execute("DROP VIEW IF EXISTS messages_fts_cjk_src")
            conn.execute(
                "DELETE FROM state_meta WHERE key IN "
                f"('{FTS_CJK_STALE_KEY}', 'fts_cjk_rebuild_high_water', "
                "'fts_cjk_rebuild_progress')"
            )
            return True
        was_stale = self._execute_write(_do)
        if was_stale:
            # Recreate outside the write transaction — _ensure_fts_cjk_schema
            # uses executescript(), which implicitly commits any pending
            # transaction and must not run inside _execute_write's BEGIN
            # IMMEDIATE. Sets fresh backfill markers on a populated DB.
            with self._lock:
                self._ensure_fts_cjk_schema(self._conn)
                self._conn.commit()

    def _fts_external_index_empty_with_messages(self, conn) -> bool:
        """True when the base FTS table exists but indexes nothing while
        ``messages`` has rows. Caller must hold ``self._lock``.

        This is the post-demote empty-index shape: external-content FTS with
        zero ``messages_fts_docsize`` rows against a non-empty messages table.
        Healthy installs (and mid-backfill installs that still hold markers)
        never match.
        """
        try:
            has_msg = conn.execute(
                "SELECT EXISTS(SELECT 1 FROM messages)"
            ).fetchone()[0]
            if not has_msg:
                return False
            # docsize is the authoritative "is this rowid indexed" surface for
            # external-content FTS5; probing the virtual table itself is
            # not reliable across SQLite builds. EXISTS instead of COUNT(*):
            # this runs on every writable open via the _init_schema stamp
            # condition, and COUNT(*) is a full b-tree scan (~100ms on a
            # 2M-row table) while EXISTS is O(1).
            has_fts = conn.execute(
                "SELECT EXISTS(SELECT 1 FROM messages_fts_docsize)"
            ).fetchone()[0]
            return not has_fts
        except sqlite3.OperationalError:
            # Table absent / FTS disabled mid-init — not this failure class.
            return False

    def _fts_index_known_empty(self, conn) -> bool:
        """True when the base external-content index holds no rows.

        A missing table counts as empty: the schema ensure that follows
        creates it fresh.
        """
        try:
            n = conn.execute(
                "SELECT COUNT(*) FROM messages_fts_docsize"
            ).fetchone()[0]
            return int(n) == 0
        except sqlite3.OperationalError:
            return True

    def _reset_fts_index_to_empty(self, conn) -> None:
        """Delete every indexed row from the v23 external-content tables.

        Uses the FTS5 ``'delete-all'`` special command — the documented O(1)
        truncate for external-content tables. A plain no-WHERE ``DELETE`` is
        O(rows) on external-content FTS5 (each row's delete tokens are
        regenerated from the content table; measured ~12µs/row, minutes on a
        large index, while holding the write lock) and corrupts the index if
        indexed rows have diverged from ``messages`` — precisely the broken-
        bookkeeping shape this repair path handles. The backfill chunk worker
        replays its whole selected id range with no anti-join, so a replay
        from zero is only safe once the index is known empty — this is how a
        partially indexed DB gets there.
        """
        for tbl in ("messages_fts", "messages_fts_trigram"):
            try:
                conn.execute(f"INSERT INTO {tbl}({tbl}) VALUES('delete-all')")
            except sqlite3.OperationalError:
                pass  # table absent — already an empty surface

    def _seed_fts_rebuild_markers(self, conn, *, force: bool = False) -> int:
        """Write ``fts_rebuild_high_water`` / ``fts_rebuild_progress`` for a
        full backfill. Returns the high-water id.

        When ``force`` is False and high_water is already set, only repairs a
        missing progress key (stuck no-op when high_water exists alone), and
        only after the index is known empty: the chunk worker replays its
        whole selected id range without an anti-join, so a partially indexed
        DB is first reset to a known-empty surface rather than rebuilt from
        zero on top of surviving rows. Caller must hold the write
        transaction / lock as appropriate.
        """
        existing_hw = conn.execute(
            "SELECT value FROM state_meta WHERE key = 'fts_rebuild_high_water'"
        ).fetchone()
        if existing_hw is not None and not force:
            hw = int(existing_hw[0])
            progress = conn.execute(
                "SELECT value FROM state_meta WHERE key = 'fts_rebuild_progress'"
            ).fetchone()
            if progress is None:
                # high_water without progress: fts_rebuild_step treats missing
                # progress as "done by another process" and optimize would
                # no-op then stamp. Re-seed progress so the chunk loop runs.
                if not self._fts_index_known_empty(conn):
                    self._reset_fts_index_to_empty(conn)
                conn.execute(
                    "INSERT INTO state_meta (key, value) VALUES "
                    "('fts_rebuild_progress', '0') "
                    "ON CONFLICT(key) DO UPDATE SET value = excluded.value"
                )
            return hw

        hw = conn.execute(
            "SELECT COALESCE(MAX(id), 0) FROM messages"
        ).fetchone()[0]
        for k, v in (
            ("fts_rebuild_high_water", str(hw)),
            ("fts_rebuild_progress", "0"),
        ):
            conn.execute(
                "INSERT INTO state_meta (key, value) VALUES (?, ?) "
                "ON CONFLICT(key) DO UPDATE SET value = excluded.value",
                (k, v),
            )
        return int(hw)

    def _repair_optimize_bookkeeping(self) -> None:
        """Heal interrupted demote/backfill bookkeeping before optimize runs.

        Covers two post-#65798 failure classes:

        1. Empty external-content index with messages present and no rebuild
           markers (demote crash window after empty v23 tables landed but
           before markers, or settle that stamped without backfill). Seed a
           full backfill.
        2. ``fts_rebuild_high_water`` present without ``fts_rebuild_progress``
           (partial meta) — seed progress so the chunk loop is not a no-op,
           resetting a partially populated index to a known-empty surface
           first so the anti-join-free chunk replay cannot duplicate rows.

        Must not invent markers on a still-legacy inline DB: that would make
        ``optimize_fts_storage`` skip demote (``legacy and not pending``) and
        attempt v23-shaped INSERTs against the inline table forever.
        """
        def _do(conn):
            existing_hw = conn.execute(
                "SELECT value FROM state_meta "
                "WHERE key = 'fts_rebuild_high_water'"
            ).fetchone()

            if existing_hw is not None:
                # Repair orphan high_water-without-progress only. Never
                # invent a fresh claim on a healthy complete index.
                progress = conn.execute(
                    "SELECT 1 FROM state_meta "
                    "WHERE key = 'fts_rebuild_progress'"
                ).fetchone()
                if progress is None:
                    if not self._fts_index_known_empty(conn):
                        self._reset_fts_index_to_empty(conn)
                    conn.execute(
                        "INSERT INTO state_meta (key, value) VALUES "
                        "('fts_rebuild_progress', '0') "
                        "ON CONFLICT(key) DO UPDATE SET value = '0'"
                    )
                return

            # No markers. On a still-legacy DB demote owns marker creation.
            if self._db_has_legacy_inline_fts(conn):
                return

            # Non-legacy empty external index (demote crash window / premature
            # stamp): seed a full backfill claim.
            if self._fts_external_index_empty_with_messages(conn):
                conn.execute(
                    "DELETE FROM state_meta WHERE key = 'fts_storage_version'"
                )
                self._seed_fts_rebuild_markers(conn, force=True)
        self._execute_write(_do)

    def fts_optimize_available(self) -> bool:
        """True when `optimize_fts_storage()` has work to do: either this DB
        is a legacy inline-FTS install that can be optimized to the v23
        external-content schema, or a previous optimize run was interrupted
        (legacy vtables already demoted, but backfill markers and/or trash
        tables remain) and re-running would resume it, or the CJK-bigram
        index needs a backfill/rebuild on this tokenizer-capable host, or
        a prior demote left an empty external-content index without markers
        (healable on re-run).
        False for fresh and fully-optimized installs (and when FTS5 is
        unavailable)."""
        if not self._fts_enabled or self.read_only:
            return False
        with self._lock:
            if self._db_has_legacy_inline_fts(self._conn):
                return True
            # Interrupted optimize: demotion already removed the legacy
            # vtables (so the check above is False), but the transition is
            # unfinished until the backfill markers are cleared and the
            # demoted trash tables are torn down. Search stays complete
            # through the gap supplement meanwhile; re-running resumes.
            if self._conn.execute(
                "SELECT 1 FROM state_meta "
                "WHERE key = 'fts_rebuild_high_water' LIMIT 1"
            ).fetchone():
                return True
            # CJK-bigram index work — only offerable when THIS process can
            # tokenize: a pending backfill (markers set at creation on a
            # populated DB) or a stale index awaiting a from-scratch rebuild.
            if self._fts_cjk_loaded and self._conn.execute(
                "SELECT 1 FROM state_meta WHERE key IN "
                f"('fts_cjk_rebuild_high_water', '{FTS_CJK_STALE_KEY}') LIMIT 1"
            ).fetchone():
                return True
            if self._has_fts_trash(self._conn):
                return True
            # Pre-fix crash window: empty external-content index with
            # messages still present, no markers, no trash (teardown already
            # finished or never needed). Re-run seeds markers and backfills.
            return self._fts_external_index_empty_with_messages(self._conn)

    def _demote_legacy_fts_to_trash(self) -> int:
        """Demote the legacy inline FTS vtables and stage their shadow tables
        for chunked teardown. Returns MAX(messages.id) as the rebuild high
        water. O(1) schema surgery — the heavy delete is deferred to the
        chunked teardown, exactly as the validated auto path did.

