docs: one normative home for the crdt sweep's build precondition

The durable half of this lane is a boundary question, not the missing
line. `scripts/gate`'s header names handoff section 3 as the owner of
its reasoning, and this precondition lived in section 5's hazard
register --- a coherent cause for the omission rather than mere
oversight. A requirement the script was never told to encode is one it
will keep not encoding.

So section 3 gains it NORMATIVELY: the build joins the protocol-bump
block as a third line, with its own load-bearing bullet covering the
mechanism (pmacs-gpu has no tests/ directory, so cargo never uplifts
its bin), the measurement that makes it conditional, and why it was
latent until per-worktree target directories stopped hiding it.

Section 5 keeps the INCIDENT and its signature, which is history rather
than contract, and now says so: twelve
`gpu_invocation_acceptance::crdt::*` failures on a target directory
with no `debug/pmacs-gpu`, first seen on PR #228's first gate run.
Recast so that seeing the signature again reads as "the script was
bypassed", not "the requirement moved".

The script's header keeps citing section 3 and ONLY section 3. Citing
both would split one executable contract across two homes and weaken
the script's only clean boundary at the same time as Q#GR-4 declines to
build any automated check for prose drift. A boundary that is neither
enforced nor singular is not a boundary.

The ledger records Q#GR-1's observed answer rather than the question:
both sweeps run alone from the same cold disposable target with
`debug/pmacs-gpu` asserted absent beforehand --- default exit 0 with
the binary still absent afterwards, crdt exit 101 with exactly twelve
failures --- plus the silent-skip finding, which is the part nobody was
looking for: a54 reported `ok` in that cold crdt sweep because its only
non-spawning path is its skip branch.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bqGA6s9tTUFzYpbeW3tai

docs/active-work.md

@@ -265,7 +265,7 @@ also removed: this branch's "R8 NEEDS A LANE" investigation block, and
 durable facts are in the retired registry row and the handoff §6
 census.
 
-## `scripts/gate --protocol` build step — BRANCHED, framing in review
+## `scripts/gate --protocol` build step — IMPLEMENTED, no PR yet
 
 **Written with the lane's first commit**, per the standing correction
 from #171 and #215.
@@ -275,15 +275,15 @@ from #171 and #215.
 authoritative tip** — the ref, not a SHA. Recover with
 `git fetch githubsucks && git checkout gate-protocol-build`.
 
