Review finding (P2), and it is this lane's own defect class one level
down. Round 1 added a `-p pmacs-protocol --features crdt` step so that
crate compiles both ways. That step EXECUTED
`InstanceCapabilities::default` in both configurations and asserted
NOTHING about it: the crate's only use of that value is a transport
round-trip, and a round-trip is invariant to the values. An all-false
default — or one whose three fields disagreed with each other — encodes,
decodes, and passes identically in both builds.
Running code is not testing it. That is the same sentence this whole
lane is about, and round 1 committed the smaller version of it while
fixing the larger one.
Three tests now pin the defaults, and the split is the point:
* under `crdt`: multi_frontend, crdt_replica and semantic_render all
default true. Advertising false on a CRDT build would strand every
frontend in single-frontend mode.
* without `crdt`: all three default false. Advertising true would be
wire-protocol false advertising — those code paths are
conditionally compiled out.
* FrontendCapabilities::default is all-false in BOTH builds, and this
test is DELIBERATELY NOT feature-gated.
That third one pins an asymmetry nothing else did.
FrontendCapabilities derives Default and is feature-INVARIANT, while
InstanceCapabilities is feature-DEPENDENT. It is load-bearing rather
than an oversight: an instance advertises what it can do, a frontend
OPTS IN through the negotiation handshake, and a v1 frontend has no
local CRDT state regardless of how the crate it links was compiled.
Making the frontend side track the feature would have frontends
claiming support they do not have. A future edit that "makes them
consistent" now fails a test that says why not to.
All three fields are asserted separately rather than by comparing whole
structs, because they track one `cfg!` and a change flipping only some
of them is exactly the regression worth catching.
Bite-verified rather than assumed: mutating `multi_frontend` to a
literal false gives `FAILED. 18 passed; 1 failed` with the expected
assertion message; restoring returns 19/19. Both configurations now
report 19 tests, up from 17, with the correct cfg-gated test running in
each.
Left untested and recorded instead: `InstanceCapabilities::crdt_replica`
carries `#[serde(default = "default_true")]`, a THIRD default mechanism
that is unconditional and therefore disagrees with the `Default` impl in
a non-CRDT build. Exercising it needs a self-describing format and this
crate's only serde dependency is postcard, which is not one. Adding
serde_json as a dev-dependency to test a divergence this lane did not
introduce is scope creep.
Also corrects a note that round 1 made stale: the ledger's "do not
subtract the two jobs' totals" figures (3,485 and 3,747) were measured
BEFORE round 1 added the protocol step, and round 2 adds two tests to
that crate. Expected totals are now 3,487 and 3,766. The root-package
census is untouched at 3,467 / 3,746 — the new tests live in a sibling
crate, which is precisely the region scripts/feature-census cannot see.
Verified: fmt, diff-check, clippy on pmacs-protocol in both feature
configurations, and workspace clippy --features crdt --keep-going.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Levi Neuwirth
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