"""worker_lane_sample — where the sizing sweep leaves what it measured.

Operator, 2026-09-23, on the System tab: *"there is a repull every time this
page loads — is there a reason this info isn't being tracked in the
background and stored in some way?"*

`/api/system/workers` ran a full celery inspect on every call — four
broadcasts on an eleven-second budget — and the page polls it every fifteen
seconds. `size_worker_lanes` was already inspecting on a timer to decide pool
sizes, computing exactly these numbers and discarding them. This table is
where they land instead, and the endpoint becomes a plain read.

## Why a new table rather than columns on `worker_lane`

`worker_lane` holds the one number an operator sets. Putting a measurement
beside it is the mistake alembic 0105 undid: `slots` sat next to `slots_cap`,
and a measurement next to a preference reads as a second preference.

No backfill. A row appears when the sweep first runs (within its period), and
until then the lane reads as not-yet-measured, which is true.

Revision ID: 0107
Revises: 0106
Create Date: 2026-09-23

"""
from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op

revision: str = "0107"
down_revision: Union[str, None] = "0106"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.create_table(
        "worker_lane_sample",
        sa.Column("lane", sa.String(length=32), primary_key=True),
        # Nullable=False with no server_default: the sweep writes every column
        # on every upsert, so a row only ever exists complete.
        sa.Column("present", sa.Boolean(), nullable=False),
        sa.Column("replicas", sa.Integer(), nullable=False),
        # Nullable on purpose — unknown, never zero. A worker that answered
        # without reporting its pool, and a queue the broker did not answer
        # for, must not be summed as empty.
        sa.Column("pool", sa.Integer(), nullable=True),
        sa.Column("active", sa.Integer(), nullable=False),
        sa.Column("reserved", sa.Integer(), nullable=False),
        sa.Column("queue_depth", sa.Integer(), nullable=True),
        sa.Column(
            "measured_at",
            sa.DateTime(timezone=True),
            nullable=False,
            server_default=sa.func.now(),
        ),
    )


def downgrade() -> None:
    op.drop_table("worker_lane_sample")