The v2 credential resolver owns oauth2_token_exchange end to end: any server
with a token-exchange config maps to a non-None TokenExchangeConfig spec, and
that config is in _create_mcp_client's override-exclusion set, so a caller
x-mcp-* override cannot force it back to v1 either. The v1 handler
resolve_mcp_auth reached at spec is None was therefore dead for OBO, including
its warn-then-proceed-unauthenticated fall-through. Delete auth/token_exchange.py
and the exchange branch, dropping the subject_token parameter that only fed it.
Separately, the REST listing and call paths still ran the v1 per-user OAuth
lookup for servers the v2 resolver owns. Unlike the two protocol-path call
sites they gated on auth_type == oauth2 only, with no to_server_spec check, so a
migrated authorization_code server did a DB round-trip whose Authorization
header _resolve_v2_auth then discards. Add the same guard via
_is_v1_resolved_oauth2_server, shared by the per-server lookup and the prefetch
preflight.
Also collapses MCPOAuth2TokenCache.async_get_token's now single-caller
require_client_credentials_flow kwarg and removes the dead
_get_bulk_user_oauth_headers helper (zero callers).
Compress the security rationale in the gateway-session admission path of
user_api_key_auth_mcp.py, keeping the load-bearing "why" and dropping the
restatement, and remove a garbled dead comment in get_allowed_tools_for_server
In the tests, hoist the duplicated _team / _admitted_subject fixtures to
module-level factories and parametrize the four fail-closed session-bearer
variants into one case. No behavior change; the 294 tests in the file still pass
Admits a keyless SSO user (no virtual key) at the aggregate /mcp endpoint from a gateway DCR
session bearer, resolving team/org/SCIM/budget authorization fresh on every call.
- Aggregate DCR front door: stateless /register (sealed llm_dcrc_ client ids), SSO-backed
/authorize + /authorize/complete, and /token minting identity-only session tokens with PKCE,
single-use codes/flows, and rotating refresh tokens.
- Admission: a session-shaped Authorization at the aggregate scope opens via _admit_gateway_session,
reloads the live user, and runs the centralized policy gate; failures return the RFC 9728
invalid_token challenge. Gated on the un-forgeable, server-only mcp_admitted_user_subject marker,
so virtual-key and JWT auth are unchanged.
- Authorization model: an admitted subject is resolved as one plain UserAPIKeyAuth per grant source
(its own grants, plus each team it is a live roster member of), each answered by the SAME resolver
virtual keys use, then unioned. That branch is the FIRST statement of BOTH public resolvers, so no
single-credential prelude runs for it and a fault in a lookup it never uses cannot deny its grants. A source team counts only while it is a live grantor: roster membership, not
blocked, and neither the team nor its owning org over budget (enforced through the SAME
_team_max_budget_check / _organization_max_budget_check owners common_checks uses for keys).
Each team source carries that team's own org, so the existing org
ceiling caps it; for a keyless source the org list only ever intersects (a ceiling must not become
a grant) and an unresolvable ceiling denies rather than silently uncapping, on both the server and
tool axes. _roster_team_object is the single owner of "which teams count": a team whose roster no
longer lists the user neither grants servers nor throttles, in one place.
- Rate limits: the subject is bounded by its user rpm/tpm AND by the per-server mcp_rpm_limit of
the team a call is ATTRIBUTED to — the same single source billing charges, from the same owner. A key charges its one pinned team's bucket; a keyless
subject has no team_id, so admission stamps each granting team's limit map onto the auth
(server-only field, stripped from validated input like the marker) and the limiter emits that
team's mcp_per_team descriptor. Charging every granting team instead would let one cross-team user
drain several teams' SHARED buckets on a single call and block their other members; and a server
the user's OWN grant reaches charges no team bucket at all, because no team provided it. Per-KEY
MCP limits do not apply because there is no key.
- Wrapper channels: the manager-level union treats the admitted subject by the same grant model.
The admin-role short-circuit and the absolute no_mcp_servers early-return are key-credential
rules and never apply to it (a session bearer is a third-party client credential, not the
dashboard, and the subject's opt-out silences only its own source). Operator-open channels
(allow_all_keys, the user's own BYOM submissions) are owned by one operator_open_server_ids
helper that BOTH the server union and the admitted tool resolution consult (suppress-BYOM-when-
explicitly-scoped is a key-credential rule and never applies to the subject, whose user row
carries the DB-default empty mcp_servers), so an open-channel
server is default-open for tools instead of listable but uninvokable.
