fix: allow runtime custom step inputs

[yottahmd]

Summary

• allow custom step type inputs to use runtime expressions while preserving static DAG validation
• keep non-string typed inputs conservative by requiring whole-value runtime expressions
• split deferred custom-step validation helpers into a focused file with unit coverage

Testing

• go test ./internal/core/spec -count=1
• go test ./internal/core/spec ./internal/service/frontend/api/v1 ./internal/intg -run 'TestValidateCustomStepInput_DefersRuntimeExpressionLeaves|TestCustomStepTypes|TestUpdateDAGSpec_AllowsCustomStepTypeRuntimeVariableInput' -count=1
• go test ./internal/service/frontend/api/v1 -count=1

Summary by CodeRabbit

• New Features

  • Custom step types now accept runtime variable placeholders (e.g., ${COUNT}) in inputs across non-string and string fields; placeholders are preserved at config/load time and expanded at execution.

• Bug Fixes

  • Validation now defers for inputs that are standalone runtime placeholders, preventing false validation failures when using runtime variables.

• Tests

  • Added unit, integration, and API tests covering deferred validation, YAML loading with placeholders, and runtime expansion during execution.

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📝 Walkthrough

Walkthrough

Adds deferred JSON Schema validation for custom step inputs: on strict-validate failure, constructs a relaxed schema that permits whole-string runtime-expression placeholders (e.g., ${COUNT}, $VAR, backtick tokens) and revalidates; if relaxed validation succeeds, input is accepted unchanged.

Changes

Cohort / File(s)	Summary
Core validation update internal/core/spec/step_types.go	Call strict validation first; on failure attempt secondary validation using a relaxed schema that allows runtime-expression placeholders.
Deferred validation implementation internal/core/spec/step_types_deferred_validation.go	New implementation: regex detection for runtime-expression tokens, schema-cloning and recursive relaxation for object/array/string nodes, and helper canDeferCustomStepInputValue logic to decide deferral eligibility.
Unit tests (deferred validation) internal/core/spec/step_types_deferred_validation_test.go	New table-driven tests asserting whole-string runtime expressions defer validation across multiple schema types and nested structures; embedded expressions and invalid typed values remain rejected.
Feature tests (YAML/load behavior) internal/core/spec/step_types_feature_test.go	New feature tests asserting YAML loads with runtime placeholders for non-string-typed inputs when using WithoutEval(), and failing when placeholders are embedded within other text.
Integration tests internal/intg/step_types_test.go	Added end-to-end tests ensuring runtime-variable inputs expand at execution time for custom step types and templates.
API tests internal/service/frontend/api/v1/dags_internal_test.go	Added test verifying UpdateDAGSpec accepts spec updates that include custom step types with runtime-variable config values (e.g., count: ${COUNT}) without error.

Sequence Diagram(s)

(omitted)

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• feat(spec): add build-time custom step types #1987 — Extends custom-step input validation logic and introduces deferred/relaxed schema handling for runtime-expression placeholders; touches the same validation area and helper logic.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: allow runtime custom step inputs' clearly and concisely summarizes the main change: enabling runtime expressions in custom step inputs while preserving static validation.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/custom-step-validation

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[yottahmd]

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