Keep the printer's name on statistics after it is deleted (issue #2873)

Every per-printer breakdown resolved the name against the printers that
exist now, so deleting a printer and choosing to keep its prints turned
"Ultron" into "Printer 1" in Prints by Printer, the success-rate and
time-accuracy lists, and Failures by Printer. Archives lose their printer
on that delete as well, so nothing was left to read a name from.

The runs themselves recorded the name they printed on. /archives/stats now
reports the last name each id was known by - taken from the newest run that
has one, so a later name-less row cannot blank it - and failure analysis
falls back to the same thing for ids with no printer left. The client keeps
preferring a live printer's own record, so a rename still shows up straight
away rather than after the next print.

backend/tests/integration/test_deleted_printer_keeps_name_2873.py

@@ -0,0 +1,112 @@
+"""Statistics keeps naming a printer that was deleted with its history (#2873).
+
+Deleting a printer while keeping its prints leaves the log rows pointing at an
+id nothing resolves any more, so every per-printer breakdown fell back to
+"Printer 1" for machines the reporter knew as "Ultron". Each run recorded the
+name it printed on, so that is what the aggregates report now.
+"""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta
+
+import pytest
+from httpx import AsyncClient
+
+from backend.app.models.print_log import PrintLogEntry
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+async def test_stats_name_history_of_a_deleted_printer(async_client: AsyncClient, db_session):
+    base = datetime(2026, 7, 15, 10, 0, 0)
+    db_session.add_all(
+        [
+            PrintLogEntry(
+                printer_id=71,
+                printer_name="Ultron",
+                status="completed",
+                started_at=base,
+                completed_at=base + timedelta(hours=1),
+                duration_seconds=3600,
+            ),
+            PrintLogEntry(
+                printer_id=71,
+                printer_name="Ultron",
+                status="failed",
+                started_at=base + timedelta(hours=2),
+                completed_at=base + timedelta(hours=3),
+                duration_seconds=3600,
+            ),
+        ]
+    )
+    await db_session.commit()
+
+    stats = (await async_client.get("/api/v1/archives/stats")).json()
+
+    assert stats["prints_by_printer"]["71"] == 2
+    assert stats["printer_names"]["71"] == "Ultron"
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+async def test_stats_reports_the_last_name_the_printer_ran_under(async_client: AsyncClient, db_session):
+    """A printer renamed before it was deleted is remembered by its last name."""
+    base = datetime(2026, 7, 15, 10, 0, 0)
+    db_session.add_all(
+        [
+            PrintLogEntry(printer_id=71, printer_name="Ultron", status="completed", started_at=base),
+            PrintLogEntry(
+                printer_id=71,
+                printer_name="Ultron Mk II",
+                status="completed",
+                started_at=base + timedelta(days=1),
+            ),
+            # A run logged before names were recorded must not blank the label.
+            PrintLogEntry(printer_id=71, printer_name=None, status="completed", started_at=base + timedelta(days=2)),
+        ]
+    )
+    await db_session.commit()
+
+    stats = (await async_client.get("/api/v1/archives/stats")).json()
+
+    assert stats["printer_names"]["71"] == "Ultron Mk II"
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+async def test_stats_names_do_not_override_a_live_printer(async_client: AsyncClient, db_session, printer_factory):
+    """Renaming a printer that still exists shows up straight away.
+
+    The client prefers the live record, so the historical name only has to be
+    present, not authoritative.
+    """
+    printer = await printer_factory(name="Renamed Later")
+    db_session.add(PrintLogEntry(printer_id=printer.id, printer_name="Original Name", status="completed"))
+    await db_session.commit()
+
+    stats = (await async_client.get("/api/v1/archives/stats")).json()
+    printers = (await async_client.get("/api/v1/printers/")).json()
+
+    assert stats["printer_names"][str(printer.id)] == "Original Name"
+    assert [p["name"] for p in printers if p["id"] == printer.id] == ["Renamed Later"]
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+async def test_failure_analysis_names_a_deleted_printer(async_client: AsyncClient, db_session, printer_factory):
+    """Failures by printer reads the recorded name once the printer is gone."""
+    live = await printer_factory(name="Still Here")
+    db_session.add_all(
+        [
+            PrintLogEntry(printer_id=71, printer_name="Ultron", status="failed"),
+            PrintLogEntry(printer_id=live.id, printer_name="Older Name", status="failed"),
+        ]
+    )
+    await db_session.commit()
+
+    analysis = (await async_client.get("/api/v1/archives/analysis/failures")).json()
+
+    assert analysis["failures_by_printer"]["Ultron"] == 1
+    assert analysis["failures_by_printer"]["Still Here"] == 1
+    assert "Printer 71" not in analysis["failures_by_printer"]