Declare CB-WP-0013: two instruments that were wrong, tier M

Declaration 8 of 12. Structural tier M (changes how the loop constrains
its own operation — a budget instrument and a gate floor); d4 = 3, no
override. Meta budget reads 0% of the trailing three, so this is in
budget without the ADR-0006 D2 repair exemption.

The SH-3 half is larger than CB-WP-0012 filed it as. "SH-3 has read
0.0% for six consecutive passes" is an artifact: --shape-budget measures
the window since the last commit, and it is read while writing the
evidence file, immediately after a commit, when that window holds one or
two responses. SH-1 and SH-2 are location statistics and survive n=2;
SH-3 is a rate, and at n=2 its only possible values are 0%, 50%, 100%.

Measured over real per-pass windows it is 1.1%-6.3%, not 0.0%. Which
exposes what the artifact hid: the pinned historical rate is 7.8%-8.6%,
so batching has got WORSE, and a metric stuck at a constant could not
have shown it.

That is the ninth recorded instance of the trusted-arithmetic class, and
the second one in this same metric — SessionShape.md §4 already records
"0 of 330 tool calls were batched" as the eighth.

Also owed: AM-4a counts proc-macro crates that never reach a binary
(89,048 lines, 36.2%). The task is explicit that the target must move
down with the instrument, or the pass must argue why 89,048 lines of
unearned headroom are legitimate.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

