Feat: fpc-fsc extension submodule

[PsychoPunkSage]

What this PR does / why we need it:

This PR migrates all FPC-related FSC (Fabric Smart Client) code out of the FSC repository and into FPC as a new extension/fsc submodule, resolving the cyclic dependency introduced by FSC importing parts of the FPC client SDK.

The changes include:

• New extension/fsc submodule: Hosts the FPC platform services (platform/fabric/services/fpc/) and NWO integration helpers (integration/nwo/fabric/fpc/, integration/nwo/fabric/topology/) previously living inside FSC.
• New echo integration test (integration/go_chaincode/echo/): End-to-end test that exercises the new extension submodule.
• Updated topology files: All topology.go files across auction, kv_test, simulation, IRB demo, and the simple testing network now import FPC topology helpers from extension/fsc instead of FSC internals. SDK import path updated from platform/fabric/sdk to platform/fabric/sdk/dig to align with post-PR-696 FSC structure.
• Updated test files: All integration test entrypoints now explicitly call ii.RegisterPlatformFactory(fpcnwo.NewPlatformFactory()) since FSC PR Go support #696 removed the built-in FPC platform registration from FSC.
• Updated view/client files: All FPC service imports redirected from fabric-smart-client/platform/fabric/services/fpc to extension/fsc/platform/fabric/services/fpc.
• Updated go.mod files: extension/fsc added as a direct dependency with local replace directives pointing to the post-PR-696 FSC clone until the upstream commit is available via a real pseudo-version.

After this PR, users who want to use FPC with FSC applications simply import FSC core + the extension/fsc submodule and wire it in via topology.go, no FPC code lives in FSC anymore.

Which issue(s) this PR fixes:
Fixes #784

Special notes for your reviewer:

• The companion change on the FSC side is hyperledger-labs/fabric-smart-client#696 (remove fpc). That PR is now merged and released as v0.11.0, all go.mod files in this PR reference the real upstream version; no local replace directives for FSC remain.
  • extension/fsc is a standalone Go module (go.mod at extension/fsc/go.mod) - Dependabot will not see it from the root. Keep this in mind for future dependency bumps.
  • The integration/go_chaincode/echo/ test is the primary validation path for this migration; it exercises the full extension wiring end-to-end.
  • go mod tidy on all affected modules auto-upgraded the Go toolchain requirement to 1.26.3 (minimum required by FSC v0.11.0).

How I tested:
Ran the echo FSC integration test from integration/go_chaincode/ with Fabric binaries (FAB_BINS) pointing to Fabric v3.1.4:

export FAB_BINS=<path-to-fabric-v3.1.4-binaries>
GOLANG_PROTOBUF_REGISTRATION_CONFLICT=warn go test -v -timeout 20m ./echo/...

Result:

Ran 2 of 2 Specs in 224.877 seconds
SUCCESS! -- 2 Passed | 0 Failed | 0 Pending | 0 Skipped
--- PASS: TestEndToEnd (224.88s)
ok  github.com/hyperledger/fabric-private-chaincode/integration/go_chaincode/echo  224.970s

Does this PR introduce a user-facing changes and/or breaks backward compatability?:

Yes. Any user currently using FPC with FSC must update their code:

1. Import paths - FPC service and topology helpers have moved out
   of FSC:

   Old (FSC)	New (extension/fsc)
   github.com/hyperledger-labs/fabric-smart-client/platform/fabric/services/fpc	github.com/hyperledger/fabric-private-chaincode/extension/fsc/platform/fabric/services/fpc
   github.com/hyperledger-labs/fabric-smart-client/integration/nwo/fabric/topology (FPC helpers)	github.com/hyperledger/fabric-private-chaincode/extension/fsc/integration/nwo/fabric/topology
   github.com/hyperledger-labs/fabric-smart-client/platform/fabric/sdk	github.com/hyperledger-labs/fabric-smart-client/platform/fabric/sdk/dig

2. New dependency - Add extension/fsc to your go.mod: require github.com/hyperledger/fabric-private-chaincode/extension/fsc v

3. Platform factory registration - Tests must now explicitly register the FPC platform factory (previously done implicitly by FSC):

ii.RegisterPlatformFactory(fpcnwo.NewPlatformFactory())

where fpcnwo is: import fpcnwo "github.com/hyperledger/fabric-private-chaincode/extension/fsc/integration/nwo/fabric/fpc"

[PsychoPunkSage]

Addressing the protobuf namespace conflict (rwset.TxReadWriteSet already registered) #958

The CI failure in the IRB and echo integration tests is caused by a protobuf namespace conflict. Two packages define the same proto message types and end up in the same binary:

• fabric-protos-go@v0.3.0: pulled in by FPC's client_sdk -> internal/utils (old API)
• fabric-protos-go-apiv2: pulled in by FSC v0.11.0 (new API)

Added GOLANG_PROTOBUF_REGISTRATION_CONFLICT=warn to the go test invocations in integration/go_chaincode/echo/Makefile and samples/demos/irb/Makefile. This is the officially documented bridge (https://protobuf.dev/reference/go/faq#namespace-conflict) from the Go protobuf team for exactly this migration scenario - it keeps the first registration and suppresses the panic.

[PsychoPunkSage]

CI Failure: Orderer Config Incompatibility (FSC v0.11.0 ↔ Fabric 2.5.9)

The IRB demo integration test panics during orderer startup: failed to parse config: Error unmarshalling config into struct: 1 error(s) decoding:

• 'General' has invalid keys: Backoff, Throttling panic: Timed out after 60.000s.

Root cause

FSC v0.11.0 generates orderer config via its NWO template (integration/nwo/fabric/topology/orderer_template.go) which includes two keys under General:

General:
  Throttling:
    Rate: 0
    InactivityTimeout: 5s
  Backoff:
    BaseDelay: 1s
    Multiplier: 1.6
    MaxDelay: 2m

These keys were introduced for Fabric v3.x. FPC's CI currently pins to Fabric 2.5.9 (config.mk, utils/docker/dev/Dockerfile) which does not recognize them -> causing the orderer to refuse startup.

Why we can't just pin FSC to an older version
FSC PR #696 (hyperledger-labs/fabric-smart-client#696) (which removed FPC code from FSC — the change this PR receives on the FPC side) landed in FSC v0.11.0. There is no FSC version that is both:

• ✅ After PR Go support #696 (FPC code removed from FSC)
• ✅ Compatible with Fabric 2.5.9 orderer config

They came together. Pinning to an older FSC means shipping an integration against a version where FSC still contains FPC internals - defeating the purpose of this PR.

Fix required

Upgrade FPC's pinned Fabric binary from 2.5.9 → 3.1.4 in:

• config.mk (FABRIC_VERSION)
• utils/docker/dev/Dockerfile
• utils/docker/dev_peer_cc-builder/Dockerfile

The echo integration test was already validated locally against Fabric 3.1.4:

Ran 2 of 2 Specs in 224.877 seconds
  SUCCESS! -- 2 Passed | 0 Failed | 0 Pending | 0 Skipped

This upgrade is the correct long-term move to align FPC with FSC v0.11.0+, but since it touches all of FPC's CI (not just the new tests), it warrants a deliberate review decision. Happy to include it in this PR or track it as a follow-up looking for guidance.