E24: Code Hygiene #254

Overview

Non-functional improvements to the codebase as a unit. Cross-cutting work
that protects properties of the code — how it's built, organised,
structured — rather than adding capabilities.

These items are typically too large to land as one-off chore PRs but don't
fit under any feature epic. They're rails, gates, and uniform pattern
adoption that improve quality and resilience without changing what the
library does.

In scope

• CI gates that protect non-functional invariants (include hygiene,
  layering, language version)
• Cross-cutting refactors that apply patterns uniformly (e.g. Nil Object
  adoption across abstractions)
• Other code-quality work that doesn't belong under a capability-focused
  epic

Out of scope

• Anything covered by a feature epic — stays where it is
• One-off chore PRs that don't need a tracked story (small refactors,
  dependency bumps, formatter changes)
• Static analysis and MISRA tooling — covered by E10
• Documentation tooling — covered by E23

Candidate ideas

Ideas live here until commitment. Each becomes a story (added to the table
below) only when scope is clear and we're ready to do the work. New ideas
are added as comments before promotion.

• Resource-leak detection in tests — every test group exercising a
  class that owns an external resource installs a balance counter in
  setup/teardown that asserts the resource is fully released by
  end-of-test. Drives out Open()-without-Close() leaks (symptom: S26.02: MbedTlsStream Open() unwinds inner transport and SSL state on failure #420
  / S26.02) and surfaces the wider class of missing failure-path tests.
  Balance counter lives in the fake (e.g. SocketFake.openFdCount); the
  first per-class story to touch a shared fake also retrofits the
  assertion to every other TEST_GROUP that uses it. Per-class story,
  raised when picked up. Classes to cover (no particular order):
  • share SocketFake: PosixTcpStream, PosixDatagram, PosixResolver
  • share WinsockFake: WinsockTcpStream, WinsockDatagram, WinsockResolver
  • share FreeRTOS net fakes: FreeRtosTcpStream, FreeRtosDatagram
  • share lwIP fakes: LwipRawTcpStream, LwipRawDatagram
  • OpenSslStream (OpenSslFake)
  • MbedTlsStream (MbedTlsFake)
  • PosixFile, WindowsFile, FatFsFile
  • PosixMessageQueueBuffer (mq_t open/close/unlink)
    Plus an integration-harness fd-balance check across N forced-failure
    cycles per platform. Closes the scope of S26.02: MbedTlsStream Open() unwinds inner transport and SSL state on failure #420 (its two specific fixes
    fall out of the OpenSslStream and MbedTlsStream stories).

Stories

The last three were raised as standalone chores and linked here during the
pre-0.1.0 issue audit so they sit in this epic's swimlane rather than off the
board. They keep their chore titles rather than being renumbered as stories.

Resolved candidates

Recorded so they are not re-proposed:

• C99 portability gate — delivered. build-linux-c99 builds Core against a
  dedicated c99 preset and then checks the platform packs, with a C89 public
  header check alongside it. S24.16 did the source work; the lane keeps it honest.
• IWYU cost versus value (comment below) — settled. Of the six directions
  listed, "downgrade IWYU to advisory" was chosen and shipped as S24.13, and the
  lanes cite it. IWYU is advisory in CI and is not part of any pre-push budget.