        Markers are written in the same BEGIN IMMEDIATE as the demote, *before*
        the empty v23 schema is created. Schema creation uses
        ``executescript`` and therefore cannot run inside that transaction
        (it issues an implicit COMMIT — see the CJK recreate path). Creating
        the empty schema only after markers are durable closes the crash
        window where trash + empty v23 tables exist with no backfill claim.
        """
        def _stage(conn):
            self._drop_fts_triggers(conn)
            conn.execute("DROP VIEW IF EXISTS messages_fts_trigram_src")
            had = bool(conn.execute(
                "SELECT 1 FROM sqlite_master WHERE type = 'table' "
                "AND name IN ('messages_fts', 'messages_fts_trigram') "
                "AND sql LIKE 'CREATE VIRTUAL TABLE%' LIMIT 1"
            ).fetchone())
            if had:
                conn.execute("PRAGMA writable_schema=ON")
                conn.execute(
                    "DELETE FROM sqlite_master WHERE type = 'table' "
                    "AND name IN ('messages_fts', 'messages_fts_trigram') "
                    "AND sql LIKE 'CREATE VIRTUAL TABLE%'"
                )
                conn.execute("PRAGMA writable_schema=RESET")
                shadows = [
                    r[0] for r in conn.execute(
                        "SELECT name FROM sqlite_master WHERE type = 'table' "
                        "AND (name LIKE 'messages_fts_%' ESCAPE '\\' "
                        "OR name LIKE 'messages_fts_trigram_%' ESCAPE '\\')"
                    ).fetchall()
                ]
                for sh in shadows:
                    conn.execute(f"ALTER TABLE {sh} RENAME TO fts_v22_trash_{sh}")
            # Claim the backfill *before* empty v23 tables exist. A crash
            # between this commit and schema ensure still leaves markers, so
            # optimize-storage resumes instead of tearing down trash and
            # stamping an empty index as complete.
            hw = self._seed_fts_rebuild_markers(conn, force=True)
            conn.execute(
                "DELETE FROM state_meta WHERE key = 'fts_optimize_available'"
            )
            return hw

        hw = int(self._execute_write(_stage))

        # Create the empty v23 schema outside the write transaction —
        # ``_ensure_fts_schema`` uses executescript(), which implicitly
        # commits any pending transaction and must not run inside
        # ``_execute_write``'s BEGIN IMMEDIATE (same rule as the CJK recreate
        # path above). Markers are already durable.
        with self._lock:
            base_ok = self._ensure_fts_schema(self._conn, "messages_fts", FTS_SQL)
            trigram_ok = self._ensure_fts_schema(
                self._conn, "messages_fts_trigram", FTS_TRIGRAM_SQL
            )
            self._trigram_available = bool(trigram_ok)
            if not base_ok:
                raise sqlite3.OperationalError(
                    "failed to create v23 messages_fts during optimize-storage demote"
                )
            self._conn.commit()
        return hw

    def optimize_fts_storage(
        self,
        *,
        progress_cb: Optional[Callable[[Dict[str, Any]], None]] = None,
        vacuum: bool = True,
    ) -> Dict[str, Any]:
        """Migrate a legacy v22 inline-FTS DB to the v23 external-content
        schema, foreground and to completion. Safe to re-run: if a previous
        attempt was interrupted it resumes from the progress marker.

        ``progress_cb`` receives {"phase", "percent", "indexed", "total"}
        dicts for a CLI progress bar. Returns a summary dict.

        The trigram tokenizer being unavailable is not fatal — the base index
        is still rebuilt (CJK falls back to LIKE), mirroring normal startup.
        """
        if not self._fts_enabled:
            return {"ok": False, "reason": "fts5_unavailable"}
        if self.read_only:
            return {"ok": False, "reason": "read_only"}

        # Heal empty-index / orphan-marker bookkeeping from an interrupted
        # demote *before* deciding whether to demote again. This re-seeds
        # markers when trash was already staged (or torn down) without a
        # backfill claim so the phases below actually run.
        self._repair_optimize_bookkeeping()

        # Only demote if we're actually still on the legacy shape. If a prior
        # run already demoted (markers/trash present), skip straight to
        # finishing the backfill + teardown — this is what makes re-running
        # after an interruption safe.
        with self._lock:
            legacy = self._db_has_legacy_inline_fts(self._conn)
        pending = self.get_meta("fts_rebuild_high_water") is not None
        if legacy and not pending:
            self._demote_legacy_fts_to_trash()
        elif pending and not legacy:
            # Resume mid-demote: markers exist, empty v23 tables may still be
            # missing if the process died between the staged demote commit and
            # schema ensure. Re-ensure is IF NOT EXISTS and cheap.
            with self._lock:
                base_ok = self._ensure_fts_schema(
                    self._conn, "messages_fts", FTS_SQL
                )
                trigram_ok = self._ensure_fts_schema(
                    self._conn, "messages_fts_trigram", FTS_TRIGRAM_SQL
                )
                self._trigram_available = bool(trigram_ok)
                if not base_ok:
                    # Fail fast: without the base table the backfill loop
                    # below would retry "no such table" errors forever.
                    raise sqlite3.OperationalError(
                        "failed to re-create v23 messages_fts "
                        "on optimize-storage resume"
                    )
                self._conn.commit()

        # A stale CJK index (triggers dropped by a tokenizer-less process)
        # can only be recovered from scratch — reset it now so the cjk
        # backfill phase below rebuilds it. No-op without the tokenizer.
        self._fts_cjk_reset_if_stale()
        # An optimized v23 DB gaining the cjk index for the first time (no
        # legacy work left, tokenizer newly installed): ensure the table +
        # markers exist so the backfill phase has work to claim.
        if self._fts_cjk_loaded:
            with self._lock:
                self._ensure_fts_cjk_schema(self._conn)
                self._conn.commit()

        def _emit(phase: str) -> None:
            if progress_cb is None:
                return
            st = self.fts_rebuild_status()
            if st is None:
                st = self.fts_cjk_rebuild_status()
            progress_cb({
                "phase": phase,
                "percent": st["percent"] if st else 100,
                "indexed": st["indexed"] if st else 0,
                "total": st["total"] if st else 0,
            })

        def _pause(chunk_seconds: float) -> None:
            """Inter-chunk throttle (see the chunk-engine note above).

            The chunk methods themselves never sleep, so this loop is the
            single place the duty cycle is enforced: without it, back-to-back
            BEGIN IMMEDIATE chunks starve any live gateway/CLI process
            sharing the DB out of its lock retries (the measured ~85%
            write-lock ownership that froze concurrent sessions).
            """
            time.sleep(max(
                self._FTS_REBUILD_MIN_PAUSE,
                chunk_seconds * self._FTS_REBUILD_DUTY_FACTOR,
            ))

        # Phase 1: backfill (foreground, throttled between chunks so a live
        # gateway sharing the DB stays responsive).
        _emit("backfill")
        while True:
            _t0 = time.monotonic()
            if not self.fts_rebuild_step():
                break
            _emit("backfill")
            _pause(time.monotonic() - _t0)
        _emit("backfill")

        # Phase 1b: backfill the CJK-bigram index (its own marker pair; a
        # no-op when the tokenizer isn't loadable or nothing is pending).
        while True:
            _t0 = time.monotonic()
            if not self.fts_cjk_rebuild_step():
                break
            _emit("backfill")
            _pause(time.monotonic() - _t0)

        # Phase 2: tear down the demoted legacy shadow tables in chunks.
        _emit("teardown")
        while True:
            _t0 = time.monotonic()
            if not self._fts_teardown_trash_step():
                break
            _emit("teardown")
            _pause(time.monotonic() - _t0)

        # Refuse to stamp "optimized" while work remains or the base index is
        # still empty against a non-empty messages table. Pre-fix code could
        # tear down trash and settle after a no-op backfill when markers were
        # missing — permanent search-index loss for historical rows.
        with self._lock:
            still_pending = self._conn.execute(
                "SELECT 1 FROM state_meta "
                "WHERE key = 'fts_rebuild_high_water' LIMIT 1"
            ).fetchone() is not None
            still_trash = self._has_fts_trash(self._conn)
            empty_index = self._fts_external_index_empty_with_messages(self._conn)
        if still_pending or still_trash or empty_index:
            reason = (
                "backfill_incomplete" if still_pending or empty_index
                else "teardown_incomplete"
            )
            logger.warning(
                "FTS storage optimization did not settle (%s): "
                "pending=%s trash=%s empty_index=%s",
                reason, still_pending, still_trash, empty_index,
            )
            return {"ok": False, "reason": reason, "vacuumed": None}

