fix(failure-class): rename 'canceled' to 'test_failure' for test_suite contract fails

[nextlevelshit]

Symptom

When a step's test_suite contract fails (e.g. go test ./... exits non-zero), the run-detail UI shows:

non-retryable failure class "canceled", skipping remaining retries

Operators read "canceled" as "someone clicked stop" — but actually it just means "the contract validator categorised this as non-retryable so retries were skipped."

Concrete trace

wave-test-hardening-20260429-161707-ab9d — harden step ran go test ./..., hit a flaky/broken test in main (NOT caused by harden's writes), the test_suite contract failed, FailureClassifier labelled it canceled, no retry. UI surfaces "canceled" → user thinks Wave aborted the run.

Root

internal/pipeline/failure_modes.go (or wherever FailureClassifier lives) returns FailureClassCanceled for contract-validator non-retryable cases. The class is doing double duty: "user-cancelled" AND "contract said no point retrying". Two different operator stories collapsed into one label.

Fix

Split the class into two:

• FailureClassUserCanceled — operator clicked cancel / SIGINT / explicit abort
• FailureClassContractFailure — contract validator categorised the result as non-retryable (test_suite failed, json_schema failed with must_pass:true, etc)

Update UI rendering to display:

• canceled → grey badge, message "Run was canceled"
• contract_failure → red badge, message "Step failed: <contract_type> —
  Details

  "

Backward-compat: existing DB rows with the old combined value continue to render correctly (default to contract_failure since user-cancellation is rarer).

Severity

Low. Cosmetic / UX clarity. No functional impact.