Validate notification batches before processing to detect malformed r…

[Johnsource-hub]

#closes
#82

Description

This PR implements an off-chain notification batch validation service within the listener/ application workspace. It introduces an early-gating validation mechanism to intercept, audit, and sanitize raw event notifications before they are queued for dispatch providers (e.g., Discord webhooks).

Problem Statement

• Issue: The listener pipeline lacked upfront validation for heavy notification processing bursts.
• Impact: Malformed event blocks or redundant network operations (such as duplicate recipient event targets) could bypass early processing layers, resulting in failed webhook payloads or inefficient system thrashing.

Technical Changes

• Implemented BatchValidator runtime utility matrix inside listener/src/utils/batch-validator.ts.
• Added explicit structure checks to verify that input batches are non-empty arrays with intact id, recipient, channel, and message strings.
• Built in-memory tracking sets (Set<string>) to isolate and intercept duplicate recipient IDs inside a single batch execution window.
• Introduced a terminal runner engine (runTerminalSimulation()) that logs human-readable verification steps and dumps processing results locally.
• Appended validate:batch automation shortcut script to the local listener/package.json manifest.

Affected Areas

• listener/src/utils/batch-validator.ts (Core validation service logic)
• listener/package.json (Script shortcuts configuration)
• listener/reports/last-validation-run.json (Local output report tracking — gitignored if applicable)

Verification & Acceptance Criteria

• Batch Structure Validation: Malformed array formats or empty payloads throw immediate, descriptive block alerts.
• Duplicate Filtering: Multi-item bursts targeted at the same user/channel endpoint flag warning validations instantly.
• Actionable Error Arrays: Rejections explicitly isolate item index numbers (e.g., Item at index [1]) to speed up troubleshooting context.
• IDE Execution Integration: Automation script successfully creates, maps, and updates files directly inside the active VS Code workspace tree pane.

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Security & Performance Safeguards

Batch Throttling Enforcement: By filtering duplicate targets and dropping empty structures before calling remote HTTP endpoints, this service acts as a buffer layer—preventing rate-limiting blocks from third-party notification APIs.