Add step-authoring actions: headers, variables, and scripts (#29)

* Fix missing return for unsupported body_type in add_body_to_step

An unsupported body_type constructed the error BaseResult but did not
return it, so execution fell through and PUT the step with an empty
body and no Content-Type header.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2Ym1SshabyXjWNdeGFDfx

* Fix copy-pasted error message in add_assertion_to_step

The non-request-step guard reported "cannot have a body added" when
rejecting an assertion.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2Ym1SshabyXjWNdeGFDfx

* Emit Content-Type header values as arrays in add_body_to_step

The REST API documents header values as arrays of strings
(e.g. {"Content-Type": ["application/json"]}); bare strings relied
on undocumented server leniency.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2Ym1SshabyXjWNdeGFDfx

* Add step authoring actions: headers, variables, and scripts

New actions on the steps tool, following the existing read-modify-PUT
mutation pattern with the request-step guard:

- add_headers_to_step: merge request headers into an existing step.
  Values are normalized to arrays per the REST API contract; a new
  header replaces an existing one whose name matches case-insensitively.
- add_variable_to_step: append an extraction variable ({name, source,
  property}) for passing response values to later steps. Source is
  validated against the documented enum and property is required for
  header/JSON/XPath sources.
- add_script_to_step: append a pre-request (before_scripts) or
  post-response (scripts) JavaScript snippet, control-char sanitized.

add_request_step now accepts optional headers and note so a complete
step can be created in a single POST.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2Ym1SshabyXjWNdeGFDfx

* Document new step-authoring capabilities in README

Reflect the headers, variables, scripts, and note support added to
the steps tool: the Test Step Management use-case list and the
blazemeter_apitest_steps tool summary previously described only
Pause/Request creation with Body and Assertions.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2Ym1SshabyXjWNdeGFDfx

* Address Copilot review: validate note type, scope variable_property

- add_request_step: reject non-string note with a clear validation
  error instead of falling through to the generic unexpected-error;
  strip the sanitized note.
- add_variable_to_step: validate variable_property is a string when
  provided, strip it, treat whitespace-only as missing, and only send
  "property" for sources that require it (dropped for response_status
  and response_text, matching the tool contract).
- Docstring: note must be a string; variable_property is ignored for
  sources that do not use it.
- Tests: 5 new cases covering the above.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ULzi7DRzKEuqaSEiJf3Few

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: benjithompson

README.md

@@ -34,7 +34,10 @@ This gives AI agents, assistants, and chatbots the ability to read and manage te
 **Test Step Management**
 - List all steps within a test to understand its workflow and structure.
 - Retrieve a single step’s details to inspect API request/response configuration, conditions, and validations.
-- Create a new test step (Pause or Request) to modify or extend test workflows.
+- Create a new test step (Pause or Request), optionally with headers and a note set in the same call, to modify or extend test workflows.
+- Add or update request headers, and attach a JSON, XML, HTML, or text body to a request step.
+- Extract values from a response into variables, and add pre-request or post-response scripts, to chain data between steps.
+- Add assertions to a step to validate response status, timing, size, or body content.
 
 > [!NOTE]
 > **For detailed documentation including use cases, available tools, integration points, and troubleshooting, see the [BlazeMeter API Test MCP Server documentation](https://help.blazemeter.com/docs/guide/integrations-api-monitoring-mcp-server.html).**
@@ -230,7 +233,7 @@ The BlazeMeter API Test MCP Server provides the following tools for interacting
 - `blazemeter_apitest_buckets`: List all the buckets, Read bucket details, and Create a new bucket.
 - `blazemeter_apitest_tests`: List all API tests within a bucket, Read test details, Create a new API test, and Get the test metrics.
 - `blazemeter_apitest_schedules`: List all schedules within a test, Read schedule details, and Create a new schedule.
-- `blazemeter_apitest_steps`: List all steps within a test, Read test step details, and Add a new Pause and Request step( with URL, Method, Body and Assertions) to a test.
+- `blazemeter_apitest_steps`: List all steps within a test, Read test step details, Add a new Pause or Request step (with URL, Method, Headers, and Note), and add a Body, Assertion, Header, extraction Variable, or pre/post Script to an existing request step.
 - `blazemeter_apitest_environments`: List all test environments, and Read test environment details.
 - `blazemeter_apitest_results`: Execute an individual test or all bucket-level tests, List last 50 test results, and Read test result and bucket-level result details.