test(cli): prove call-order tolerance without losing the strictness

[AminChirazi]

Milestone 2, criterion 7. Closes #258. Based on main.

The gap

0.8.0 dropped positional cassette matching. goose issues its task call and a session-title call concurrently and does not wait, so whichever landed first at record decided the order, and a positional matcher reported a divergence when nothing about the agent had changed. As docs/agent-testing.md puts it: order between concurrent calls is not something the agent guarantees, so a recording cannot assert it either.

Nothing exercised the new behaviour, in either direction.

Two proofs, and the second keeps the first honest

Tolerance	two INDEPENDENT calls recorded a-then-b replay b-then-a, and the run still passes
Discrimination	an agent that changes what it SENDS still diverges

Without the discrimination proof, "order-tolerant matching" is indistinguishable from "the request is not checked at all". A matcher that accepted anything would satisfy the tolerance proof perfectly — and every cassette in the product would stop proving anything about what was sent.

That is the shape a relaxation turns into a false green: the loosening is correct, and nothing pins how far it goes. So the pair ships together rather than the first alone.

The fixture

two-call-agent.py makes two calls that are deliberately independent of each other. That independence is the premise of the whole proof — it is what makes their relative order meaningless and the tolerance correct, rather than merely convenient. The header says so, and says not to make them depend on each other.

Two knobs live in files beside the script rather than the environment — the convention mcp_stdio_e2e.rs already uses — so record and replay differ without a race.

Result

Both proofs behave. No false green.

Verified locally

Replay runs with no model reachable, per invariant 1. Tests pass both with --test-threads=1 and in parallel (checked deliberately, since CI runs cargo test --workspace without that flag). fmt --check = 0, clippy --all-targets -D warnings = 0. Each exit code captured directly.

🤖 Generated with Claude Code

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.