fix(mcp): correct MCPToolResult.data type annotation for MCP 1.4.0 content list format #3032
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Summary
Fixes a type annotation incompatibility in
MCPToolResult.dataintroduced by MCP 1.4.0, which changed the success content format from a plaindictto alistof typed content objects. This PR normalises the list-format response on the adapter side so thatMCPToolResult.dataremains consistently typed asdict[str, Any], preserving backward compatibility for all downstream consumers.Changes
MCPToolAdapter.invoke()success path normalisation: When the MCP server returns content in MCP 1.4.0 list format (i.e., alist), the adapter now wraps it as{"content": [...]}before assigning toMCPToolResult.data. This ensures the declareddict[str, Any]type annotation is always satisfied, regardless of which MCP protocol version the server speaks.MockMCPTransport.call()updated to MCP 1.4.0 compliance:invoke_resultspayloads are now returned as[{"type": "text", "text": json.dumps(payload)}]— matching the actual MCP 1.4.0 wire format — rather than the previously non-standard bare-dict format. This makes the mock a faithful stand-in for a real MCP 1.4.0 server.MCPToolResult.datadocstring updated: Documents the normalisation behaviour explicitly, clarifying that list-format content from MCP 1.4.0 servers is wrapped under the"content"key, and that non-list (legacy) responses are passed through unchanged.Existing
mcp_adapter.featurescenario updated: The assertion now checks for the"content"key inresult.data, reflecting the fact that the mock transport now emits MCP 1.4.0 list-format content.Two new Behave scenarios added: Cover the MCP 1.4.0 list-format content path end-to-end — one for a standard list-format success response and one verifying the graceful fallback for non-standard (non-list) server responses.
Corresponding step definitions added: New Gherkin steps wired up to exercise the normalisation logic through the full adapter call path.
Design Decisions
Option B (normalise to
dict) was chosen over Option A (broaden the type annotation todict | list).Broadening the type annotation would have pushed the burden of handling two distinct shapes onto every downstream caller that accesses
result.data. Any code performingresult.data["key"]would require a type guard or conditional branch, risking runtimeTypeErrors on unguarded call sites and introducing churn across the codebase.By normalising at the adapter boundary — wrapping list content as
{"content": [...]}— thedict[str, Any]contract is preserved end-to-end. Downstream code continues to work without modification, and the single normalisation point is easy to audit and test.The fallback path (non-list content passed through as-is) ensures that legacy or non-standard MCP server responses are handled gracefully without raising exceptions.
Testing
Related Issues
Closes #2743
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Overall Assessment
The design decision (Option B — normalise at the adapter boundary) is sound and well-reasoned. The mock update to MCP 1.4.0 compliance, the new Behave scenarios, and the docstring improvements are all good. However, there is one blocking violation of CONTRIBUTING.md that must be fixed before this can be approved.
❌ Blocking Issue
# type: ignore[assignment]on line 540 ofsrc/cleveragents/mcp/adapter.pyCONTRIBUTING.md explicitly states: "Never use
# type: ignoreor any other mechanism to suppress type checking errors." This is a hard project rule with zero exceptions.The fallback path suppresses Pyright's valid concern that
raw_content(typed asAnyfromdict.get()) may not be adict[str, Any]. The fix is to use properisinstancenarrowing instead of suppression:This eliminates the type suppression entirely while handling all three cases (list, dict, unexpected) safely and maintaining the
dict[str, Any]contract.✅ What Looks Good
{"content": [...]}at the adapter boundary is the right call — it preserves thedict[str, Any]contract and avoids pushing type-guard burden to every downstream caller.MockMCPTransportnow returns MCP 1.4.0 compliant[{"type": "text", "text": ...}]format, making tests more realistic."id"→"content") correctly reflects the new mock format.MCPToolResult.datadocstring accurately describes the normalisation behaviour.Type/Buglabel, milestone v3.8.0 (matches issue), andCloses #2743.Summary
Fix the
# type: ignoresuppression with properisinstancenarrowing and this PR is ready to merge. Only one line needs to change.Automated by CleverAgents Bot
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Overall Assessment
The design decision (Option B — normalise at the adapter boundary) is correct and well-executed. The mock update to MCP 1.4.0 compliance is faithful, the new Behave scenarios are well-structured, and the docstring improvements are accurate. However, there is one blocking CONTRIBUTING.md violation that was already flagged in the previous self-review and has not been addressed.
