chore(p0): remove the improve lever and the plane improvement loop

Off every active line (PATHFINDER-2026-10-13/03-unified-proposal.md, cuts).
Deleted: src/openultrasast/improve/ (1,175 lines), the ousast improve
subcommand, plane/tasks/loop.py and loop.yaml with the --loop generation,
the memory-snapshot step in memory.seed, pairs.build_pair_signals, and the
four improve tests plus the loop cases in other tests. Docs no longer
describe the lever. Net: 3,073 lines deleted, 83 added. Targeted tests:
154 passed; 3,436 tests collect.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docs/memory.md

@@ -25,10 +25,9 @@ replaces itself. The kinds (`KINDS`) and who writes them:
 | `facts` | `remember` task | the facts entry of a case (points at `facts/<sha256>.json`; reused by memory key) |
 | `verdict` | `remember` task | per candidate: each verify pass's answer, the final outcome, whether a tie-break ran, cost |
 | `unit_cost` | `remember` task | per verify pass and file: usd, calls and token usage |
-| `alert` | `remember` task | a quick-scan or engine alert on the vulnerable or fixed pin (loop Runs) |
+| `alert` | `remember` task | a quick-scan or engine alert on the vulnerable or fixed pin |
 | `coverage` | `remember` task | per language and pin: whether any rule could have fired there |
 | `features` | `remember` task, from the `features` task | one feature record per candidate and family |
-| `proposal_outcome` | `ousast improve --memory` (not with `--dry-run`), and the loop's `improve` step | what happened to each memory proposal in a round |
 | `example` | `ousast learn memory build` | a labelled case: label + feature record + excerpt sha (no rationale) |
 | `experiment` | `ousast learn experiment register` (task `register`) and `run` (task `run`) | a registered manifest's digests and provenance; a run's counts-only summary. Repo `experiments/<id>`, pin the registering commit |
 | `arm_outcome` | `ousast learn experiment run` | one decision per (unit, arm, replicate): score, verdict, usd, order |
@@ -52,8 +51,6 @@ flowchart LR
     tasks["Plane tasks: facts, verify a/b/c, agree, alerts, features"] --> rem["remember task: memory.jsonl"]
     rem --> recv["Delivered to the host with the run's artifacts"]
     recv --> ingest["ingest after ousast plane run, or ousast plane remember RUN"]
-    loop["Loop improve step: proposal_outcome"] --> ingest
-    improve["ousast improve --memory: proposal_outcome"] --> put
     build["ousast learn memory build: labels + features + excerpts"] --> put["put_rows, put_blob"]
     embed["ousast learn memory embed"] --> put
     compile["ousast learn compile, evaluate"] --> put
@@ -79,26 +76,16 @@ flowchart LR
 flowchart LR
     store[("Memory store")] --> seed["seed before a Run"]
     seed --> reuse["Facts reused by memory key: repo, pin, candidates, runner image"]
-    seed --> snap["memory-snapshot: rows after the train-on-test guard"]
     store --> examples["learn: load example rows, excerpts, embeddings"]
     examples --> retr["Retrieval of similar labelled cases"]
     store --> responses["Response cache: replay at no cost"]
-    store --> imp["ousast improve --memory: alert, verdict, coverage rows"]
-    imp --> guard["Train-on-test guard"]
-    guard --> rules["Rules M1, M2 to rule-status proposals"]
-    rules --> gate{"Unchanged validator and gate"}
 ```
 
 - **Seed** (`memory.seed`).
   - A Run task gets stored facts when its `openultrasast.io/memory-key` matches them. It is then marked done.
   - A changed pin, candidate set or runner image finds nothing and recomputes.
-  - The loop's `memory-snapshot` is seeded the same way. A sandboxed task cannot read the store.
 - **Retrieval** (`learn/retrieve.py`): see
   [Memory and detection](memory-and-detection.md#3-retrieval-of-similar-labelled-cases).
-- **`improve --memory`** (`improve/memory.py`). Some rows are dropped before any rule sees them:
-  rows from holdout pairs, from the gated manifest's own cases, and from any `--qualify-population`. See
-  [Architecture](architecture.md#proposals-from-plane-memory).
-
 ## Backends: FileStore and the S3 store
 
 `OUSAST_MEMORY` selects the backend (`open_store`):