feat(mcp): integrate tools with functions.Client API instead of CLI shell-out

[vishwas-droid]

Summary

• Replace MCP tool handlers that shelled out to the func binary with a native Service layer backed by functions.Client
• Wire cmd/mcp start to construct clients via the existing ClientFactory, decoupling MCP startup from WithMCPServer on the same client instance
• Add four new MCP tools: describe, invoke, run, and logs
• Return structured JSON outputs from tool handlers (e.g. BuildOutput.Image, DeployOutput.URL, ListOutput.Functions) instead of parsing CLI stdout

Help resources (func://help/*) and templates listing continue to use CLI subprocess for --help text.

The MCP server had an explicit comment that shell-out should be replaced with direct functions.Client integration. The subprocess approach caused cwd/path issues (documented in pkg/mcp/instructions.md) and produced unstructured stdout that agents could not reliably parse.

Test plan

• CGO_ENABLED=0 go test ./pkg/mcp/...
• CGO_ENABLED=0 go test ./cmd/ -run MCP
• Manual: func mcp start with Cursor/Claude MCP client
• Manual: verify build, deploy, list, describe, invoke tools return structured JSON
• Manual: verify readonly mode still blocks deploy and delete

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[knative-prow]

Hi @vishwas-droid. Thanks for your PR.

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[Copilot]

Pull request overview

This PR migrates the MCP server implementation from shelling out to the func CLI toward a native Service layer backed by functions.Client, enabling structured JSON outputs for tool responses and avoiding subprocess cwd/path fragility.

Changes:

• Introduces a Service abstraction that executes MCP tool operations via functions.Client (build/deploy/list/delete/create + new describe/invoke/run/logs tools).
• Refactors MCP server startup (cmd/mcp start) to inject a client factory into the MCP server, decoupling MCP from fn.WithMCPServer(...).
• Updates MCP resources (e.g., languages, function state) to use the native service layer where possible, while keeping help/templates via CLI executor.

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
pkg/mcp/types.go	Adds ClientConfig and ClientFactory types for constructing functions.Client instances.
pkg/mcp/tools_test.go	Adds initTestFunction helper to create an initialized function for tests.
pkg/mcp/tools_run.go	Adds new run MCP tool and handler wired to the service layer.
pkg/mcp/tools_logs.go	Adds new logs MCP tool and handler wired to the service layer.
pkg/mcp/tools_list.go	Switches list tool from CLI executor output to service-backed structured output.
pkg/mcp/tools_list_test.go	Updates list tool tests to use the service-backed implementation.
pkg/mcp/tools_invoke.go	Adds new invoke MCP tool and handler wired to the service layer.
pkg/mcp/tools_describe.go	Adds new describe MCP tool and handler wired to the service layer.
pkg/mcp/tools_deploy.go	Switches deploy tool to service-backed deploy and structured output.
pkg/mcp/tools_deploy_test.go	Updates deploy tool tests (keeps readonly rejection coverage).
pkg/mcp/tools_delete.go	Switches delete tool to service-backed delete while retaining input validation + readonly behavior.
pkg/mcp/tools_delete_test.go	Updates delete tool tests (keeps readonly rejection coverage).
pkg/mcp/tools_create.go	Switches create tool to service-backed create and structured output.
pkg/mcp/tools_create_test.go	Updates create tool test to create into a temp dir via service-backed handler.
pkg/mcp/tools_config_volumes.go	Switches config volumes tools to service-backed operations.
pkg/mcp/tools_config_volumes_test.go	Updates config volumes tests to use real service-backed behavior.
pkg/mcp/tools_config_labels.go	Switches config labels tools to service-backed operations.
pkg/mcp/tools_config_labels_test.go	Updates config labels tests to use real service-backed behavior.
pkg/mcp/tools_config_envs.go	Switches config envs tools to service-backed operations (validation still present).
pkg/mcp/tools_config_envs_test.go	Updates config envs tests to use real service-backed behavior.
pkg/mcp/tools_build.go	Switches build tool to service-backed build and structured output.
pkg/mcp/tools_build_test.go	Updates build test to avoid requiring CLI executor; checks for missing factory error.
pkg/mcp/service.go	Adds the core service implementation for MCP tool operations using functions.Client.
pkg/mcp/service_test.go	Adds service-level tests for config operations + list/create basics.
pkg/mcp/resources_test.go	Adjusts resource tests for languages/templates now that languages is service-backed.
pkg/mcp/resources_language.go	Switches languages resource from CLI executor to service Runtimes().
pkg/mcp/resources_function.go	Switches function-state resource to service FunctionState().
pkg/mcp/mcp.go	Adds WithClientFactory, registers new tools/resources, and retains executor only for help.
pkg/mcp/mcp_test.go	Injects a test client factory into server construction.
pkg/mcp/client_options.go	Adds shared helpers to build functions.Client options for builders/deployers/credentials.
cmd/mcp.go	Refactors mcp start to create an MCP server with a client factory (no longer uses fn.WithMCPServer).
cmd/mcp_test.go	Updates MCP start tests to validate server startup via in-memory transports.

