CB-RES-0005 + CB-WP-0007: session shape measures the wrong window

Tier M — structural S by the letter of InnerLoop's table (no capability
port, no canonical interface, no new dependency), declared M because the
table's triggers only cover code capabilities and this decides whether the
loop constrains its own operation. Chaos d4=2, no override. Survey and ADR
merged per tier M.

The gap is not the one CB-WP-0006 assumed. SH-1/2/3 ARE measured —
cb-cost emits all three every run. The defect is that SH-1 and SH-2 are
cumulative means over every response ever recorded, so they cannot detect
a worsening trend: the history outvotes the present.

  cumulative -> dfd0d6d   923 resp   mean 206,952   p90 389,733   9.6%
  CB-WP-0006 alone        156 resp   mean 503,464   p90 607,105   0.0%

Read cumulatively, session shape looks stable and improving. Read by
window, the last pass ran at 2.4x the mean of all preceding history and
batched nothing at all — 146 tool calls in 146 responses.

This is the third shape of one disease. CB-WP-0005 found numbers that were
unmeasured; CB-WP-0006 found numbers measured but unasserted; these are
measured AND asserted and still cannot fire, because they are aggregated
over a window in which nothing can move them.

Decisions: window SH-1/SH-2 and keep cumulative as labelled history;
enforce with a live budget modelled on CB-01/CB-02, NOT `make all` —
failing the build on context would block committing, and committing is
what closes the attribution window and is the natural point to compact, so
a gate that blocks the remedy is a trap; targets do not move, since all
three are unmet by wide margins and adjusting them in the pass that first
enforces them is the retarget §Step 4 forbids; and SH-3 is tested by
batching deliberately rather than by argument.

Recorded and not fixed: InnerLoop's tier table triggers on code
properties, so this pass would be tier S despite deciding how the loop
governs itself. Changing the taxonomy on one instance is the
invention-in-isolation INTENT warns against — the same argument used to
amend K14 and to leave v1.4 alone. A second instance should trigger it.

CB-WP-0007 executes in 6 tasks. T04's third outcome is the interesting
one: if batching stays below 5% despite trying, 20% is the number to
challenge with evidence, in an ADR rather than a quiet edit.

