Studio: exclude mlx-lm 0.31.3 (broke gemma4/qwen3_5 QK-norm load on Apple Silicon) (#6803)

* Studio: exclude mlx-lm 0.31.3 (broke gemma4/qwen3_5 QK-norm load)

mlx-lm 0.31.3 regressed the QK-norm archs: its strict load_weights rejects the
q_norm/k_norm tensors with "Received N parameters not in model", so gemma4 and
qwen3_5 checkpoints fail to load. Studio installs the MLX stack unpinned at
latest, which pulls 0.31.3. Verified on a real macos-14 runner: gemma4 fails to
load on 0.31.3 but loads and generates coherently on 0.31.2 and on git-main
(future 0.31.4). See mlx-lm #1242.

Exclude just that release (!=0.31.3) in the installer and the self-heal floor so
--upgrade still resolves to the newest good build, and treat an already-installed
0.31.3 as unsatisfied so the self-heal replaces it.

* Studio MLX: cover fresh-install path + robust bad-version compare

Address PR review:
- Fresh install.sh (Apple Silicon) runs the base 'uv pip install unsloth' with
  SKIP_STUDIO_BASE=1, skipping the guarded MLX-stack step, so transitive
  resolution could still pull mlx-lm 0.31.3. install.sh already exports
  UV_OVERRIDE -> overrides-darwin-arm64.txt before that install, so exclude
  mlx-lm 0.31.3 there too; this also strengthens the self-heal (same override).
- Match the known-bad version with parsed packaging.Version so 0.31.3 == 0.31.3.0
  (trailing-zero normalization) instead of raw string equality.

* Studio: exclude mlx-lm 0.31.3 on the fresh Apple Silicon install too

The overrides file only applies via UV_OVERRIDE when it exists relative to the
script, which is not true for a curl-piped install, and the guarded MLX step in
install_python_stack.py is skipped there (SKIP_STUDIO_BASE=1). So the base
install could still resolve the transitive mlx-lm to the broken 0.31.3. Append
mlx-lm!=0.31.3 to the base install on Apple Silicon (empty elsewhere), so the
fresh path pins away from 0.31.3 without waiting for the runtime self-heal.

* Studio: exclude mlx-lm 0.31.3 on the migrated install; keep the >=0.22.0 floor

The with-deps migrated install did not append ${_MLX_LM_EXCLUDE_ARG:-}, so a
curl-piped Apple Silicon migration (no repo overrides file, UV_OVERRIDE unset)
could resolve mlx-lm 0.31.3 transitively. Append the exclusion there, matching
the fresh install path. The no-torch migration is left alone since --no-deps
never resolves mlx-lm (same as the fresh no-torch path).

Also restore the >=0.22.0 floor in overrides-darwin-arm64.txt: a uv override
replaces the transitive constraint, so a bare !=0.31.3 could let the resolver
drop below the supported minimum that mlx_repair.py enforces at runtime.

* Triage huggingface_hub 1.22.0 / fastapi / multiprocess scanner false positives

The scan-packages gate red-failed on all three shards after transitive deps
bumped. Every new CRITICAL is a benign false positive, verified against upstream:

- huggingface_hub 1.22.0 added _sandbox.py for the remote HF sandbox feature.
  Its job-startup bootstrap string (fetch sbx-server into the container /tmp and
  exec it) and the SandboxPool host-reservation loop trip the staged-dropper and
  C2-loop heuristics; that script runs inside a remote HF container, not on the
  user machine. The bump also re-hashed the already-reviewed benign polling loops
  in hf_api.py and utils/_http.py. The PyPI artifact is byte-identical to the
  official v1.22.0 tag.
- fastapi 0.139.0 routing.py re-hashed the websocket keepalive while-True loop;
  byte-identical to upstream 0.139.0.
- multiprocess 0.70.19 forkserver.py and tests/__init__.py re-hashed the AF_UNIX
  fork-server IPC and fd-inheritance tests; genuine uqfoundation release, local
  IPC not network.

Added 7 reviewed allowlist entries (no blind regenerate). All three shards
(hf-stack, studio, extras) exit 0 locally.

* Tighten mlx-lm 0.31.3 exclusion comments

* Trim mlx-lm 0.31.3 exclusion comments

scripts/scan_packages_baseline.json

@@ -1545,6 +1545,22 @@
       "severity": "HIGH",
       "evidence": "Obfusc: L52:     compiled = compile(source=pysrc, filename=filename, mode='exec')\nExec: L53:     exec(compiled, globs, globs)",
       "evidence_hash": "c429e4c977a61db6b7c717b5a552fce74eda622213e49eb5467a3782fd746fb9"
+    },
+    {
+      "package": "multiprocess",
+      "file": "multiprocess/forkserver.py",
+      "check": "Reverse shell / bind shell pattern",
+      "severity": "CRITICAL",
+      "evidence": "L6: import socket sha256:6c707119169286c9a798e2c8d13a48614e481d8a503950916fd4ffb4c94d3182",
+      "evidence_hash": "50fec0f0522a8e4e636bf348b752002d7935d8455af31fb78c6f11e2eba19f6d"
+    },
+    {
+      "package": "multiprocess",
+      "file": "multiprocess/tests/__init__.py",
+      "check": "Reverse shell / bind shell pattern",
+      "severity": "CRITICAL",
+      "evidence": "L3569:                     os.dup2(conn.fileno(), i) | L3601:                          \"test needs os.dup2()\") | L3619:             os.dup2(fd, newfd) | L20: import socket sha256:c824dc0f409f242420c3fbb324790c53cb3078d2c8b07ee8f2a05694b01c2946",
+      "evidence_hash": "3878a2b430c175dbc5877a95195bfe52f9588ff73fb74e2261ed5e33087915ad"
     }
   ]
 }