Sækja hellogrok-cli 0.1.20

Added
- Per-channel absorb layer for transient upstream soft failures. While the upstream response headers have not been sent, retryable failures (busy/overloaded 503, 429, retryable 5xx, response-header timeouts) are retried inside the proxy with exponential backoff (2s–30s, honoring an upstream Retry-After up to 60s) for up to 90 seconds by default (absorb_retry_max_secs, absorb_retry_backoff_cap_secs). Grok Build's native 15-attempt retry budget stays untouched during the window; only when the window is exhausted does the failure pass through, still retryable. Transport errors are not absorbed so Grok Build's first-retry HTTP/1.1 client rebuild keeps working. UP absorb log lines record each wait.
- Synthesized 30-second Retry-After on retryable busy/overloaded 5xx passthroughs that carried none, pacing Grok Build's own retries. Upstream Retry-After headers are preserved.
- Opt-in dead-channel breaker (dead_channel_fail_fast, default off; dead_channel_fail_threshold, default 6). Only dial-level failures (connection refused, DNS, TLS handshake) count, because those can never succeed on retry; after the streak the proxy answers a non-retryable 503 proxy_circuit_open with X-Should-Retry: false, with one probe allowed after a 5-minute cooldown and any upstream response closing the breaker.
Changed
- The circuit breaker no longer fast-fails soft failures. Busy 503, 429, timeouts, transport resets, and error-body read failures pass through as retryable (or are absorbed first), so Grok Build keeps its complete native retry budget. X-Should-Retry: false is reserved for deterministic failures whose retries cannot succeed (authentication, permission, billing, quota, invalid request/model).