Fix: McpIntegration.list_tools() always returns empty inputSchema (#1073)

[kaluli123123]

Summary

McpIntegration.list_tools() (prime-agent-runtime/src/rlm/mcp_base.py) always returns "inputSchema": {} for every tool of every MCP server, even though the server sends a full JSON Schema. This was already reported and diagnosed in #1073, which is one of the "related reports" under the still-open tracker #1383 (Harden MCP OAuth discovery and Codex transports — "preserve MCP tool schemas ..."). The merged stack PR #1164 for that tracker didn't touch this file, so the bug is still present on main (verified on 06860844e).

Root cause

mcp.types.Tool is a pydantic model whose schema field is the snake_case input_schema, with a camelCase alias inputSchema:

from mcp.types import Tool
Tool.model_fields['input_schema'].alias  # -> 'inputSchema'

Aliases are honored on validation and on model_dump(by_alias=True), never as a plain attribute. So the existing code

"inputSchema": getattr(t, "inputSchema", None) or {},

always misses and silently substitutes {}. The same value feeds the per-tool docstring in __getattr__, so the documented discovery path ("call help(<tool>) for the argument schema") returns nothing for every MCP integration, and callers have to reverse-engineer arguments from the server's validation errors one field at a time — this is exactly what the original report describes with Context7.

The existing regression test in test_mcp_base.py didn't catch this because its fake session built tools from a bare duck-typed stub that set the camelCase attribute directly (t.inputSchema = schema), which happens to satisfy the buggy getattr and therefore encodes the bug rather than catching it.

Fix

Read the schema via model_dump(by_alias=True) first (falls back to plain getattr for non-pydantic stand-ins used in tests):

def _tool_input_schema(t: Any) -> dict[str, Any]:
    if hasattr(t, "model_dump"):
        dumped = t.model_dump(by_alias=True, exclude_none=True)
        schema = dumped.get("inputSchema")
        if schema:
            return schema
    return getattr(t, "inputSchema", None) or {}

Also rebuilt the test double to construct a real mcp.types.Tool instead of the duck-typed stub, and added a regression test asserting the schema round-trips through list_tools() and the bound-tool docstring. Confirmed the new test fails against the pre-fix code and passes after the fix.

Validation

cd prime-agent-runtime
uv run python -m unittest discover -s test   # 99 passed (was 98; +1 new test)

Also ran the full npm run check at the repo root (biome, tsgo --noEmit, installer render check, browser smoke check) — all green; this change doesn't touch packages/*, so no .changes/ fragment is required by the changelog-fragment CI check.

Patch

Branch pushed here, diff is two files / ~55 lines: https://github.com/kaluli123123/prime-agent/tree/fix/mcp-tool-input-schema-alias

Diff: main...kaluli123123:prime-agent:fix/mcp-tool-input-schema-alias

Happy to open a PR from this branch if a maintainer wants to invite implementation, per CONTRIBUTING.md.