Migration 86's queued-input index rejects user messages whose payload is not valid JSON #36894

Migration 86 (086_QueuedTurnInputIndex, from #23420) adds a partial index whose WHERE calls json_extract(payload_json, '$.inputIntent') without a json_valid guard. SQLite evaluates that term on every write of a user_message turn item, so a user message whose payload is not valid JSON can no longer be inserted or updated, and a database that already holds one cannot upgrade past migration 85.

Reproduction with sqlite3 3.54.0, the turn-item table as the projection migration creates it and the index exactly as migration 86 creates it:

CREATE TABLE orchestration_v2_projection_turn_items (
  turn_item_id TEXT PRIMARY KEY, thread_id TEXT NOT NULL, run_id TEXT, node_id TEXT,
  provider_thread_id TEXT, provider_turn_id TEXT, parent_item_id TEXT,
  ordinal INTEGER NOT NULL, type TEXT NOT NULL, status TEXT NOT NULL,
  updated_at TEXT NOT NULL, payload_json TEXT NOT NULL
);
CREATE INDEX orchestration_v2_projection_turn_items_queued_input_idx
  ON orchestration_v2_projection_turn_items(run_id)
  WHERE type = 'user_message' AND json_extract(payload_json, '$.inputIntent') = 'queued_turn';

INSERT INTO orchestration_v2_projection_turn_items
  (turn_item_id, thread_id, run_id, ordinal, type, status, updated_at, payload_json)
  VALUES ('u1', 't1', 'r1', 1, 'user_message', 'completed', '2026-11-14T00:00:00Z', '{not json');
-- Error: malformed JSON

INSERT INTO orchestration_v2_projection_turn_items
  (turn_item_id, thread_id, run_id, ordinal, type, status, updated_at, payload_json)
  VALUES ('a1', 't1', 'r1', 2, 'assistant_message', 'completed', '2026-11-14T00:00:00Z', '{not json');
-- OK

On a database that already holds such a user message, the index itself cannot be built:

-- same table, without the index, holding the 'u1' row above
CREATE INDEX orchestration_v2_projection_turn_items_queued_input_idx
  ON orchestration_v2_projection_turn_items(run_id)
  WHERE type = 'user_message' AND json_extract(payload_json, '$.inputIntent') = 'queued_turn';
-- Error: malformed JSON

Through the server's own migrations on main @ 2137f360e this shows up as Migration "86_QueuedTurnInputIndex" failed … malformed JSON, with the database left at 85. An UPDATE that sets a non-JSON payload on a user message fails the same way.

Assistant messages are unaffected, because the type = 'user_message' term is false before json_extract runs. Migration 89 already guards its expression indexes this way: "json_valid keeps a malformed payload writable, as the other payload indexes do."

Suggested fix: in a new migration, recreate the index with json_valid(payload_json) AND before the json_extract term, and add json_valid(held.payload_json) AND to the two shell-count queries that name it with INDEXED BY; without the matching term SQLite rejects them with "no query solution".

The server normally writes only JSON payloads, so this is defensive.