Complete F8D O2 causal finalization and fulfillment

[garykocsis]

Summary

Completes F8D — O2 Causal Finalization / Remaining Reduction and closes G8D — PASS.

This slice completes the planned production O2 lifecycle by converting a causally proven, executed, settled, and directly delivered exercise into exactly one durable fulfillment consequence.

What changed

• added Hook-owned O2 finalization from the proven EXECUTED causal context;
• bound finalization to the authorized ExerciseRouter and exact commitment identity;
• re-read authoritative commitment state at finalization;
• verified final backing from actual post-execution Supporting Capacity;
• reduced authoritative commitment Remaining exactly by the context-bound exercise quantity;
• consumed the transaction-scoped causal context exactly once;
• preserved the existing ExerciseRouter completion barrier so successful production exercises satisfy it naturally;
• added focused unit, integration, fuzz, and failure-path evidence for partial/full fulfillment, replay resistance, backing equality, causal consumption, and whole-exercise atomicity.

Verification

Repository verification completed successfully:

58 suites
539 tests passed
0 failed
0 skipped

G8D was independently reviewed and closed:

G8D-A — Causal Authority             PASS
G8D-B — Final Economic Backing       PASS
G8D-C — Exact Fulfillment            PASS
G8D-D — Exact-Once Consumption       PASS
G8D-E — Atomicity                    PASS
G8D-F — Integration / Regression     PASS

Verification infrastructure

The local Forge execution gas limit was increased to preserve deterministic HookMiner-based fixture execution as Hook bytecode grew.

This is local verification infrastructure only and does not change deployed-chain gas limits or Standby protocol semantics.

Engineering baseline

Captured the post-F8D / pre-GI engineering baseline:

• .gas-snapshot
• docs/reports/gas-snapshot.md
• docs/reports/coverage-summary.md

These artifacts are non-normative engineering evidence and do not establish protocol requirements or verification gates.

Status

• F8D — O2 Causal Finalization / Remaining Reduction: COMPLETE
• G8D: PASS
• GI — Full Stateful Invariant Verification: next authorized implementation slice / current blocker

GI has not started.

Scope boundary

This PR does not introduce new GI, F9, or F10 behavior and does not change the frozen protocol semantics.