`src/stream/handler.rs` — `StreamHandler` [feature: streaming]

The resilience wrapper around every streaming turn: retries, three timeout guards, rate-limit ladder, and non-streaming rescue. (~7,200 lines — the largest file in the crate, mostly tests.)

Key items

• StreamHandler::new() — production defaults; passthrough() — no resilience; builders with_timeout_config / with_retry_config / with_rate_limit_config / with_rate_limiter / with_rate_limit_max_wait.
• stream_turn(client, request, options, cancel) — yields HandlerEvent: Stream(event), AttemptReset, Fallback { message, ... }.
• StreamOutcome — Completed, TotalTimeout, EventTimeout, RateLimited, InitFailed (historical name; also covers mid-stream failures and truncation), FallbackToNonStreaming, Cancelled.
• StreamHandlerError — including RateLimitEscalation (escalate to the model breaker, not the same-model fallback).
• Config defaults: initial event timeout 2 min, per-event 3 min, total 5 min, 10 consecutive timeouts (2 for empty streams); transport retries 3 (100ms base, 10s cap, ±10% jitter); rate-limit retries 5 hard / escalate after 3, Retry-After honored up to 1 min; rate-limiter wait cap 30s.

Behavior notes

• Truncated streams (no terminal event) are retried, not reported complete. Permanent errors (401/404) never retry. Rate-limit escalation and transport budgets are independent.
• has_partial_data means “at least one flushed part” — deltas without a part-stop don’t count as salvageable.
• Everything is cancel-aware, including backoff sleeps and the fallback request.

Deep dive: Stream events.