        # Phase 3: reclaim freed pages to the OS.
        vacuum_ok = None
        if vacuum:
            _emit("vacuum")
            try:
                with self._lock:
                    self._conn.execute("VACUUM")
                vacuum_ok = True
            except sqlite3.OperationalError as exc:
                # Most common cause: not enough free disk for VACUUM's temp
                # copy. The optimization still succeeded; space just isn't
                # reclaimed until a later VACUUM. Non-fatal.
                logger.warning("VACUUM after FTS optimize failed: %s", exc)
                vacuum_ok = False
            # Best-effort: fold the WAL back into the main file so the on-disk
            # size settles now rather than at close(). NOTE this is REFUSED
            # (SQLITE_BUSY) while any other connection holds a WAL read-mark —
            # e.g. a live gateway sharing the DB — so it is not sufficient on
            # its own. Callers must therefore NOT size the result by stat()ing
            # the file; use :meth:`logical_size_bytes`, which is truthful
            # immediately regardless of readers.
            try:
                with self._lock:
                    self._conn.execute("PRAGMA wal_checkpoint(TRUNCATE)")
            except Exception as exc:
                logger.debug(
                    "WAL checkpoint (TRUNCATE) after optimize VACUUM failed: %s",
                    exc,
                )

        # Phase 4: stamp the FTS storage layout as current, clear the "available"
        # flag, and advance schema_version if it was somehow still behind (the
        # main version normally advances on open now, but bump defensively so a
        # DB opened only by pre-decoupling code still settles). The FTS-layout
        # marker is the source of truth for "is this DB optimized".
        def _settle(conn):
            # Re-check inside the write transaction so a concurrent writer
            # cannot race a stamp past incomplete work. Returns a refusal
            # reason (stamping nothing) or None once the stamp is written.
            if conn.execute(
                "SELECT 1 FROM state_meta "
                "WHERE key = 'fts_rebuild_high_water' LIMIT 1"
            ).fetchone() is not None:
                return "backfill_incomplete"
            if self._has_fts_trash(conn):
                return "teardown_incomplete"
            if self._fts_external_index_empty_with_messages(conn):
                return "backfill_incomplete"
            conn.execute(
                "INSERT INTO state_meta (key, value) VALUES ('fts_storage_version', ?) "
                "ON CONFLICT(key) DO UPDATE SET value = excluded.value",
                (str(FTS_STORAGE_VERSION),),
            )
            conn.execute("DELETE FROM state_meta WHERE key = 'fts_optimize_available'")
            conn.execute(
                "UPDATE schema_version SET version = ? WHERE version < ?",
                (SCHEMA_VERSION, SCHEMA_VERSION),
            )
            return None
        refusal = self._execute_write(_settle)
        if refusal is not None:
            # A concurrent process re-seeded markers, left trash, or emptied
            # the index between the pre-vacuum check above and this write
            # transaction. Nothing was stamped. Report the failure instead of
            # crashing the CLI with a traceback; a re-run can still settle.
            logger.warning(
                "FTS storage optimization settle refused (%s)", refusal
            )
            return {"ok": False, "reason": refusal, "vacuumed": vacuum_ok}
        _emit("done")
        logger.info(
            "FTS storage optimization complete (layout v%d).", FTS_STORAGE_VERSION
        )
        return {"ok": True, "vacuumed": vacuum_ok}

    def get_anchored_view(
        self,
        session_id: str,
        around_message_id: int,
        window: int = 5,
        bookend: int = 3,
        keep_roles: Optional[Tuple[str, ...]] = ("user", "assistant"),
    ) -> Dict[str, Any]:
        """Return an anchored window plus session bookends.

        Built on top of ``get_messages_around``. Three slices:

          - ``window``: messages immediately surrounding the anchor. Filtered
            to ``keep_roles`` (tool-response noise dropped by default), EXCEPT
            the anchor itself is always preserved regardless of role.
          - ``bookend_start``: first ``bookend`` user/assistant messages of the
            session — but only those whose id is strictly before the window's
            first message id. Empty when the window already overlaps the
            session head. Empty-content messages (tool-call-only assistant
            turns) are skipped so they don't crowd out actual prose openings.
          - ``bookend_end``: last ``bookend`` user/assistant messages of the
            session, same non-overlap rule at the tail.

        Bookends let an FTS5 hit anywhere in a long session yield the goal
        (opening) and the resolution (closing) on a single call — without
        loading the whole transcript.

        Returns ``{"window": [], "messages_before": 0, "messages_after": 0,
        "bookend_start": [], "bookend_end": []}`` when the anchor isn't in
        the session.

        ``keep_roles=None`` disables role filtering (raw window + raw
        bookends).
        """
        if bookend < 0:
            bookend = 0

        # Reuse the primitive — handles anchor-existence, content decoding,
        # tool_calls deserialisation, and boundary counts.
        primitive = self.get_messages_around(
            session_id, around_message_id, window=window
        )
        window_rows = primitive["window"]
        if not window_rows:
            return {
                "window": [],
                "messages_before": 0,
                "messages_after": 0,
                "bookend_start": [],
                "bookend_end": [],
            }

        # Apply role filter to the window, but never drop the anchor itself.
        if keep_roles is not None:
            keep_set = set(keep_roles)
            filtered_window = [
                m for m in window_rows
                if m.get("id") == around_message_id or m.get("role") in keep_set
            ]
        else:
            filtered_window = window_rows

        window_min_id = window_rows[0]["id"]
        window_max_id = window_rows[-1]["id"]

        # Fetch bookends only when there's room outside the window. SQL filters
        # by id range, role, and non-empty content — tool-call-only assistant
        # turns (content='' with tool_calls populated) are excluded so they
        # don't crowd out actual prose openings/closings.
        bookend_start_rows: List[Any] = []
        bookend_end_rows: List[Any] = []
        if bookend > 0:
            with self._read_ctx() as conn:
                role_clause = ""
                role_params: list = []
                if keep_roles is not None:
                    role_placeholders = ",".join("?" for _ in keep_roles)
                    role_clause = f" AND role IN ({role_placeholders})"
                    role_params = list(keep_roles)

                bookend_start_rows = conn.execute(
                    f"SELECT * FROM messages "
                    f"WHERE session_id = ? AND id < ?{role_clause} "
                    f"AND length(content) > 0 "
                    f"ORDER BY id ASC LIMIT ?",
                    (session_id, window_min_id, *role_params, bookend),
                ).fetchall()

                bookend_end_rows = conn.execute(
                    f"SELECT * FROM messages "
                    f"WHERE session_id = ? AND id > ?{role_clause} "
                    f"AND length(content) > 0 "
                    f"ORDER BY id DESC LIMIT ?",
                    (session_id, window_max_id, *role_params, bookend),
                ).fetchall()
                # End rows came back DESC for the LIMIT cap; flip to ASC.
                bookend_end_rows = list(reversed(bookend_end_rows))

        def _hydrate(row) -> Dict[str, Any]:
            msg = dict(row)
            if "content" in msg:
                msg["content"] = self._decode_content(msg["content"])
            if msg.get("tool_calls"):
                try:
                    msg["tool_calls"] = json.loads(msg["tool_calls"])
                except (json.JSONDecodeError, TypeError):
                    logger.warning(
                        "Failed to deserialize tool_calls in get_anchored_view, falling back to []"
                    )
                    msg["tool_calls"] = []
            if msg.get("display_metadata") is not None:
                msg["display_metadata"] = self._decode_display_metadata(msg["display_metadata"])
            return msg

        return {
            "window": filtered_window,
            "messages_before": primitive["messages_before"],
            "messages_after": primitive["messages_after"],
            "bookend_start": [_hydrate(r) for r in bookend_start_rows],
            "bookend_end": [_hydrate(r) for r in bookend_end_rows],
        }

    def list_recent_user_messages(
        self,
        session_id: str,
        limit: int = 20,
        include_inactive: bool = False,
    ) -> List[Dict[str, Any]]:
        """Return the *limit* most-recent user messages, newest first.

        Each entry is a dict with keys ``id``, ``timestamp``, ``preview``.
        ``preview`` is the first 80 characters of the message content
        (with line breaks collapsed to spaces). Used by the /rewind
        slash command picker, CLI/TUI/gateway ``/undo [N]``, and any other
        caller that needs real user-turn targets.

        Bookkeeping timeline rows (``display_kind`` set — e.g. model_switch,
        async_delegation_complete, auto_continue, hidden) are excluded. They
        are durable ``role='user'`` rows for the API transcript, but no client
        counts them as user turns (desktop demotes them to system / drops them;
        the CLI already uses ``not m.get("display_kind")``). Including them here
        made ``/undo`` soft-delete from a marker instead of the last real turn —
        same class of index skew as the prompt.submit ordinal bug.

