S29.03: Extract shared FreeRTOS BDD-target pipeline; main.c keeps only network wiring

[DavidCozens]

Parent epic: #512 (E29) · Depends on: S29.01 (done). Independent of S29.04.

Motivation

S29.01 deliberately duplicated the store/security-policy/lifecycle machinery into Bdd/Targets/FreeRtosLwip/main.c rather than DRY it then. The two FreeRTOS target main.c files (1258 + 1111 lines) now share ~600 lines near-verbatim — every store/policy function, the whole OnSet body, the Service task, the SD setup, ErrorHandlerEx, and the message-state globals. The only genuine divergence is the network backend (PlusTcp vs LwipRaw adapter wiring + platform bring-up) and GetHostname (different IP-stack read). Extract the shared surface so a future change (e.g. S29.05's Plus-FAT swap, a new store policy) is made once, not twice-in-sync.

Approach (agreed): one focused refactor

New Bdd/Targets/Common/BddTargetFreeRtosPipeline.{c,h} owning everything platform-independent:

• State: message globals (appName/msgid/msg/port/…), SD handles + sdList + atomicCounter, CircularBuffer + mutex + ring, lifecycle mutex, solidSyslog + config + ready/teardown flags, all store/policy state.
• Functions: the helpers, all store/policy lifecycle (RebuildWithFileStore, EnsureFatFsMounted, Create/DestroySecurityPolicy, DestroyCurrentStore, callbacks), the full OnSet, ServiceTask, ErrorHandlerEx, GetAppName/TimeQuality/Endpoint/EndpointVersion, SemihostingExit, the SD/config assembly, and the InteractiveTask body.

Each main.c shrinks to the platform seam — it injects the built switchingSender (its PlusTcp / LwipRaw adapters), a GetHostname callback (reads its IP stack), and a sender-teardown callback, then runs the shared pipeline. main(), IP/tcpip bring-up, hooks, and adapter construction stay in main.c.

Acceptance criteria

• Shared pipeline TU in Bdd/Targets/Common/; both targets link it; the ~600 duplicated lines exist once.
• Each main.c retains only network wiring + the injected seam (GetHostname, sender build, sender teardown).
• Both FreeRTOS targets cross-build clean; no Platform/PlusTcp symbols in the lwIP ELF.
• Full BDD suite green on both targets (the Tier-3 safety net), incl. the @store suite from S29.01.
• No behaviour change — pure refactor.

Out of scope

• The Plus-FAT swap (S29.05); Platform/PlusFat/ (S29.04); any library/Tier-1/2 code.

Environments

freertos-cross (both targets) + docker-compose BDD oracle run for validation.