P3: wire trusted SCL-assisted connect into Workbench product path #88

Goal

Make the already-implemented trusted-SCL MMS path a real Workbench product behavior, not only a core API.

P3 starts after P2's MmsTcpLiveDiscoverySession::synchronize_scl(...) contract. The application must deterministically choose the online model source and surface failures without silently changing model identity.

Product contract

Trusted SCL loaded

• A successfully loaded SCL/CID arms MmsClientController::trustedSclPath.
• Connect parses that exact engineering source, associates to the requested endpoint, and invokes synchronize_scl(...).
• Workbench tree topology/types come from the trusted SCL projection.
• Initial successful FC-root values are applied to their exact SCL leaves.
• Missing/failed FC roots do not delete SCL topology and do not shift values onto neighbouring leaves.
• The same MMS association remains usable by normal Read/Write/report workflows after the initial snapshot.
• Full NamedVariable/GVAA/DataSet discovery must not run silently on this path.

No trusted SCL loaded

• Connect uses the existing full live-discovery path.
• Clearing the trusted SCL source is the explicit user-controlled fallback from SCL-assisted mode to live discovery.

Invalid trusted SCL

• Fail closed and expose the error.
• Do not silently fall back to a different online model while an engineering source is explicitly armed.

Current implementation

Already present on PR #82 before this issue was opened:

• MmsClientController has trustedSclPath / trustedSclAvailable.
• trusted path invokes session->synchronize_scl(...).
• MmsSclClientProjection.hpp builds the Workbench model from SCL and initial snapshot evidence.
• Main.qml arms the path only after sclWorkspace.loaded succeeds.
• model source is recorded as Trusted SCL + initial snapshot versus Live MMS discovery.

P3 hardening added in this work:

• dedicated runtime QA ied_mms_scl_assisted_workbench_qa.cpp;
• standalone exact-product build gate under apps/ied_simulator/tests/scl_assisted_workbench;
• dedicated SCL-Assisted Workbench CI.

Acceptance gates

• Dedicated P3 Workbench QA passes using tests/fixtures/scl/client-workbench.scd.
• It proves initial SP value mapping, preservation of an unavailable SCL-declared ST root, persistent association, explicit clear-SCL fallback, and invalid-SCL fail-closed behavior.
• Existing IED Simulator Qt, SCL-Assisted Connect CI, C++ CI and Release Hardening stay green.
• Retained Embedded Profile regression must also be green before P3 is considered internally complete.
• PR feat: lightweight IEC 61850 engineering simulator workspace #82 stays OPEN + DRAFT.
• External vendor external IEC 61850 client claims remain separately gated by real-client evidence; this issue does not close that gate.