TBI - Refactor: reduce architectural friction in @sap-ux/cf-deploy-config-writer MTA config layer

[longieirl]

Description (include screenshots)

Four independent internal refactors to @sap-ux/cf-deploy-config-writer that reduce complexity and eliminate architectural friction in the MTA configuration layer. No public API or mta.yaml output is affected.

Candidate 2 — AppRouter Orchestration (appendAppRouter)
appendAppRouter() in app-config.ts was mutating cfConfig at four separate points interleaved with async MTA calls, making the final state hard to reason about. destinationName is now resolved upfront and all cfConfig mutations are grouped into a single block after MTA state is finalised. An early-return guard replaces the wrapping if (mtaInstance) block.

Candidate 3 — Hardcoded MTA Timing Delays
getMtaConfig() and generateCAPConfig() used fixed setTimeout delays (up to 5 × 1000 ms) to work around @sap/mta-lib requiring mta.yaml to be fully written before it can be parsed. Replaced with waitForMtaFile() — a predicate-based poller that returns as soon as the file is ready. New file: src/mta-config/wait-for-mta.ts.

Candidate 4 — Global BTP Destinations Cache
getBTPDestinations() and getDestinationProperties() in utils.ts used a module-level variable to cache BTP destinations for the lifetime of the process, causing cross-test contamination and preventing mid-session refresh. The module-level variable is removed; both functions now accept an optional cache parameter scoped to the call site. Backwards-compatible — existing callers are unaffected.

Candidate 5 — Scattered Template Rendering
EJS template rendering (readFileSync + render + writeFileSync) was duplicated across mta.ts and index.ts with hardcoded __dirname-relative paths inside business logic. Consolidated into a single renderTemplateToDisk() function in src/mta-config/template-renderer.ts, making the intentional mem-fs bypass explicit and documented.

Value

• Maintainability: Each change narrows the scope of individual functions and files, reducing the cost of future modifications.
• Quality: Eliminates hidden side-effects (scattered mutations, process-wide cache, silent delays) that have caused test-order dependencies and hard-to-diagnose failures.
• Testability: New units (waitForMtaFile, renderTemplateToDisk, scoped cache) are independently testable without full MTA fixture setup.

Architecture Elaboration

No. All changes are internal to @sap-ux/cf-deploy-config-writer. Public API signatures (generateAppConfig, generateBaseConfig, generateCAPConfig) and mta.yaml output format are unchanged.

Notes

• Each candidate is on its own isolated branch with a changeset; they can be reviewed and merged independently.
• The MtaConfig god-class decomposition (Candidate 1 — MtaDeployment builder) is a larger change and is tracked separately.
• Branches:
  • refactor/cf-deploy-config-approuter-mutations
  • refactor/cf-deploy-config-hardcoded-delays
  • refactor/cf-deploy-config-btp-destinations-cache
  • refactor/cf-deploy-config-template-rendering

Tasks

• Review and merge refactor/cf-deploy-config-approuter-mutations — group cfConfig mutations in appendAppRouter
• Review and merge refactor/cf-deploy-config-hardcoded-delays — replace hardcoded MTA delays with predicate-based polling
• Review and merge refactor/cf-deploy-config-btp-destinations-cache — scope BTP destinations cache to call site
• Review and merge refactor/cf-deploy-config-template-rendering — consolidate disk-write template rendering