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

workplans/CB-WP-0007-session-shape.md

@@ -0,0 +1,186 @@
+---
+id: CB-WP-0007
+title: "Make session shape measurable in the window that matters, then enforce it"
+status: proposed
+---
+
+# Purpose
+
+[CB-RES-0005](../research/CB-RES-0005-session-shape.md) (tier M, survey
+and ADR merged; chaos d4=2, no override):
+
+> **SH-1 and SH-2 are cumulative means over every response ever recorded.
+> They cannot detect a worsening trend, because the history outvotes the
+> present.**
+
+| window | responses | SH-1 mean | SH-2 p90 | SH-3 batching |
+|---|---|---|---|---|
+| cumulative → `dfd0d6d` | 923 | **206,952** | **389,733** | 9.6% |
+| **CB-WP-0006 alone** | 156 | **503,464** | **607,105** | **0.0%** |
+
+Read cumulatively, session shape looks stable and improving. Read by
+window, the last pass ran at **2.4× the mean** of all preceding history
+and batched **nothing at all** — 146 tool calls in 146 responses.
+
+This is the third shape of one disease. CB-WP-0005 found numbers that were
+**unmeasured**; CB-WP-0006 found numbers that were measured but
+**unasserted**; this pass has numbers that are measured *and* asserted and
+still cannot fire, because they are **aggregated over a window in which
+nothing can move them**.
+
+Per InnerLoop §Step 4, no target moves in the commit that measures it —
+and CB-RES-0005 D3 states that up front, because all three targets are
+currently unmet by wide margins and the temptation is obvious.
+
+## Phase A — measure the right window
+
+## Task: window the session-shape metrics
+
+```task
+id: CB-WP-0007-T01
+status: todo
+priority: high
+```
+
+`cb-cost`'s session-shape block reports over every response in scope. With
+`--since` it already windows correctly; without it, it reports a
+cumulative mean that a bad pass cannot move.
+
+Deliver: the session-shape block **states its window explicitly** and, when
+run without `--since`, reports **both** — the window since the last commit
+*and* the cumulative history, labelled so they cannot be confused. The
+cumulative figure stays useful for the long view and stops being what a
+target compares against.
+
+**Predicted:** the windowed figure differs sharply from cumulative.
+**Refuted if** it lands within 20% of the cumulative number, in which case
+the aggregation was not the problem and this pass should re-plan.
+
+## Task: SH-4 — a windowed trend the instrument can see
+
+```task
+id: CB-WP-0007-T02
+status: todo
+priority: medium
+```
+
+A ceiling catches a bad pass. It does not catch a slow slide, which is how
+SH-1 got from 232k to 503k without any single pass looking anomalous.
+
+Deliver a reported (not gated) SH-4: **mean context of the current window
+against the previous window**, so a rising trend is visible before it
+breaches. Provenance `adapted:criterion` — the same shape as the >3%
+merge-blocking regression rule against our own last evidence file, but
+reported rather than blocking, because CB-RES-0005 §4 argues a build gate
+is the wrong instrument for behaviour.
+
+State the limit in the output, as every other gate here does: two windows
+is not a trend, and the first run has nothing to compare against.
+
+## Phase B — enforce it where enforcement belongs
+
+## Task: `make shape-budget` — a live budget, not a build gate
+
+```task
+id: CB-WP-0007-T03
+status: todo
+priority: high
+```
+
+Per CB-RES-0005 D2, modelled on CB-01/CB-02, which measures spend since
+the last commit, warns at $10, stops at $22, and is surfaced by
+`make status` — never by `make all`.
+
+**Why not a build gate, restated so it is not quietly reversed later:**
+failing `make all` on context size would **block committing**, and
+committing is what closes the attribution window and is the natural point
+to compact. A gate that blocks the remedy when the metric breaches is a
+trap, not a gate. It also punishes the wrong artifact — a long session
+does not break the tree.
+
+Deliver `make shape-budget` and a line in `make status`:
+
+| threshold | value | action |
+|---|---|---|
+| SH-1 soft | 200,000 mean context in the window | warn |
+| SH-1 hard | **300,000** | report loudly: compact before continuing |
+| SH-2 soft | 300,000 p90 | warn |
+| SH-3 floor | 20% batching | warn |
+
+**The hard threshold is set here, before the next measurement**, per
+§Step 4. It is 1.5× the soft target, matching CB-02's 2.2× ratio on spend
+scaled down because context is bounded by the model and spend is not.
+
+Carries `--self-test`. Its positive control is the one this project keeps
+needing: a budget that reports `ok` because it measured nothing must
+abort instead.
+
+## Task: batch deliberately, and report what the rate reaches
+
+```task
+id: CB-WP-0007-T04
+status: todo
+priority: medium
+```
+
+SH-3 is **0.0%** across two consecutive passes. The target is 20%. Nobody
+has ever tried to hit it, so its reachability is unknown and the number is
+currently unfalsified rather than wrong.
+
+This task is the trial: batch independent tool calls deliberately through
+the pass and report the rate the instrument measures.
+
+**Three outcomes, all publishable, and the third is the interesting one:**
+
+1. **≥20%** — the target is reachable; it stops being aspirational.
+2. **5–20%** — partially reachable; report the ceiling and what blocked it.
+3. **<5% despite trying** — then **20% is the number to challenge, with
+   evidence**, and the challenge belongs in an ADR rather than a quiet
+   edit. Per §Step 4 the target does not move in this pass regardless.
+
+## Phase C — measure, and say what it cost
+
+## Task: control loop — did windowing change what fires?
+
+```task
+id: CB-WP-0007-T05
+status: todo
+priority: high
+```
+
+Commit `evidence/CB-EV-0006-session-shape.md`. Four tests, all reported:
+
+1. **Does the windowed metric differ from cumulative?** Against T01's
+   prediction; refuted if within 20%.
+2. **Did the budget fire on this pass?** A budget that never reports a
+   breach across a full pass is either miscalibrated or measuring nothing —
+   both are findings.
+3. **What did SH-3 reach?** T04's three outcomes.
+4. **Did quality hold?** `make all` green, and the honest question this
+   pass cannot dodge: **did compacting to satisfy a context budget cause
+   work to be repeated or detail to be lost?** `SessionShape.md` §5 says
+   the loop cannot detect this. Record the judgment explicitly rather than
+   letting the cost number imply it.
+
+## Task: retrospective
+
+```task
+id: CB-WP-0007-T06
+status: todo
+priority: medium
+```
+
+The question: **three passes have now found three different ways a number
+can exist and not bind — unmeasured, unasserted, and aggregated so it
+cannot fire. Is there a fourth, and is the loop discovering a pattern or
+enumerating an infinite set?**
+
+CB-WP-0003 concluded that class-by-class hardening does not converge.
+Three passes later, the *instrument* failures have their own taxonomy and
+it is also not converging. Say plainly whether that changes the design
+goal, or confirms it.
+
+Also due: **the tier-taxonomy gap** CB-RES-0005 §6 recorded but did not
+fix. This pass is the first instance. Per the standing argument used for
+K14 and InnerLoop v1.4, a second instance triggers the change — say
+whether this counts as one or two.