--- id: CB-WP-0007 kind: meta title: "Make session shape measurable in the window that matters, then enforce it" status: done state_hub_workstream_id: "bee19b76-fb60-4dcf-94d0-9242b43e0e42" --- # 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. ## Scope cut, 2026-08-01 (maintainer decision) A spend review before starting found the project **38% product / 62% loop-meta**, with cost per response degraded 2.9× from its best window and INTENT stage 0 still missing a CLI player and bots. CB-WP-0005 and CB-WP-0006 cost **~$74 — 31% of all spend — for zero measured efficiency gain** (their return was correctness of claims, which is real but is not optimization). So this workplan is **cut to T01 and T03**, the two tasks that attack the 2.9× regression directly. **T02 and T04 are cancelled**, not deferred — SH-4 trend reporting and the batching trial are more instrument work, and the instrument-failure taxonomy is not converging. T06 becomes the project-level retrospective the maintainer asked for. **A soft 25% meta budget is established here** (T03), because the review's finding needs a standing number, not a memory. ## Phase A — measure the right window ## Task: window the session-shape metrics ```task id: CB-WP-0007-T01 status: done priority: high state_hub_task_id: "7e036db4-d97a-45bd-a70a-20fe68225402" ``` `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 (CANCELLED) > **Cancelled unstarted 2026-08-01.** More instrument work, against a > review finding that instrument work has stopped paying. The ceiling T03 > adds catches a bad pass; a trend line would catch a slow slide, which is > a real gap — recorded as open, not built. ```task id: CB-WP-0007-T02 status: cancel priority: medium state_hub_task_id: "1d5a32ef-4086-4021-b874-24ed2160c4dd" ``` 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: done priority: high state_hub_task_id: "126a6313-b1f7-462c-8771-5100d38f9429" ``` 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 (CANCELLED) > **Cancelled unstarted 2026-08-01.** `SessionShape.md` §4 already puts > the ceiling at **$2–4 on a $93 pass** — the cheapest of the three > metrics to move and the least valuable. Spending a task on it while > stage 0 lacks a CLI player is the misallocation the review found. > SH-3 remains measured, unmet at 0.0%, and unfalsified. ```task id: CB-WP-0007-T04 status: cancel priority: medium state_hub_task_id: "c284db6f-2e16-40fb-be8b-83ae5391c058" ``` 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? (CANCELLED) > **Cancelled 2026-08-02 (CB-WP-0010 T01), overtaken.** Both questions > were answered with measurements two passes later: > [CB-EV-0008](../evidence/CB-EV-0008-adaptive-gates.md) §1 compares the > windowed metric against cumulative on real passes, and §4 records the > shape budget firing. Writing CB-EV-0006 now would re-derive them from > the same transcripts. ```task id: CB-WP-0007-T05 status: cancel priority: high state_hub_task_id: "2f78b272-e1f9-4530-bc8c-3a9d82833546" ``` Commit `evidence/CB-EV-0006-session-shape.md`. **Reduced with the scope cut** — tests 1, 2 and 4 remain; test 3 (SH-3) is cancelled with T04. 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 (CANCELLED) > **Cancelled 2026-08-02 (CB-WP-0010 T01), answered elsewhere.** The > question was whether there is a *fourth* way a number can fail to bind. > There is, and it is on record: CB-EV-0007 §3 found a number **aggregated > over a window that cannot move it** — the meta budget, reintroducing the > defect two tasks after the same one was fixed for session shape. The > tier-taxonomy gap this task also carried was closed by ADR-0006 D5. ```task id: CB-WP-0007-T06 status: cancel priority: medium state_hub_task_id: "93fbd2bb-403b-4be9-a5ff-d6142b916aba" ``` 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.