fix: follow-up compiler fixes from the 0.14 audit

[mr-zwets]

Opened on behalf of Mathieu G. (mr-zwets), written by Claude Opus 5.5.

Replaces #459, which was opened from the wrong branch by mistake.

Follow-up to the 0.14 audit, meant to land after the 0.14.0 release: the important compiler findings are fixed in #463, #464, #465 and #466, and this PR holds the smaller ones that were left out to keep the release's scope small. Rebased on next, without the parts those PRs cover.

Changes

• Compiler options passed as undefined: { enforceLocktimeGuard: config.x } with x unset disabled the locktime guard (and the same for enforceFunctionParameterTypes), while the artifact recorded compiler.options: {}, which reads as the defaults. Options now fall back to their defaults, and only the known options are recorded (unknown keys and the files map were copied into the artifact).
• Stale stack slots: after a reassignment outside a loop or branch, the old value stays on the stack under the same name. It is now made anonymous, so a mismatch between where the symbol table records a final use and where code generation reads the variable (the class of fix: fix slice() variable final-use handling #464 and fix: fix init-reassign for-loop bug #466) is a compile error instead of a stale read. No bytecode changes. As a side effect, console.log shows the current value of a reassigned variable after its final use, instead of the old one.
• Tuple destructuring: bytes a, bytes b = a.split(1); crashed with an internal error (no location); it is now an UndefinedReferenceError, like int a = a + 1;.

No release notes yet, since the 0.14 section will be closed by then. Suggested lines for the next release:

• 🐛 Fix bug where compiler options passed as undefined were disabled instead of using their default value, and unknown compiler options were included in the artifact.
• 🐛 Fix bug where using a newly declared variable on the right-hand side of its own tuple destructuring caused an internal compiler error instead of an UndefinedReferenceError.
• 🐛 Fix bug where console.log showed an outdated value for a reassigned variable after its final use.

Tests

• A test that no variable is read after its final use, for every valid contract file and for a contract that reads the same variable in every child of each expression node type.
• Compiler option tests (undefined options still inject the guard, unknown keys are dropped) and a tuple error fixture.
• SDK: console.log of a reassigned variable after its final use.

The option, tuple and console.log tests fail on the current next. Recompiling the fixtures gives unchanged bytecode.

yarn build, yarn test, yarn lint and yarn spellcheck pass.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
cashscript	Ready	Preview	Sep 29, 2026 9:58am UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.26%. Comparing base (625d844) to head (37f664f).

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #461      +/-   ##
==========================================
+ Coverage   89.23%   89.26%   +0.02%     
==========================================
  Files          61       61              
  Lines        5074     5087      +13     
  Branches      949      951       +2     
==========================================
+ Hits         4528     4541      +13     
  Misses        421      421              
  Partials      125      125              

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[github-actions]

Pull request stats

	Source	Tests	Total	Net	Share
Compiler (cashc)	+33 −7	+154 −1	+187 −8	+179	92%
SDK (cashscript)		+16 −0	+16 −0	+16	8%
Total	+33 −7	+170 −1	+203 −8	+195	100%

Reviewable churn: 211 lines (net +195), version bumps and generated files excluded.
Test lines per line of source: 4.28.
Comments: 5 of 29 added source lines, 17%.

New files: 2

• packages/cashc/test/compiler/UndefinedReferenceError/tuple_target_used_in_own_declaration.cash
• packages/cashc/test/generation/final-use.test.ts

Package source changed without an update to website/docs/releases/release-notes.md.