COVER: Causally Ordered, Verified Event Records for Schedule-Robust LLM Memory

Stateful language-model memory can interpret the same event differently depending on which other events have already arrived. Deduplicating or sorting records after extraction cannot repair this semantic change. We introduce COVER, which compiles each event from its causal ancestors, retains source-bound records, and joins them independently of delivery order. Under authenticated causal dependencies and a fixed deterministic compiler, COVER produces identical terminal states and answers across legal schedules and retries. Our analysis characterizes the local conditions for this guarantee and the information that compression must preserve for future queries. Experiments separate structural reliability from semantic utility. In a controlled action relay, COVER improves success across all tested schedules by 2.50 percentage points over typed FIFO with the same content and budget. Source-retaining readers also improve complete-history LongMemEval and LoCoMo accuracy in selected configurations. Strong canonical controls account for much of the reliability benefit, however, and restrictive typed adapters lose utility on natural dialogue. COVER provides a causal interface for reliable memory construction; its semantic gains depend on the compiler, reader, and evidence budget.