fix: key MCP identity on the canonical issuer, not the token issuer

Verifying against OIDC_ISSUER_MCP fixed the 401, but would have introduced a
quieter bug. Identity is keyed on (oidc_iss, oidc_sub) and
userContextFromClaims UPSERTS rather than failing, so a token carrying the MCP
application's issuer would have created a SECOND user row for the same person:
MCP calls would succeed against an account holding none of their memories, and
nothing would appear broken.

Authentik's `sub` is `user.uid`, a user-level value that is identical across
providers (verified against the live instance), so the issuer is the only
differing component. Pin it to OIDC_ISSUER after verification.

No stray rows exist to clean up — verification failed before this path could
ever create one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

README.md

@@ -335,6 +335,13 @@ reliable pattern:
 > curl -s https://auth.example.com/application/o/shared-memory-mcp/.well-known/openid-configuration | jq .issuer
 > ```
 >
+> **Identity note:** the app verifies MCP tokens against `OIDC_ISSUER_MCP` but
+> keys the user record on `OIDC_ISSUER`. Authentik's `sub` is `user.uid`, which
+> is stable across providers, so the same person resolves to the same row
+> whether they arrive via the Web UI or the MCP endpoint. Without that
+> normalization the MCP path silently creates a second, empty account instead
+> of failing visibly.
+>
 > Note also that Claude Code sends an RFC 8707 `resource` parameter on the
 > authorize request; Authentik 2026.5 ignores it, so it cannot be relied on
 > for audience binding. The scope mapping is what sets `aud`.

apps/web/lib/auth/jwt.ts

@@ -135,7 +135,24 @@ export async function authenticateBearer(authHeader: string | null): Promise<Aut
         buildWwwAuthenticate("invalid_token", "missing sub"),
       );
     }
-    return { ...payload, groups: extractGroupsClaim(payload) } as AuthenticatedClaims;
+    // Normalize the issuer for identity purposes.
+    //
+    // The token was just verified against mcpIssuer() — that check is done.
+    // But identity is keyed on (oidc_iss, oidc_sub), and the Web UI signs
+    // people in through a DIFFERENT application whose tokens carry
+    // OIDC_ISSUER. Authentik's `sub` is stable across providers (it is
+    // `user.uid`, a user-level value), so the only thing that differs is the
+    // issuer.
+    //
+    // Leave it un-normalized and userContextFromClaims — which UPSERTS rather
+    // than failing — quietly creates a SECOND user row for the same human:
+    // MCP writes would land in an account with none of their memories, and
+    // nothing would look broken. Pin identity to the canonical issuer.
+    return {
+      ...payload,
+      iss: env().OIDC_ISSUER,
+      groups: extractGroupsClaim(payload),
+    } as AuthenticatedClaims;
   } catch (err) {
     if (err instanceof UnauthorizedError) throw err;
     const desc =