Fix Gradio Playground MCP argument parsing

[lakshayxi]

Fixes #1080.

Summary

• Parse JSON string arguments for MCP call_tool actions at the web preprocessing boundary.
• Preserve strict deserialization for normal typed payloads.
• Keep invalid, non-object, and malformed JSON subject to existing Pydantic validation.
• Add regression coverage for both serialization behavior and the /web/step path.
• Remove the stale Gradio MCP workaround from AGENTS.md.

Tests

• PYTHONPATH=src:envs uv run pytest tests/core/ -q
• PYTHONPATH=src:envs uv run pytest tests/ -q
• uv run usort check src/openenv/core/env_server/serialization.py tests/core/test_mcp/test_mcp_types.py tests/core/test_web_interface_mcp.py
• uv run ruff format src/openenv/core/env_server/serialization.py tests/core/test_mcp/test_mcp_types.py tests/core/test_web_interface_mcp.py --check
• uv run ruff check src/openenv/core/env_server/serialization.py tests/core/test_mcp/test_mcp_types.py tests/core/test_web_interface_mcp.py

Full suite: 1641 passed, 129 skipped.

---

Note

Low Risk
Scoped to the web preprocessing deserialization path with clear validation boundaries and broad test coverage; no auth or data-model changes.

Overview
Fixes Gradio Playground and POST /web/step failures when MCP call_tool actions send arguments as a JSON string (textbox) instead of an object.

deserialize_action_with_preprocessing now JSON-decodes string arguments for type: call_tool into a dict on a copy of the payload (input is not mutated). deserialize_action stays strict—string arguments still fail validation. Malformed JSON, arrays, and scalar JSON strings still raise ValidationError.

Regression tests cover serialization edge cases and an integration test on /web/step. AGENTS.md drops the old workaround note about the broken Playground Step form.

^{Reviewed by Cursor Bugbot for commit 9b765f8. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Stale comment

Reviewed at 9b765f8e2e1dbf2319db74395a4cc94552964c2b: JSON-dict preprocessing fixes the MCP Playground form while preserving strict validation for malformed, list, and scalar inputs; the regression coverage is appropriate and no alignment issue was found. Before merge, refresh onto current main, approve the first-contributor workflow run, and require green exact-head CI. The required workflows are currently action_required and never executed.

  

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[cursor]

Stale comment

Refresh review vs main b12450f2 (Ben ask):

Verdict: LGTM after rebase. Exact head 9b765f8e is ~66 behind main. Preprocessing-only JSON parse of Gradio string arguments for call_tool is correct; strict deserialize_action still rejects strings; tests cover dict/valid JSON/malformed/array/scalar and non-mutation. AGENTS.md gotcha removal matches the fix. Please rebase + refresh CI (Approve-and-run if needed), then squash-merge.

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[burtenshaw]

LGTM

[cursor]

Refresh review (Wed 2026-09-16)

Still BEHIND main (9b765f8e), but content is still correct: JSON-decode string arguments for Gradio call_tool in deserialize_action_with_preprocessing, with focused tests.

No conflict with #1169. This exact change is already included in #1172 (cdcd41a5). Prefer landing via #1172 (after #1172 drops the unrelated #1000 commit); then close this PR as superseded.

If #1172 is split differently, an on-repo replacement of these four files onto current main is fine.

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