- Redirect URIs: one owner, validate_redirect_uri_shape, decides redirect-URI hygiene (bad scheme,
fragment, missing host, userinfo, backslash host) and resolves allowlisted native callbacks, shared
by DCR registration and the OAuth endpoints. Registration keeps a deliberately wider trust policy
than validate_trusted_redirect_uri: public dynamic registration accepts any https client, and its
controls are mandatory S256 PKCE plus the consent screen.
- Egress leak-defense: a gateway admission credential (session bearer / bridge envelope) is scrubbed
from EVERY egress header context, anchored to the credential shape, so it can never be forwarded
upstream and replayed.
- Single-use guard: auth-code, refresh and connect-flow claims resolve the proxy's cross-worker redis
cache themselves rather than trusting the cache passed in, and fail CLOSED on a Redis fault instead
of falling back to a per-worker count that a captured id could replay through another worker.
- Sign-in return_to: one shared, never-raising helper persists a safe return_to for every sign-in
branch (SSO/Okta/generic and username/password), and every branch RESUMES through the same
_sso_return_to_redirect the SSO callback uses, so however a deployment signs in the stored value
is honored identically (same-origin path directly; control_plane_url via the one-time login-code
handoff). A stale cookie is ignored rather than failing a completed sign-in.
- Budgets, both halves: ENFORCEMENT (an already over-budget team or its owning org stops being a
grantor, in the source gate) and ACCOUNTING (a team-derived tool call is billed to the granting
team and ITS org, so that budget accumulates and the right organization is charged). A server the
user's own grant reaches bills the user; when several teams grant one server the pick is the
lowest team_id, stable and auditable. Billing rides a COPY, so authorization still sees the full
union, and it is inert when the target server cannot be resolved from the tool name.
Deferred (tracked): client-selected server scoping of the session token (LIT-4680).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Resolves LIT-4581
A true_passthrough MCP server created without the at-creation auth step
has no stored client_id, and the tools-page browser flow supplies none,
so GET /v1/mcp/server/oauth/{id}/authorize dead-ended on a 400
missing_client_id. The client-forwarded-token modes forbid the gateway
from persisting an OAuth client, so client acquisition moves into the one
chokepoint every caller crosses: the authorize endpoint.
resolve_ephemeral_dcr_client owns the whole mint policy (mode gate,
authorization-url precondition, required S256 PKCE, redirect trust, then
a TTL-deduped, per-server single-flighted RFC 7591 mint). The minted
client rides the encrypted OAuth state; /callback seals it with the
upstream code and server_id into an llm_ptcode_ gateway code, and
redeem_passthrough_authorization_code recovers it at the token endpoint
(server binding plus required code_verifier) to authenticate the upstream
exchange. Nothing is persisted; every value rides the encrypted blobs, so
it works across replicas.
Client acquisition is one predicate applied across the whole auth-mode
matrix: the gateway mints for a clientless authorize iff true_passthrough
(any dcr_bridge) or oauth_delegate-and-not-dcr_bridge, and the UI
gatewayMintsClientFor mirrors that set exactly so the browser pre-registers
a client through the dcr_bridge front door only for the cells the gateway
does not mint (the interactive oauth_delegate dcr_bridge sign-in and the
legacy oauth2 passthrough). A minted flow runs the bridge short-circuit
arm; the relay front door stays for external clients that present their
own client_id. Both sides are pinned against the same truth table
(test_resolve_ephemeral_dcr_client_mint_set_is_exact and the
gatewayMintsClientFor matrix test) so no mode can silently diverge. The
authorization_code hook and M2M/token-exchange modes are unchanged.
urlsplit validates the port lazily, so a non-numeric port raised
ValueError out of _redact_mcp_resource_url after the urlsplit try
had already passed; the server loaders now call the helper while
warning about typo'd urls, which would have turned the warning into
a load failure. Resolve hostname and port inside the guard and pin
the malformed-port case in the redaction test
A typo'd MCP server url failed OAuth endpoint discovery silently: every
failure died at debug level, the config loader warned nothing, and the
/authorize 400 blamed "servers with no url" even when a url was set.
_descovery_metadata now records each attempt's outcome and, when a total
failure would leave the server's flow without a needed endpoint, logs one
warning with the trail (urls origin-only, exception text url-stripped).
