fix(collector,trainer): migrate an existing collector DB on open; trainer handlers answer 500 JSON

The reviewer host's collector.sqlite was created by an earlier build, before the
`kind` column. CREATE TABLE IF NOT EXISTS shapes only a new database, so every query
naming the column failed: the collector's /health (container unhealthy), every
booth ingest, and the trainer's readiness — whose stdlib server printed the
traceback and dropped the socket, which the collector could only render as
"trainer not reachable: fetch failed". Nine days like that.

- CollectorDb.#migrate(): PRAGMA table_info against the list of columns added
  since the first deploy; ALTER TABLE ADD COLUMN for each missing one (all
  nullable or defaulted). Append to that list whenever a column joins the CREATE.
  Test replays the original schema: health, ingest, stats, a legacy row reads
  back with the defaults.
- Trainer Handler._guarded(): any unexpected exception → 500 JSON naming it,
  never a dropped connection; /health keeps answering. Test drives readiness
  against an old-schema DB.
- The collector's training status proxy includes the trainer's error text.

Wiki: the incident and the schema rule (vision-review-outbox), what the message
means (bodytype-classifier-training), log. Deploy: the new collector migrates on
start; nothing manual.

Claude-Session: https://claude.ai/code/session_01FWncR69HgGPuei1dLrW3cU

apps/collector/src/db.ts

@@ -71,6 +71,39 @@ export class CollectorDb {
       CREATE INDEX IF NOT EXISTS items_pending ON items (reviewed_at, received_at);
       CREATE INDEX IF NOT EXISTS items_booth ON items (booth, received_at);
     `);
+    this.#migrate();
+  }
+
+  /** Columns added after the first deploy, with the DDL that adds them to an EXISTING
+   *  table. `CREATE TABLE IF NOT EXISTS` above only shapes a NEW database; a volume that
+   *  was created by an earlier build keeps its old columns, and every query naming a new
+   *  one then fails ("no such column: kind" — art-docker-station, 2026-09-16: the
+   *  collector's /health, every ingest, and the trainer's readiness all broke on a DB
+   *  from before `kind`). Each entry must be addable to a populated table, i.e. nullable
+   *  or carrying a DEFAULT. Append here whenever a column joins the CREATE above. */
+  static readonly #ADDED_COLUMNS: ReadonlyArray<readonly [name: string, ddl: string]> = [
+    ["kind", "TEXT NOT NULL DEFAULT 'wash'"],
+    ["operator_ref", "TEXT NOT NULL DEFAULT ''"],
+    ["operator_category_id", "TEXT NOT NULL DEFAULT ''"],
+    ["operator_category_name", "TEXT NOT NULL DEFAULT ''"],
+    ["operator_classes", "TEXT NOT NULL DEFAULT '[]'"],
+    ["vision_category_id", "TEXT"],
+    ["downgraded", "INTEGER NOT NULL DEFAULT 0"],
+  ];
+
+  /** Bring an existing `items` table up to the current column set (idempotent). */
+  #migrate(): void {
+    const present = new Set(
+      (this.#db.prepare("PRAGMA table_info(items)").all() as { name: string }[]).map((c) => c.name),
+    );
+    for (const [name, ddl] of CollectorDb.#ADDED_COLUMNS) {
+      if (!present.has(name)) this.#db.exec(`ALTER TABLE items ADD COLUMN ${name} ${ddl}`);
+    }
+  }
+
+  /** The current column names of `items` (for tests and diagnostics). */
+  columns(): string[] {
+    return (this.#db.prepare("PRAGMA table_info(items)").all() as { name: string }[]).map((c) => c.name);
   }
 
   close(): void {