filter_tasks_by_metadata masks connection/timeout errors with AttributeError (catches bare Exception, reads .http_code)

[prabhaharanv]

Description

ServiceMetadataProvider.filter_tasks_by_metadata
(metaflow/plugins/metadata_providers/service.py) catches bare Exception and
then reads e.http_code:

try:
    resp, _ = cls._request(None, url, "GET")
except Exception as e:
    if e.http_code == 404:
        ...
    raise e

http_code is only defined on ServiceException — every other handler in the
file uses except ServiceException as ex. When cls._request() raises a
non-ServiceException (e.g. a requests ConnectionError/Timeout, which
_request re-raises unwrapped on its final retry via the bare
except: ... raise at the end of its retry loop), reading e.http_code raises
AttributeError, replacing the real network error with a confusing one.

Steps to reproduce

Point METAFLOW_SERVICE_URL at an unreachable host and trigger a Client
operation that routes through filter_tasks_by_metadata. Instead of the
underlying connection error, the call fails with
AttributeError: 'ConnectionError' object has no attribute 'http_code'.

Minimal mechanism (no Metaflow import needed):

class ServiceException(Exception):
    def __init__(self, msg, http_code=None):
        self.http_code = http_code

def handler(exc):                     # current behavior
    try:
        raise exc
    except Exception as e:            # <-- too broad
        if e.http_code == 404:        # <-- AttributeError on non-ServiceException
            return "internal-error"
        raise

handler(ConnectionError("refused"))   # -> AttributeError, not ConnectionError

Expected vs. actual

• Expected: the underlying ConnectionError/Timeout propagates so the user
  sees the real cause.
• Actual: an AttributeError masks it.

Root cause

except Exception as e catches everything; e.http_code assumes a
ServiceException. _request only attaches http_code when it constructs a
ServiceException from an HTTP response — connection/timeout errors from
requests propagate unwrapped, so they reach this handler without an
http_code attribute.

Proposed fix

Narrow the catch to except ServiceException as e (matching every other handler
in the file), so non-service errors propagate unchanged. A PR follows with a
regression test.

Environment

• Metaflow version: 2.19.35 (also present on current master)
• File: metaflow/plugins/metadata_providers/service.py