        By default only active messages are returned.
        """
        active_clause = "" if include_inactive else " AND active = 1"
        # Match CLI/desktop: only real user turns, not timeline bookkeeping.
        display_clause = " AND (display_kind IS NULL OR display_kind = '')"
        with self._lock:
            cursor = self._conn.execute(
                "SELECT id, timestamp, content FROM messages "
                "WHERE session_id = ? AND role = 'user'"
                f"{active_clause}{display_clause} "
                "ORDER BY id DESC LIMIT ?",
                (session_id, int(limit)),
            )
            rows = cursor.fetchall()

        result: List[Dict[str, Any]] = []
        for row in rows:
            decoded = self._decode_content(row["content"])
            if isinstance(decoded, list):
                # Multimodal — flatten text parts.
                text_parts = [
                    p.get("text", "") for p in decoded
                    if isinstance(p, dict) and p.get("type") == "text"
                ]
                preview = " ".join(t for t in text_parts if t).strip()
                if not preview:
                    preview = "[multimodal content]"
            elif isinstance(decoded, str):
                # A /skill turn embeds the whole skill body; show what the user
                # typed instead of the skill's opening prose.
                preview = describe_skill_invocation(decoded) or decoded
            else:
                preview = ""
            preview = " ".join(preview.split())  # collapse whitespace
            if len(preview) > 80:
                preview = preview[:77] + "..."
            result.append(
                {
                    "id": row["id"],
                    "timestamp": row["timestamp"],
                    "preview": preview,
                }
            )
        return result

    @staticmethod
    def _sanitize_fts5_query(query: str) -> str:
        """Sanitize user input for safe use in FTS5 MATCH queries.

        FTS5 has its own query syntax where characters like ``"``, ``(``, ``)``,
        ``+``, ``*``, ``{``, ``}``, the column-filter operator ``:`` and bare
        boolean operators (``AND``, ``OR``, ``NOT``) have special meaning.
        Passing raw user input directly to MATCH can cause
        ``sqlite3.OperationalError``.

        Strategy:
        - Preserve properly paired quoted phrases (``"exact phrase"``)
        - Strip unmatched FTS5-special characters that would cause errors
        - Wrap unquoted hyphenated and dotted terms in quotes so FTS5
          matches them as exact phrases instead of splitting on the
          hyphen/dot (e.g. ``chat-send``, ``P2.2``, ``my-app.config.ts``)
        """
        # Cap user-controlled FTS input before any regex processing. Search
        # queries do not need to be arbitrarily large, and bounding them keeps
        # sanitizer/runtime behavior predictable under adversarial input.
        query = query[:MAX_FTS5_QUERY_CHARS]

        # Step 1: Extract balanced double-quoted phrases and protect them
        # from further processing via numbered placeholders. Do this with a
        # single linear scan rather than a regex so pathological quote runs
        # cannot induce backtracking.
        _quoted_parts: list = []
        pieces: list[str] = []
        i = 0
        while i < len(query):
            ch = query[i]
            if ch != '"':
                pieces.append(ch)
                i += 1
                continue
            end = query.find('"', i + 1)
            if end == -1:
                # Unmatched quote: replace with whitespace like the old
                # sanitizer's special-char stripping step.
                pieces.append(" ")
                i += 1
                continue
            _quoted_parts.append(query[i:end + 1])
            pieces.append(f"\x00Q{len(_quoted_parts) - 1}\x00")
            i = end + 1

        sanitized = "".join(pieces)

        # Step 2: Strip remaining (unmatched) FTS5-special characters.  ``:`` is
        # FTS5's column-filter operator (``col:term``); since the FTS table has a
        # single ``content`` column, an unquoted colon query like ``TODO: fix``
        # parses as ``column:term`` and raises "no such column" — swallowed at
        # the execute site into zero results.  Strip it like the others.
        sanitized = re.sub(r'[+{}():\"^]', " ", sanitized)

        # Step 3: Collapse repeated * (e.g. "***") into a single one,
        # and remove leading * (prefix-only needs at least one char before *)
        sanitized = re.sub(r"\*+", "*", sanitized)
        sanitized = re.sub(r"(^|\s)\*", r"\1", sanitized)

        # Step 4: Remove dangling boolean operators at start/end that would
        # cause syntax errors (e.g. "hello AND" or "OR world")
        sanitized = re.sub(r"(?i)^(AND|OR|NOT)\b\s*", "", sanitized.strip())
        sanitized = re.sub(r"(?i)\s+(AND|OR|NOT)\s*$", "", sanitized.strip())

        # Step 5: Wrap unquoted dotted and/or hyphenated terms in double
        # quotes.  FTS5's tokenizer splits on dots and hyphens, turning
        # ``chat-send`` into ``chat AND send`` and ``P2.2`` into ``p2 AND 2``.
        # Quoting preserves phrase semantics.  A single pass avoids the
        # double-quoting bug that would occur if dotted, hyphenated and underscored
        # patterns were applied sequentially (e.g. ``my-app.config``).
        sanitized = re.sub(r"\b(\w+(?:[._-]\w+)+)\b", r'"\1"', sanitized)

        # Step 6: Restore preserved quoted phrases
        for i, quoted in enumerate(_quoted_parts):
            sanitized = sanitized.replace(f"\x00Q{i}\x00", quoted)

        return sanitized.strip()

    @staticmethod
    def _is_cjk_codepoint(cp: int) -> bool:
        return (0x4E00 <= cp <= 0x9FFF or    # CJK Unified Ideographs
                0x3400 <= cp <= 0x4DBF or    # CJK Extension A
                0x20000 <= cp <= 0x2A6DF or  # CJK Extension B
                0x3000 <= cp <= 0x303F or    # CJK Symbols
                0x3040 <= cp <= 0x309F or    # Hiragana
                0x30A0 <= cp <= 0x30FF or    # Katakana
                0xAC00 <= cp <= 0xD7AF)      # Hangul Syllables

    @staticmethod
    def _contains_cjk(text: str) -> bool:
        """Check if text contains CJK (Chinese, Japanese, Korean) characters."""
        for ch in text:
            cp = ord(ch)
            if (0x4E00 <= cp <= 0x9FFF or    # CJK Unified Ideographs
                0x3400 <= cp <= 0x4DBF or    # CJK Extension A
                0x20000 <= cp <= 0x2A6DF or  # CJK Extension B
                0x3000 <= cp <= 0x303F or    # CJK Symbols
                0x3040 <= cp <= 0x309F or    # Hiragana
                0x30A0 <= cp <= 0x30FF or    # Katakana
                0xAC00 <= cp <= 0xD7AF):     # Hangul Syllables
                return True
        return False

    @classmethod
    def _count_cjk(cls, text: str) -> int:
        """Count CJK characters in text."""
        return sum(1 for ch in text if cls._is_cjk_codepoint(ord(ch)))

    @classmethod
    def _has_lone_cjk_run(cls, query: str) -> bool:
        """True when any maximal CJK run in the query is a single char.

        The cjk-bigram index stores bigrams for runs >=2 chars and unigrams
        only for isolated chars, so a 1-char CJK term can't match inside
        longer runs there — those queries keep the LIKE substring route.
        """
        run = 0
        for ch in query:
            if cls._is_cjk_codepoint(ord(ch)):
                run += 1
            else:
                if run == 1:
                    return True
                run = 0
        return run == 1

    @staticmethod
    def _trigram_eligible_tokens(query: str) -> bool:
        """True when every non-operator token is long enough for the trigram
        tokenizer to match (>=3 chars).

        The trigram tokenizer indexes overlapping 3-character sequences, so a
        token shorter than 3 chars produces no trigrams and can never match.
        With FTS5's implicit-AND between tokens, a single short token makes the
        whole MATCH return nothing, so the trigram path is only worth taking
        when every searchable token qualifies.
        """
        tokens = [
            t for t in query.strip('"').strip().split()
            if t.upper() not in {"AND", "OR", "NOT"}
        ]
        return bool(tokens) and all(len(t) >= 3 for t in tokens)

    def _run_trigram_search(
        self,
        raw_query: str,
        *,
        table: str = "messages_fts_trigram",
        order_by_sql: str,
        include_inactive: bool,
        source_filter: List[str] = None,
        exclude_sources: List[str] = None,
        role_filter: List[str] = None,
        limit: int = 20,
        offset: int = 0,
    ) -> Optional[List[Dict[str, Any]]]:
        """Run a search against a substring-capable FTS index.

        ``table`` is ``messages_fts_trigram`` (default) or
        ``messages_fts_cjk``. The trigram tokenizer indexes overlapping
        3-byte sequences, so it matches substrings regardless of word
        boundaries — both CJK phrases the unicode61 tokenizer splits into
        single characters and Latin runs the unicode61 tokenizer fuses onto
        adjacent CJK (e.g. ``修改youer服务端``). The cjk-bigram tokenizer
        splits Latin runs off adjacent CJK, giving the same recovery as an
        exact ranked token match. Each non-operator token is quoted to
        neutralise FTS5 special characters while boolean operators
        (AND/OR/NOT) are preserved.

