[claude-code] [BUG] >=2.1.154 breaks `--resume` with `ANTHROPIC_CUSTOM_HEADERS` set in settings.

## Observed symptom [BUG] >=2.1.154 breaks `--resume` with `ANTHROPIC_CUSTOM_HEADERS` set in settings. - [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet - [x] This is a single bug report (please file separate reports for different bugs) - [x] I am using the latest version of Claude Code In `2.1.153` I can run `claude` and then `claude --resume` In `2.1.154`, upon `--resume`, completion requests return: `API Error: 400 Either x-portkey-config or x-portkey-provider header is required` I'm using the follwing in `$HOME/.claude/settings.json`: `{ ` ## Literal error text ``` API Error: 400 Either x-portkey-config or x-portkey-provider header is required ``` ## Environment GitHub anthropics/claude-code #96863 ## Trigger / context Public GitHub report in anthropics/claude-code (FRESH_14D). ## Source evidence - https://github.com/anthropics/claude-code/issues/96863 (2026-09-24T20:58:35Z) — evidence_class: PRIMARY_ISSUE_REPORT — #96863 ## Freshness - classification: FRESH_14D - retrieved_at: 2026-10-02T10:50:53.329738Z - scout_id: C1eac6c067e ## 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.