❌ Blocking Issue:
# type: ignore[assignment](CONTRIBUTING.md violation)File:
src/cleveragents/mcp/adapter.py, fallback path inMCPToolAdapter.invoke()success normalisationCONTRIBUTING.md states: "Never use
# type: ignoreor any other mechanism to suppress type checking errors." This is a hard project rule with zero exceptions.The fallback path uses
# type: ignore[assignment]to suppress Pyright's valid concern thatraw_content(typed asAnyfromdict.get()) may not satisfydict[str, Any]. The previous self-review (comment #109551) already flagged this exact issue and provided the fix. It has not been addressed.Required fix — replace the current if/else with proper
isinstancenarrowing:This eliminates the type suppression entirely while handling all three cases (list, dict, unexpected) safely and maintaining the
dict[str, Any]contract.⚠️ Minor Issue: Missing test coverage for fallback path
Both new Behave scenarios exercise the list-format normalisation path (
isinstance(raw_content, list)→ True). Neither scenario covers the fallback path where content is already a dict or an unexpected type. Consider adding a scenario with a mock transport that returns{"content": {"key": "value"}}(dict format) to verify the fallback path works correctly.✅ What Looks Good
{"content": [...]}at the adapter boundary preserves thedict[str, Any]contract and avoids pushing type-guard burden to every downstream caller. Sound engineering decision.MockMCPTransportnow returns MCP 1.4.0 compliant[{"type": "text", "text": ...}]format, making tests more realistic."id"→"content"correctly reflects the new mock format.MCPToolResult.datadocstring accurately describes the normalisation behaviour.ISSUES CLOSEDfooter.Type/Buglabel, milestone v3.8.0, andCloses #2743.Summary
One change required: remove the
# type: ignore[assignment]suppression on the fallback path insrc/cleveragents/mcp/adapter.pyand replace with properisinstancenarrowing. This was already identified in the previous review cycle. Once fixed, this PR is ready to merge.Automated by CleverAgents Bot
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da486dae297c2f5a1c76✅ Independent Review: APPROVED
Review Summary
This PR fixes a type annotation incompatibility in
MCPToolResult.dataintroduced by MCP 1.4.0, which changed the success content format from a plaindictto alistof typed content objects. The fix normalises the list-format response at the adapter boundary so thatMCPToolResult.dataremains consistently typed asdict[str, Any].What Was Reviewed
src/cleveragents/mcp/adapter.py— Core normalisation logic inMCPToolAdapter.invoke()andMCPToolResult.datadocstring updatefeatures/mocks/mock_mcp_transport.py— Mock transport updated to MCP 1.4.0 compliant list-format contentfeatures/mcp_adapter.feature— Existing scenario updated + 2 new Behave scenariosfeatures/steps/mcp_adapter_steps.py— New step definitions for MCP 1.4.0 content verificationCriteria Assessment
dict[str, Any]contract preserved, no breaking changeisinstancenarrowing, no type suppressionsCloses #2743,Type/Bug, milestone v3.8.0Note on Previous Reviews
The
# type: ignore[assignment]violation flagged in two previous review cycles has been resolved. The fallback path now uses properisinstance(raw_content, dict)narrowing instead of type suppression, which is the correct approach per CONTRIBUTING.md.Minor Observation (Non-blocking)
The
elif isinstance(raw_content, dict)andelsefallback branches do not have dedicated test scenarios. This is acceptable for now since the primary MCP 1.4.0 list path is well-tested, but a future PR could add coverage for the dict-passthrough and unexpected-type-wrapping paths.Merge Plan
CI is currently running on the updated commit (
7c2f5a1c). Will merge once all checks pass. This is a single-commit PR, somergestyle will be used.Automated by CleverAgents Bot
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Code Review — LGTM ✅
PR: fix(mcp): correct MCPToolResult.data type annotation for MCP 1.4.0 content list format
Review Checklist
✅ Correctness: Fixes type annotation incompatibility introduced by MCP 1.4.0 (success content changed from
dicttolistof typed content objects). Normalises list-format response on adapter side.✅ Type Safety: No
# type: ignore. Pyright passes.✅ Commit Format:
fix(mcp):follows Conventional Changelog format.✅ Labels/Milestone:
Priority/Medium,Type/Bug, milestonev3.8.0— correctly assigned.Decision: LGTM — Proceeding to merge when CI passes.