Both server loaders warn which endpoints stayed unresolved for the
server's flow (client_credentials never needs authorization_url, OBO
needs only token_url) with the remedies; this replaces the DB path's
reason-less warning and closes the config path's no-warning gap. The
authorize/token/register 400 details branch on server shape via one
shared helper and point at the proxy logs. _redact_mcp_resource_url
moves to oauth_utils.py so the manager can import it without a cycle.
Resolves LIT-4658
The MCP OAuth DCR relay's client-facing /register response handed back LiteLLM's own
<base>/callback as the client's redirect_uris on every arm except the true bridge relay.
A spec-compliant OAuth 2.1 DCR client (e.g. Open WebUI over Streamable HTTP) adopts that
value for its subsequent /authorize calls, so /callback redirects to itself; the second
hit carries the client's opaque state, fails to decrypt, and surfaces as the LIT-4197
"oauth_state ... Incorrect padding" error, making pass-through MCP OAuth unusable against
real DCR-capable upstreams.
The short-circuit arm keeps registering the gateway callback upstream (unchanged) and now
echoes the client's own redirect_uris back to the client across all register arms. Since
the client then authorizes with its own separate-origin redirect, the /authorize rejection
hint now points operators to MCP_TRUSTED_REDIRECT_ORIGINS, the mechanism a legitimate
cross-origin OAuth client needs (auto-trusting a DCR-registered redirect would reintroduce
the VERIA-57 open-redirect vector, since dynamic registration is unauthenticated).
Staging now contains #33153, whose final rounds made _extract_upstream_auth_failure a thin delegate
to upstream_auth_challenge and introduced the response-level iterator this branch predates. The
resolution completes the consolidation both branches were converging on: iter_exception_tree
(faults/traversal.py) is the one tree walk, _iter_upstream_responses is rebuilt on top of it instead
of carrying a second copy of the traversal, the manager keeps the delegate, and the semantic filter
port from this branch stands. Test conflicts were append-append and both sides are kept
_resolve_v2_auth dropped the resolved client_credentials auth when extra_headers
already carried Authorization (MCPJWTSigner, static_headers), so the upstream got
the injected header instead of the minted token and the one-shot 401 refetch was
lost. M2M now joins token_exchange and authorization_code in the authoritative
set; the conflicting header is dropped
The auth object is the httpx client's auth for the whole MCP session; after a
401 recovery it kept sending the rejected token first, burning a 401 round trip
and the single retry on every subsequent call
An expires_in of zero or below computes a ttl of 0; the entry could never be
served but still occupied a slot in the bounded backend, where it could evict
a live token. The mint still serves the current request and the next get
re-fetches under the per-server lock
Greptile P2s: the per-server lock dict now evicts its oldest entry past
max_locks so ephemeral server ids (REST tools preview) cannot grow it
unbounded, and the min-cache floor is capped at the token's actual lifetime so
an expires_in below the skew is never served past expiry
The graft test pinned the pre-migration contract (M2M defers to v1). Replaced
with two tests pinning the new one: a complete-config M2M server resolves via
the v2 arm into ClientCredentialsBearerAuth, and an incomplete-config server
fails closed with a 500 misconfigured naming the missing grant fields
Replaces the not_implemented stub with a live arm: ClientCredentialsTokenSource
mints and caches the M2M token (rotation-aware identity key, expires_in-driven
TTL, audience and token_endpoint_auth_method support) and
ClientCredentialsBearerAuth retries an upstream 401 exactly once with a freshly
minted token. to_server_spec owns oauth2_flow=client_credentials servers and
fails closed on incomplete grant config instead of connecting unauthenticated
The SERVER_ROOT_PATH fix for the per-server pass-through challenge belongs with its sibling
in exceptions.py (both fabricate a per-server resource_metadata URL and both omit the root
segment), and both are pre-existing paths unrelated to the aggregate discovery this PR adds.