        Returns the matching rows, or ``None`` when the query cannot be
        executed (e.g. the tokenizer is unavailable at runtime) so the
        caller can fall back to another strategy.
        """
        tokens = raw_query.split()
        parts = []
        for tok in tokens:
            if tok.upper() in {"AND", "OR", "NOT"}:
                parts.append(tok)
            else:
                parts.append('"' + tok.replace('"', '""') + '"')
        trigram_query = " ".join(parts)
        tri_where = [f"{table} MATCH ?"]
        tri_params: list = [trigram_query]
        if not include_inactive:
            tri_where.append("(m.active = 1 OR m.compacted = 1)")
        if source_filter is not None:
            tri_where.append(f"s.source IN ({','.join('?' for _ in source_filter)})")
            tri_params.extend(source_filter)
        if exclude_sources is not None:
            tri_where.append(f"s.source NOT IN ({','.join('?' for _ in exclude_sources)})")
            tri_params.extend(exclude_sources)
        if role_filter:
            tri_where.append(f"m.role IN ({','.join('?' for _ in role_filter)})")
            tri_params.extend(role_filter)
        tri_sql = f"""
            SELECT
                m.id,
                m.session_id,
                m.role,
                snippet({table}, -1, '>>>', '<<<', '...', 40) AS snippet,
                m.content,
                m.timestamp,
                m.tool_name,
                s.source,
                s.model,
                s.started_at AS session_started
            FROM {table}
            JOIN messages m ON m.id = {table}.rowid
            JOIN sessions s ON s.id = m.session_id
            WHERE {' AND '.join(tri_where)}
            {order_by_sql}
            LIMIT ? OFFSET ?
        """
        tri_params.extend([limit, offset])
        with self._read_ctx() as conn:
            try:
                tri_cursor = conn.execute(tri_sql, tri_params)
            except sqlite3.OperationalError:
                # Query failed at runtime — let the caller fall back.
                return None
            return [dict(row) for row in tri_cursor.fetchall()]

    def search_messages(
        self,
        query: str,
        source_filter: List[str] = None,
        exclude_sources: List[str] = None,
        role_filter: List[str] = None,
        limit: int = 20,
        offset: int = 0,
        sort: str = None,
        include_inactive: bool = False,
        fields: Optional[Collection[str]] = None,
    ) -> List[Dict[str, Any]]:
        """Instrumented wrapper around :meth:`_search_messages_impl`.

        Logs one line per slow search with the routing path taken, so
        production latency stays attributable per query shape (the 2026-07
        session_search investigation needed trace archaeology to discover
        the LIKE full scans; this makes the next regression a grep).
        Threshold: HERMES_SEARCH_SLOW_MS (default 1000; 0 logs every call).
        """
        started = time.time()
        rows = None
        try:
            rows = self._search_messages_impl(
                query,
                source_filter=source_filter,
                exclude_sources=exclude_sources,
                role_filter=role_filter,
                limit=limit,
                offset=offset,
                sort=sort,
                include_inactive=include_inactive,
                fields=fields,
            )
            return rows
        finally:
            try:
                threshold = float(os.getenv("HERMES_SEARCH_SLOW_MS", "1000"))
            except (TypeError, ValueError):
                threshold = 1000.0
            elapsed_ms = (time.time() - started) * 1000.0
            if elapsed_ms >= threshold:
                logger.info(
                    "slow session search: path=%s elapsed=%.0fms rows=%s query=%r",
                    self._describe_search_path(query),
                    elapsed_ms,
                    len(rows) if rows is not None else "err",
                    query[:200],
                )

    def _describe_search_path(self, query: str) -> str:
        """Best-effort name of the routing path a query takes (log-only)."""
        try:
            sanitized = self._sanitize_fts5_query(query or "")
            if not sanitized:
                return "empty"
            if not self._contains_cjk(sanitized):
                return "fts5"
            raw = sanitized.strip('"').strip()
            if self._fts_cjk_available and not self._has_lone_cjk_run(raw):
                return "fts_cjk"
            tokens = [
                t for t in raw.split()
                if t.upper() not in {"AND", "OR", "NOT"} and self._contains_cjk(t)
            ]
            short = any(self._count_cjk(t) < 3 for t in tokens)
            if self._count_cjk(raw) >= 3 and not short and self._trigram_available:
                return "trigram"
            return "like_scan"
        except Exception:
            return "unknown"

    def _search_messages_impl(
        self,
        query: str,
        source_filter: List[str] = None,
        exclude_sources: List[str] = None,
        role_filter: List[str] = None,
        limit: int = 20,
        offset: int = 0,
        sort: str = None,
        include_inactive: bool = False,
        fields: Optional[Collection[str]] = None,
    ) -> List[Dict[str, Any]]:
        """
        Full-text search across session messages using FTS5.

        Supports FTS5 query syntax:
          - Simple keywords: "docker deployment"
          - Phrases: '"exact phrase"'
          - Boolean: "docker OR kubernetes", "python NOT java"
          - Prefix: "deploy*"

        Returns matching messages with session metadata, content snippet,
        and surrounding context (1 message before and after the match).
        ``fields`` selects a result projection; omitting it preserves the
        complete legacy result. Context is only loaded when that projection
        consumes it.

        ``sort`` controls temporal ordering:
          - ``None`` (default): FTS5 BM25 relevance only. Time-neutral.
          - ``"newest"``: order by message timestamp DESC, then by rank.
          - ``"oldest"``: order by message timestamp ASC, then by rank.

        The short-CJK LIKE fallback already orders by timestamp DESC and
        ignores ``sort``. The trigram CJK path honours ``sort`` like the main
        FTS5 path.

        Rewound (``active=0``, ``compacted=0``) rows are excluded by default —
        the user took those back. Compaction-archived rows (``active=0``,
        ``compacted=1``) ARE included by default: they were summarized away from
        the live context but remain part of the conversation's record, so the
        pre-compaction transcript stays discoverable after in-place compaction
        (#38763). Pass ``include_inactive=True`` to search every row regardless.
        """
        result_fields = self._search_message_fields(fields)

        if not self._fts_enabled:
            return []

        if not query or not query.strip():
            return []

        query = self._sanitize_fts5_query(query)
        if not query:
            return []

        # Normalise sort. Anything not in the allowed set falls back to None
        # (FTS5 rank-only) so callers can pass through user input without
        # validation.
        if isinstance(sort, str):
            sort_norm = sort.strip().lower()
            if sort_norm not in ("newest", "oldest"):
                sort_norm = None
        else:
            sort_norm = None

        # ORDER BY shared across the main FTS5 path and trigram CJK path.
        # With sort set, timestamp is primary and rank is the tiebreaker.
        if sort_norm == "newest":
            order_by_sql = "ORDER BY m.timestamp DESC, rank"
        elif sort_norm == "oldest":
            order_by_sql = "ORDER BY m.timestamp ASC, rank"
        else:
            order_by_sql = "ORDER BY rank"

        # Build WHERE clauses dynamically
        where_clauses = ["messages_fts MATCH ?"]
        params: list = [query]
        if not include_inactive:
            # Live rows (active=1) AND compaction-archived rows (compacted=1)
            # are discoverable; only rewind/undo rows (active=0, compacted=0)
            # are hidden. See archive_and_compact() / #38763.
            where_clauses.append("(m.active = 1 OR m.compacted = 1)")

        if source_filter is not None:
            source_placeholders = ",".join("?" for _ in source_filter)
            where_clauses.append(f"s.source IN ({source_placeholders})")
            params.extend(source_filter)

        if exclude_sources is not None:
            exclude_placeholders = ",".join("?" for _ in exclude_sources)
            where_clauses.append(f"s.source NOT IN ({exclude_placeholders})")
            params.extend(exclude_sources)

        if role_filter:
            role_placeholders = ",".join("?" for _ in role_filter)
            where_clauses.append(f"m.role IN ({role_placeholders})")
            params.extend(role_filter)

        where_sql = " AND ".join(where_clauses)
        params.extend([limit, offset])

        sql = f"""
            SELECT
                m.id,
                m.session_id,
                m.role,
                snippet(messages_fts, -1, '>>>', '<<<', '...', 40) AS snippet,
                m.content,
                m.timestamp,
                m.tool_name,
                s.source,
                s.model,
                s.started_at AS session_started
            FROM messages_fts
            JOIN messages m ON m.id = messages_fts.rowid
            JOIN sessions s ON s.id = m.session_id
            WHERE {where_sql}
            {order_by_sql}
            LIMIT ? OFFSET ?
        """

        # CJK queries bypass the unicode61 FTS5 table.  The default tokenizer
        # splits CJK characters into individual tokens, so "大别山项目" becomes
        # "大 AND 别 AND 山 AND 项 AND 目" — producing false positives and
        # missing exact phrase matches.
        #
        # For queries with 3+ CJK characters, we use the trigram FTS5 table
        # (indexed substring matching with ranking and snippets).  For shorter
        # CJK queries (1-2 chars), trigram can't match (it needs ≥9 UTF-8
        # bytes = 3 CJK chars), so we fall back to LIKE.
        matches: List[Dict[str, Any]] = []
        is_cjk = self._contains_cjk(query)
        if is_cjk:
            raw_query = query.strip('"').strip()
            cjk_count = self._count_cjk(raw_query)

            # Per-token CJK length check (#20494): trigram needs >=3 CJK chars
            # per token. A query like "广西 OR 桂林 OR 漓江" has cjk_count=6
            # (>=3) but each individual token is only 2 chars — trigram returns 0.
            # Route to LIKE when any non-operator CJK token is <3 CJK chars.
            _tokens_for_check = [
                t for t in raw_query.split()
                if t.upper() not in {"AND", "OR", "NOT"} and self._contains_cjk(t)
            ]
            _any_short_cjk = any(
                self._count_cjk(t) < 3 for t in _tokens_for_check
            )

