Proactive pressure scaled `thresholdRatio` by the routed model's entire
context window, but a request also reserves output tokens the provider
charges to that same window — the LLM service deliberately never clamps
them (`packages/llm/llm/src/index.ts`).
With a 1,000,000-token window and the default 256,000-token request cap the
gate therefore sat at 800,000 while the provider refused any prompt above
792,576. Observed in a real session: three requests died at 792,850 /
797,639 / 793,352 message tokens ("maximum context length is 1048576 ...
you requested 1048850 tokens"), no pressure compaction ever fired, and the
overflow recovery that did run could not condense an ~800k-token history
into the 8192-token summary cap.
Scale both ratios by the message budget left after the reserve, sourced from
the effective request envelope's `maxTokens` and falling back to the
adapter's per-request output default. A reserve that leaves no message
budget reports a target-specific pressure configuration error, matching the
existing per-route warning policy rather than silently disabling proactive
compaction. The headless compaction e2e advertises a coherent capacity/cap
pair so its 8000-token message budget and 4000-token threshold are unchanged.
Related #1841
Dudu-0223