fix(mcp): block build --push in read-only MCP mode

[Ankitsinghsisodya]

Note: Re-submission of #3741, accidentally closed when the head repository was deleted.

Summary

When the MCP server runs in read-only mode (default unless FUNC_ENABLE_MCP_WRITE enables writes), deploy and delete are already rejected. build with push: true could still push images to a registry. This change rejects that path with a clear error.

Motivation

Read-only mode is meant to avoid mutating external state. Pushing a built image to a registry is such a mutation and should align with the same policy as deploy/delete.

Changes

• pkg/mcp/tools_build.go: in buildHandler, return an error when s.readonly is true and the tool input requests push (Push != nil && *input.Push).

Testing

• go test ./pkg/mcp/... or make test

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Ankitsinghsisodya
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[knative-prow]

Hi @Ankitsinghsisodya. Thanks for your PR.

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a guard to prevent image pushes when the MCP server is running in read-only mode.

Changes:

• Short-circuits buildHandler when input.Push is explicitly enabled while s.readonly is true
• Returns a user-facing error message instructing how to enable write mode for pushing images

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[knative-prow]

@Ankitsinghsisodya: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
unit-tests_func_main	85c2957	link	true	/test unit-tests

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