test: harden executor import contract

[dgenio]

Summary

Hardens the executor determinism import contract for #430 by extending the existing #354 guard to catch obvious literal dynamic import bypasses. This keeps the executor / _execution boundary protected against LLM, network, and randomness imports without adding dependencies or a separate CI job.

Changes

• tests/test_executor_import_contract.py: add AST detection for __import__("..."), importlib.import_module("..."), and simple aliases when the target is a string literal; add self-tests; treat banned in-repo submodules as banned too.
• docs/agent-context/invariants.md: document the dynamic-import hardening and its deliberate string-literal scope.
• AGENTS.md: point agents at the mechanical import-contract enforcement.
• CHANGELOG.md: record the Formalize and CI-protect the executor determinism invariants (no LLM / no network / no randomness) #430 hardening under Unreleased / Fixed.

Why

#430 asks for CI protection of the executor invariants: no LLM calls, no network I/O, and no randomness in executor.py / _execution. PR #384 already added direct import and transitive in-repo reach checks; this PR closes the remaining reviewable bypass where a banned module could be imported dynamically with a literal string.

Testing

• Linting passes (ruff check chainweaver/ tests/ examples/) - All checks passed!
• Formatting check passes (ruff format --check chainweaver/ tests/ examples/) - 233 files already formatted
• Type checking passes (python -m mypy chainweaver/ tests/) - Success: no issues found in 196 source files
• All existing tests pass (python -m pytest tests/ -v) - 1705 passed, 1 skipped, 1 warning; coverage 92.78%
• New tests added for new functionality - python -m pytest tests/test_executor_import_contract.py -v --no-cov collected 5 tests, 5 passed
• Docs build passes (python -m mkdocs build --strict) - exited 0; existing MkDocs Material 2.0 warning and existing nav/link INFO notices only

Tradeoffs / risks

• The dynamic-import detector intentionally covers literal, AST-visible patterns only. It does not evaluate runtime-built strings; executor code should not use runtime-built imports.
• No runtime behavior, public API, dependency, or package metadata changes.

Scope notes

• Changes are limited to Formalize and CI-protect the executor determinism invariants (no LLM / no network / no randomness) #430 import-contract hardening and docs/changelog alignment.
• Codify and CI-enforce the zero-LLM-SDK dependency guarantee for the base package #378 remains separate: this PR does not broaden base-package dependency scanning.

Related Issues

Closes #430

Checklist

• Code follows project conventions (see AGENTS.md and docs/agent-context/)
• Public API changes are documented (N/A: no public API changes)
• No secrets or credentials included

[Copilot]

Pull request overview

This PR strengthens ChainWeaver’s executor determinism import-contract guard (introduced in #354) by extending the static AST checks to also reject obvious string-literal dynamic import bypasses in executor.py and chainweaver/_execution/, and updates the agent-facing docs/changelog to describe the expanded enforcement.

Changes:

• Extend tests/test_executor_import_contract.py with AST detection for __import__("...") / importlib.import_module("...") (including simple aliases) and add self-tests.
• Update docs/agent-context/invariants.md and AGENTS.md to document the expanded, mechanical enforcement and its intended scope.
• Add a CHANGELOG entry under Unreleased/Fixed for the #430 hardening.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/test_executor_import_contract.py	Adds literal dynamic-import detection and tightens banned in-repo module matching to include banned submodules.
docs/agent-context/invariants.md	Documents the new literal dynamic-import enforcement and its deliberate limitations.
AGENTS.md	Points contributors/agents to the mechanical executor import-contract guard.
CHANGELOG.md	Records the #430 import-contract hardening under Unreleased/Fixed.