fix: persist the sandbox namespace with a single dill dump

[YoanSallami]

Problem

MirageSandbox persists the REPL namespace between run calls by pickling it with dill. It did so item by item, which is quadratic: dill pickles a function together with a copy of its globals, so N sandbox-defined functions cost N full-namespace pickles.

Measured on this branch's test snippet (120 defs in one run):

	old	new
persist 120 functions	~3.8 s	~0.4 s
a few hundred functions	RecursionError, namespace lost	fine

A second, sharper bug hid in the same loop: one unpicklable value dropped every sandbox-defined function. The offending object was reachable through the shared globals each function copied, so dill.dumps(item) failed for all of them:

sandbox.run("gen = (i for i in range(3))\ndef survivor(x):\n    return x * 3")
sandbox.run("print(survivor(5))")  # NameError: name 'survivor' is not defined

Fix

• One dill.dumps of the whole namespace, which memoizes the shared globals once.
• The per-item filter stays as a fallback for a namespace holding something unpicklable (a generator, an open socket), now pickling with recurse=True so a function carries only the globals it references rather than the whole namespace. Restored functions are re-homed onto the live namespace on the next run, so the reduced globals are never observable.
• The state file is written to a sibling temp file and os.replaced, so a run killed mid-write (host timeout) cannot leave a truncated state file.

Tests

Two regression tests in mirage_sandbox_test.py: test_many_functions_persist and test_unpicklable_value_does_not_drop_the_namespace (the latter fails on the old code with the NameError above).

uv run pytest synalinks/src/sandboxes/mirage_sandbox_test.py → 124 passed, 9 skipped. uvx ruff check clean.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GfeWSiwmNYwhbPNLR75mer