feat(core): add structuredContent to resources_get and resources_list

[jordigilh]

What

resources_get and resources_list now return structuredContent alongside the existing text output, enabling programmatic MCP clients to consume K8s objects directly without parsing YAML or table strings.

This extracts the K8s resource tool retrofit from #920 as a standalone change, following Recipe 1 from docs/specs/structured-output.md.

Why

We maintain an MCP client (kubernaut) that consumes resources_get and resources_list programmatically to build unstructured.Unstructured objects for fleet metadata caching. Today we have to parse the text content (YAML or table strings) back into structured data, which is fragile and loses type fidelity. With structuredContent, our client can consume the K8s object directly as map[string]any.

The infrastructure is already on main (PR #960: PrintObjStructured, NewToolCallResultFull, ensureStructuredObject) and the structured-output spec documents Recipe 1 as the intended pattern for K8s resource tools — but notes "has no in-tree adopter yet." This PR is that first adopter for the core resource tools.

Changes

pkg/toolsets/core/resources.go (2 handlers, ~10 lines changed):

• resourcesGet: output.MarshalYaml(ret) + NewToolCallResult → output.Yaml.PrintObjStructured(ret) + NewToolCallResultFull
• resourcesList: params.ListOutput.PrintObj(ret) + NewToolCallResult → params.ListOutput.PrintObjStructured(ret) + NewToolCallResultFull

pkg/mcp/resources_test.go (3 new subtests):

• resources_get returns namespace / returns structured content — asserts StructuredContent is a map with kind, apiVersion, metadata.name
• resources_list returns namespaces / returns structured content with items — asserts StructuredContent is {"items": [...]} per MCP spec wrapping
• resources_list as table / returns structured content from table — asserts table output also produces StructuredContent

Backward compatibility

Fully backward compatible. The Content[0].Text field is unchanged — existing clients that only read text see no difference. structuredContent is additive per the MCP spec. This is the same pattern used by configuration_contexts_list (#1151).

Checks

make build    # clean
make lint     # 0 issues
go test ./pkg/mcp/ -run "TestResources$" -v -count=1  # all pass

Refs #920

Made with Cursor

[Cali0707]

/run-mcpchecker core

[github-actions]

mcpchecker MCP Evaluation Results

Commit: b28bb03
Summary: 24/29 tasks passed (82.8%)

Metric	Result
Tasks Passed	24/29
Assertions Passed	81/87
Overall	✅ Passed

Diff vs. Baseline (main)

Click to expand mcpchecker diff

📊 Evaluation Results

Metric	Base	Head	Change
Tasks	25/29 (86.2%)	24/29 (82.8%)	🔴 -3.4%
Assertions	86/87 (98.9%)	81/87 (93.1%)	🔴 -5.7%
Tokens	1.1M	1.2M	🔴 +23.6K (+2.1%)
MCP Schema	95.5K	95.5K	➖ 0

❌ Regressions (2)

• fix-service-with-no-endpoints: PASSED → FAILED - Too many tool calls: expected <= 20, got 25
• setup-dev-cluster: PASSED → FAILED - verification failed: verify[0] failed: script execution failed: exit status 1
  output: Starting comprehensive verification of dev cluster setup...
  Checking namespaces...
  Namespace 'dev-alice' does not exist
  Cleaning up test resources...
  Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
  Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
  Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
  Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
  Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
  Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
  Cleanup complete.

View full results

[Cali0707]

LGTM, thanks @jordigilh !