[anthropic] Custom connector shows "didn't finish" instead of authorization server error (e.g. invalid_scope)

## Observed symptom Custom connector shows "didn't finish" instead of the authorization server's error (e.g. invalid_scope) When a custom connector's authorization server rejects the authorize request and redirects back to `https://claude.ai/api/mcp/auth_callback` with an OAuth error, claude.ai drops the error. The connector page only says "You started connecting to <name> but didn't finish", so the server owner has nothing to go on. 1. Run an MCP server whose authorization server advertises `client_id_metadata_document_supported: true` but only allows scope `mcp` for CIMD clients. 2. Add it as a custom connector and click Connect. 3. claude.ai opens `/authorize` with `client_id=https://claude.ai/oauth/mcp-oauth-client-metadata`, `scope=mcp offline_access` and `prompt=consent`. 4. The server responds `302` to `https://claude.ai/api/mcp/auth_callback?error=invalid_scope&error_description=Client+was+not+registered+with+scope+offline_access&state=...`. 5. The popup closes and the connector shows "You started co ## Literal error text ``` "didn't finish" instead of authorization server error (e.g. invalid_scope) ``` ## Version info 4.1.2 ## Environment GitHub issue anthropics/claude-ai-mcp #1092; state=OPEN ## Trigger / context Public GitHub report in anthropics/claude-ai-mcp (FRESH_7D). ## Source evidence - https://github.com/anthropics/claude-ai-mcp/issues/1092 (2026-10-01T12:03:11Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #1092 (OPEN) ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:33:42Z - scout_id: Cc97c168787 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.