fix(process)!: bound terminal buffers before capture

Validate columns × (rows + scrollback) against a 1,000,000-cell xterm working-buffer budget, including every resize with the selected scrollback. Document the budget in the advertised MCP input and process-capture guide; never clamp caller dimensions.

Validation: default/exact-boundary schema cases, prelaunch MCP rejection, compiled CLI capture, terminal rendering, normalization, cancellation, and lifecycle checks pass on macOS. This is resource admission, not a measured serializer throughput improvement; Linux-only and real deep-analysis providers were not exercised.

BREAKING CHANGE: process scenarios whose initial or resized terminal exceeds 1,000,000 combined visible-plus-scrollback cells are now rejected before launch.

docs/process-capture.md

@@ -114,6 +114,12 @@ from launch, must be ordered, and must fall within `timeout_ms`. Inputs marked
 Environment overrides are recorded in the scenario commitment; inherited
 values are not copied into Evidence.
 
+Terminal dimensions must satisfy `columns × (rows + scrollback) ≤ 1,000,000`.
+Every scheduled resize uses the same selected scrollback and must fit this
+working-buffer budget. REA rejects oversized scenarios before launching the
+command; it never clamps the requested dimensions. This limit is independent
+of `limits.output_bytes`, which bounds retained terminal observations.
+
 The capture contains raw PTY output chunks and rendered terminal states,
 interaction dispatch outcomes, exit reason, sampled process-tree observations,
 and settlement status. When filesystem paths are selected, REA records