[codex] Preserve valid PyCharm sibling SDKs

[jpmorard]

Summary

• Preserve valid uv (...) PyCharm SDKs whose interpreter paths still exist, even when they are not part of the active checkout keep list.
• Continue pruning stale uv (...) SDK entries whose interpreter path is missing.
• Add a regression for two sibling AGILAB checkouts, keeping uv (agilab-src) while removing a stale checkout SDK.

Repro

Run pycharm/setup_pycharm.py from one AGILAB checkout, then from a sibling checkout such as /Users/agi/agilab-src. The second run can remove the first checkout's valid SDK entry from JetBrains jdk.table.xml, leaving that project XML pointing at an SDK name PyCharm no longer knows.

Root Cause

JdkTable.prune_uv_names() removed every uv (...) SDK not in the active checkout's generated keep list. That was too aggressive for machines with multiple valid AGILAB source checkouts.

Regression Test

test_prune_uv_names_keeps_valid_sibling_checkout_sdks_and_removes_stale proves a valid sibling checkout SDK is retained while a missing-interpreter SDK is pruned.

Validation

• uv --preview-features extra-build-dependencies run python tools/impact_validate.py --files pycharm/setup_pycharm.py test/test_setup_pycharm.py
• uv --preview-features extra-build-dependencies run pytest -q -o addopts='' test/test_setup_pycharm.py
• pre-push guard passed; scoped guards for docs mirror, release proof, agent instructions, and app contracts were skipped as unchanged

Review Evidence

Not used.

Agent Metadata

• Tokki version: not used
• Agent/runtime: Codex CLI, version unavailable
• Model: GPT-5 Codex
• Reasoning effort: unknown
• /fast mode: unknown