[good-circle]

Update the DiffTest gitlink from 29e80f852 to 1349e6038 for two independent single-core REF checkpoint policies:

• --take-cpt-interval=N: periodic checkpoints in normal emu and FPGA host, measured in retired instructions; supports K/M/B. Default -1 explicitly disables scheduling.
• --take-cpt-on-fault: explicit emu-only opt-in; also requires --enable-fork and a DiffTest failure. The awakened child writes one REF checkpoint from the saved pre-fault state before replay.

Remove the old auto-checkpoint options, including the directory override. Output is created automatically under $NOOP_HOME/build/-ref-cpt/ on the first request. The shared comparison hook uses the slow REF path; NEMU retains M-mode skipping and serialization policy.

Dependencies:

• DiffTest: feat(difftest): add periodic and fork-fault REF checkpoints OpenXiangShan/difftest#1005
• NEMU PMEM default: fix(difftest): store REF checkpoints in PMEM by default OpenXiangShan/NEMU#1271

Update the gitlink to the final merged DiffTest commit before merging.

Validation on 103: normal Verilator emu and XDMA host builds pass; CLI/default/-1/interval and source-derived scheduling checks pass. Periodic smoke writes valid 10K/15K/20K U-mode checkpoints, skips M-mode at 5K, and reaches GOOD TRAP at the same 22,017 instructions / 78,627 cycles as the disabled control. A separate test-only DUT x10 mismatch reproduces during fork replay; only enabled fault+fork writes one pre-fault checkpoint. No injection code is included. The saved fault checkpoint restores to GOOD TRAP with the final production emulator using only -i, without an external restorer. DiffTest format CI passes on the pinned revision.

Full Linux checkpoint/restore and current-revision real FPGA acceptance remain pending. A Linux regression attempt with the new FPGA firmware stopped at its UART address 0x310b0004, which normal SimMMIO does not map (UART there is 0x40600000); this RTL assertion does not request a fault checkpoint.