workplans/CB-WP-0013-instrument-corrections.md

@@ -0,0 +1,171 @@
+---
+id: CB-WP-0013
+kind: meta
+title: "Two instruments that were wrong, and the record they wrote"
+status: todo
+---
+
+# Purpose
+
+```
+structural tier  M   (changes how the loop constrains its own operation:
+                      a budget instrument and a gate floor — InnerLoop
+                      v1.6, ADR-0006 D5)
+chaos            d4 = 3  → no override
+declared tier    M
+```
+
+Declaration 8 of 12 in the calibration window. Tier M means the survey and
+the ADR merge into one document and the adversarial review is optional.
+
+**Meta budget: 0% of the trailing three**, so this pass is in budget
+without the ADR-0006 D2 repair exemption — though it would qualify for it,
+since both halves repair an instrument that reports a breach.
+
+## Why now
+
+CB-WP-0012 ended owing two corrections, and one of them turns out to be
+larger than it was filed as.
+
+### SH-3 has never read what six evidence files say it read
+
+CB-EV-0010 §5 states *"SH-3 has now read 0.0% for six consecutive passes"*
+and calls it the oldest unargued number in the project. The number is an
+artifact.
+
+`--shape-budget` measures **the window since the last commit**, and it is
+read while writing the evidence file — immediately *after* a commit, when
+that window holds one or two responses. SH-1 and SH-2 are location
+statistics and survive a sample of two. **SH-3 is a rate**, and at n=2 its
+only possible values are 0%, 50% and 100%. One window, three metrics, and
+it is only wrong for one of them.
+
+Measured over real per-pass windows instead:
+
+| window since | responses | SH-3 |
+|---|---:|---:|
+| `0d2ab22` | 115 | 6.2% |
+| `6fb0aea` | 113 | 6.3% |
+| `331e7e9` | 95 | 1.1% |
+| `c5fa610` | 74 | 1.4% |
+| `883b608` | 70 | 1.4% |
+| `84d6886` | 24 | 4.3% |
+
+So the substantive claim survives — SH-3 is badly unmet — but **the figure
+quoted in six evidence files was never the measurement**. Worse, the real
+numbers say something the artifact hid: the historical rate pinned in
+`specs/SessionShape.md` is **7.8–8.6%**, and these windows are **1.1–6.3%**.
+Batching has got *worse*, and a metric stuck at a constant 0.0% could not
+show a trend at all.
+
+### AM-4a overstates every figure it has ever reported by 36%
+
+ADR-0007 Decision 4, filed and unimplemented. AM-4a counts
+`--edges normal`, which includes proc-macro crates that run in the compiler
+and never reach a binary: **89,048 lines, 36.2%** of the shipped-runtime
+figure, `syn` alone 66,916.
+
+## Task: fix SH-3's instrument, and correct the record
+
+```task
+id: CB-WP-0013-T01
+status: todo
+priority: high
+```
+
+A rate needs a sample. `--shape-budget` must **refuse to report SH-3**
+below a stated minimum rather than print a number the window cannot
+support — `insufficient sample (n responses)`, not `0.0%`.
+
+**The choice to argue, not assume:** whether SH-3 should instead be
+windowed differently from SH-1/SH-2 — over the pass rather than since the
+last commit — since it is the only one of the three that a two-response
+window destroys. Pick one and say why the other was rejected.
+
+**Controls.** A minimum-sample rule is exactly the kind of guard that can
+be satisfied vacuously: assert that a window *above* the floor still
+reports a rate, that one below reports the refusal, and that the refusal
+is distinguishable from a genuine 0.0%. Mutate each.
+
+**Correct the record.** Six evidence files quote 0.0%. They are history and
+are not rewritten; the correction is recorded once, where a reader will
+find it, and named as what it is — the same class as CB-WP-0002's
+"0 of 330 tool calls were batched", which `specs/SessionShape.md` §4
+already records as the eighth trusted-arithmetic instance. **This is the
+ninth, and it is in the same metric.** That coincidence is worth a
+sentence: SH-3 is the number this project keeps getting wrong.
+
+## Task: argue SH-3's floor, or move it
+
+```task
+id: CB-WP-0013-T02
+status: todo
+priority: high
+```
+
+The declaration CB-EV-0010 said was owed. `specs/SessionShape.md` is
+explicit that the 20% floor was set above the measured rate deliberately
+and that *"whether 20% is reachable or arbitrary is unknown until a pass
+tries"*. Seven passes have now reported it and none has tried.
+
+Decide, with the real numbers rather than the artifact:
+
+- is 20% reachable, and at what cost to how the work is actually done;
+- is the measured decline from 7.8–8.6% to 1.1–6.3% a behavioural change
+  worth reversing, or an artifact of tier-L passes doing more sequential
+  reading than tier-S ones;
+- **and the honest option: retire SH-3.** `specs/SessionShape.md` §4 puts
+  the ceiling at **$2–4 on a $93 pass** and says *"batch because it is
+  free, not because it is the lever."* A floor that is 3–20× the measured
+  rate, cannot be moved by the party measured, and is worth single-digit
+  dollars is a candidate for `retire_if`, not a standing breach.
+
+**Do not retarget to match the measurement.** `specs/SessionShape.md`
+already forbids exactly that, and CB-WP-0003 T07 exists to prevent it. If
+the floor moves, it moves on an argument about what batching is worth, and
+the argument is written down before the number changes.
+
+## Task: correct AM-4a to count what ships
+
+```task
+id: CB-WP-0013-T03
+status: todo
+priority: high
+```
+
+ADR-0007 Decision 4. `tools/dep-weight.py` counts
+`--edges normal,no-proc-macro`.
+
+**The targets do not move with the instrument.** Correcting a metric that
+reports 246,250 down to 157,202 while leaving the target at 250,000 hands
+this project 89,048 lines of headroom it did not earn, in the same commit
+that reveals the error. Either the target moves down by the same amount
+the instrument does, or the pass states plainly why the extra headroom is
+legitimate. It is not obviously legitimate; argue it or give it back.
+
+**Positive control.** `dep-weight.py` already has the guard that an
+unlocatable crate must not silently count as zero. The new flag must not
+be able to drop crates it should have counted: assert that the proc-macro
+set is exactly the five expected crates and that removing the flag
+restores the old figure.
+
+## Task: evidence
+
+```task
+id: CB-WP-0013-T04
+status: todo
+priority: medium
+```
+
+`evidence/CB-EV-0011-instrument-corrections.md`.
+
+Carry: whether tier M's merged survey-and-ADR was the right weight for two
+instrument corrections; the cost of a meta pass immediately after two
+product passes; and the standing question of whether **three** consecutive
+evidence files reporting their own pass's cost low means the loop should
+simply stop quoting it.
+
+Also carry the one that is now overdue: **`cb-play` is three modes in one
+binary.** CB-EV-0009 §5 named the third mode as the trigger to reconsider
+the shape, CB-EV-0010 §6 recorded that it had arrived and that the pass
+did not act. Either do it or state why not, and stop carrying it.