Prefix materialize prefetch has fixed launch and coordination overhead, so tiny cache-hit prefixes should stay on the simpler synchronous path. The default threshold is now expressed as a cached import-time token threshold while the existing page override remains available for workload-specific tuning.
Both MLA and index prefix prefetchers use the same page-size-aware threshold, so CP shared-KV prefix prefetch is enabled only when the prefix covers at least one page per CP lane and at least the configured token threshold.
Constraint: The default token threshold must be read once to avoid hot-path env lookups
Constraint: Existing page threshold override must continue to disable or force the gate
Rejected: Hard-code 1024 tokens | tuning needs to be possible without code changes
Rejected: Read token threshold on every maybe_create call | unnecessary hot-path env lookup
Confidence: medium
Scope-risk: narrow
Directive: Keep MLA and index prefetch threshold logic shared; do not let their gates diverge
Tested: Not rerun per user request; prior py_compile, diff check, and isolated env-cache check had passed before commit
Not-tested: full pytest in local environment due missing optional dependencies/kernel import constraints
Not-tested: GLM5 E2E throughput after this threshold change
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