One shared session serves every pod, and `requests`' stock adapter keeps ten
connections per host. `ocr.max_concurrency` defaults to 64 and is 128 on the
install this came from, so from the ELEVENTH concurrent page onward urllib3
opened a connection, used it, found the pool full on release and threw it
away:

    urllib3.connectionpool: Connection pool is full, discarding connection:
    194.68.245.54. Connection pool size: 10

74 of those in five minutes — about fourteen a minute against one pod — while
that run's health checks were timing out. Every discarded connection means the
next page pays a full TLS handshake to a machine in another country: several
round trips of latency each, and handshake CPU on the orchestrator at precisely
the moment it is busiest. It does not CAUSE a slow run, but it multiplies one,
and it is the part that is ours.

The pool is now sized from the concurrency the install is configured for:
`ocr.max_concurrency`, floored at 64 and capped at 256. Read at session
creation rather than at import, because the config is not loaded when this
module is imported — and because an operator raising max_concurrency should not
have to know a connection pool exists. An idle connection costs a socket and
nothing else, which is the cheap side of this trade.

The adapter also carries the floor as its own default, so a `_PinnedAdapter`
built anywhere cannot silently fall back to ten.

Routing is deliberately unchanged: only https-to-a-bare-IP uses the pinned
session, everything else still goes through `requests` untouched, so callers
and tests that patch `requests.get` keep working.

Not a fix for the slowness that exposed it. That host was running MariaDB at
534% CPU, four Postgres parallel workers, and a backup that had been streaming
over SFTP for three hours, against coderai's own 8.8% of one core out of
sixteen — the orchestrator was waiting for a CPU, not using one.

9 tests. Suite: 3151 passed, the same 13 known-stale failures.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KnfkxBpcZ1v6ypRFFyhrVM