Surface Compound decimals-guard failure via errored flag (#36)

[szhygulin]

Summary

• Closes get_compound_positions returns empty for wallet with 184k cUSDCv3 on ethereum (no errored flag) #36. PR Add verifiable transaction preview (swiss-knife + payload-hash proof) #35 tightened three of the four position-critical multicalls in Compound V3, but left the base-token decimals() guard at return null. A transient failure on that read (with a nonzero base balance) silently dropped the market while coverage.compound.errored stayed false — the aggregator reported clean coverage with a curated-registry market silently missing.
• Throw instead so the Promise.allSettled wrapper in getCompoundPositions classifies the market as errored and surfaces it via erroredMarkets.
• Regression test in test/session-regression.test.ts now asserts result.errored === true and that erroredMarkets names the failing market, rather than just checking the old silent-skip behavior.

Test plan

• npx tsc --noEmit
• npx vitest run — 395/395 pass
• Updated regression test exercises the decimals-read-fails-with-nonzero-base-balance path and asserts the new errored surface.

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