agent-2pc v1.4.0: Transparent Command Execution Side-Effect Staging Runner

⚡ What's New in v1.4.0

• Transparent Command Side-Effect Staging (src/exec.rs):
  • Run arbitrary compilers, linters, migration scripts, or test harnesses directly against the workspace (ExecRunner::execute_and_stage).
  • Automatic directory-wide file fingerprinting (CRC32) before and after process execution.
  • Automatically identifies all newly created and modified files, creates clean .bak snapshots, and auto-stages mutations into Phase 1 2PC receipts with zero manual effort.
• Atomic Failure Neutralization:
  • If a command fails (exit code != 0), all workspace modifications are immediately reverted to pre-execution state without dirty residue.
• Surfaces & CLI:
  • CLI subcommand: agent-2pc exec --tid <TID> [--dir <PATH>] -- <COMMAND...>.
• Verification:
  • 37/37 passing tests including automated staging and failure rollback tests in tests/exec_staging_test.rs.