refactor(platform): phase 6 migrate daemon IPC lifecycle

[zackees]

Closes #1312

Summary

• add the neutral fbuild_core::platform::ipc local endpoint, peer-facts, TCP listener, and readiness APIs
• move running-process backend endpoint transport, daemon TCP socket policy, and Windows native shutdown notifications out of shared daemon callers
• enforce owner-only local endpoints — atomic pre-bind fchmod on Linux, post-bind chmod of the socket path on Darwin (interprocess mode() relies on fchmod-on-socket-fd, which Darwin rejects), and a protected Windows Owner Rights DACL
• move interprocess/socket2 ownership into fbuild-core and extend exact boundary enforcement for the IPC capability

Compatibility

• broker frame routing and running-process probe behavior are unchanged
• HTTP/protobuf surfaces are unchanged
• daemon bind retry/yield policy remains in fbuild-daemon; only one-attempt native listener construction moved
• Windows close/logoff/shutdown events still feed the existing Tokio shutdown channel

Characterization and validation

• RED: empty IPC facade failed local endpoint roundtrip/peer-facts and TCP readiness tests
• GREEN: platform tests pass, including Windows anonymous-identity denial for the owner-only named pipe
• daemon readiness test passes
• serialized daemon ownership tests: 8 passed, 1 subprocess helper ignored by design
• platform-boundary Python tests: 28 passed
• workspace clippy with -D warnings passes
• clud-review: clean
• full Windows repo suite reached two unrelated long-run abnormal process exits; both affected crates pass isolated (fbuild-packages-fetch: 131/131, fbuild-serial: 184 passed/1 ignored)

Inventory

• exact enforcement ledger: 107 -> 94
• normalized Dylint projection: 103 -> 92
• research inventory: 137 -> 142 (94 caller rows + 48 exact authorized boundary rows)
• remaining caller IPC rows: 0

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📥 Commits

Reviewing files that changed from the base of the PR and between 662569f and ef36a1e.

⛔ Files ignored due to path filters (3)

• Cargo.lock is excluded by !**/*.lock
• ci/platform_boundary_ledger.tsv is excluded by !**/*.tsv
• ci/platform_boundary_research.tsv is excluded by !**/*.tsv

📒 Files selected for processing (27)

• Cargo.toml
• ci/enforce_platform_boundary.py
• ci/platform_boundary_research.py
• ci/test_enforce_platform_boundary.py
• ci/test_platform_boundary_research.py
• crates/fbuild-core/Cargo.toml
• crates/fbuild-core/src/platform/README.md
• crates/fbuild-core/src/platform/ipc.rs
• crates/fbuild-core/src/platform/linux/ipc.rs
• crates/fbuild-core/src/platform/linux/mod.rs
• crates/fbuild-core/src/platform/linux/process.rs
• crates/fbuild-core/src/platform/macos/ipc.rs
• crates/fbuild-core/src/platform/macos/mod.rs
• crates/fbuild-core/src/platform/macos/process.rs
• crates/fbuild-core/src/platform/process.rs
• crates/fbuild-core/src/platform/windows/ipc.rs
• crates/fbuild-core/src/platform/windows/mod.rs
• crates/fbuild-core/src/platform/windows/process.rs
• crates/fbuild-daemon/Cargo.toml
• crates/fbuild-daemon/src/broker/backend.rs
• crates/fbuild-daemon/src/main.rs
• docs/architecture/portability.md
• docs/architecture/runtime.md
• docs/platform-boundary-research-inventory.md
• docs/platform-boundary-research.md
• dylints/enforce_platform_boundary/src/baseline.txt
• dylints/enforce_platform_boundary/src/lib.rs

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