feat(security): add sandboxed mfe container and dynamic csp generator

[Dopezapha]

Closes #600
Closes #576

PR Description

This pull request implements two security-focused frontend features for SoroTask: a sandboxed Micro-Frontend (MFE) container and a dynamic Content Security Policy (CSP) header generator. Both features have been designed to enforce strict security boundaries, handle edge cases resiliently, provide observability hooks, and satisfy 100% of their respective acceptance criteria.

Issue #600: [Frontend] Develop Secure Micro-Frontend (MFE) Container Application

Implementation & Fixes Details

• Resilient Heartbeat & Timeout Mechanism: Since standard error events on HTML <iframe> elements do not fire reliably for cross-origin network errors, 404s, or remote application crashes, a custom handshake design was implemented. The container initializes a configurable timer (initTimeoutMs, default 5 seconds) on mount. The child micro-frontend must notify the parent container by posting a MFE_READY or HEARTBEAT message within this time frame. Once received, the timer is cleared, and the loading spinner is unmounted. If the timer runs out before receiving a valid heartbeat, the container unmounts the iframe and renders the fallback UI.
• Explicit Error Handover: Whitelisted child micro-frontends can explicitly post an MFE_ERROR message to indicate an internal application failure. Upon receipt of this message, the container immediately unmounts the iframe and presents the fallback UI.
• Strict Origin Whitelisting: Any incoming message event is filtered against a whitelisted array of origins. Messages from unauthorized origins are logged as warnings and rejected immediately.
• Sandboxed Execution Boundary: The iframe sandbox attributes are restricted to allow-scripts allow-same-origin allow-forms allow-popups to prevent top-level navigation, parent hijacking, or other elevated access.
• Referrer Policy: Set to no-referrer to prevent passing authentication tokens or sensitive path metadata in outbound request headers.

Acceptance Criteria Verification

• Feature implemented according to requirements: Yes. Sandboxed boundary, origin validation, and the heartbeat-based error handling are fully operational.
• Unit and integration tests passing: Yes. Jest tests cover loaders, error signaling, timeout fallback, whitelists, and event cleanup.
• Security review completed: Yes. Applied strict sandbox limitations, referrer headers, and origin check boundaries.
• Comprehensive documentation written: Yes. Time/space complexities and architectural choices have been documented in frontend/docs/mfe-container.md.

Issue #576: [Frontend] Implement Content Security Policy (CSP) Dynamic Generator

Implementation & Fixes Details

• Directive Dictionary Builder: Programmatically builds policy string using a dictionary of core directives (including default-src 'self', object-src 'none', frame-ancestors 'none', and upgrade-insecure-requests).
• Dynamic Nonce Injection: Supports generating script-src policies using cryptographically secure script nonces ('nonce-<token>') to allow trust-anchored inline scripts when using strict-dynamic.
• Environment-Aware Exceptions: Automatically checks if process.env.NODE_ENV is set to development (or reads a passed override flag) to append 'unsafe-eval' and 'unsafe-inline', which are required for Vite/Webpack hot module reloading.
• Observabilities & Violation Reporting: Supports appending the report-uri directive to the CSP header, allowing browsers to post JSON violation reports to the specified endpoint when a policy breach occurs.
• Directive Merging & De-duplication: Features an extraDirectives parameter allowing developers to merge additional application-specific paths or domains while automatically deduplicating existing array values.

Acceptance Criteria Verification

• Feature implemented according to requirements: Yes. Programmatic generator supporting nonces, environment flags, extra directive merges, and report-uri violation tracking.
• Unit and integration tests passing: Yes. Jest tests cover basic header outputs, nonces, dev-mode alterations, custom directives, and report-uri formatting.
• Security review completed: Yes. Defaulted to strict directives, disabled object-src/frame-ancestors, and enforced upgrade-insecure-requests.
• Comprehensive documentation written: Yes. Documented generator structure and O(D + E) complexity in frontend/docs/csp-generator.md.

Changes Made

• Created frontend/components/mfe-container.tsx containing the sandboxed iframe container and postMessage/heartbeat validation logic.
• Created frontend/components/__tests__/mfe-container.test.tsx verifying sandbox attribute assignment, loading indicators, trusted message handling, untrusted message rejection, timeout fallback, and message-driven error handling.
• Created frontend/lib/csp-generator.ts with options for script nonces, dev mode bypasses, custom directives, and report-uri violation tracking.
• Created frontend/lib/__tests__/csp-generator.test.ts testing base generation, nonce injection, development flags, custom directive merging, and report-uri construction.
• Created frontend/docs/mfe-container.md and frontend/docs/csp-generator.md to house the architectural and security documentation for each issue.
• Modified frontend/jest.config.js to include the components and lib directories in Jest's matching patterns so that the new test suites run.

Testing

• Jest tests executed successfully using:

  npx jest components/__tests__/mfe-container.test.tsx lib/__tests__/csp-generator.test.ts --coverage --collectCoverageFrom='components/mfe-container.tsx' --collectCoverageFrom='lib/csp-generator.ts' --coverageReporters=text

• Result: Both files successfully passed verification with >97% code coverage:

  PASS  components/__tests__/mfe-container.test.tsx
  PASS  lib/__tests__/csp-generator.test.ts
  

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