            _trigram_succeeded = False
            # Tool rows are excluded from the trigram index (they're ~90% of
            # message bytes and machine noise — see FTS_TRIGRAM_SQL). A CJK
            # query explicitly filtering on role='tool' must therefore use
            # the LIKE fallback, which scans the base table directly.
            _wants_tool_rows = bool(role_filter) and "tool" in role_filter

            # ── CJK-bigram route (messages_fts_cjk, cjk_unicode61) ──────
            # When the bigram index is available it serves EVERY CJK query
            # shape the legacy code split between trigram (>=3 chars/token)
            # and LIKE full scans (1-2 char tokens) — the whole point of the
            # index (PR #65544). Exceptions stay on the legacy routes:
            #   - role_filter=['tool'] queries (tool rows aren't in the cjk
            #     index, same exclusion as trigram),
            #   - queries containing a LONE 1-char CJK run: the index stores
            #     bigrams for runs >=2, so a single-char term can only match
            #     isolated chars — LIKE substring semantics are broader.
            if (
                self._fts_cjk_available
                and not _wants_tool_rows
                and not self._has_lone_cjk_run(raw_query)
            ):
                tokens = raw_query.split()
                parts = []
                for tok in tokens:
                    if tok.upper() in {"AND", "OR", "NOT"}:
                        parts.append(tok)
                    else:
                        parts.append('"' + tok.replace('"', '""') + '"')
                cjk_query = " ".join(parts)
                cjk_where = ["messages_fts_cjk MATCH ?"]
                cjk_params: list = [cjk_query]
                if not include_inactive:
                    cjk_where.append("(m.active = 1 OR m.compacted = 1)")
                if source_filter is not None:
                    cjk_where.append(f"s.source IN ({','.join('?' for _ in source_filter)})")
                    cjk_params.extend(source_filter)
                if exclude_sources is not None:
                    cjk_where.append(f"s.source NOT IN ({','.join('?' for _ in exclude_sources)})")
                    cjk_params.extend(exclude_sources)
                if role_filter:
                    cjk_where.append(f"m.role IN ({','.join('?' for _ in role_filter)})")
                    cjk_params.extend(role_filter)
                cjk_sql = f"""
                    SELECT
                        m.id,
                        m.session_id,
                        m.role,
                        snippet(messages_fts_cjk, -1, '>>>', '<<<', '...', 40) AS snippet,
                        m.content,
                        m.timestamp,
                        m.tool_name,
                        s.source,
                        s.model,
                        s.started_at AS session_started
                    FROM messages_fts_cjk
                    JOIN messages m ON m.id = messages_fts_cjk.rowid
                    JOIN sessions s ON s.id = m.session_id
                    WHERE {' AND '.join(cjk_where)}
                    {order_by_sql}
                    LIMIT ? OFFSET ?
                """
                cjk_params.extend([limit, offset])
                try:
                    with self._read_ctx() as conn:
                        cjk_cursor = conn.execute(cjk_sql, cjk_params)
                        matches = [dict(row) for row in cjk_cursor.fetchall()]
                        _trigram_succeeded = True
                except sqlite3.OperationalError:
                    # Tokenizer missing on this connection / query syntax —
                    # the trigram + LIKE routes below still answer.
                    logger.debug(
                        "messages_fts_cjk query failed; falling back to "
                        "trigram/LIKE", exc_info=True,
                    )
                except sqlite3.DatabaseError as exc:
                    # Same corruption class as the other FTS reads: rebuild
                    # in place once and retry; on refusal/failure fall back.
                    if self._try_runtime_fts_rebuild(exc):
                        try:
                            with self._read_ctx() as conn:
                                cjk_cursor = conn.execute(
                                    cjk_sql, cjk_params
                                )
                                matches = [
                                    dict(row) for row in cjk_cursor.fetchall()
                                ]
                                _trigram_succeeded = True
                        except sqlite3.DatabaseError:
                            logger.warning(
                                "CJK-bigram FTS search still failing after "
                                "in-place rebuild; falling back to "
                                "trigram/LIKE."
                            )
                    else:
                        logger.warning(
                            "CJK-bigram FTS search hit a corruption error "
                            "(%s) and no in-place rebuild was possible; "
                            "falling back to trigram/LIKE.", exc,
                        )

            if (
                not _trigram_succeeded
                and cjk_count >= 3
                and not _any_short_cjk
                and self._trigram_available
                and not _wants_tool_rows
            ):
                # Trigram FTS5 path — quote each non-operator token to handle
                # FTS5 special chars (%, *, etc.) while preserving boolean
                # operators (AND, OR, NOT) for multi-term queries.
                tokens = raw_query.split()
                parts = []
                for tok in tokens:
                    if tok.upper() in {"AND", "OR", "NOT"}:
                        parts.append(tok)
                    else:
                        parts.append('"' + tok.replace('"', '""') + '"')
                trigram_query = " ".join(parts)
                tri_where = ["messages_fts_trigram MATCH ?"]
                tri_params: list = [trigram_query]
                if not include_inactive:
                    tri_where.append("(m.active = 1 OR m.compacted = 1)")
                if source_filter is not None:
                    tri_where.append(f"s.source IN ({','.join('?' for _ in source_filter)})")
                    tri_params.extend(source_filter)
                if exclude_sources is not None:
                    tri_where.append(f"s.source NOT IN ({','.join('?' for _ in exclude_sources)})")
                    tri_params.extend(exclude_sources)
                if role_filter:
                    tri_where.append(f"m.role IN ({','.join('?' for _ in role_filter)})")
                    tri_params.extend(role_filter)
                tri_sql = f"""
                    SELECT
                        m.id,
                        m.session_id,
                        m.role,
                        snippet(messages_fts_trigram, -1, '>>>', '<<<', '...', 40) AS snippet,
                        m.content,
                        m.timestamp,
                        m.tool_name,
                        s.source,
                        s.model,
                        s.started_at AS session_started
                    FROM messages_fts_trigram
                    JOIN messages m ON m.id = messages_fts_trigram.rowid
                    JOIN sessions s ON s.id = m.session_id
                    WHERE {' AND '.join(tri_where)}
                    {order_by_sql}
                    LIMIT ? OFFSET ?
                """
                tri_params.extend([limit, offset])
                try:
                    with self._read_ctx() as conn:
                        tri_cursor = conn.execute(tri_sql, tri_params)
                        matches = [dict(row) for row in tri_cursor.fetchall()]
                        _trigram_succeeded = True
                except sqlite3.OperationalError:
                    # Trigram query failed at runtime — fall through to LIKE.
                    pass
                except sqlite3.DatabaseError as exc:
                    # Same corruption class the main FTS5 MATCH branch
                    # self-heals above: a corrupt trigram shadow table raises
                    # malformed / "fts5: corrupt structure record", which is a
                    # DatabaseError (parent of the OperationalError syntax arm
                    # caught first). Rebuild once outside the lock — the lock
                    # is released here so rebuild_fts() can re-acquire it —
                    # and retry the trigram query. If the rebuild is refused
                    # (already attempted / FTS disabled / different error
                    # class) or the retry fails again, fall through to the
                    # LIKE substring path, which reads only the canonical
                    # messages table, so CJK search stays available.
                    if self._try_runtime_fts_rebuild(exc):
                        try:
                            with self._read_ctx() as conn:
                                tri_cursor = conn.execute(
                                    tri_sql, tri_params
                                )
                                matches = [
                                    dict(row) for row in tri_cursor.fetchall()
                                ]
                                _trigram_succeeded = True
                        except sqlite3.DatabaseError:
                            logger.warning(
                                "Trigram FTS search still failing after "
                                "in-place rebuild; falling back to LIKE."
                            )
                    else:
                        logger.warning(
                            "Trigram FTS search hit a corruption error (%s) "
                            "and no in-place rebuild was possible; falling "
                            "back to LIKE.", exc,
                        )
            if not _trigram_succeeded:
                # Short / mixed CJK query, trigram unavailable, or trigram
                # <3 CJK chars. Fall back to LIKE substring search.
                # For multi-token OR queries (e.g. "广西 OR 桂林 OR 漓江"),
                # build one LIKE condition per non-operator token so each term
                # is matched independently (#20494).
                non_op_tokens = [
                    t for t in raw_query.split()
                    if t.upper() not in {"AND", "OR", "NOT"}
                ] or [raw_query]
                token_clauses = []
                like_params: list = []
                for tok in non_op_tokens:
                    esc = tok.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")
                    token_clauses.append(
                        "(m.content LIKE ? ESCAPE '\\' OR m.tool_name LIKE ? ESCAPE '\\' OR m.tool_calls LIKE ? ESCAPE '\\')"
                    )
                    like_params += [f"%{esc}%", f"%{esc}%", f"%{esc}%"]
                like_where = [f"({' OR '.join(token_clauses)})"]
                if not include_inactive:
                    # Same visibility rule as the FTS5 paths: live rows and
                    # compaction-archived rows are discoverable; rewind/undo
                    # rows (active=0, compacted=0) are hidden (#38763).
                    like_where.append("(m.active = 1 OR m.compacted = 1)")
                if source_filter is not None:
                    like_where.append(f"s.source IN ({','.join('?' for _ in source_filter)})")
                    like_params.extend(source_filter)
                if exclude_sources is not None:
                    like_where.append(f"s.source NOT IN ({','.join('?' for _ in exclude_sources)})")
                    like_params.extend(exclude_sources)
                if role_filter:
                    like_where.append(f"m.role IN ({','.join('?' for _ in role_filter)})")
                    like_params.extend(role_filter)
                like_sql = f"""
                    SELECT m.id, m.session_id, m.role,
                           substr(m.content,
                                  max(1, instr(m.content, ?) - 40),
                                  120) AS snippet,
                           m.content, m.timestamp, m.tool_name,
                           s.source, s.model, s.started_at AS session_started
                    FROM messages m
                    JOIN sessions s ON s.id = m.session_id
                    WHERE {' AND '.join(like_where)}
                    ORDER BY m.timestamp DESC
                    LIMIT ? OFFSET ?
                """
                like_params.extend([limit, offset])
                # instr() for snippet uses first search token
                like_params = [non_op_tokens[0]] + like_params
                with self._read_ctx() as conn:
                    like_cursor = conn.execute(like_sql, like_params)
                    matches = [dict(row) for row in like_cursor.fetchall()]
        else:
            try:
                with self._read_ctx() as conn:
                    cursor = conn.execute(sql, params)
                    matches = [dict(row) for row in cursor.fetchall()]
            except sqlite3.OperationalError:
                # FTS5 query syntax error despite sanitization — return empty
                return []
            except sqlite3.DatabaseError as exc:
                # A corrupt FTS index raises the malformed / "fts5: corrupt
                # structure record" class on the MATCH read, the same class the
                # write path self-heals (#66296). OperationalError (query
                # syntax) is a subclass caught above; this arm is the corruption
                # parent. Rebuild the index in place once — the read context
                # holds no writer lock, so rebuild_fts() can acquire it — and
                # retry, so search self-heals for read-only sessions (cron/CLI
                # history search) that never trigger a write to repair it first.
                if not self._try_runtime_fts_rebuild(exc):
                    raise
                with self._read_ctx() as conn:
                    cursor = conn.execute(sql, params)
                    matches = [dict(row) for row in cursor.fetchall()]

