[Calls] Preserve complete symbolic exceptional observations for class replay diagnostics #497

Part of #483.

Observed boundary

Priority: P2. strict symbolic observation gap; native primary coverage already fixed in MR #479.

The original EMPTY_FRESH HashMap reproduction had five symbolic THREW candidates with incomplete strict snapshots; their native coverage was real.

Implementation scope

Provide comparable bounded exceptional observations for symbolic class scenarios: actual thrown kind/value and observable receiver state/effects at the throw point, including constructor failure. Reuse native error/value snapshots and existing engine catch semantics. Suspended prefixes must remain input-only and never acquire an invented terminal observation.

Acceptance criteria

• Source cases throwing a primitive or modeled Error retain the observable state/effects and compare against the exact native outcome.
• Constructor failures distinguish an unavailable external receiver from an incomplete observation; no invented successful construction.
• Strict applicability/rejection is separate from complete agreeing native coverage. This work must not restore the old gate that discarded genuine native coverage on symbolic mismatch.

Existing work to reuse or coordinate

• [TS] Route thrown exceptions into catch blocks #427
• [TS Calls][Research] Capture stopped-path frontiers for article experiments #373

Evidence and delivery rules

Use the frozen v7 200-class ledger and the source-linked reproducer; do not overwrite sealed experiment output. Reuse existing loaders, domain projection, source instrumentation, candidate/replay contracts and bounded observations. Keep original class members and independently frozen domain policies. Run focused source/native checks for the changed contract and leave broad suites to CI; unsupported and newly exposed later gates remain recorded.

Local evidence: iccq2026-paper/experiments/class-coverage-round-robin-20261002/real-class-campaign-20261014/{original/selection-ledger-v7.json,V7_INFRASTRUCTURE_FRONTIER.md} and real-class-machine-diagnostic-20261014/revised-protocol-v8/README.md.