fix(escalation): require fresh consistent failure evidence

[pst2154]

Summary

• deduplicate equivalent Terminus raw-command and structured-tool serialization only in the escalation judge transcript
• require fresh, same-category failure evidence across distinct turns before switching
• preserve the maximum-one-switch and post-switch latch invariants
• add focused Rust coverage and a 40-task paired SWE-Atlas report

Benchmark evidence

On 20 RF and 20 TW tasks, the patched router scored 15/40 versus 10/40 for the original router and reduced switches from 9 to 5. Under the documented cached-token-aware synthetic rates, estimated cost fell from $1.171/task to $0.889/task. Direct GLM also scored 15/40 at $0.501/task, so this PR claims a false-positive fix and improvement over the original escalation policy, not superiority over the best fixed model.

Full methodology, task-level observations, formulas, limitations, and validation evidence are in benchmark/SWE_ATLAS_ESCALATION_REPORT.md.

Validation

• cargo fmt --all --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-features
• uv run ruff check .
• uv run mypy switchyard
• uv run maturin develop --uv
• uv run pytest tests/ -v

All passed on Rust 1.96.1. Pytest reported 115 passed, 2 deselected, and 2 subtests passed.