fix(mcp): security hardening for 4 issues (#54, #68, #49, #77) - #1
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May 22, 2026
Four findings from Copilot's review on PR NousResearch#22891, all in the AX elements-array cap added by 22fa1ed: 1. The truncation note ("response truncated to N of M elements") was appended unconditionally — including in the som/vision multimodal path, whose response carries a screenshot rather than an `elements` array. The note described a payload field that wasn't present. Moved the note into the AX-text branch where the array actually appears. 2. `_format_elements(cap.elements)` ran on the full untrimmed list with its own `max_lines=40` cap, so a caller passing `max_elements=10` would see summary lines referencing `NousResearch#11..NousResearch#40` even though the JSON `elements` array only held #1..NousResearch#10. Format on `visible_elements` instead so the summary indices always exist in the response. 3. `_coerce_max_elements` enforced a lower bound but no upper bound, so `max_elements=10_000_000` silently disabled the safeguard and reintroduced the original context-blow-up. Added a hard cap (`_MAX_ALLOWED_MAX_ELEMENTS = 1000`) that clamps oversized values. 4. The schema string said "Default 100" but the property carried no `default` field, and claimed `max_elements` had no effect on som/ vision while the image-missing fallback path can still return an elements array. Added `"default": 100`, `"maximum": 1000`, and clarified the fallback-path wording. Each finding gets a regression test: - test_capture_ax_clamps_oversized_max_elements_to_hard_cap - test_capture_ax_summary_indices_match_returned_elements - test_capture_multimodal_summary_omits_truncation_note - test_schema_max_elements_documents_default_and_upper_bound Verified with `pytest tests/tools/test_computer_use.py` (53 passed, including the 5 new cases). Confirmed each new test fails on the pre-fix code path before applying the production change. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Fixes 4 MCP security issues:
NousResearch#54 - MCP stderr logs credentials verbatim with no redaction
NousResearch#68 - MCP sampling has no token budget cap
NousResearch#49 - MCP tool descriptions pass prompt injection unfiltered
NousResearch#77 - Env interpolation resolves from full os.environ leaking secrets
All 281 existing MCP tests pass.