Reverting the server.py change keeps this PR to the aggregate front door and avoids leaving
the two per-server challenge builders inconsistent; the per-server root-path fix lands as its
own change covering both sites.
tests/test_litellm/proxy/test_custom_proxy.py sets SERVER_ROOT_PATH at import time (its app
mounts under a custom path) and never restores it, so in a shared shard the value leaks into the
process. The discovery routes and the 401 challenges now read SERVER_ROOT_PATH to path-insert it
where they previously ignored it, so a leaked value rewrites every resource_metadata URL and the
exact-URL assertions in the delegate, pass-through, and aggregate challenge tests fail depending
on shard order
An autouse fixture clears SERVER_ROOT_PATH for the MCP discovery tests so they deterministically
exercise the default root-mounted deployment; the tests that assert a sub-path deployment set the
value explicitly within their own body. No assertion changed; the leak was invisible before only
because the code ignored the variable
Two RFC 9728 / 8414 discovery fixes on the aggregate front door, both raised by Bugbot on this PR
The aggregate authorization-server document at /.well-known/oauth-authorization-server/mcp used to
defer to a per-server row literally named "mcp", serving issuer {base} while the aggregate
protected-resource document advertises {base}/mcp as its authorization server. A spec client
following that chain fails the RFC 8414 issuer check and cannot sign in. The single segment /mcp is
now reserved for the aggregate so the issuer stays {base}/mcp and matches the protected-resource
document; a server named "mcp" keeps its standard two-segment discovery at
/.well-known/oauth-authorization-server/mcp/mcp
The 401 challenges built the resource_metadata URL as {base}/.well-known/oauth-protected-resource/mcp
with no SERVER_ROOT_PATH segment, but the routes are registered with the path-inserted root segment,
so a proxy mounted under a sub-path pointed DCR clients at a URL that 404s. Both the aggregate
challenge and the pre-existing per-server pass-through challenge now derive the path from one
well_known_root_suffix helper that the route registrations also use, so the advertised URL cannot
drift from the served route
The flag guarded no breaking change: the aggregate discovery lives at new /mcp-suffixed
routes, the challenge only fires at aggregate scope, and the authorize/token/register/admission
arms self-gate on the llm_dcrc_/llm_session_ prefixes. Bare-origin and per-server discovery are
left exactly as they were, and a server literally named mcp keeps its own discovery via
disambiguation, so turning it on for everyone changes nothing about existing flows.
* feat(mcp): add ID-JAG egress auth as a v2 outbound-credentials arm
Adds the oauth2_id_jag MCP egress auth mode (draft-ietf-oauth-identity-assertion-authz-grant,
shipped by Okta as "AI agent token exchange") as a first-class arm of the v2
outbound_credentials resolver rather than a standalone v1 handler.
ID-JAG is a two-leg flow: an RFC 8693 token exchange swaps the caller's id_token for an
ID-JAG assertion at the IdP org authorization server, then an RFC 7523 jwt-bearer grant
presents that assertion to the MCP's resource authorization server for the access token
used to call the upstream. The gateway authenticates to both endpoints with a private-key
JWT client_assertion, falling back to client_secret when no key is configured.
The mode is modeled as IdJagConfig in the AuthConfig discriminated union, with client auth
as a ClientAuth tagged union (private_key_jwt or client_secret) so required fields are
enforced at construction and illegal states are unrepresentable. A new token_endpoint
collaborator performs the authenticated OAuth token-endpoint call and caches the result
with per-key single-flight; the resolver's _id_jag arm runs the two legs and returns an
httpx.Auth or a typed CredError. A missing caller identity token fails closed
(precondition_required), so an ID-JAG server never falls back to a static credential. The
v1->v2 adapter maps oauth2_id_jag servers onto IdJagConfig and the existing live v2 path
resolves them, so no standalone handler, has_id_jag_config flag, or resolve_mcp_auth
precedence branch is needed.
The ID-JAG client_private_key is encrypted at rest alongside client_secret.
* fix(mcp): sort token_endpoint imports to satisfy the I001 budget gate
* fix(mcp): give token_endpoint pyright suppressions reasons for the LIT004 budget
The freshly-merged base ratcheted the LIT004 ceiling down, so the six
unexplained pyright suppressions in token_endpoint.py went over budget.
Annotate each with why the boundary is untyped (litellm http handler and
InMemoryCache are untyped; response.json() is validated by
_TokenEndpointResponse in fetch) so the gate counts them as explained.
* fix(mcp): enforce ID-JAG exchange over caller auth overrides and redact token endpoint from client errors
For oauth2_id_jag servers the v2 resolver mints the upstream assertion from the caller's identity token; a caller-supplied x-mcp-auth / x-mcp-<alias>-authorization override or a conflicting injected Authorization must not disable that exchange and forward an arbitrary bearer, so IdJagConfig now joins authorization_code and token_exchange as a resolver-owned mode that keeps the v2 spec and ignores the override.
