fix: agent must check dependency availability before claiming to satisfy requirements that depend on them #236

Problem

Issue #215 acceptance criteria states: "Captures RSS with psutil when available and has a no-psutil fallback." The agent implemented current_rss_mb() with a Linux /proc path and a macOS ru_maxrss fallback, but never attempted to use psutil. When asked why, the implicit reasoning was "psutil is not in pyproject.toml."

However, the agent did not:

1. Flag this as a dependency gap ("Suppress guardrail gitignore prompts in team workers #215 requires psutil but it is not listed — should I add it?")
2. Propose adding psutil as a dependency
3. Make the fallback semantics explicit in the output ("rss_source": "ru_maxrss_high_water_macos")

Instead, it implemented a solution that does not satisfy the criterion and moved on.

Root Cause

1. Silent scope reduction without flagging: The agent reduced the scope of a requirement without asking the user or flagging the gap. This is more dangerous than asking — the user sees "RSS captured" in the PR and assumes psutil-level accuracy.

2. Did not check pyproject.toml for dependencies needed by acceptance criteria: Before planning the implementation, the agent should have checked: "Does this criterion require a dependency that is not yet installed?"

Prevention

For the agent

1. Before implementing, check each acceptance criterion against available dependencies. If a criterion mentions a specific library (psutil), verify it is in pyproject.toml or requirements.txt. If not, flag it explicitly:

   • "AC5 requires psutil but it is not a dependency. Options: (a) add psutil to pyproject.toml, (b) implement a fallback that clearly labels the source. Recommendation: ..."

2. Never silently reduce the scope of a requirement. If the implementation cannot satisfy a criterion as written, the agent must:

   • Flag the gap in the plan
   • Propose options (add dependency / split criterion / implement partial)
   • Get user confirmation before proceeding

3. When a fallback is used instead of the preferred path, include a machine-readable field in the output indicating which source was used: "rss_source": "psutil_process_info" or "rss_source": "ru_maxrss_high_water_macos".

References

• PR fix: agent must not conflate separate metrics — enumerate all requested metrics and verify none are missing #237 review finding guardrails: plugin MVP for policy enforcement #4: https://github.com/Cor-Incorporated/persona-village-v2/pull/237#issuecomment-4525916917
• Issue Suppress guardrail gitignore prompts in team workers #215 AC5: "Captures RSS with psutil when available and has a no-psutil fallback"