Graph llm nodes (and the structured-output extractor they share with agent
nodes) now obtain the model reply through a quiet streaming transport,
`call_chat_completions_streaming_quiet`, instead of the non-streaming call.
Because chunks arrive as they are generated, reqwest's client-level
`read_timeout` (default 300s) bounds only a genuine stall between chunks and
the node's own `timeout` becomes the effective bound on total generation.
Previously zero bytes arrived until the whole reply finished, so a 300s
read_timeout silently capped every llm node regardless of its `timeout`
(seen live: code-reviewer's `synthesize` node dying on a 61-file review).
The quiet transport renders nothing (silent SseHandler, no spinner), keeps
tool-call handling identical to the non-streaming path (call-loop detection
off), falls back to the non-streaming request for catalog `no_stream` models
(raced against the abort), and never returns partial output as success.
Supporting changes:
- `sse_stream`/`json_stream` keep the typed `reqwest::Error` in the anyhow
chain so `is_transient_error` still classifies read_timeout stalls as
transient and `max_attempts` retries them (previously stringified).
- `structured::extract` takes the graph/session AbortSignal and refuses to
issue an extraction request for an already-aborted graph.
- `run_chat_loop` gains an injectable CompletionRunner seam (owning client
construction + the before-hook) so the timeout/retry/abort behaviour is
unit-testable over a paused clock; a fake `impl Client` drives the real
trait-default streaming for 600s of virtual time; real-socket tests pin
that read_timeout fires on a stall but not on a slow continuous stream.
Dark-Alex-17