feat!: cross-platform almcp launcher and tool-store-only resolution

[Arthurvdv]

Base / CI: retargeted to main on 2026-09-13 so CI runs; until PR #25 merges the GitHub diff also shows PR #25's three commits. CI run 34774977712 is green: on the Ubuntu Test (v18.0.41.39415) job all nine almcp-backed tests executed (ALCOPS_TESTS_REQUIRE_ALMCP=1, almcp.dll launched through the dotnet host), 111 tests total.

Summary

• Launch almcp through dotnet almcp.dll on Linux and macOS where the nupkg ships no native launcher, making the proxy functional on every OS.
• Drop the AL VS Code extension probe from BcToolsLocator — the dotnet tool store is now the only automatic probe (after --devtools-path and BCDEVELOPMENTTOOLSPATH).
• Enable the almcp-backed integration tests on the Ubuntu CI matrix and add ALCOPS_TESTS_REQUIRE_ALMCP to fail loudly instead of silently skipping.
• Document the platform support matrix and the updated resolution order.

What changed

BcToolsLocator

• New AlMcpLaunch record (FileName, LeadingArgs, Description) replaces the raw AlMcpPath-based availability check. Constructor resolution: native almcp.exe/almcp → dotnet almcp.dll via DotnetHost → null.
• TryAlExtension removed; error message now enumerates every probe with its outcome and gives the exact install command.

DotnetHost (new)

• Pure, testable resolution: DOTNET_HOST_PATH → process path → DOTNET_ROOT/DOTNET_ROOT_X64 → PATH scan → bare "dotnet".

AlMcpProxy

• Stores AlMcpLaunch instead of a path string; LaunchChild prepends LeadingArgs to the argument list.

AlMcpFixture (tests)

• Falls back to BcToolsLocator.ResolveToolsDirectory() when the baked BcToolsPath is absent, so CI's BCDEVELOPMENTTOOLSPATH is honoured.
• ALCOPS_TESTS_REQUIRE_ALMCP=1 turns skips into hard failures.

CI workflow

• Extracts the full tools/net10.0/any/ payload (with runtimeconfig, deps.json) alongside the flat DLL extraction.
• Sets BCDEVELOPMENTTOOLSPATH and ALCOPS_TESTS_REQUIRE_ALMCP=1 on the test step when the full payload exists.

Docs

• README: requirements updated, "Platform support" table added, resolution list updated, extension references removed.
• src/ALCops.Mcp/README.md: extension reference removed.
• AGENTS.md: BcToolsLocator bullet updated with launch shapes and no-auto-install note.
• .github/ISSUE_TEMPLATE/bug_report.yml: "AL Language extension version" field replaced with "BC Development Tools version".

Corrects PR #20's known-issue note

PR #20 noted that the nupkg ships only almcp.exe/almcp.dll with no extension-less launcher, making the proxy unavailable from the tool store on Linux/macOS. This PR resolves that by falling back to dotnet almcp.dll when no native launcher exists.

Breaking changes

The AL VS Code extension is no longer probed for BC DevTools. Users who relied on the extension as their sole DevTools source must either:

• Install the dotnet tool: dotnet tool install -g Microsoft.Dynamics.BusinessCentral.Development.Tools
• Or point --devtools-path / BCDEVELOPMENTTOOLSPATH at the extension's bin/<platform> folder.

Test plan

• dotnet build --configuration Release — 0 warnings, 0 errors
• dotnet test --configuration Release — 111 tests pass (including 4 almcp-backed tests on Windows)
• New DotnetHostTests (6 tests): precedence order, bare fallback
• New BcToolsLocatorTests: AlMcp_PrefersNativeLauncher, AlMcp_FallsBackToDotnetWhenOnlyDllShips, AlMcp_AbsentWhenNeitherShips, Resolve_NothingInstalled_ErrorNamesEveryProbeAndTheInstallCommand
• almcp-backed tests run for real on the Windows dev machine (native almcp.exe)
• CI: Ubuntu matrix ran the almcp-backed tests via dotnet almcp.dll (run 34774977712: all nine AlMcpProxyTests/AlMcpProxyStartupTests executed and passed, no platform load error)

Note: Built on top of feat/alcops-analyzer-provisioning (PR #25); merge #25 first, after which this PR shows only its own four commits.

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