-- **Framing `docs/gate-protocol-build-framing.md`, revision 3**, in
-  review. Narrow by design: one missing step in one script, plus the
-  boundary question that let it go missing. No `src/`, no protocol, no
-  feature work.
-- **The defect.** `--protocol` adds the CRDT workspace sweep, whose
-  documented precondition is `cargo build --workspace
-  --no-default-features --features luajit,crdt` (handoff §5:532-535).
-  The plan emitter (`scripts/gate:187-204`) has **no build step at
-  all** — read from the source, not inferred from the failure.
+- **Framing `docs/gate-protocol-build-framing.md`, revision 3,
+  APPROVED and implemented.** Narrow by design: one missing step in one
+  script, plus the boundary question that let it go missing. No `src/`,
+  no protocol, no feature work.
+- **The defect, as found.** `--protocol` adds the CRDT workspace sweep,
+  whose documented precondition is `cargo build --workspace
+  --no-default-features --features luajit,crdt` — documented in handoff
+  **§5** at the time, **§3** now. The plan emitter had **no build step
+  at all** — read from the source, not inferred from the failure.
 - **Why it was latent, and why that makes it urgent rather than tidy.**
   Before #225 every worktree shared one `CARGO_TARGET_DIR`, which
   almost always already held a `pmacs-gpu` binary, so the precondition
@@ -308,14 +308,52 @@ authoritative tip** — the ref, not a SHA. Recover with
   build any automated check for prose drift. This entry recorded that
   superseded decision until now; a recovering machine reading the stale
   version would have rebuilt revision 1's wrong boundary.
-- **Q#GR-1 must be settled by OBSERVATION before implementation** —
-  whether the default sweep needs the binary too. The entire defect is
-  a precondition nobody checked; establishing its replacement by
-  reading would repeat the error at one remove.
+- **Q#GR-1 — SETTLED BY OBSERVATION, 2026-08-09, before any fix was
+  written.** On a **disposable** target directory (never a live lane's),
+  with `debug/pmacs-gpu` asserted **absent before each run** as a
+  recorded precondition, each sweep run **alone** from that same cold
+  state so neither could have built the binary for the other:
+
+  | sweep | exit | result | `pmacs-gpu` after |
+  |---|---|---|---|
+  | default | **0** | green, 114 test targets | **still absent** |
+  | crdt | **101** | exactly **12** failures, all `gpu_invocation_acceptance::crdt::*`, all *"build pmacs-gpu before this acceptance suite"* | still absent |
+
+  So framing §3's inference **holds** and §4's *"only under
+  `--protocol`"* is correct — the default sweep never builds the binary
+  and never needs it. **Mechanism, now established rather than
+  guessed:** `pmacs-gpu` has no `tests/` directory, so cargo never
+  uplifts its bin to `debug/pmacs-gpu`; only an explicit `cargo build`
+  produces it.
+
+  **Found while doing it, and worse than the twelve:**
+  `bottom_panel_stage2b_gpu` a54 reported **`ok`** in that cold crdt
+  sweep. Its only path that does not spawn `pmacs-gpu` is its skip
+  branch, so a test whose whole purpose is real wgpu rendering passed
+  having rendered nothing. The missing build does not merely fail
+  twelve tests — it voids coverage in tests that report green.
+  (`vterm_stage3` a37 has the same shape by source read; cargo captures
+  passing tests' output, so the skip is invisible in the log.)
+- **What landed.** A named `build-crdt` step emitted immediately before
+  `sweep-crdt` under `--protocol`, carrying the exact §5 invocation —
+  **not** folded into the sweep command, because `cargo build … &&
+  cargo test …` reports a *build* failure under the name `sweep-crdt`.
+  Plus **`--self-test`** (Q#GR-5): a hardcoded three-line synthetic plan
+  — pass, fail-named-`build-crdt`, **pass sentinel** — driven through
+  the *real* runner loop, which is what makes attribution *and*
+  continuation observable at all. `PLAN_FILE` is deliberately **not**
+  injectable: that would turn the runner's `eval` into a general command
+  executor, the same defect this script's review caught in
+  `--acceptance`.
 - **Blocks PR #228 (discovery Stage 2).** That lane's `--protocol`
   result needs re-establishing on a fresh target dir under the repaired
-  script. Deliberately **not** folded into that feature branch.
-- **Gates:** `scripts/gate --acceptance gate_script_acceptance`.
+  script. Deliberately **not** folded into that feature branch, and it
+  happens **after** this lands, not inside it.
+- **Gates:** `scripts/gate --acceptance gate_script_acceptance`. Note
+  the recursion — this lane edits the script that runs its own gates,
+  so `--print-plan`, `--help` and `--self-test` were also checked by
+  hand after each edit: a change that breaks the script cannot be
+  reported honestly by the script.
 
