feat: Admin Decomposition Phase D — pre-processing steps for domain routes (#88)

[intel352]

Summary

Implements Phase D+ of the admin config decomposition (issue #88): adds pre-processing pipeline steps before delegation for key domain routes.

New Pipeline Step Types

Three new config-driven pipeline step types registered in the pipelinesteps plugin:

Step Type	Purpose
step.validate_path_param	Validates path parameters exist and match a format (e.g. UUID)
step.validate_pagination	Validates/normalises page/limit query params with configurable defaults and max
step.validate_request_body	Parses JSON request body and validates required fields are present

Updated Admin Routes

Pre-processing steps added before delegation on 7 routes:

Execution routes (admin-queries):

• GET /executions — pagination validation (max 100, default 20)
• GET /executions/{id} — UUID format validation on path param
• GET /executions/{id}/steps — UUID validation + pagination validation

DLQ routes (admin-commands):

• POST /dlq/{id}/retry — path param parse → UUID validation → rate limit (30/min)
• POST /dlq/{id}/discard — path param parse → UUID validation → rate limit (30/min)

Engine routes (admin-commands):

• POST /engine/reload — rate limit (5/min, burst 2) → audit log before delegate
• POST /engine/validate — request body validation (requires config field)

Testing

• All new step types have comprehensive unit tests
• All existing tests pass (go test ./...)
• golangci-lint run reports 0 issues

Closes #88

[Copilot]

Pull request overview

This PR implements Phase D+ of the admin config decomposition by adding three new pre-processing pipeline step types (step.validate_path_param, step.validate_pagination, step.validate_request_body) and applying them to 7 domain routes in the admin API configuration.

Changes:

• Three new pipeline step types registered in the pipelinesteps plugin for input validation before delegation
• Pre-processing steps added to engine management routes (body validation, rate limiting, audit logging)
• Pre-processing steps added to execution query routes (UUID validation, pagination validation)
• Pre-processing steps added to DLQ command routes (UUID validation, rate limiting)

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
plugins/pipelinesteps/plugin.go	Registered three new step types and updated plugin description/manifest
plugins/pipelinesteps/plugin_test.go	Updated test expectations to reflect 16 total step factories
module/pipeline_step_validate_path_param.go	Implemented path parameter validation with UUID format checking
module/pipeline_step_validate_path_param_test.go	Comprehensive tests for path parameter validation
module/pipeline_step_validate_pagination.go	Implemented pagination query parameter validation with defaults
module/pipeline_step_validate_pagination_test.go	Comprehensive tests for pagination validation
module/pipeline_step_validate_request_body.go	Implemented JSON body parsing and required field validation
module/pipeline_step_validate_request_body_test.go	Comprehensive tests for request body validation
admin/config.yaml	Added pre-processing steps to 7 admin routes (engine validate/reload, executions list/get/steps, DLQ retry/discard)
plugins/api/plugin.go	Formatting change (multi-line constructor for newWorkflowRegistry)
module/query_handler_test.go	Removed trailing blank line
module/command_handler_test.go	Removed trailing blank line