        # Deferred-rebuild supplement (schema v23): while the background
        # backfill is pending, the FTS indexes only cover rows outside the
        # (progress, high_water] gap. Top the results up with a bounded LIKE
        # scan over just that id range so search never silently loses old
        # messages mid-rebuild. The range shrinks as the backfill advances,
        # so this cost decays to zero. The CJK LIKE-fallback path above
        # already scans the whole base table and needs no supplement.
        rebuild_status = self.fts_rebuild_status()
        if rebuild_status is not None and len(matches) < limit:
            try:
                gap_matches = self._search_unindexed_gap(
                    query,
                    limit - len(matches),
                    include_inactive=include_inactive,
                    source_filter=source_filter,
                    exclude_sources=exclude_sources,
                    role_filter=role_filter,
                )
                seen_ids = {m["id"] for m in matches}
                matches.extend(m for m in gap_matches if m["id"] not in seen_ids)
            except sqlite3.OperationalError as exc:
                logger.debug("Unindexed-gap supplement skipped: %s", exc)

        # Pure-Latin queries run against the unicode61 ``messages_fts`` table,
        # whose tokenizer does not insert a boundary between Latin letters and
        # adjacent CJK characters: "修改youer服务端" is indexed as one token,
        # so MATCH "youer" finds nothing even though the substring is present
        # (#54242). When the exact-token search returns nothing, retry on the
        # substring-capable indexes. Preference order:
        #   1. messages_fts_cjk (when built): its tokenizer splits Latin runs
        #      off adjacent CJK, so "youer" is an exact ranked token match.
        #   2. messages_fts_trigram: substring matching, needs >=3-char
        #      tokens (shorter tokens produce no trigrams).
        # Gated on a zero-result miss so successful Latin searches keep their
        # unicode61 ranking — strictly additive, never reorders existing
        # hits. Trade-off on the trigram leg: any zero-result Latin query
        # gains substring semantics (e.g. "cat" can then match
        # "concatenate"). Genuinely absent terms still return []. Skipped for
        # role_filter=['tool'] queries — both fallback indexes exclude tool
        # rows (v23), so a retry could never add hits.
        if (
            not matches
            and not is_cjk
            and not (bool(role_filter) and "tool" in role_filter)
        ):
            _fb_query = query.strip('"').strip()
            if self._fts_cjk_available:
                cjk_fb = self._run_trigram_search(
                    _fb_query,
                    table="messages_fts_cjk",
                    order_by_sql=order_by_sql,
                    include_inactive=include_inactive,
                    source_filter=source_filter,
                    exclude_sources=exclude_sources,
                    role_filter=role_filter,
                    limit=limit,
                    offset=offset,
                )
                if cjk_fb:
                    matches = cjk_fb
            if (
                not matches
                and self._trigram_available
                and self._trigram_eligible_tokens(query)
            ):
                tri_matches = self._run_trigram_search(
                    _fb_query,
                    order_by_sql=order_by_sql,
                    include_inactive=include_inactive,
                    source_filter=source_filter,
                    exclude_sources=exclude_sources,
                    role_filter=role_filter,
                    limit=limit,
                    offset=offset,
                )
                if tri_matches:
                    matches = tri_matches

        # Add surrounding context (1 message before + after each match) only
        # when the selected result projection consumes it. Each query takes
        # its own fresh read transaction via _read_ctx, so we never hold a
        # lock across N sequential queries.
        context_matches = (
            matches if result_fields is None or "context" in result_fields else ()
        )
        for match in context_matches:
            try:
                with self._read_ctx() as conn:
                    ctx_cursor = conn.execute(
                        """WITH target AS (
                               SELECT session_id, timestamp, id
                               FROM messages
                               WHERE id = ?
                           )
                           SELECT role, content
                           FROM (
                               SELECT m.id, m.timestamp, m.role, m.content
                               FROM messages m
                               JOIN target t ON t.session_id = m.session_id
                               WHERE (m.timestamp < t.timestamp)
                                  OR (m.timestamp = t.timestamp AND m.id < t.id)
                               ORDER BY m.timestamp DESC, m.id DESC
                               LIMIT 1
                           )
                           UNION ALL
                           SELECT role, content
                           FROM messages
                           WHERE id = ?
                           UNION ALL
                           SELECT role, content
                           FROM (
                               SELECT m.id, m.timestamp, m.role, m.content
                               FROM messages m
                               JOIN target t ON t.session_id = m.session_id
                               WHERE (m.timestamp > t.timestamp)
                                  OR (m.timestamp = t.timestamp AND m.id > t.id)
                               ORDER BY m.timestamp ASC, m.id ASC
                               LIMIT 1
                           )""",
                        (match["id"], match["id"]),
                    )
                    context_msgs = []
                    for r in ctx_cursor.fetchall():
                        raw = r["content"]
                        decoded = self._decode_content(raw)
                        # Multimodal context: render a compact text-only
                        # summary for search previews.
                        if isinstance(decoded, list):
                            text_parts = [
                                p.get("text", "") for p in decoded
                                if isinstance(p, dict) and p.get("type") == "text"
                            ]
                            text = " ".join(t for t in text_parts if t).strip()
                            preview = text or "[multimodal content]"
                        elif isinstance(decoded, str):
                            preview = decoded
                        else:
                            preview = ""
                        context_msgs.append(
                            {"role": r["role"], "content": preview[:200]}
                        )
                match["context"] = context_msgs
            except Exception:
                match["context"] = []

        # Remove full content from result (snippet is enough, saves tokens)
        for match in matches:
            match.pop("content", None)

        if result_fields is not None:
            matches = [
                {field: match[field] for field in result_fields if field in match}
                for match in matches
            ]

        return matches

    def _search_unindexed_gap(
        self,
        fts_query: str,
        limit: int,
        *,
        include_inactive: bool = False,
        source_filter: Optional[List[str]] = None,
        exclude_sources: Optional[List[str]] = None,
        role_filter: Optional[List[str]] = None,
    ) -> List[Dict[str, Any]]:
        """LIKE-scan the rows the deferred rebuild hasn't indexed yet.

