fix(ipython): keep in-session history in memory only

Assisted-by: DeepSeek Harness (deepseek-flash)

home/base/tui/editors/ipython/README.md

@@ -2,7 +2,9 @@
 
 [`default.nix`](./default.nix) manages `~/.ipython/profile_default` with two pieces:
 
-- `ipython_config.py` disables SQLite history because interactive sessions may contain secrets.
+- `ipython_config.py` keeps SQLite history in memory (`HistoryManager.hist_file = ":memory:"`), so
+  arrow keys and `%history` recall the current session while nothing is written to disk, because
+  interactive sessions may contain secrets.
 - `startup/10-data-helpers.py` loads JSON, YAML, TOML, and CSV helpers at every IPython start. It
   also pre-imports a small set of common standard-library names such as `Path`, `Counter`, and
   `datetime`.

home/base/tui/editors/ipython/default.nix

@@ -1,13 +1,14 @@
 { ... }:
 {
   # Interactive IPython sessions routinely handle credentials and other
-  # sensitive values, so keep the SQLite history disabled rather than relying
-  # on the profile directory's lifetime. Home Manager recreates these files
-  # from the Nix store on every activation.
+  # sensitive values, so keep the SQLite history in memory instead of on disk:
+  # arrow-key recall and %history still work within a session, but no history
+  # file is written. Home Manager recreates these files from the Nix store on
+  # every activation.
   home.file = {
     ".ipython/profile_default/ipython_config.py".text = ''
       c = get_config()
-      c.HistoryManager.enabled = False
+      c.HistoryManager.hist_file = ":memory:"
     '';
     ".ipython/profile_default/startup/10-data-helpers.py".source = ./data-helpers.py;
   };

hosts/idols-ai/preservation.nix

@@ -222,10 +222,10 @@ in
         ".config/Joplin" # joplin-desktop
 
         ".local/share/jupyter"
-        # Deliberately not persisted: ~/.ipython contains history.sqlite, and
-        # interactive sessions may contain credentials or other sensitive
-        # values. Home Manager recreates the profile config and startup helpers
-        # from the Nix store on every activation.
+        # Deliberately not persisted: IPython keeps its history database in
+        # memory (HistoryManager.hist_file = ":memory:") and the profile config
+        # and startup helpers are recreated from the Nix store on every
+        # activation, so this directory holds no state worth preserving.
 
         # ======================================
         # Cloud Native