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🔍 Independent Review: APPROVED
Review focus areas: error-handling-patterns, edge-cases, boundary-conditions
What Was Reviewed
src/cleveragents/mcp/adapter.py— Core normalisation logic inMCPToolAdapter.invoke()success path,MCPToolResult.datadocstring updatefeatures/mocks/mock_mcp_transport.py— Mock transport updated to MCP 1.4.0 compliant list-format contentfeatures/mcp_adapter.feature— Existing scenario updated + 2 new Behave scenarios for MCP 1.4.0 contentfeatures/steps/mcp_adapter_steps.py— New step definitions (_ListContentTransport, data key assertion, content list assertions)Deep Dive: Error Handling & Edge Cases
Given special attention to the normalisation logic's handling of boundary conditions:
result.get("content", [])[{"type": "text", "text": "..."}](MCP 1.4.0 standard)isinstance(list)→ True{"content": [...]}[](empty content list)isinstance(list)→ True{"content": []}{"key": "value"}(legacy dict format)isinstance(dict)→ True{"key": "value"}passthroughNone(key exists, value is None)else{"content": None}"string"(unexpected type)else{"content": "string"}[]→isinstance(list){"content": []}All six edge cases are handled correctly. The three-branch
isinstancenarrowing ensures thedict[str, Any]contract is always satisfied, and Pyright can verify this statically without any type suppressions.The error path (
result.get("isError")) was already handling MCP 1.4.0 list-format content correctly before this PR — it checksisinstance(content, list)and extractscontent[0].get("text"). No regression there.Criteria Assessment
dict[str, Any]contract# type: ignore; properisinstancenarrowing on all branchesMockMCPTransportnow returns MCP 1.4.0 compliant[{"type": "text", "text": ...}]ISSUES CLOSED: #2743,Type/Bug, milestone v3.8.0dict[str, Any]Note on Previous Reviews
The
# type: ignore[assignment]violation flagged in two previous review cycles (comments #109551 and #110460) has been properly resolved. The current commit (7c2f5a1c) uses three-branchisinstancenarrowing (list→ wrap,dict→ passthrough,else→ wrap), which is the correct approach per CONTRIBUTING.md.Minor Suggestions (Non-blocking)
Test coverage for fallback branches: The
elif isinstance(raw_content, dict)andelsebranches lack dedicated test scenarios. Consider adding scenarios in a follow-up PR that exercise: (a) a mock transport returning{"content": {"key": "value"}}(dict passthrough), and (b) a mock returning{"content": None}(unexpected type wrapping). This would bring the normalisation logic to 100% branch coverage.Gherkin step pluralisation: The step
"the invocation result content list should have {count:d} item"uses singular "item". If a future scenario needs to assert multiple items (e.g., "2 items"), a separate step or a regex-based step would be needed. Minor concern — the current usage is correct.Decision: APPROVED ✅
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Milestone Triage Decision: Moved to Backlog
This spec alignment issue has been moved out of v3.3.0 during aggressive milestone triage. While important for consistency, it does not relate to the core focus of Corrections + Subplans + Checkpoints.
Reasoning:
Will be addressed in a future milestone focused on CLI specification compliance and consistency.