[bitmaster162]

H3 G1 — read-only Windows MIDL toolchain inventory

This Draft PR adds only .github/workflows/h3-r7b1b1-toolchain-preflight.yml (R3) to inspect preinstalled MSVC, Windows SDK and the MIDL driver/engine pair on the GitHub-hosted windows-2025-vs2026 runner.

Exact review anchors

• Protected base master: 719ed32a64301fc8083a5aad0c4ed7bed316040e
• Proposed head commit: 6246fc6d9c5df99b60eb8a896dd5ddf872293e38
• Head tree: d786000179db23c134413f65c0fdfa29f5f0d2e4
• Sole added file relative to master: .github/workflows/h3-r7b1b1-toolchain-preflight.yml
• New Git blob: e083f1f7ddfb395a73b5afbc6ef3518c475e7d9c
• R3 UTF-8 LF source: 9106 bytes, SHA256 afb1c1ba9a59a6c9ec7ec85db06969b314a4b2fb5691a212edf5759f62be723d

Permission boundary

• Allow automatic PR-triggered review-gates, CodeQL, P0 and the G1 inventory job.
• No source checkout, toolchain installation, compilation, RPC registration, service creation, protected DB/memory access, secret consumption or artifact upload in the new G1 job.
• No manual dispatch/rerun, merge, auto-merge, deploy, branch deletion or Windows/Scheduler/TPM/DB/MCP/production mutation is authorized.
• This inventory never qualifies a native H3 broker security PASS. C0 remains UNVERIFIED/HOLD; T11/T12 remain UNEXECUTED; PRODUCTION HOLD.

Any branch/base SHA drift or incomplete/mismatched MIDL evidence requires STOP/HOLD.