fix(reactivity): resolve Python scopes correctly in the dependency analyzer - #517

Problem

The dependency-graph analyzer (packages/reactivity/src/scripts/ast-analyzer.py) approximated Python scope with a per-block global_vars set and a stack of scope names. Block boundaries are not scope boundaries, so this went wrong in both directions:

• Under-reporting (Reactive execution misses globals read inside functions, producing silently stale output #512). A global read inside a function or method body was only recorded if the global was defined in the same block. A global defined in another block produced no edge, so "run with dependents" scheduled nothing and downstream blocks kept showing a successful but stale result.
• Over-reporting (Dependency graph publishes comprehension targets and lambda parameters as notebook variables #513). There was no scope for Lambda, ListComp, SetComp, DictComp or GeneratorExp, so comprehension targets were published as block inputs and outputs, and lambda parameters as inputs. Same-named loop variables (x, i, o, row, df) then produced phantom edges and spurious re-execution.

The same root cause also dropped reads in decorators, default arguments and annotations, because those were walked inside the function's scope.

Change

The visitor now tracks scope as a stack of sets of locally bound names, and a load is a module-level read whenever no enclosing scope binds it, at any depth:

• Functions, async functions, lambdas push a scope containing their parameters plus every name bound anywhere in the body (_bound_names, which does not descend into nested scopes). Pre-collecting is necessary because Python binds a name for the whole function: x = x + 1 reads the local, not a global. Decorators, defaults, annotations and return annotations are visited in the enclosing scope before the push.
• Comprehensions and generator expressions visit the first iterable in the enclosing scope, then push a scope with their targets for the remaining iterables, conditions and element expressions.
• Class bodies push a scope for their own assignments; methods still cannot see class attributes, matching Python.
• global declarations continue to bypass the local check, so the existing global num behaviour is unchanged.

Analyzer diff is ~95 lines changed. No TypeScript source changes; dag-builder.ts consumes the same output shape.

Tests

• ast-analyzer.test.ts: a Python scoping table of 15 cases covering both issues' repros plus the surrounding edge cases (method bodies, attribute reads, read-before-assign locals, global, decorators/defaults/annotations, class attributes, nested/dict/set/generator comprehensions, lambda defaults).
• dag.test.ts: two end-to-end DAG tests mirroring the issue reproductions — the missing source_value edge from Reactive execution misses globals read inside functions, producing silently stale output #512 now exists, and the phantom o/x edges from Dependency graph publishes comprehension targets and lambda parameters as notebook variables #513 do not.
• Full suite: 3163 tests pass; pnpm typecheck and pnpm biome:check clean.

Not touched: scripts/test-ast-analyzer.py fails identically on main because its expected output predates the importedPackages and linesOfCode fields. It is not part of pnpm test; left for a separate cleanup.

Fixes #512
Fixes #513

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved Python dependency analysis across functions, classes, lambdas, comprehensions, decorators, annotations, and default arguments.
  • Correctly handles local bindings and global declarations when determining variable usage.
  • Improved dependency relationships for code blocks that reference variables defined elsewhere, including code nested within separate scopes.
  • Excludes comprehension targets and lambda parameters from unrelated dependency relationships.
  • Improved handling of class-level bindings so they do not incorrectly affect variable resolution inside methods.