fix(storage): survive oversized rows in postgres history search

to_tsvector was computed inline over full row content, so one row
whose tsvector exceeds PostgreSQL's 1MB limit aborted every
search_history scan. Cap the FTS input at 250K chars (worst-case
tsvector expansion stays under the limit; giant rows remain findable
by their head). The ILIKE fallback also never ran on postgres: the
failed statement leaves the autobegun transaction aborted, so roll it
back before falling back.

(cherry picked from commit 51ed336989)

tests/test_storage_sqlite.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from typing import Any
 
+import pytest
 import sqlalchemy as sa
 
 from turnstone.core.storage._schema import workstreams
@@ -576,6 +577,48 @@ class TestSearch:
         results = backend.search_history_recent(limit=1)
         assert len(results) == 1
 
+    def test_search_history_survives_oversized_row(self, backend):
+        # A multi-MB row of mostly-unique words: on PostgreSQL its full
+        # tsvector exceeds the 1MB hard limit, which used to abort every
+        # search_history scan ("string is too long for tsvector") — one
+        # giant tool dump silently killed history recall entirely.
+        backend.register_workstream("s1")
+        giant = "gargantuan beacon " + " ".join(f"w{i}" for i in range(300_000))
+        assert len(giant) > 2_000_000
+        backend.save_message("s1", "tool", giant)
+        backend.save_message("s1", "user", "hello world")
+
+        results = backend.search_history("hello")
+        assert any("hello" in str(r[3]) for r in results)
+
+        # The oversized row itself stays findable by its head.
+        results = backend.search_history("gargantuan beacon")
+        assert any("gargantuan" in str(r[3]) for r in results)
+
+    def test_search_history_fts_error_falls_back_to_ilike(self, request, backend, monkeypatch):
+        # PostgreSQL only: a failed FTS statement aborts the connection's
+        # autobegun transaction, and the ILIKE fallback runs on that same
+        # connection — without a rollback first it dies with
+        # InFailedSqlTransaction instead of returning results.
+        if request.config.getoption("--storage-backend") != "postgresql":
+            pytest.skip("exercises PostgreSQL aborted-transaction fallback")
+
+        backend.register_workstream("s1")
+        backend.save_message("s1", "user", "hello fallback world")
+
+        real_execute = sa.engine.Connection.execute
+
+        def failing_fts_execute(self, statement, *args, **kwargs):
+            if "to_tsvector" in str(statement):
+                # A genuine server-side error, so the transaction is aborted
+                # exactly as when to_tsvector rejects a row.
+                return real_execute(self, sa.text("SELECT 1/0"))
+            return real_execute(self, statement, *args, **kwargs)
+
+        monkeypatch.setattr(sa.engine.Connection, "execute", failing_fts_execute)
+        results = backend.search_history("fallback")
+        assert any("fallback" in str(r[3]) for r in results)
+
 
 # -- Workstream operations -----------------------------------------------------
 

turnstone/core/storage/_postgresql.py

@@ -178,6 +178,13 @@ from turnstone.core.workstream import BULK_CLOSE_STATE_VALUES, WorkstreamKind
 
 log = get_logger(__name__)
 
+# PostgreSQL rejects any tsvector larger than 1MB ("string is too long for
+# tsvector"), and search_history computes tsvectors inline per row — so one
+# oversized row would abort the whole scan and every search with it.  Worst
+# case a tsvector runs ~4x its input (unique short lexemes + position data),
+# so 250K chars keeps even pathological rows safely under the limit.
+_FTS_INPUT_CAP_CHARS = 250_000
+
 
 def _resolve_pg_listen_url(override: str, sqlalchemy_url: str) -> str:
     """Resolve the URL used by the dedicated LISTEN connection.
@@ -1289,26 +1296,31 @@ class PostgreSQLBackend:
             scope_params["excl_ws"] = exclude_ws_id
             scope_params["excl_after"] = -1 if exclude_after is None else exclude_after
         with self._conn() as conn:
-            # Use PostgreSQL full-text search if search_vector column exists
+            # Full-text search over an inline tsvector (there is no indexed
+            # search_vector column).  The input is capped — see
+            # _FTS_INPUT_CAP_CHARS — so a single giant row (multi-MB tool
+            # dumps exist) cannot trip PostgreSQL's 1MB tsvector limit and
+            # abort every search; oversized rows stay findable by their head.
             try:
                 return list(
                     conn.execute(
                         sa.text(
                             "SELECT c.timestamp, c.ws_id, c.role, c.content, c.tool_name "
                             "FROM conversations c "
-                            "WHERE to_tsvector('english', COALESCE(c.content, '')) "
+                            "WHERE to_tsvector('english', left(COALESCE(c.content, ''), :fts_cap)) "
                             "   @@ plainto_tsquery('english', :query) "
                             # Exclude compaction-checkpoint markers (resume-only
                             # summary artifacts); IS DISTINCT FROM is NULL-safe so
                             # normal rows (_source NULL) are not dropped.
                             "AND c._source IS DISTINCT FROM :compaction_source "
                             + scope_sql
-                            + "ORDER BY ts_rank(to_tsvector('english', COALESCE(c.content, '')), "
+                            + "ORDER BY ts_rank(to_tsvector('english', left(COALESCE(c.content, ''), :fts_cap)), "
                             "   plainto_tsquery('english', :query)) DESC "
                             "LIMIT :limit OFFSET :offset"
                         ),
                         {
                             "query": query,
+                            "fts_cap": _FTS_INPUT_CAP_CHARS,
                             "compaction_source": _COMPACTION_SOURCE,
                             "limit": capped,
                             "offset": capped_offset,
@@ -1317,6 +1329,11 @@ class PostgreSQLBackend:
                     ).fetchall()
                 )
             except Exception:
+                # The failed statement aborted the connection's autobegun
+                # transaction; PostgreSQL then refuses every command until a
+                # rollback, so without this the fallback can never run
+                # (InFailedSqlTransaction).
+                conn.rollback()
                 # Fallback to ILIKE
                 return list(
                     conn.execute(