Tin Chi Lo 109a1637a0 refactor(mcp): one traversal and one carrier choice-point for upstream listing failures ... Both review findings shared one root cause: two exception-tree walkers with drifted semantics. _extract_upstream_auth_failure walked the incidental __context__ chain before explicit causes, so a 403 raised while handling the causal 401 could shadow it; and the generic _get_tools_from_server arm classified without extracting the challenge, so a nested 401 at client-build time surfaced without the WWW-Authenticate the client needs. upstream_auth_challenge and raise_classified_list_failure in faults/list_outcomes.py are now the single traversal and the single choice-point; both fetch arms and _extract_upstream_auth_failure (also serving tool calls and the connect-time probe) delegate to them, with dcr_bridge challenge suppression as a parameter so it holds on every path. The stale _fetch_tools_with_timeout docstring describing the pre-change 403 absorb is rewritten to the actual contract: 403 relays with its own status, an upstream-sent challenge relays verbatim per RFC 6750 insufficient_scope, and a challenge is only ever fabricated for a challenge-less 401		2026-07-14 20:03:56 -07:00
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mcp_server	refactor(mcp): one traversal and one carrier choice-point for upstream listing failures	2026-07-14 20:03:56 -07:00