[Bug] File clobbering during Write tool operations with /fast mode

Bug Description
Asked claude to describe what happened -- this is accurate: File clobbering — facts only Setup. Three files created in sequence in directory D via Write tool: X.md (137 lines), Y.md (139 lines), Z.md (153 lines). All distinct content; D was a newly created subdirectory. Separate file P.md exists in D's parent directory (370 lines, 43401 bytes). Event 1. After the third Write call completed, the next system-reminder reported file modification for Y.md and Z.md. Bash diff confirmed Y.md and Z.md were each byte-identical to P.md (43401 bytes, 370 lines, same header). X.md was unchanged. Both Y.md and Z.md restored via Write tool from conversation history. Event 2. After Event 1 restore, the next system-reminder reported file modification for Z.md only. Bash diff confirmed Z.md was byte-identical to X.md (137 lines, header matching X.md). Y.md and X.md were unchanged. Z.md restored via Write tool. No subsequent events. Each clobber was detected within one conversation turn of the preceding Write call. No git commands ran between Write calls and detection in either event. Both system-reminder messages framed the change as "intentional" (the standard framing on file-modified reminders). The two clobber sources (P.md at 43401 bytes; X.md at 10725 bytes) are different files of different sizes — the pattern is not a single repeated overwrite of one target with one source.
Note that this was using /fast -- one of the only times I've used /fast. Also, was using the /impeccable skill (v3.1.1) freeform for the copywriting.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.144
• Feedback ID: a281501e-cefd-4801-8c0a-957a09310198

Errors

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