mars(mnemosyne): fix env build and plugin symlink target

- fetchPypi: sdists are published underscore-named, so the hyphenated
  pname 404'd.
- sitePackages is relative; prefix the env path so the unit's -d check
  and the symlink point at the store.
- hermes_memory_provider ships in mnemosyne-memory, not mnemosyne-hermes;
  move the import check accordingly.
- Drop the unused /opt/data/mnemosyne-env mount, the orphaned
  requirements.txt, and trim comments.

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

pkgs/mnemosyne-env.nix

@@ -1,86 +1,56 @@
-# Mnemosyne memory provider for Hermes on mars — packaged for real (Nix).
+# Mnemosyne memory provider for Hermes. Built here rather than pip-installed:
+# the image's Python has no pip and is PEP 668 managed.
 #
-# Why derivations instead of a runtime side-venv: the official Hermes image
-# vendors its own Python and stays off-limits to pip (no pip module, PEP 668),
-# and a runtime venv built host-side breaks twice over inside the container:
-# the venv's pyvenv.cfg records a /nix/store python home the container never
-# mounts, and a plugins symlink with an absolute host path points nowhere
-# from /opt/data. Building here means nothing is fetched at boot, nothing
-# under the provider's control is writable from inside the container, and
-# the closure is as reproducible as the rest of the host.
-#
-# Package set (one shared site-packages — the plugin wrapper imports its
-# sibling `mnemosyne` core package, so withPackages, not separate envs):
-#
-#   mnemosyne-memory  core engine: SQLite/FTS5 storage, recall, tools.
-#                     Base deps only (PyYAML); the optional extras (llm,
-#                     embeddings via fastembed/onnxruntime, mcp, sync) are
-#                     deliberately NOT pulled — recall uses the bundled FTS5
-#                     lexical path, and the heavyweight ML stack (~hundreds of
-#                     MB, live network on first vector use) buys nothing for
-#                     a first deployment. Adding the embeddings extra later
-#                     is pinning fastembed + sqlite-vec here.
-#   mnemosyne-hermes  the wrapper Hermes discovers under $HERMES_HOME/plugins
-#                     (installs itself as package `hermes_memory_provider`).
-#                     Hard dependency: mnemosyne-memory, PyYAML.
-#
-# Platform note: both sdists are pure Python (build no C extensions), so
-# nothing here constrains the host arch beyond the interpreter itself.
+# Core deps only: the embeddings extra (fastembed/onnxruntime) is optional at
+# runtime, and recall falls back to FTS5.
 {
   python3,
   fetchPypi,
 }:
 
 let
-  python = python3;
-
-  mnemosyneMemory = python.pkgs.buildPythonPackage rec {
+  mnemosyneMemory = python3.pkgs.buildPythonPackage rec {
     pname = "mnemosyne-memory";
     version = "3.15.1";
     pyproject = true;
 
     src = fetchPypi {
-      inherit pname version;
-      sha256 = "sha256-lspUMxc0pUSkhSUrNdiiO5OJ1NMC/S853EYSanXtXKM=";
+      pname = "mnemosyne_memory";
+      inherit version;
+      hash = "sha256-lspUMxc0pUSkhSUrNdiiO5OJ1NMC/S853EYSanXtXKM=";
     };
 
-    build-system = with python.pkgs; [ setuptools ];
+    build-system = with python3.pkgs; [ setuptools ];
+    dependencies = with python3.pkgs; [ pyyaml ];
 
-    # Base dependency set — everything else in the upstream metadata is an
-    # optional extra (llm / embeddings / mcp / sync / test / dev) and is not
-    # installed; see the file-level comment.
-    dependencies = with python.pkgs; [ pyyaml ];
-
-    doCheck = false; # upstream tests want a live Hermes + LLM key present
-    pythonImportsCheck = [ "mnemosyne" ];
+    doCheck = false; # tests want a live Hermes + LLM key
+    # Ships the Hermes plugin package too, not just the core.
+    pythonImportsCheck = [
+      "mnemosyne"
+      "hermes_memory_provider"
+    ];
   };
 
-  mnemosyneHermes = python.pkgs.buildPythonPackage rec {
+  mnemosyneHermes = python3.pkgs.buildPythonPackage rec {
     pname = "mnemosyne-hermes";
     version = "0.5.0";
     pyproject = true;
 
     src = fetchPypi {
-      inherit pname version;
-      sha256 = "sha256-CzEvnUw5oPFtT5bHQQ/GBdy2C/E7qShQn32irIRYKqw=";
+      pname = "mnemosyne_hermes";
+      inherit version;
+      hash = "sha256-CzEvnUw5oPFtT5bHQQ/GBdy2C/E7qShQn32irIRYKqw=";
     };
 
-    build-system = with python.pkgs; [ setuptools ];
-
-    # The wrapper declares `mnemosyne-memory[embeddings]>=3.11.1` on PyPI, but
-    # the embeddings extra is only consulted when vector recall is enabled
-    # (see above) — pass the core dependency explicitly rather than dragging
-    # in onnxruntime for nothing.
-    dependencies = [ mnemosyneMemory ] ++ (with python.pkgs; [ pyyaml ]);
+    build-system = with python3.pkgs; [ setuptools ];
+    # Upstream asks for mnemosyne-memory[embeddings]; see the header.
+    dependencies = [ mnemosyneMemory ] ++ (with python3.pkgs; [ pyyaml ]);
 
     doCheck = false;
-    pythonImportsCheck = [ "hermes_memory_provider" ];
+    pythonImportsCheck = [ "mnemosyne_hermes" ];
   };
-
-  # The exposed value is the python env itself (a store path mounted :ro).
-  # Hermes only needs the site-packages dir inside it; `sitePackages` is a
-  # passthru the python interpreter derivation (and hence withPackages envs)
-  # exposes, so the caller uses `${env.sitePackages}` instead of guessing
-  # the python version in a path literal.
 in
-python.withPackages (_: [ mnemosyneMemory mnemosyneHermes ])
+python3.withPackages (_: [
+  mnemosyneMemory
+  mnemosyneHermes
+])