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claude-code - 💡(How to fix) Fix [MODEL] Opus 4.7 silently substitutes proxy identifiers in integrity-critical code [1 participants]

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anthropics/claude-code#56354•Fetched 2026-05-06 06:30:22
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Fix Action

Fix / Workaround

Suggested mitigation: stronger model self-check before edits to integrity invariants — require explicit statement of substitution's injectivity / surjectivity, or refuse the substitution and fall back to the primary key.

Code Example

see above

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Preflight Checklist

  • I have searched existing issues for similar behavior reports
  • This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Other unexpected behavior

What You Asked Claude to Do

When editing code that enforces a data-integrity invariant (a leakage / cross-split / dedup check keyed on a primary identifier), Opus 4.7 substituted a derived/proxy identifier in place of the primary one and justified the substitution as "1:1 equivalent" without proving the bijection. The substitution silently weakened the check (lost cases where the primary key was non-unique through the proxy). The model repeated the same shortcut on a second attempt after the user raised the issue. Required two corrective rounds of user pushback before the model acknowledged the proxy was strictly weaker.

Risk: silent correctness loss in safety / leakage / dedup logic, where over-confident "should be equivalent" reasoning produces test-set contamination or duplicate-record bugs that are very hard to detect downstream.

Suggested mitigation: stronger model self-check before edits to integrity invariants — require explicit statement of substitution's injectivity / surjectivity, or refuse the substitution and fall back to the primary key.

Repro: any task where the model is asked to modify a uniqueness / no-cross-split / dedup check on a dataframe whose manifest doesn't contain the primary key directly. Model will reach for whatever's already in the manifest and rationalize.

Environment: Claude Code on Windows / PowerShell, Opus 4.7.

What Claude Actually Did

see above

Expected Behavior

see above

Files Affected

see above

Permission Mode

I don't know / Not sure

Can You Reproduce This?

Haven't tried to reproduce

Steps to Reproduce

see above

Claude Model

Opus

Relevant Conversation

see above

Impact

High - Significant unwanted changes

Claude Code Version

Identifier anthropic.claude-code Version 2.1.126

Platform

Anthropic API

Additional Context

above

extent analysis

TL;DR

The issue can be mitigated by implementing a stronger model self-check to ensure explicit statement of substitution's injectivity/surjectivity before editing integrity invariants.

Guidance

  • Review the model's substitution logic to identify cases where it assumes "1:1 equivalence" without proof, and modify it to require explicit injectivity/surjectivity statements.
  • Test the model with various dataframes that do not contain the primary key directly to ensure it falls back to the primary key instead of making unjustified substitutions.
  • Consider adding a fallback mechanism to refuse substitutions that cannot be proven to be bijective, to prevent silent correctness loss in safety/logic checks.
  • Evaluate the model's performance on tasks that require modifying uniqueness/no-cross-split/dedup checks to ensure the mitigation is effective.

Example

No code snippet is provided as the issue does not contain specific code examples.

Notes

The suggested mitigation may require significant changes to the model's logic and may have performance implications. Further testing and evaluation are necessary to ensure the effectiveness of the mitigation.

Recommendation

Apply workaround: Implement a stronger model self-check to require explicit injectivity/surjectivity statements before editing integrity invariants, as this directly addresses the identified issue and can help prevent silent correctness loss.

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