docs(code-runtime-python): register the log-envelope reservation, SIGXCPU unblock, budget floor, and syntax label
The review flagged four mechanism changes shipped without note registration:
- Log ledgers start one byte below the budget (outer-array envelope reservation)
and the constructor floors maxLogBytes at 62 (the smallest budget that can
serialize its own truncation marker plus the envelope).
- die_if_cpu_exhausted restores SIG_DFL before unblocking a program-masked
SIGXCPU, so a trap+mask program cannot run a re-masking handler at the unblock.
- ast.parse passes filename="<model>" so parse-time syntax diagnostics share the
compile/runtime source label.
Decision and Testing (en + zh) now record all four with their fail-before cases
(exact-limit, budget rejection, syntax label, SIGXCPU-mask, trap+mask); pairing
re-recorded and consistent.
Chinesezjc