[Kshot3000]

Summary

decimalize() and undecimalize() in @fleet-sdk/common (packages/common/src/utils/bigInt.ts) wrote their resolved defaults back into the caller's options object:

options.decimals = options.decimals || 0;
options.decimalMark = options.decimalMark || ".";

Two observable effects:

• The caller's object comes back changed. Passing { decimals: 2 } returns with a decimalMark: "." the caller never set. These helpers are exactly the kind that get called with shared or reused option objects — the spec's own roundtrip test passes one options object to both functions — so the writes leak resolved defaults into caller state.
• A frozen options object throws. decimalize(1763874n, Object.freeze({ decimals: 2 })) throws TypeError: Cannot assign to read only property 'decimals', and undecimalize("1.23", Object.freeze({})) throws TypeError: Cannot add property decimals, object is not extensible — even though both functions only ever read from the object.

Fix

Resolve decimals/decimalMark into local variables (keeping the exact same || default semantics, including an explicitly-undefined field falling back to the default) and pass a fresh object to buildFormattedDecimal. The caller's object is never written to. All outputs are byte-identical — every pre-existing vector passes unchanged.

Tests

Five new cases in bigInt.spec.ts, all failing on pristine master:

• decimalize: should not mutate the caller's options object — deep-equal mismatch on pristine ({ decimals: 2 } gained decimalMark).
• decimalize: should accept a frozen options object — previously threw TypeError.
• undecimalize: should not mutate the caller's options object — same deep-equal mismatch.
• undecimalize: should accept a frozen options object — previously threw TypeError.
• undecimalize: should accept frozen options relying on defaults — previously threw TypeError (adding a property to a non-extensible object).

Results: bigInt spec 21/21; full monorepo suite 1137/1137 (66 files); biome clean on the changed files. Changeset included (@fleet-sdk/common: patch).

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Independent community contribution — @Kshot9000 (https://x.com/kshot9000). If this work is useful, tips are welcome: ERG 9fcM5RWnAjmP4vx5bnW6yohB6H9bLq8sJbaPLHtwZLtQPB32Pvy

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Latest commit: b207c86

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@fleet-sdk/common	Patch

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