Keep the A/B, and the harness that produced it

The run that justified MEMORY_MAX_WORDS lived in a scratch directory and
would have been gone with the container. The numbers in plan/18 were
therefore assertions nobody could check.

plan/18-appendix-memory-ab-run.md now carries the whole transcript: both
memories, both summaries, and the thirteen-action story they were
written from.

backend/tools/memory_ab.py reproduces it. It replaces the throwaway
script the first run used, and differs in two ways that matter. It goes
through OpenAICompatibleProvider rather than calling a model directly,
so a run exercises the provider, the streaming path and complete()
instead of a stub. And it reads the control prompt out of git at the
commit given to --before, so the thing being compared against cannot
drift from what actually shipped.

There was already a claude_shim.py serving an OpenAI-compatible endpoint
backed by the CLI, which is exactly what the throwaway script had
reinvented. memory_ab.py points at it by default, so a run spends a
Claude subscription rather than API credit, and --endpoint aims it at
the provider the deployed app really uses — which is the one question
this whole exercise could not answer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NPyQN926gkZTAYfgugcaok

plan/18-persona-and-memory-quality.md

@@ -460,12 +460,23 @@ is the first thing to try.
 
 ## Run with a real model, and what it changed
 
-Run end to end against a real model, using the `claude` CLI as the provider: one
-story generated through the app's own `build_context` a turn at a time, then
-**both** memory prompts run over the **same** blocks, so the story is held
-constant and the prompt is the only variable. Every call is a fresh process, so
-no arm can see the other's output and the model is never told what is being
-tested. The control is the exact prompt from commit `9cdcb55`, not a paraphrase.
+Run end to end against a real model. One story generated through the app's own
+`build_context` a turn at a time, then **both** memory prompts run over the
+**same** blocks, so the story is held constant and the prompt is the only
+variable. Neither arm sees the other's output, and the model is never told what
+is being measured. The control is `MEMORY_SYSTEM_PROMPT` as of commit `9cdcb55`,
+read out of git rather than pasted, so it cannot drift from what shipped.
+
+The harness is `backend/tools/memory_ab.py`, and it goes through
+`OpenAICompatibleProvider` rather than calling a model directly, so the run
+exercises the provider, the streaming path and `complete()`. Pointed at
+`tools/claude_shim.py` it spends a Claude subscription instead of API credit:
+
+    python tools/claude_shim.py --port 8787 &
+    python tools/memory_ab.py --out ab.md
+
+**The full transcript, with every memory, both summaries and the story they were
+written from, is in `plan/18-appendix-memory-ab-run.md`.**
 
 ### The reported fault reproduced, and the fix held