jcp: count the joules a cache hit did not spend, without ever calling it spend #75

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dcharlot merged 1 commit from jcp/avoided-energy into main 2026-09-03 15:11:51 -04:00

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dcharlot commented 2026-09-03 15:07:02 -04:00

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MCP's 2026-07-28 revision added CacheableResult with ttlMs/cacheScope, so a served result can declare itself reusable. When it is reused, work that would have run did not — and for a family whose doctrine is that inference is the last resort, the cheapest joule is the one never spent. Nothing in the family bound a reused result to an energy figure.

It is also the easiest quantity here to lie with, so it deliberately does not become another Energy.

It is a counterfactual, not a measurement

Nothing measures a joule that was not spent. An avoided figure is a claim about what would have happened, and the only thing making it checkable is a pointer to the execution it stands in for.

So AvoidedEnergy cannot be constructed without naming the receipt whose measured cost it claims to have avoided. Without that, "this hit saved 10 mJ" is unfalsifiable — and unfalsifiable savings are how an efficiency programme reports progress it never made.

It must never be added to energy spent

If avoided joules were summed with spent joules, or subtracted from them, a system could manufacture arbitrary efficiency and, with enough hits, report negative consumption.

Physics has no negative-joule case. An accounting system that does has a bug that looks like a triumph.

So this type produces no Energy, offers no arithmetic against a spend total, and AvoidedSummary::saving_ppm_of takes the spend as an argument rather than holding it — the two totals meet in exactly one place, expressed as a ratio to spend and never a deduction from it. A test drives five million-microjoule hits against a 200 µJ spend and shows there is no path to a negative spend figure.

A cache hit is not free

The net subtracts what serving the hit cost, since claiming the full prior cost over-claims by exactly that amount. When a lookup costs more than recomputing would have, the saving is reported negative rather than clamped — a cache that doesn't pay for itself is a real outcome, and rounding it to "no saving" hides the one case an operator most needs to act on.

unprofitable_hits is counted separately, so a cache that is net-positive overall while losing on most requests is visible rather than averaged away.

The saving inherits the basis measurement's acquisition class, because a saving standing in for an Estimator figure is an estimated saving, however precisely it prints.

Provenance

Ranked by the 2026-08-29 sweep as the one remaining item it called unclaimed territory rather than an adapter.

Verification

265 jcp-rs tests pass (5 new) · conformance passes all classes · no clippy warnings in the new file.

🤖 Generated with Claude Code

MCP's 2026-07-28 revision added `CacheableResult` with `ttlMs`/`cacheScope`, so a served result can declare itself reusable. When it is reused, work that would have run did not — and for a family whose doctrine is that **inference is the last resort**, the cheapest joule is the one never spent. Nothing in the family bound a reused result to an energy figure. It is also the easiest quantity here to lie with, so it deliberately does **not** become another `Energy`. ## It is a counterfactual, not a measurement Nothing measures a joule that was *not* spent. An avoided figure is a claim about what would have happened, and the only thing making it checkable is a pointer to the execution it stands in for. So `AvoidedEnergy` **cannot be constructed** without naming the receipt whose measured cost it claims to have avoided. Without that, *"this hit saved 10 mJ"* is unfalsifiable — and unfalsifiable savings are how an efficiency programme reports progress it never made. ## It must never be added to energy spent If avoided joules were summed with spent joules, or subtracted from them, a system could manufacture arbitrary efficiency and, with enough hits, **report negative consumption**. > Physics has no negative-joule case. An accounting system that does has a bug that looks like a triumph. So this type produces no `Energy`, offers no arithmetic against a spend total, and `AvoidedSummary::saving_ppm_of` **takes the spend as an argument rather than holding it** — the two totals meet in exactly one place, expressed as a ratio *to* spend and never a deduction *from* it. A test drives five million-microjoule hits against a 200 µJ spend and shows there is no path to a negative spend figure. ## A cache hit is not free The net subtracts what serving the hit cost, since claiming the full prior cost over-claims by exactly that amount. When a lookup costs **more** than recomputing would have, the saving is reported **negative rather than clamped** — a cache that doesn't pay for itself is a real outcome, and rounding it to "no saving" hides the one case an operator most needs to act on. `unprofitable_hits` is counted separately, so a cache that is net-positive overall **while losing on most requests** is visible rather than averaged away. The saving inherits the basis measurement's acquisition class, because a saving standing in for an `Estimator` figure is an *estimated* saving, however precisely it prints. ## Provenance Ranked by the 2026-08-29 sweep as the one remaining item it called **unclaimed territory** rather than an adapter. ## Verification 265 jcp-rs tests pass (5 new) · conformance passes all classes · no clippy warnings in the new file. 🤖 Generated with [Claude Code](https://claude.com/claude-code)

dcharlot added 1 commit 2026-09-03 15:07:03 -04:00

jcp: count the joules a cache hit did not spend, without ever calling it spend ... 50b5efaad0

MCP's 2026-07-28 revision added `CacheableResult` with `ttlMs`/`cacheScope`, so
a served result can declare itself reusable. When it is reused, work that would
have run did not — and for a family whose doctrine is that inference is the last
resort, the cheapest joule is the one never spent. Nothing in the family bound a
reused result to an energy figure.

It is also the easiest quantity here to lie with, so it does not become another
`Energy`.

**It is a counterfactual, not a measurement.** Nothing measures a joule that was
not spent; an avoided figure is a claim about what would have happened. The only
thing making it checkable is a pointer to the execution it stands in for, so
`AvoidedEnergy` cannot be constructed without naming the receipt whose measured
cost it claims to have avoided. Without that, "this hit saved 10 mJ" is
unfalsifiable — and unfalsifiable savings are how an efficiency programme
reports progress it never made.

**It must never be added to energy spent.** If avoided joules were summed with
spent joules, or subtracted from them, a system could manufacture arbitrary
efficiency and, with enough hits, report negative consumption. Physics has no
negative-joule case; an accounting system that does has a bug that looks like a
triumph. So this type produces no `Energy`, offers no arithmetic against a spend
total, and `AvoidedSummary::saving_ppm_of` takes the spend as an argument rather
than holding it — the two totals meet in exactly one place, expressed as a ratio
*to* spend and never a deduction *from* it. A test drives five million-microjoule
hits against a 200 µJ spend and shows no path to a negative spend figure.

**A cache hit is not free.** The net subtracts what serving the hit cost, since
claiming the full prior cost over-claims by exactly that amount. When a lookup
costs more than recomputing would have, the saving is reported **negative rather
than clamped**: a cache that does not pay for itself is a real outcome, and
rounding it to "no saving" hides the one case an operator most needs to act on.
`unprofitable_hits` is counted separately, so a cache that is net-positive
overall while losing on most requests is visible rather than averaged away.

The saving inherits the basis measurement's acquisition class, because a saving
standing in for an `Estimator` figure is an estimated saving however precisely
it prints.

Ranked by the 2026-08-29 sweep as the one remaining item it called unclaimed
territory rather than an adapter.

Verified: 265 jcp-rs tests pass (5 new), conformance passes all classes, no
clippy warnings in the new file.

Co-Authored-By: Claude Opus 5 <[email protected]>

dcharlot merged commit f524313376 into main 2026-09-03 15:11:51 -04:00

dcharlot referenced this pull request from a commit 2026-09-03 15:11:52 -04:00

Merge pull request 'jcp: count the joules a cache hit did not spend, without ever calling it spend' (#75) from jcp/avoided-energy into main

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