feat(json_response): support _from references for raw value injection in body templates

[Copilot]

• Add tests for _from references in step.json_response body
• Implement resolveBodyValue method on JSONResponseStep to handle _from map references
• Modify resolveResponseBody to use resolveBodyValue for nested _from resolution
• Add test for _from inside arrays (TestJSONResponseStep_BodyFromRefInArray)
• Improve resolveBodyValue doc comment explaining _from semantics and limitation
• Fix staticcheck SA4006 linter error (unused exists variable in missing-path test)
• Verify with linting and tests

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[Copilot]

Pull request overview

This PR adds support for _from references in step.json_response body templates to inject raw values from pipeline context without stringification. This enables composing multi-field API responses like {data: [...rows], meta: {total: N}} where data contains an array of objects rather than a stringified representation.

Changes:

• Introduced resolveBodyValue method that recursively processes body values with special handling for {"_from": "path.to.value"} maps
• Modified resolveResponseBody to use per-key resolveBodyValue instead of ResolveMap to enable raw value injection throughout the body tree
• Added comprehensive test coverage for the new feature including nested structures, missing paths, and composite responses

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
module/pipeline_step_json_response.go	Implements recursive resolveBodyValue method that detects _from references (single-key maps) and injects raw values; replaces ResolveMap with manual iteration
module/pipeline_step_json_response_test.go	Adds three test cases covering basic _from usage, nested structures with mixed literal/reference values, and missing reference paths

[intel352]

@copilot apply changes based on the comments in this thread

address all linter errors, ensure all tests pass.

[intel352]

@copilot I'm still seeing linter errors

[Copilot]

@copilot I'm still seeing linter errors

Fixed in commit 52d5ad7 — the SA4006: this value of exists is never used staticcheck error in TestJSONResponseStep_BodyFromRefMissingPath was removed by replacing the unused if _, exists := body["data"] check with _ = body["data"].