[M0-CORE-02] Structured logging facade - #2
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The one structured logging facade for the engine (AGENTS §14 LOG-001…LOG-007, FR-12.2): laige-core gains include/laige/logging.h and logging.cpp. Facade: laige::log::Logger — a process-lifetime Meyers singleton that owns its current Sink (unique_ptr). LAIGE_LOG_TRACE/DEBUG/INFO/ WARN/ERROR/FATAL macros put the level gate before argument evaluation, so a disabled event costs exactly one atomic load + branch: no message/field evaluation, no formatting, no allocation, no lock (LOG-003). Gating is an atomic global minimum plus a per-subsystem level table (init-phase mutation, one facade mutex, CONC-001). Fields: scalars render locale-free via std::to_chars into a 64-byte stack buffer; string-like values copy in full; field values must avoid spaces/'=' (the line is '| k=v' machine-parseable, LOG-001). Rate limiting (LOG-004): per (subsystem, event, severity) for Warn/Error/Fatal only. The first event of a key is always recorded (an everEmitted flag — a time_point::min() sentinel overflowed the window subtraction, CPP-004); repeats are counted and reported as a stable 'rate_limited' summary event (event=<orig>, suppressed=N) at window rollover, and pending counts are drained at shutdown. Sinks: ConsoleSink (does not own the stream — stderr must outlive the process) and FileSink (owns the FILE*; create() returns Result<unique_ptr<FileSink>>, open failure = ErrorCode::IoError, the new slot-5 registry code; the LOG-007 minimal fallback keeps the console sink and reports the failure). Fatal records, flushes, and terminates via std::abort() (AGENTS §14 controlled termination). Crash handling: POSIX sigaction (SA_RESETHAND one-shot) for SIGSEGV/ABRT/BUS/FPE/ILL and a vectored SEH handler on Windows — raw write(2) notice, allocation-free try_lock sink flush, re-raise. shutdown() is idempotent (CONC-006): drain summaries, flush, retire (post-shutdown logs discarded). Timestamps: system_clock, UTC RFC 3339, rendered with an in-code Hinnant civil-from-days (no libc date functions). Additive M0-CORE-01 extensions required by this step's FileSink→facade hand-off: Result::takeValue() && (move the success value out of an rvalue result) and ErrorCode::IoError (5), both covered in the result_status suite; docs/api/errors.md documents the new code. Tests: 'logging' CTest entry (27 GTest cases in the shared laige-core_tests executable) — gate semantics, field formatting, both sinks (exact line format, dtor flush, create failure → IoError), rate limiting (suppression, summary after window, window edge, key independence, Warn/Error/Fatal only, opt-out, shutdown drain), Fatal (gate + forked child that emits, flushes, and dies on SIGABRT with the line in the file), crash/shutdown behavior, concurrency (4 threads × 250), and LogPerformance: 100k disabled Trace events → 0 allocations via a test-only global operator new counter (excluded from the sanitizer trees, whose runtimes define their own new/delete — there the same spam loop runs leak-free plus the timing property, the fallback the step names). Measured: disabled ≈46 ns/event vs ≈1207 ns/event enabled (N=200000). Verified locally 2026-09-10 (GCC 16.2.1 static, shared, ASan/UBSan, TSan trees; fresh Clang 22.1.8 static + shared trees): ctest 8/8 and ctest -R logging green in every tree, zero warnings. API contract: docs/api/logging.md. Roadmap: M0-CORE-02 checked with Decision/Verify/Size notes; Progress Board M0 11/22; change log line.
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M0-CORE-02 from roadmap/M0-foundations.md: the one structured logging facade (AGENTS §14) in laige-core.
Verified locally: GCC static/shared/ASan/TSan + Clang static/shared — ctest 8/8 and ctest -R logging green in every tree, zero warnings (disabled ≈46 ns/event vs ≈1207 ns/event enabled).