test(mcp): pin RFC #110 cache-prefix claims with 6 unit tests#112
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test(mcp): pin RFC #110 cache-prefix claims with 6 unit tests#112
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The reconnect RFC's central claim — "re-bridging tools mid-session breaks the prompt prefix when the new tool surface differs from the old" — was so far an architecture-derived assertion, not an empirical result. Cheap to lock down at the prefix-fingerprint layer. `tests/mcp-reconnect-prefix-invariant.test.ts` covers six cases the RFC directly references: - identical tool list → fingerprint unchanged (the safe-reconnect case) - one tool added → fingerprint changes - one tool removed → fingerprint changes - description-only edit on an existing tool → fingerprint changes - parameter-schema edit → fingerprint changes - same tools reordered → fingerprint changes (array order is part of the prefix bytes via JSON.stringify) This gives RFC #110 a concrete reference to point at when weighing the strict / permissive / `--force` approaches: any drift past the "identical bytes" line is a guaranteed cache miss, full stop. Refs #110.
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Refs #110.
What
The reconnect RFC's central claim — "re-bridging tools mid-session breaks the prompt prefix when the new tool surface differs from the old" — was an architecture-derived assertion, not an empirical result. Cheap to lock down at the
ImmutablePrefix.fingerprintlayer.tests/mcp-reconnect-prefix-invariant.test.tscovers six cases the RFC directly references:Why
This gives RFC #110 a concrete reference to point at when weighing strict / permissive /
--forceapproaches: any drift past the "identical bytes" line is a guaranteed cache miss, full stop. So the design conversation can focus on UX policy ("refuse vs warn vs flag-gated"), not on whether the underlying claim is actually true.This is a tests-only change, no source files touched. Doesn't unblock C2b implementation by itself — that still needs the design call in #110 first.
Test plan
npm run verifypasses locally (1760 tests, +6)ImmutablePrefix(no behavior change in src/)