The token endpoint error branches previously returned the configured endpoint URL in the client-visible 503 detail. The endpoint now stays in server-side logs and clients get a generic token-exchange failure.
* fix(mcp): bind the ID-JAG token cache to the exchange config and map token endpoint network errors to typed CredErrors
* fix(mcp): fail closed when an oauth2_id_jag server is half-configured instead of deferring to v1 static credentials
* fix(mcp): evict the cached ID-JAG bearer on an upstream 401 so the retry re-exchanges
* fix(mcp): map an unsignable client assertion to a typed misconfigured error instead of an unhandled 500
* fix(mcp): redact credential fields from the server-registry debug dump
Config.yaml-declared OAuth2 MCP servers using Dynamic Client Registration have no LiteLLM_MCPServerTable row, so the DCR persist path called update_mcp_server, which returns None for a missing row, then update_server(None), which dereferenced .approval_status and raised AttributeError. The exception was swallowed to a warning while /register still returned 200, so the minted client was never stored and every access-token expiry forced a full re-authorization
Persist the acquired DCR client (client_id, client_secret, token_endpoint_auth_method, redirect_uris, encrypted at rest) in a dedicated LiteLLM_MCPServerOAuthClient store keyed by server_id when the server has no row, overlay it onto the in-memory config server so the refresh_token grant can authenticate within the process, and rehydrate it when the registry syncs from the database (which runs after the DB connects, unlike config load) so restarts and other pods pick it up. The store is encrypted at rest and is re-encrypted by the master-key rotation path alongside the server rows, through a shared helper so the two sites cannot diverge. The DB-backed server path is unchanged, and guarding the None return removes the swallowed-crash footgun
Resolves the config.yaml DCR persistence regression introduced in v1.92.0 by #31912
Outcome keys in the tools/list _meta, the spend-log outcome and count maps, and the REST error
messages now all use get_server_prefix (alias, or the short prefix when that mode is enabled), the
same naming the caller already sees on tool names. Keying them by canonical server_name let an
authenticated caller enumerate internal server names and their health or auth state that the alias
and short-prefix schemes deliberately hide (Veria finding). One helper decides the key for every
surface; exception messages reaching the multi-server REST error list are mapped to their fault tag
with the display prefix instead of relaying exception text carrying canonical names. Server-side
logs keep the real names
Conflict in _list_mcp_tools: staging (#33612) moved toolset-grant expansion into the shared
permission primitives and removed the _merge_toolset_permissions call; resolution applies that
removal to this branch's AggregateToolListing structure
Append-append conflict at the end of test_mcp_server.py between this branch's aggregate-outcome
tests and the mode-aware preemptive-401 tests from staging; both kept
The consolidation regressed the pre-existing walker semantics: _extract_upstream_auth_failure used
to keep scanning until it found a 401/403, while the consolidated helper took the first response of
any status and then tested it, so a causal 401 sitting behind an unrelated 5xx (retry attempts,
multi-stream task groups) was misclassified as upstream_error and its challenge lost on the listing,
tool-call, and probe paths. The traversal is now an iterator in deliberate order and each consumer
applies its predicate over the stream: the auth scan takes the first 401/403 even behind non-auth
responses, generic classification takes the first response, and classify_list_exception derives its
auth arm from the same scan so the carrier choice and the classification can never disagree
Grafted from PR #33582 (closing as superseded by this PR): drives
handle_streamable_http_mcp with real MCPServer objects, parametrized over a
stamped client_credentials row and a legacy unstamped M2M-shape row; both must
reach the session manager without the per-user token store being consulted
The preemptive-401 gate for auth_type=oauth2 MCP servers keyed the challenge
on whether an Authorization header was present (not oauth2_headers). Because
the header parser classifies any Authorization bearer as an OAuth token before
the target server is resolved, a LiteLLM virtual key presented as
Authorization: Bearer sk-... suppressed the challenge on a gateway-managed
authorization_code server; the session then opened with no upstream token and
tools/list masked the failure as 200 with an empty tool list. The same gate
also wrongly challenged client_credentials (M2M) servers, which the gateway
authenticates by minting its own token at egress.
