feat(gpu): video-ready regions + the HTTP GPU-job queue engine (#114 slice 3)

Answers "how are videos/all media handled by the GPU worker": a job is per ITEM,
but the agent fans a VIDEO into per-frame instances (ffmpeg in the agent, the
existing cadence), each stored with a timestamp — so a video becomes a BAG of
frame embeddings (fixes the mean-embedding muddle) instead of one washed-out
vector. Stills → frame_time NULL; animated GIF/WebP treated like short video.

- image_region.frame_time (migration 0061, not yet deployed so folded in): the
  source frame's seconds for video/animated media; NULL for stills. RegionService
  passes it through. A whole frame is just kind='frame'.
- gpu_job + GpuJobService (migration 0062): the durable work list that keeps the
  desktop agent HTTP-only — enqueue (dedupes (image,task)) / lease (FOR UPDATE
  SKIP LOCKED, re-claims expired leases so the queue self-heals) / heartbeat /
  complete / fail (re-queues until MAX_ATTEMPTS then 'error'). The server enqueues;
  the agent leases+submits over the web API; Redis/Postgres stay private.

Tests: enqueue dedupe, lease-then-skip-when-held, expired-lease reclaim, scoped
heartbeat, complete, fail-requeue-then-error. region test now covers frame_time.

NEXT: the thin HTTP API (lease/submit/heartbeat) + bearer-token auth, then the
agent container + control UI.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

alembic/versions/0061_image_region.py

@@ -32,6 +32,8 @@ def upgrade() -> None:
             sa.ForeignKey("image_record.id", ondelete="CASCADE"), nullable=False,
         ),
         sa.Column("kind", sa.String(length=16), nullable=False),
+        # Video/animated: source frame timestamp (seconds); NULL for stills.
+        sa.Column("frame_time", sa.Float(), nullable=True),
         sa.Column("rx", sa.Float(), nullable=False),
         sa.Column("ry", sa.Float(), nullable=False),
         sa.Column("rw", sa.Float(), nullable=False),

alembic/versions/0062_gpu_job.py

@@ -0,0 +1,55 @@
+"""gpu_job: the HTTP-leased GPU work queue for the desktop agent (#114)
+
+The agent stays HTTP-only — the server enqueues per-(image, task) jobs here and
+the agent leases/submits over the web API; Redis/Postgres stay private.
+
+Revision ID: 0062
+Revises: 0061
+Create Date: 2026-06-29
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0062"
+down_revision: Union[str, None] = "0061"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "gpu_job",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "image_record_id", sa.Integer(),
+            sa.ForeignKey("image_record.id", ondelete="CASCADE"), nullable=False,
+        ),
+        sa.Column("task", sa.String(length=32), nullable=False),
+        sa.Column(
+            "status", sa.String(length=16), nullable=False,
+            server_default="pending",
+        ),
+        sa.Column("lease_token", sa.String(length=64), nullable=True),
+        sa.Column("leased_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("lease_expires_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("attempts", sa.Integer(), nullable=False, server_default="0"),
+        sa.Column("error", sa.Text(), nullable=True),
+        sa.Column(
+            "created_at", sa.DateTime(timezone=True), nullable=False,
+            server_default=sa.func.now(),
+        ),
+        sa.Column(
+            "updated_at", sa.DateTime(timezone=True), nullable=False,
+            server_default=sa.func.now(),
+        ),
+    )
+    op.create_index("ix_gpu_job_image_record_id", "gpu_job", ["image_record_id"])
+    op.create_index("ix_gpu_job_status", "gpu_job", ["status"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_gpu_job_status", table_name="gpu_job")
+    op.drop_index("ix_gpu_job_image_record_id", table_name="gpu_job")
+    op.drop_table("gpu_job")