fix: arg/kwarg collision for local numpy vars in caching

[dmadisetti]

📝 Summary

We do not properly detect local (defined in same cell) kwarg/arg defs, causing invalid collisions.

Came across this when doing some benchmarking.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jun 2, 2026 2:14am

[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant UserCode as User Cell
    participant Cache as @mo.cache Decorator
    participant Hash as _is_memoizable()
    participant Graph as Cell Graph
    participant ContentHash as Content Hash

    Note over UserCode,ContentHash: Cache memoization check flow

    UserCode->>Cache: Call f(a=ndarray) with args/kwargs
    Cache->>Hash: Check memoizability(local_ref, value)
    Hash->>Graph: Look up definitions.get(local_ref)
    Graph-->>Hash: Return set of defining cell IDs (or empty set)
    
    alt local_ref defined in same cell
        Note over Hash: defs = {self.cell_id}
        Hash->>Hash: bool(defs) is True, self.cell_id in defs
        Hash-->>Cache: Return False (not memoizable)
        Cache->>ContentHash: Recompute content hash
        ContentHash-->>Cache: New hash from runtime value
        Cache-->>UserCode: cache miss, execute function
        
    else local_ref defined in different cell
        Note over Hash: defs = {other_cell_id}
        Hash->>Hash: bool(defs) is True, self.cell_id not in defs
        Hash-->>Cache: Return True (memoizable)
        Cache->>ContentHash: Use cached content hash
        ContentHash-->>Cache: Existing hash from storage
        Cache-->>UserCode: cache hit, return cached result
        
    else local_ref not defined in any cell (local variable)
        Note over Hash: defs = empty set
        Hash->>Hash: bool(defs) is False
        Hash-->>Cache: Return False (not memoizable)
        Cache->>ContentHash: Recompute content hash
        ContentHash-->>Cache: New hash from runtime value
        Cache-->>UserCode: cache miss, execute function
    end

    Note over UserCode,ContentHash: Key fix: distinguish local vars (empty defs) from cross-cell refs

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_{Re-trigger cubic}

[Copilot]

Pull request overview

This PR fixes incorrect content-hash memoization during @mo.cache calls where locally-scoped values (not defined by any cell) could be memoized by name, causing different ndarray argument values (positional or keyword) to reuse a prior digest and incorrectly collide.

Changes:

• Restrict content-hash memoization to references that are actually defined by (other) cells in the notebook graph.
• Add a regression test ensuring distinct NumPy ndarray arguments to a cached function never collide across calls (positional/keyword forms).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
marimo/_save/hash.py	Tightens _is_memoizable so only graph-defined refs are eligible for hash memoization, preventing memo collisions for function args/kwargs.
tests/_save/test_hash.py	Adds a NumPy regression test validating cached function calls with distinct ndarray inputs don’t produce erroneous cache hits.

[kirangadhave]

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