        Only touches ids in (fts_rebuild_progress, fts_rebuild_high_water] —
        a range that shrinks to nothing as the backfill advances. The FTS
        query is degraded to per-token substring terms (AND-joined; quoted
        phrases kept whole), which is deliberately recall-over-precision:
        temporary results beat silently missing ones mid-rebuild.
        """
        status = self.fts_rebuild_status()
        if status is None or limit <= 0:
            return []
        progress, high_water = status["indexed"], status["total"]

        # Degrade the FTS query to LIKE terms: strip operators/wildcards,
        # keep quoted phrases intact, AND the rest.
        terms: List[str] = []
        for raw_tok in re.findall(r'"[^"]+"|\S+', fts_query):
            tok = raw_tok.strip('"').strip("*").strip()
            if not tok or tok.upper() in {"AND", "OR", "NOT", "NEAR"}:
                continue
            terms.append(tok)
        if not terms:
            return []

        where = ["m.id > ? AND m.id <= ?"]
        params: list = [progress, high_water]
        for term in terms:
            esc = term.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")
            where.append(
                "(m.content LIKE ? ESCAPE '\\' OR m.tool_name LIKE ? ESCAPE '\\' "
                "OR m.tool_calls LIKE ? ESCAPE '\\')"
            )
            params += [f"%{esc}%"] * 3
        if not include_inactive:
            where.append("(m.active = 1 OR m.compacted = 1)")
        if source_filter is not None:
            where.append(f"s.source IN ({','.join('?' for _ in source_filter)})")
            params.extend(source_filter)
        if exclude_sources is not None:
            where.append(f"s.source NOT IN ({','.join('?' for _ in exclude_sources)})")
            params.extend(exclude_sources)
        if role_filter:
            where.append(f"m.role IN ({','.join('?' for _ in role_filter)})")
            params.extend(role_filter)

        sql = f"""
            SELECT m.id, m.session_id, m.role,
                   substr(m.content,
                          max(1, instr(m.content, ?) - 40),
                          120) AS snippet,
                   m.content, m.timestamp, m.tool_name,
                   s.source, s.model, s.started_at AS session_started
            FROM messages m
            JOIN sessions s ON s.id = m.session_id
            WHERE {' AND '.join(where)}
            ORDER BY m.timestamp DESC
            LIMIT ?
        """
        params = [terms[0]] + params + [limit]
        with self._read_ctx() as conn:
            rows = conn.execute(sql, params).fetchall()
        return [dict(r) for r in rows]

    def search_sessions_by_id(
        self,
        query: str,
        limit: int = 20,
        include_archived: bool = True,
        source: str = None,
        sources: List[str] = None,
        exclude_sources: List[str] = None,
    ) -> List[Dict[str, Any]]:
        """Search surfaced sessions by exact/prefix/substring session id.

        Desktop search uses this alongside FTS message search so users can paste
        a session id from logs, CLI output, or another Hermes surface and jump
        straight to that conversation.  Matching also checks ``_lineage_root_id``
        for projected compression-chain tips, so an old root id still resolves to
        the live continuation row.
        """
        needle = (query or "").strip().lower()
        if not needle or limit <= 0:
            return []

        # SQL-bounded: list_sessions_rich pushes the id LIKE filter into the
        # query (matching the row's own id AND any id in its forward
        # compression chain), so we only materialize matching rows instead of
        # scanning every session. Fetch a small multiple of `limit` so the
        # in-Python exact/prefix/substring ranking below has enough candidates
        # to order, then truncate.
        candidates = self.list_sessions_rich(
            source=source,
            sources=sources,
            exclude_sources=exclude_sources,
            limit=max(limit * 4, limit),
            offset=0,
            include_archived=include_archived,
            order_by_last_active=True,
            id_query=needle,
        )

        def score(row: Dict[str, Any]) -> int:
            ids = [str(row.get("id") or ""), str(row.get("_lineage_root_id") or "")]
            normalized = [value.lower() for value in ids if value]
            if any(value == needle for value in normalized):
                return 0
            if any(value.startswith(needle) for value in normalized):
                return 1
            return 2

        ranked = sorted(
            enumerate(candidates),
            key=lambda item: (score(item[1]), item[0]),
        )
        return [row for _, row in ranked[:limit]]

    def _fts_table_exists(self, name: str) -> bool:
        """True if an FTS5 virtual table is queryable in this DB."""
        try:
            self._conn.execute(f"SELECT 1 FROM {name} LIMIT 0")
            return True
        except sqlite3.DatabaseError:
            # OperationalError ("no such table") or the broader
            # DatabaseError class ("vtable constructor failed", raised when
            # e.g. a required tokenizer is missing or the table is mid-
            # teardown) — in every case the table is not queryable.
            return False

    def optimize_fts(self) -> int:
        """Merge fragmented FTS5 b-tree segments into one per index.

        FTS5 indexes grow as a series of incremental segments — one per
        ``INSERT`` batch driven by the message triggers. Over tens of
        thousands of messages these segments accumulate, which both bloats
        the ``*_data`` shadow tables and slows ``MATCH`` queries that must
        scan every segment. The special ``'optimize'`` command rewrites each
        index as a single merged segment.

        This is purely a maintenance operation — it changes neither search
        results nor ``snippet()`` output, only on-disk layout and query
        speed. It is complementary to VACUUM: ``optimize`` compacts the FTS
        index internally, then VACUUM returns the freed pages to the OS.

        Skips any FTS table that does not exist (e.g. the trigram index when
        disabled via ``HERMES_DISABLE_FTS_TRIGRAM`` or not yet created), so
        it is safe to call unconditionally.

        Returns the number of FTS indexes that were optimized.
        """
        optimized = 0
        with self._lock:
            for tbl in self._FTS_TABLES:
                if not self._fts_table_exists(tbl):
                    continue
                try:
                    # The column name in the INSERT must match the table name
                    # for FTS5 special commands.
                    self._conn.execute(
                        f"INSERT INTO {tbl}({tbl}) VALUES('optimize')"
                    )
                    optimized += 1
                except sqlite3.OperationalError as exc:
                    logger.warning(
                        "FTS optimize failed for %s: %s", tbl, exc
                    )
        return optimized

    def rebuild_fts(self) -> int:
        """Rebuild FTS5 indexes from the canonical ``messages`` table.

        Uses the FTS5 ``'rebuild'`` command, which rewrites the internal
        b-tree segments from the content rows. This is the documented
        recovery for a corrupt FTS index that rejects message writes while
        reads still succeed (issue #50502). Unlike ``optimize_fts`` (which
        merges existing segments), ``rebuild`` discards and recreates the
        index data entirely.

        Safe to call when FTS tables don't exist (skips them).
        Returns the number of FTS indexes that were rebuilt.
        """
        rebuilt = 0
        with self._lock:
            for tbl in self._FTS_TABLES:
                if not self._fts_table_exists(tbl):
                    continue
                try:
                    self._conn.execute(
                        f"INSERT INTO {tbl}({tbl}) VALUES('rebuild')"
                    )
                    self._conn.commit()
                    rebuilt += 1
                except sqlite3.OperationalError as exc:
                    self._conn.rollback()
                    logger.warning(
                        "FTS rebuild failed for %s: %s", tbl, exc
                    )
        return rebuilt

    def _merge_fts_incrementally(
        self, *, max_pages: int, max_commands: Optional[int] = None
    ) -> int:
        """Run bounded FTS5 ``'merge'`` commands against each present index.

        A positive merge rank tells SQLite to stop after approximately that
        many output pages, so each command holds the write lock for
        milliseconds regardless of index size — unlike ``'optimize'``, which
        rewrites the whole index in one transaction (measured 9-18 s per
        index on a 10 GB production DB, long enough to exhaust a competing
        writer's entire lock-retry patience).

        Protocol (SQLite FTS5 §6.8-6.9):

        - ``usermerge`` is lowered to its minimum of 2 (persisted in the
          ``%_config`` shadow table, applied once per instance) so a
          positive merge acts on ANY level holding >= 2 segments. With the
          default of 4, levels below that threshold are never merged by a
          positive-rank command and a fragmented index cannot converge.
        - Up to *max_commands* merge commands run per index, stopping early
          on the documented no-progress signal: the delta in
          ``total_changes`` is < 2 (the command's own INSERT accounts
          for 1 change; >= 2 means real merge work happened).

        Each command is its own implicit transaction (the connection runs
        with ``isolation_level=None``), so the SQLite write lock is released
        between commands and competing processes can interleave writes
        mid-pass. Missing tables are valid schema variants (FTS variants are
        optional, and ``optimize_fts_storage`` legitimately drops + backfills
        these tables while writers keep running) and are skipped, mirroring
        ``optimize_fts``. Other SQLite errors propagate to the caller.

        Returns the number of merge commands executed.
        """
        if isinstance(max_pages, bool) or not isinstance(max_pages, int):
            raise TypeError("max_pages must be an integer")
        if max_pages <= 0:
            raise ValueError("max_pages must be greater than zero")
        if max_commands is None:
            max_commands = self._FTS_MERGE_COMMANDS_PER_PASS
        if isinstance(max_commands, bool) or not isinstance(max_commands, int):
            raise TypeError("max_commands must be an integer")
        if max_commands <= 0:
            raise ValueError("max_commands must be greater than zero")

        executed = 0
        with self._lock:
            for tbl in self._FTS_TABLES:
                if not self._fts_table_exists(tbl):
                    continue
                # One-time (per instance) usermerge floor; the value is
                # persisted in the index's config shadow table so future
                # connections inherit it. Setting config is a metadata-only
                # write — it never touches segment data.
                if not getattr(self, "_fts_usermerge_floor_applied", False):
                    self._conn.execute(
                        f"INSERT INTO {tbl}({tbl}, rank) "
                        "VALUES('usermerge', 2)"
                    )
                for _ in range(max_commands):
                    before = self._conn.total_changes
                    self._conn.execute(
                        f"INSERT INTO {tbl}({tbl}, rank) VALUES('merge', ?)",
                        (max_pages,),
                    )
                    executed += 1
                    if self._conn.total_changes - before < 2:
                        break
            self._fts_usermerge_floor_applied = True
        return executed