fix(ocsf): attribute MXC proxy events to sandboxes

[prekshivyas]

Summary

Give every Windows MXC host proxy its own immutable OCSF event context so denied HTTP/network events retain the sandbox ID and name when one gateway hosts multiple sandboxes. This removes the incorrect dependency on the process-global fallback context for top-level CONNECT and forward-proxy decisions.

Related Issue

NVBug 6783086 (internal)

Changes

• build and validate a per-sandbox EventContext from HostProxyConfig
• attach that context to the static Windows proxy identity and use it for proxy lifecycle, CONNECT, and forward allow/deny/error events
• add a regression test that interleaves two sandbox contexts and validates both class-4002 events against the OCSF schema
• document the multi-sandbox concurrency invariant
• align Windows host-proxy startup with the current endpoint-observation argument on the windows branch

Testing

• mise run pre-commit passes — blocked on Windows ARM64 because grpcio-tools 1.78.0 invokes MSVC with incompatible /std:c++17 and /std:c11 flags; attempted with the repository Python 3.14 and an isolated Python 3.13 environment
• Unit tests added/updated
• E2E tests added/updated (N/A: audit-context plumbing only; no E2E surface changed)
• cargo check -p openshell-supervisor-network --lib
• focused cargo clippy -p openshell-supervisor-network --all-targets --no-deps --target aarch64-pc-windows-msvc
• changed-path OCSF, host-context, host-authentication, and compatibility tests
• cargo test -p openshell-supervisor-network — 1,230 passed, 2 ignored, and 3 pre-existing Windows failures caused by an unescaped executable path in an MCP YAML fixture

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

Scope note

This PR fixes container.uid and container.name attribution. The static Windows proxy identity still has no trustworthy per-process PID, so the existing actor PID behavior is unchanged.

[prekshivyas]

Live Windows ARM64 MXC qualification completed against the current windows content (PR #3468) and this PR.

• Baseline: qualified fix(windows): restore MXC qualification and cold-start readiness #3468 artifact at acd2a5721 reproduced NVBug 6783086. A denied GET http://microsoft.com/ emitted one class-4002 event with destination microsoft.com:80 and status_detail = "network connections not allowed by policy", but container.uid and container.name were empty (actor PID remained 0).
• Fixed: ARM64 release build of fix(windows): restore MXC qualification and cold-start readiness #3468 + ed94456aa succeeded. Repeating the identical request emitted one class-4002 denial with container.uid = cd47baeb-e748-4263-9b79-04cb0f6d5b0f and container.name = n678-s-f-e43944f5, exactly matching the created sandbox. Destination, denial reason, and wire behavior were unchanged.
• Current upstream/windows is fb2980e07; git merge-tree --write-tree upstream/windows ed94456aa succeeds without conflict and yields the same tested combined tree 565d4d988613cb79bcda5c3d7859218156ba0652.
• Cleanup verified: the two temporary gateways/sandboxes and CLI registrations were removed; the pre-existing gateway was left untouched.

This live run confirms both the original failure and the fix. The unchanged actor PID 0 behavior remains outside this PR's scope, as noted in the description.

[prekshivyas]

Qualification before/after summary

NVBug: 6783086 — MXC proxy OCSF events can be attributed to the wrong sandbox

Before: Host-proxy audit decisions depended on process-global fallback context. With multiple sandboxes under one gateway, denied CONNECT/forward-proxy events could lose or misattribute sandbox ID/name.

After: Each Windows MXC host proxy carries an immutable per-sandbox EventContext. The regression test interleaves two sandbox contexts and validates both class-4002 events against the OCSF schema. Focused check/Clippy and changed-path OCSF, authentication, context, and compatibility tests passed. The broader crate run reached 1,230 passed and 2 ignored, with 3 pre-existing Windows MCP-fixture path failures.

Qualification status: Focused scenario PASS; full current-tip qualification pending. Rebase onto the current windows tip, repair the shared mise.lock gate, run hosted CI, and include this runtime proxy change in the combined two-cycle qualification with #3472.