fix(toolwalk): observe displaced submission terminal outcome without acting on replacement run

[dennisonbertram]

Problem

Combined review of #1129/#1131 found ToolWalk.waitForTerminal returns .displaced immediately when B replaces submitted A. A per-run SSE can terminal/fail later and its RunSubmission handle retains that outcome, but ToolWalk has already produced a displaced result and never judges A. This violates submission-local outcome intent.

Acceptance criteria

• On B displacement, stop all automatic A controls and never act on B, but passively observe A handle terminal/failure until deadline.
• A terminal/failure after B selection produces the correct A verdict; no B cancel/approve/input/plan action.
• True timeout still cancels only exact A; B remains visually selected and unaffected.
• Add deterministic B-before-A-terminal/failure full ToolWalk integration tests, plus preserve existing action ownership and delayed-ACK behavior.
• Sol medium diagnosis, cheap re-review, full gates/hosted checks.

Scope

ToolWalk outcome policy only, stacked after #1131. Blocks promotion.