Original exit-rule prefix priority pending clocks and transition gates

RE-821. Reproduce with python3 scripts/analyze_qvm_exit_prefix.py; focused validation: cargo xtask test-group exit-prefix. Machine report.

144 source-prefix fixtures cover nonzero/negative blocked values, empty/pending clocks, signed timestamp boundaries and exact threshold sides. Independent tests verify captured child request order, global writes and the stop before mode-specific rules.7525/6825 effects, mode-specific exits and full publication integration remain open.

Original executable/native runtime and complete Linux/macOS Rust/Bevy/Solari acceptance remain unverified.