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/app/services/source_catalog_probe_service.py

@@ -18,6 +18,7 @@ from sqlalchemy.orm import Session
 
 from app.core.config import Settings, get_settings
 from app.core.errors import AppError
+from app.services.outbound_request_guard import guarded_opener
 from app.models import Dataset, Project
 from app.schemas.source_catalog import (
     SourceCatalogProbeItem,
@@ -179,7 +180,7 @@ def _bounded_fetch(
     )
     max_bytes = (max_response_mb or settings.source_catalog_probe_max_response_mb) * 1024 * 1024
     try:
-        with (opener or urlopen)(request, timeout=settings.source_catalog_probe_timeout_seconds) as response:
+        with (opener or guarded_opener(url))(request, timeout=settings.source_catalog_probe_timeout_seconds) as response:
             content_length = _header(response.headers, "Content-Length")
             if content_length:
                 try: