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An access service may apply the same policy thousands of times.

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Rebuilding its internal representation for every request can repeat preparation that has

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already been done.

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This lesson follows one small policy through new requests, a policy

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revision, and a process restart.

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We will separate the rule we can reuse from the answer we must obtain

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for the current request.

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That distinction matters whenever cached work outlives the circumstances

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that made it valid.

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Our examples are about exact behavior and reuse.

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They are not new speed measurements.

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They are not new speed measurements.

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For this teaching policy, role means that the person is approved staff.

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Region means that the request comes from an allowed location.

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One means the condition is true, and zero means it is false.

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Version one permits access only when both conditions are true.

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We write that as role and region.

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The word and requires both inputs to be one.

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These are deliberately simple conditions.

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The application is responsible for supplying their current values

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and keeping their meanings consistent.

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Our first request has role one and region one.

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The person is approved staff, and the location is allowed.

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Substitute those values into the rule.

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One and one gives one.

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Both requirements are satisfied, so this request is allowed.

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This allow decision belongs to this request under version one.

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It is not a promise about the next request.

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It is not a promise about the next request.

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Compilation turns the source expression into an internal representation

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that an evaluator can use.

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For our small rule, it records the inputs and the and operation connecting them.

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The input values are supplied when we evaluate a request.

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The resulting allow or deny bit is a different object from the compiled representation.

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In the current C M I R path, the persistent cache stores compiled representation nodes.

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Reusing those nodes does not mean that every later preparation step or every requested

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output has already been computed.

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A cache keeps reusable work under an identifying key.

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Before lookup, this compiler checks that the expression graph is

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acceptable, including its structural limits.

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With the cache enabled and initially empty, the lookup misses.

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The system builds the representation and stores it.

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A later admitted lookup for the same compatible structure can hit that entry and reuse it.

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In the current implementation, the key includes an expression-structure

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digest and the flattening option.

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A hit also depends on the entry still being present.

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Clearing the cache or evicting an entry can turn a later lookup into a miss.

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Reuse is conditional, even inside the same process.

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Reuse is conditional, even inside the same process.

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Now a second request arrives.

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The person is still approved staff, but the location is not allowed.

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The policy remains role and region.

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We can reuse the compiled representation and evaluate it with these new inputs.

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One and zero gives zero, so the second request is denied.

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The same program has produced two different answers.

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Copying the previous allow bit would be wrong.

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Caching a representation and caching a request result

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require different validity conditions.

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Suppose the policy changes.

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Version two adds a resource requirement.

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Resource is one when the requested resource meets that requirement, and zero

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when it does not.

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The new rule requires role, region, and resource all to be true.

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This changes the expression structure.

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It is a new complete rule to compile or retrieve under its own compatible identity.

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We have changed the policy, not merely the request values.

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Keep both versions visible while we work the consequence.

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Keep both versions visible while we work the consequence.

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Consider one request with role one, region one, and resource zero.

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Version one looks only at role and region.

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It computes one and one, and allows access.

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Version two begins with the same two values, giving an intermediate one.

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It then combines that one with resource zero.

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One and zero gives zero, so the revised policy denies access.

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The old result is not an approximate answer to the new policy.

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It is the answer to a different rule.

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The complete version-one artifact cannot substitute for version two.

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The complete version-one artifact cannot substitute for version two.

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Changing the complete rule does not mean that every unchanged piece must be thrown away.

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The subexpression role and region still occurs inside version two.

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The current compiler can reuse compatible cached subtrees in suitable contexts.

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Where shared associative structure makes compilation context-dependent, it uses a

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root-level cache path instead.

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The practical conclusion is precise: do not reuse an obsolete complete rule, but do not

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confuse that requirement with discarding all valid shared work.

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The compiler decides which compatible pieces it can safely reuse.

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The compiler decides which compatible pieces it can safely reuse.

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There is another kind of change.

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Suppose the expression still says role and region, but the application's definition of an

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allowed location changes.

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A structural digest cannot discover a meaning that was never encoded in the expression.

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The application must update the values or dependencies that represent

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the new location policy.

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The same representation may still be usable with correctly updated inputs.

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What is unsafe is treating unchanged symbols or a matching digest as evidence that an old

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decision remains valid.

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decision remains valid.

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A process is one running instance of the program.

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While process A runs, it can retain its cache between calls.

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Now end that process.

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Start a fresh, independent process B.

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The source expression may be identical, but the old in-memory cache entry has not

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automatically travelled into the new process.

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In this C M I R API, persistent describes reuse within the process.

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The cache itself does not promise storage on disk or survival across this restart.

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To carry structure across a restart, something must explicitly save

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it and later reconstruct it.

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That is a separate serialization and reload path.

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The repository has bounded research bundles containing flat instructions or clauses.

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Those bundles exclude cached query answers.

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Loading their structure is not the same operation as finding a live node

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in the process cache.

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A reload includes decoding, validation, and reconstruction before

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the requested outputs are evaluated.

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Those steps have their own cost and correctness obligations.

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Those steps have their own cost and correctness obligations.

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For these research bundles, first check the format and backend.

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Then check the expected scenario, variable count, and version identities.

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A file for a different scenario is not interchangeable just because it can be decoded.

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Next validate the serialized instructions or clauses and reconstruct the structure.

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The research validation also compares the resulting behavior with independently computed

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scalar reference outputs.

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These are separate checks.

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A byte hash can identify the payload being examined, but it does not replace format

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admission or an exact behavior check.

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Imagine a saved bundle that still names the expected scenario, but

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declares an unsupported format version.

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Keep the source identity fixed and change only this format field.

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The loader must refuse that artifact.

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It has not evaluated the policy and found the request false.

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It has declined to accept this representation.

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The application can use a supported rebuild path where available.

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It must not silently turn a loading failure into a cached allow decision, or mistake it

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for a valid deny result.

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for a valid deny result.

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For a new request under the same valid rule, reuse the representation when available and

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evaluate the current inputs.

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For a revised rule, use the revised complete artifact.

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For a fresh process, rebuild or follow a separately supported and validated reload path.

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For an unsupported saved format, refuse the artifact rather than infer a policy decision.

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Reliable reuse means knowing what was saved, what stayed valid, and what still

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has to be computed.

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That is the foundation for both correct behavior and an honest measurement

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of any saved work.