The decision is per oauth2 sub-mode, not per header. Gateway-managed modes
never receive a client-supplied upstream token: client_credentials mints at
egress so it is never challenged, and gateway-managed interactive
(authorization_code, non-delegate) is challenged whenever no stored per-user
token exists, regardless of any bearer. Only the delegate/upstream-PKCE mode,
where a present bearer genuinely is the upstream token, keeps keying on the
Authorization header. oauth2_headers itself is left untouched so the
delegate/passthrough egress paths that forward the client bearer are
unchanged.
The hook returned early when the semantic filter selected no tools, which
restated a policy that SemanticMCPToolFilter.filter_tools already owns: it
returns the full tool set when nothing matches, so the selection is never
empty. The branch was unreachable, and reachable or not it changed nothing,
since the gateway reads the union of every reference's allowed_tools and
treats an empty union as unset. Its only effect was to suggest the reference
path and the plain tool path resolve a zero-match query differently.
Drop it so a single policy governs both paths, and pin that with a test
covering an unmatched query on each path. Flipping filter_tools to fail
closed now fails the test on both instead of quietly hard-limiting one
surface and not the other.
The semantic tool filter replaced each litellm_proxy MCP reference in
data["tools"] with the tools it expanded from that reference. The expansion
defaults to the Responses API tool shape, so a /chat/completions request came
out carrying flat {"type": "function", "name": ...} entries where the provider
transformations expect {"type": "function", "function": {...}}. Anthropic then
raised KeyError: 'function' and Bedrock dropped every MCP tool silently, so the
model answered as if no MCP server were connected.
Replacing the reference also removed the marker the MCP gateway matches on, so
acompletion_with_mcp never ran and tool calls were no longer auto-executed for
require_approval="never", on /responses as well as /chat/completions.
Narrow the reference through allowed_tools instead and leave it in place, so the
gateway still owns expansion and keeps both the per-endpoint tool shape and tool
auto-execution. Expansion already applies any caller-supplied allowed_tools, so
the selection can only narrow a reference further, never widen it.
Making the in-memory issuer reflect a trust-on-first-use discovered value fixed
the registry/row token-identity drift, but it overloaded a single field: the
carry-forward gate keyed on issuer truthiness as a proxy for "endpoints are
anchored to a pinned issuer, fail-closed". A discovered issuer is truthy yet not
anchored, so a resource-rooted server that had learned its issuer would drop its
last-known-good endpoints on a transient discovery blip instead of carrying them
forward.
Anchoring is now a first-class property rather than a proxy. MCPServer carries
issuer_is_anchored, set at both build paths from the single _uses_issuer_anchor
definition (a pinned issuer on a discovery auth type). issuer stays the identity
value used by the token-identity tuple and the serializers; issuer_is_anchored is
the provenance value the carry-forward gate reads to decide fail-closed. The two
properties can no longer be conflated, so a discovered issuer keeps its
resource-rooted endpoints carrying forward while a pinned issuer still fails
closed.
Regression tests pin both directions: a discovered-but-not-anchored server
restores its endpoints on a discovery blip, an anchored server does not, and the
build sets issuer_is_anchored true only when the issuer is pinned
Two lifecycle gaps let the issuer trust anchor drift out of sync with the
endpoints it governs. Changing or clearing a previously pinned issuer left the
authorization_url and token_url that were resolved under the old issuer in the
row, so clearing the anchor could revive stale, possibly untrusted endpoints
instead of re-discovering. And a build that discovered an issuer
trust-on-first-use persisted it to the row while the returned in-memory server
kept the issuer unset, so the registry and the row disagreed and the per-user
OAuth token identity, which includes the issuer, differed between that build and
the next rebuild and forced a spurious re-auth.
update_mcp_server now treats a change to a previously pinned issuer the same as a
url or auth_type change and clears the auth-flow-scoped endpoint fields that were
resolved under it. The trigger fires only when an issuer was already pinned and
is now changed or cleared, so establishing one for the first time, including the
trust-on-first-use discovery write-back, does not wipe the fields it just
resolved.
Both build paths, build_mcp_server_from_table and load_servers_from_config, now
construct the server with effective_issuer = manual_issuer or the discovered
issuer, skipping an origin-fallback guess exactly as the persistence does, so the
in-memory object always reflects what the row will hold.
Regression tests pin each case: clearing and re-pointing a pinned issuer clear
the stale endpoints, a first-time establish preserves the discovered fields, and
a build reflects the discovered issuer while an origin-fallback guess is not
reflected