---

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[gauron99]

Hi, did you run anything manually? test this works as expected? worked through some scenarios yourself with the different func commands? any screenshots showing anything important? highlights?

[vishwas-droid]

@gauron99 Yes, I tested this on my machine.

I went through the main MCP tools — create, config, list, healthcheck, run, and invoke — and they all return proper structured JSON now instead of shelling out to the CLI. Readonly mode correctly blocks deploy/delete too. Unit tests pass as well.

Also fixed a few things I noticed while testing — push default, deployer from func.yaml, and deployDecorator.

Couldn't test build/deploy on a real cluster since I don't have Docker/k8s set up locally. would be good if someone with a cluster setup can give that a quick pass.

[matejvasek]

Some check are failing.

[codecov]

Codecov Report

❌ Patch coverage is 31.08108% with 663 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.19%. Comparing base (cdf3c96) to head (f795888).

Files with missing lines	Patch %	Lines
pkg/mcp/service.go	23.02%	498 Missing and 47 partials ⚠️
pkg/mcp/client_options.go	51.97%	70 Missing and 3 partials ⚠️
pkg/mcp/tools_describe.go	0.00%	7 Missing ⚠️
pkg/mcp/tools_invoke.go	0.00%	7 Missing ⚠️
pkg/mcp/tools_logs.go	0.00%	7 Missing ⚠️
pkg/mcp/tools_run.go	0.00%	7 Missing ⚠️
cmd/mcp.go	60.00%	5 Missing and 1 partial ⚠️
pkg/mcp/mcp.go	84.21%	2 Missing and 1 partial ⚠️
pkg/mcp/resources_language.go	50.00%	2 Missing and 1 partial ⚠️
pkg/mcp/tools_delete.go	0.00%	2 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3889      +/-   ##
==========================================
- Coverage   53.72%   52.19%   -1.53%     
==========================================
  Files         200      206       +6     
  Lines       23674    24469     +795     
==========================================
+ Hits        12719    12772      +53     
- Misses       9730    10400     +670     
- Partials     1225     1297      +72     

Flag	Coverage Δ
e2e	32.27% <0.00%> (-1.19%)	⬇️
e2e go	28.30% <0.00%> (?)
e2e node	24.76% <0.00%> (?)
e2e python	28.62% <0.00%> (?)
e2e quarkus	24.89% <0.00%> (?)
e2e rust	24.38% <0.00%> (?)
e2e springboot	23.11% <0.00%> (?)
e2e typescript	24.88% <0.00%> (?)
e2e-config-ci	25.92% <0.00%> (-1.01%)	⬇️
integration	15.15% <0.00%> (-0.52%)	⬇️
unit macos-14	41.53% <34.13%> (-1.28%)	⬇️
unit macos-latest	41.53% <34.13%> (-1.28%)	⬇️
unit ubuntu-24.04-arm	41.78% <31.08%> (-1.35%)	⬇️
unit ubuntu-latest	42.36% <34.13%> (-1.30%)	⬇️
unit windows-latest	41.60% <34.13%> (-1.28%)	⬇️

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[vishwas-droid]

@matejvasek @gauron99 @davidhadas @lkingland @jrangelramos PTAL.