fix: address compiler findings from the 0.14 audit

[rkalis]

Fixes the remaining compiler findings from the 0.14 audit (follow-up items 1, 2 and 7.1, and the early return TODO from the first review's item 6).

Changes

• LockingBytecodeNullData push opcodes: the push opcode of a chunk was built from OP_SIZE, which is a signed VM number. Empty chunks therefore got no push opcode (a bare 6a instead of the SDK's 6a4c00), and chunks of 128-255 bytes got a malformed 4c <size> 00 prefix. The generated script now matches encodeNullDataScript() (and so addOpReturnOutput()) for every chunk size up to 255 bytes:
  • Chunks with a value known at compile time (hex literals and string literals like bytes('memo')) are pushed together with their push opcode as a single constant.
  • Chunks with a length known at compile time (e.g. bytes20) are preceded by a constant push opcode.
  • Other chunks use a runtime check that converts the size to a single byte and prepends OP_PUSHDATA1 for empty chunks and chunks of 76-255 bytes.
  • All of these are smaller than before. Chunks whose size is known to be larger than 255 bytes are now a compile error (NullDataChunkTooLargeError).
  • This changes the bytecode of every contract that uses LockingBytecodeNullData.
• Tuple reassignment narrowing: after require(x.length == 20), x, bytes rest = y.split(5); kept x typed as bytes20 while it held 5 bytes. Tuple reassignment targets are now checked against their current (narrowed) type, like plain assignments.
• Odd-length hex literals: 0x123 was silently compiled to 0x1203 and is now a compile error. Test contracts that used odd-length literals were updated without changing their bytes.
• Early return TODO: removed from EnsureFinalRequireTraversal, early and conditional returns are tracked in Consider allowing conditional returns (multi returns) in user-defined reusable functions #416 and Allow for passing through multiple return values from a function return #424.
• Docs: LockingBytecodeNullData chunk encoding and release notes.

Tests

• cashc: compile error fixtures for too large hex literal, string literal and bytesN chunks, odd-length hex literals and the tuple reassignment narrowing bypass, new tuple_reassignment_narrowing.cash and locking_bytecode_nulldata_chunks.cash fixtures, and updated fixtures for announcement.cash and the contracts whose hex literals changed.

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

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Project	Deployment	Actions	Updated
cashscript	Ready	Preview	Sep 25, 2026 3:24pm UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.76%. Comparing base (37bf465) to head (768508d).

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #452      +/-   ##
==========================================
+ Coverage   88.63%   88.76%   +0.13%     
==========================================
  Files          61       61              
  Lines        4980     5012      +32     
  Branches      920      927       +7     
==========================================
+ Hits         4414     4449      +35     
+ Misses        436      433       -3     
  Partials      130      130              

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