claim analysis jobs atomically and keep acquisition on its official host

Two defects of the same kind: work that is supposed to be bounded is not.

The analysis worker selected queued jobs and then set them to running in a
second statement. A restarted process overlapping the previous one, or a second
replica, could both select the same row and both start tiled GPU inference on
it — duplicate analysis runs and double the GPU load. The AOI worker beside it
already claims with FOR UPDATE SKIP LOCKED; this uses a conditional update,
which is the same guarantee in one statement. run_once now reports jobs it
actually claimed rather than jobs it looked at.

urlopen follows redirects, so although every acquisition URL is built from
settings and cannot be steered by a request payload, a misconfigured or
compromised upstream could send the runtime to the loopback interface, to
another container on the compose network, or to a cloud metadata endpoint — and
the bytes would then be persisted under an official provenance. That is exactly
the substitution the product forbids. All eight fetch sites now open through a
guard that refuses private, loopback and link-local destinations (resolving the
host first, so a DNS name cannot hide one) and refuses a redirect that leaves
the configured origin or downgrades from HTTPS.

The guard is proven by calling the services' own fetch paths, not by grepping
for the call: every existing acquisition test injects an opener, which bypasses
it by design.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/tests/test_analysis_job_queue.py

@@ -26,6 +26,16 @@ class FakeQuery:
     def filter(self, *criteria):
         return self
 
+    def update(self, values, **_kwargs) -> int:
+        """Stand in for the conditional claim: succeeds while still queued."""
+
+        claimed = 0
+        for row in self.rows:
+            if getattr(row, "status", None) == "queued":
+                row.status = "running"
+                claimed += 1
+        return claimed
+
     def order_by(self, *_args):
         return self