Introduce VM macros and opcode/scanner refactor — fixes #30

[snakedye]

Summary

This PR brings the 30-macros branch into main and implements VM-level macros along with a substantial refactor of opcodes, the scanner, and execution logic. These changes implement the design described in #30 and add a number of ergonomics and correctness improvements to the VM.

Key changes

• Add helm-core/src/vm/macros.rs and a macro-aware Scanner that yields Expr values. Macros supported include:
  • OP_CLONE — repeat an opcode N times
  • OP_PRAGMA / OP_ENDPRAGMA — embed a pre-encoded sequence to be re-scanned
  • OP_VERIFYSIG — convenience macro to expand the common signature verification sequence
• Scanner now produces macro expressions and the VM flattens them before execution. This enables static sequences and small expansion-time macros (reduces repetition in common scripts).
• Reworked opcode definitions (helm-core/src/vm/op.rs):
  • OutAmt, OutData, OutComm are now zero-argument opcodes that pop the output index at runtime (previously they carried an immediate operand).
  • Added OutCount opcode (pushes number of outputs in the tx).
  • Introduced OP_ERR, OP_VERIFYSIG, OP_PRAGMA, OP_ENDPRAGMA, OP_CLONE and associated Op variants.
  • Removed the False/True Op variants in favor of OP_PUSH_BYTE uses.
• VM executor refactor (helm-core/src/vm/mod.rs):
  • VM accepts a flattened iterator of Op (macros are flattened before exec).
  • Added pop_stack helper to centralize stack pop + error handling.
  • Many stack-manipulating ops refactored to use pop_stack and to pop indices at runtime for Out* ops.
  • Introduced OP_ERR handling as a runtime verification error.
  • check_sig_script() now returns the OP_VERIFYSIG macro sequence.
• Scanner implementation (helm-core/src/vm/scanner.rs) rewritten to support macros and safer byte parsing (no index arithmetic). Several new tests for macro scanning were added.
• Updated tests across the VM and transaction modules to reflect API/behavior changes (notably: push-index-then-call for Out* ops, OP_VERIFYSIG expansion and OP_ERR expectations).
• Minor transaction updates: imports adjusted to use the new macros and helper functions.

Migration notes

• Call sites that previously emitted OP_OUT_AMT, OP_OUT_DATA, or OP_OUT_COMM with an immediate index must now OP_PUSH_BYTE <index> before the opcode. Example:

  • Old: [OP_OUT_AMT, 0]
  • New: [OP_PUSH_BYTE, 0, OP_OUT_AMT]

• Code/tests that relied on OP_VERIFY as a single opcode should be updated to expect the new behaviour; OP_VERIFY is implemented as a macro expansion using OP_ERR for clearer failure semantics.

Files with major changes

• helm-core/src/vm/macros.rs (new)
• helm-core/src/vm/mod.rs
• helm-core/src/vm/op.rs
• helm-core/src/vm/scanner.rs
• helm-core/src/transaction.rs (small import/test adjustments)

Why this helps

• Macros reduce repetition for common instruction patterns (e.g. signature verification), reducing bytecode size and improving maintainability.
• Moving index handling for output opcodes to runtime makes the opcodes more flexible (no immediate operand required) and simplifies the scanner.
• Centralized pop/error handling reduces duplication and makes executor paths easier to reason about.

Request for reviewers

• Focus areas: correctness of macro expansion (scanner), stack safety across refactored opcodes, and that the new runtime semantics for Out* opcodes are compatible with all callers.

Closes: #30

[snakedye-pr-agent]

✨ Copilot Agent Review

Summary

• Verdict: Action required — unable to access PR Introduce VM macros and opcode/scanner refactor — fixes #30 #40 in this environment; please provide the PR diff, list of changed files, or grant repository access so a complete audit can be performed.
• Referenced issues: status unknown / pending.

Details

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What’s Covered

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Confidence

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