fix(runtime): archive failed inference through the discard lifecycle #75

Keep the intentional post-error context reset/cache-cost policy. Classify a failed uncommitted provider completion separately from invariant corruption, and return the existing discard loop exit in both main/frontend. Committed history and completed tool results enter the normal discard archive; failed partial output does not. Resume checkpoints are removed, existing rest snapshots retain existing semantics, tool effects are not rolled back or automatically replayed. Other fatal/invariant errors still quarantine. OMP-authored patch, independently reviewed: 13/13 focused Context/discard tests, 325/325 full tests, full workspace typecheck. Regression uses only isolated fake providers and state, includes completed tool followed by EOF, archive readback and a separate-process restart. No unconditional full-context preservation, no deployment.