 ## QoL arc retirement — PR #224 OPEN (docs only)
 

docs/agent-handoff.md

@@ -529,10 +529,21 @@ someone forgot.
   which is why name-keyed lists are not trustworthy.
 - **`basedpyright` hangs forever** — always
   `cargo test --test m4_acceptance -- --skip basedpyright`.
-- **The crdt sweep needs `cargo build --workspace` first**, or twelve
-  `gpu_invocation_acceptance` tests fail on a missing `pmacs-gpu`
-  binary. `cargo build --workspace --no-default-features --features
-  luajit,crdt` is the invocation that produces both binaries.
+- **INCIDENT — the crdt sweep's missing build step. §3 now owns this
+  requirement; what stays here is the history and the signature.**
+  Signature: twelve `gpu_invocation_acceptance::crdt::*` failures, each
+  *"build pmacs-gpu before this acceptance suite"*, on a target
+  directory with no `debug/pmacs-gpu` in it. Seen on **PR #228's first
+  gate run** (2026-08-09) — the first `--protocol` run in a *fresh*
+  per-worktree target directory after #225. Latent for the whole life
+  of the shared `CARGO_TARGET_DIR`, which nearly always already held
+  the binary, so the precondition was met by accident. Reproduced
+  deliberately the same day on a disposable cold target: default sweep
+  exit 0, crdt sweep exit 101 with exactly those twelve.
+  **`scripts/gate --protocol` now runs the build as a named
+  `build-crdt` step**, so this signature appearing again means the
+  script was bypassed, not that the requirement moved. The invocation,
+  the measurement and the reasoning are in §3.
 - **A shared `CARGO_TARGET_DIR` makes concurrent sweeps unattributable.**
   Every worktree on this machine resolves to the same target directory,
   so `target/debug/pmacs` is a **shared mutable file**: a
@@ -2298,15 +2309,50 @@ eight broken version assertions on CI. When the two disagree, **this
 list wins**.
 
 **Touching `PROTOCOL_VERSION` STRENGTHENS the sweep line. It does not
-replace it:**
+replace it — and the crdt sweep has a BUILD PRECONDITION:**
 
 ```
 cargo test --workspace --no-fail-fast -- --skip basedpyright
+cargo build --workspace --no-default-features --features luajit,crdt
 cargo test --workspace --features crdt --no-fail-fast -- --skip basedpyright
 ```
 
 Every part is load-bearing:
 
+- **The build before the crdt sweep is a PRECONDITION, not a courtesy,
+  and it is gate policy rather than an ops tip.** The crdt sweep spawns
+  `pmacs-gpu` as a *process*, and no `cargo test` run produces that
+  binary: `pmacs-gpu` has no `tests/` directory, so cargo never uplifts
+  its bin to `debug/pmacs-gpu`. Omit the build on a cold target
+  directory and twelve `gpu_invocation_acceptance::crdt::*` tests fail
+  on *"build pmacs-gpu before this acceptance suite"* — and, worse,
+  crdt tests that drive the real binary (`vterm_stage3` a37,
+  `bottom_panel_stage2b_gpu` a54) take their skip branch and report
+  **`ok`**, so the missing build also voids coverage *silently*.
+  `scripts/gate --protocol` emits it as its own named `build-crdt`
+  step, never folded into the sweep command, so a build failure is
+  attributed to the build rather than to the sweep.
+
+  **Only the crdt sweep needs it, and that is MEASURED rather than
+  reasoned.** On 2026-08-09, on a disposable target directory with
+  `debug/pmacs-gpu` asserted **absent before each run** and each sweep
+  run alone from that cold state: the **default** sweep exited **0**
+  (114 test targets green) and left `debug/pmacs-gpu` **still absent**
+  — it never builds the binary and never needs it — while the **crdt**
+  sweep exited **101** with exactly those twelve failures. An
+  unconditional build would be a real cost paid for nothing on every
+  ordinary lane.
+
+  **Why this was latent for years.** Before per-worktree target
+  directories (#225) every worktree on this machine shared one, which
+  nearly always already held a `pmacs-gpu` from some earlier build, so
+  the precondition was satisfied **by accident** on essentially every
+  run. The hazard is not the red gate — a red gate stops you. It is a
+  **green** `--protocol` run whose crdt sweep was decided by what
+  happened to be in the build directory rather than by the diff, which
+  is a gate reporting coverage it does not have. §5 keeps the incident
+  and its signature as history; **this section owns the requirement.**
+
 - **`--workspace`, never `--tests`.** `--tests` selects 108 targets
   where `--workspace` selects 110, and the two it drops are
   **`pmacs_protocol` and `pmacs_gpu`**. On a protocol bump, dropping