2.4 — Software Engineering Foundations

CCDV-F Domain 2 · Task 2.4

What You Need to Know

Bounded Concurrency

Serial loop wastes the rate limit. Unbounded fan-out trips the token-bucket limiter and turns the run into a 429 storm. Correct shape: worker pool or semaphore sized against documented RPM/ITPM/OTPM headroom. Transient failures retried with jittered exponential backoff honouring retry-after.

SDKs already retry twice by default — a hand-rolled loop that ignores this multiplies attempts. Set max_retries=0 when hand-rolling. OTPM counts tokens generated; lowering max_tokens is no rate-limit lever. Monthly spend-cap 429 has no retry-after and error_code enforced_spend_limit_reached — no retry clears it.

Concurrency or Batch: the Deadline Decides

Results needed within hours → realtime with bounded concurrency. Results acceptable within a day, cost the main concern → batch.

Prompts Are Source Code

A prompt change is a behaviour change with the blast radius of a code change. Live in the repository, change through branches and review, carry history and roll back like code. Eval suite is the regression gate.

Review and Refactoring Discipline

AI-assisted diffs get the same review bar as human ones. Green tests do not prove behaviour unchanged when no test pinned that behaviour. Small refactors go in behaviour-preserving steps. Large work on a poorly covered module first builds characterisation tests, then migrates incrementally.

Exam Traps

• Retrying immediately in a tight loop to clear a 429 storm
• Lowering max_tokens to relieve rate-limit pressure or cut costs
• Skipping human review of AI-generated changes because the tests pass
• Rewriting an under-tested module in one atomic pass with a contract change bundled in